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Okay, car people. What could it be?

Well … calling on the Car Commentariat once again. Sigh.

I mentioned the other day that I had doubts Tuesday’s wrenching actually cured the Xterra. I was right.

This morning I drove into the woods with the dogs and all was fine. We took a short walk, then when I started up again, the idle was rough. Not rough enough to threaten to die. Just “rumbly” with the tach lightly bouncing up and down.

I put it in drive and we got rolling. And after maybe 100 yards, I felt it losing power, the tach dropped. Several seconds later the engine died and all the dash lights came on.

As usual, it started right back up. But then … death again. Every 100 or 200 yards. Always the drop in power followed a few seconds later by the engine quitting.

After that happened eight or ten times, there was a final “episode” in which the tach dropped almost — but not quite — to zero. This time the engine didn’t die and everything was fine (except my nerves) the rest of the way home. This is far and away the worst thing it’s done to date.

After the third or fourth death, I put it in park and revved the engine hard a few times, in case something needed to be blown out of the system. That had zero effect.

I’m stumped. Any ideas?

On Tuesday the mechanic:

  • Changed sparkplugs and wires
  • Replaced the distributor cap and rotor
  • Replaced the air filter
  • Replaced the fuel filter
  • Cleaned the mass air-flow sensor and throttle body
  • Replaced the cold-start sensor
  • Checked for vacuum leaks

At his suggestion, I also added Heet and fuel-injector cleaner to the gas tank. Did that Tuesday and all has been well until this morning.

I haven’t talked with the mechanic yet this morning (too early for him), but I’m not sure our Plan B — replacing the idle air control valve — is the next logical thing to try.

ADDED: I called him. He has no idea what it could be. I’m also going to post this to an Xterra forum.

My other thought, based on looking around on the ‘Net, is that something might be wrong with the crankshaft position sensor.

But if you knew how little I know about auto repair, you wouldn’t take my word for anything.

Ideas?

57 Comments

  1. Jim Bovard
    Jim Bovard June 5, 2015 8:56 am

    My only similar experience with an auto going stone cold dead while driving (unfortunately down a mountain surrounded by 18 wheel trucks) occurred when my alternator failed. I presume you checked that option long ago?

  2. HP
    HP June 5, 2015 9:13 am

    We had something very similar with our 2007 Toyota Matrix. Rough idle, stall, starts, repeat. The dealership said it was a bad CPU (the main computer controller) and since it was under warrenty at the time, they replaced the very expensive controller. The problem was fixed completely.

    About six months later Toyota issued a recall on all CPU controllers for that year vehicle, so I think the diagnosis was right. I don’t kmow if it was a software or hardware problem in the CPU – probably hardware.

    I would not want to have had to replace it myself – it was something like $1500. If that turns out to be the problem – I wonder if used units are available from wrecks?

  3. Claire
    Claire June 5, 2015 9:22 am

    Thanks, guys.

    HP — A shop did tell me that the computer needed to be replaced, but the mechanic was obviously just guessing. I’ll replace the ECM if I have to, but as you note, it’s a very expensive repair (but yes, parts are available from junk yards and online sources if it has to be done).

    Jim — Arrgh! That must have been ever-so-slightly scary! I don’t think the alternator is the problem because the Xterra always starts right up, first crank.

  4. Claire
    Claire June 5, 2015 9:25 am

    Hm. Well, I just looked up bad alternator symptoms and I see that failed starts aren’t necessarily among them. Maybe this is something I need to check after all?

  5. Mike
    Mike June 5, 2015 9:29 am

    It’s always something simple once you find it.

    Here’s a story I went through a couple of years ago with my truck. It runs fine for days and then suddenly it will die going down the road. No coughing or other symptom, just dead. After a few minutes it would start and run fine for a few days and then die again. Over the course of a few months it got progressively worse until it reached the point I couldn’t trust it. No codes are coming up and the check engine light isn’t coming on. New spark plugs and new cap and rotor didn’t fix things.

    I start prowling through the threads on a ford truck enthusiast’s site and actually spent probably two days looking at various threads trying to find a thread listing the same symptoms. Finally hit paydirt and the opening post went something like this:

    You guys have to help me. My truck runs fine and then it will suddenly die. Sometimes it starts right up and other times it takes several minutes before it will start. It’s getting progressively worse. I’ve changed the plugs, plug wires, coil, cap & rotor. I even changed the oil and washed the truck. Nothing is helping.

    Three or four posts down was my answer. There’s a chip in the distributor that occasionally goes bad. It doesn’t go bad all at once but dies slowly. $47 dollars for a new distributor off of ebay and the problem disappeared.

    The point of all of that is you’ve got something that is giving out slowly. A wire connection that is gradually getting more corroded, a chip that is dying slowly, a sensor slowly failing, or something similar. The last few years, my best hope for finding the problem is a thorough search of the applicable car forums looking for a thread that details your symptom.

    If your car uses a distributor (not all do nowadays), that would be a relatively cheap attempt at a fix. After my experience, I did some nosing around and they fail more often than I’d have thought.

    Which brings me to my problem. My neighbor used the lift in my shop to change the gas tank on his Jeep. While he was at it, he changed all the fluids and greased all the fittings. Now there’s no power to the dash or ignition and he’s out of ideas. My wife doesn’t care for him and her brother is coming over tomorrow so I can put his car on the lift. I had other things I was planning on doing this afternoon.

  6. Kent McManigal
    Kent McManigal June 5, 2015 9:29 am

    I once had a pickup that started dying regularly. It would sputter and die, and then after 5 or 10 minutes would run again- for a few minutes (which got fewer and fewer over time). Turned out it had a fuel filter no one knew about, which had never been changed with the others. Even the dealer didn’t know where it was. I think a guy at the auto parts store was the one who actually “found” it. Changed that one and had no more problems. BUT, I’m betting I know less about vehicles than you do, so don’t listen to me.

  7. Claire
    Claire June 5, 2015 9:44 am

    Kent — Had the fuel filter changed. Given the dirty conditions I drive in, it was a good bet. No luck.

  8. Claire
    Claire June 5, 2015 9:49 am

    Mike — I love the bit about washing it. Really, that should take care of everything. Maybe add one of those little stinky pine trees for extra security.

    Something slowly going bad is a really good bet. The distributor was the first thing two mechanics suggested (based on the diagnostic code), but when one of them replaced it it didn’t solve the problem. So he un-installed it. Ignition coils are one suggestion I keep running into for this problem, and I believe those are inside the distributor. But …

    I’m going to go back and talk to the mechanic who tried the distributor fix and who guessed at the need for a computer replacement. Going to ask him exactly what he observed, if he can recall three weeks later.

    Sorry about your neighbor!

  9. Mike
    Mike June 5, 2015 10:25 am

    Maybe a bad ground wire/cable from battery to frame. Had a ford with that issue and it all sorts of strange symptoms. Internally shorting coil could be possible too.

  10. Claire
    Claire June 5, 2015 10:36 am

    Mike — Oh, it would be glorious if it were just a wire shorting out!

    When you say “internally shorting coil” — you mean an ignition coil? If I recall correctly, those are inside the distributor on the Xterra and this discussion keeps circling back to distributors despite the failed dist. replacement.

    I’ve now got a call in to the mechanic who did that failed replacement. I was too preoccupied with pain that day to ask him why he said it wasn’t the distributor after all. I’ll see if I can get him to come up with some memory of the reasons.

  11. Claire
    Claire June 5, 2015 10:59 am

    Suggestions I’m getting from an Xterra forum:

    * Fuel sending unit (a recall item; don’t know whether mine’s been done or not since the car was 10 when I bought it)
    * Cam position sensor (already have crankshaft position sensor on my list)

  12. MamaLiberty
    MamaLiberty June 5, 2015 12:05 pm

    Ever wonder how the cars managed to run before there were all those “sensors?” LOL

    In 1963 I got my first car. A 1947 Ford coupe, manual transmission. Extra manual, it turned out. The gear shift was on the steering column. The actual gear box was very handy to the driver’s side in the engine compartment, and that was good because the thing would hang up in second gear so easily, and I had to get out, raise the hood and use a rag to jiggle it loose. Unfortunately, it was impossible to do that without getting grease on something I was wearing.

    Ugly car, but aside from the 2nd gear hanging up, it ran like a champ. 🙂
    http://tinyurl.com/qgcem7t for a picture, except mine was black. Wish I still had it… I think I gave about $150. for mine… and this one is selling for $29,000. 🙂

    I have no suggestions for you here, Claire. Just hope you can find the answer before it costs more than just replacing the car.

  13. Claire
    Claire June 5, 2015 12:32 pm

    I hear ya, ML. I know all those sensors must have some useful purpose (e.g. communicating with the central computer). But sensor problems have been suggested so many times I’m starting to wonder if there are any engine parts that actually DO anything anymore.

    FWIW, I’m narrowing in on crankshaft and camshaft position sensors as the most likely causes, with ignition coil (inside the dist., I believe!) and some sort of relay or connection to the computer being next in line. And I’m about to insert the shop manual DVD in the drive and dive in deep.

    Fortunately, those sensors are inexpensive parts; I have no idea how complicated they are to change out.

  14. Claire
    Claire June 5, 2015 1:00 pm

    The plot thickens. If I understand the diagram and instructions on the shop manual, both the ignition coil and the camshaft position sensor (possible culprits) are inside the distributor and they only way they can be replaced is by replacing the entire distributor.

    This opens the possibility that the distributor the shop installed (and uninstalled) was simply faulty, as I think somebody suggested earlier this month.

    The other likely culprit, the crankshaft position sensor, appears to be a separate item that can be tested and replaced on its own.

  15. Claire
    Claire June 5, 2015 1:32 pm

    I talked with the mechanic who did the failed distributor replacement.

    The sole reason he concluded that the distributor didn’t fix the problem was that the service engine light didn’t go out. So is it possible the distributor would have fixed the problem, just didn’t fix the light?

    He also confirmed that he did NO testing of anything outside of the parameters of the P1320 diagnostic code. He didn’t check anything else that might cause a rough idle. Now that the car has begun stalling while driving, he says he’d check other things including the fuel system. I’m not going to take the Xterra back to him. But at least now I have more clues.

    And I’m tired. And discouraged. Sun’s shining. I’m going to get away from the computer for a while.

    Funny thing; when I’ve thought about the Xterra getting old and dying (which it shouldn’t do yet, with only 155,000 miles on it), I’ve just figured I’d go on foot for a while. Done it before; no reason not to do it again. Never in the world did I think about the Xterra going out while I had a broken freakin’ ankle.

  16. Kyle MacLachlan
    Kyle MacLachlan June 5, 2015 1:44 pm

    Claire,

    I’m no mechanic (I don’t even play one on TV 😉 ), but you might want to have your guy check out all the wiring (if he hasn’t done so yet). There could be a wire with some insulation cracked or rubbed through and that would make it arc against the frame/block, not letting the electricity go where it is actually needed.
    I think the reason why it always starts right up is because the computer has a “start mode” that will override any sensors for a short time, until the engine is up to speed. Once those sensor come online and start feeding the computer information it will react based upon that info; so if there’s a little short somewhere along the line it won’t get all the info it needs and start to do weird things. That’s how my mechanic explained it to me a few years back.
    A faulty alternator would not cause you starting trouble as long as your battery is charged. It won’t make the “Check engine” light come on either (at least in older cars) but instead your battery warning light. The alternator is solely there to produce electricity to run your car and charge the battery back up.
    Hope this helps and GOOD LUCK!!!!

  17. KiA
    KiA June 5, 2015 2:10 pm

    interesting. so you show distaste for “the mechanics’ blind adherence to diagnostic codes” and scold them for suggesting part replacement on guess work, yet you trust internet folk’s remote intuition/guess work based on limited personal experience and blindly replace parts based on … guess work. hmm.

    the solution to not replacing unnecessary parts is proper diagnostics. measuring things, tracing things, etc. otherwise it’s just a bunch of possibilities that you eliminate by replacing with a (supposedly) functioning unit.

    i think there’s less work and more money for mechanics in doing part replacements than doing diagnostics. there’s also the possibility in spending time doing fruitless diag which may be seen as unfair to charge the customer for time spent. also over time experience bloats their ego and they make professional guesses. so i do understand your frustration in not finding a mechanic that “measures thrice, replaces once”.

    anyway, my psychic senses say that it’s electrical, and if the car shuts off, then it’s probably the ECU not sending an ignition signal. it also seems heat related — in that the problem occurs more frequently when the ECU has warmed up. it may be a fractured solder joint that’s separating with heat. there are companies that refurbish ECUs. you will have downtime while the ECU is being worked on. you could also go the junk yard route. something i would try personally would be to carry a can of compressed air. when the problem occurs, open the ECU housing and spray the inside of the housing with the can upside down. this will spray the liquid that evaporates quickly, providing a cooling effect. there are also freeze sprays but the upside down compressed air may be a cheaper solution.

  18. Claire
    Claire June 5, 2015 2:15 pm

    Thanks for the info, KiA.

    As to this: “interesting. so you show distaste for “the mechanics’ blind adherence to diagnostic codes” and scold them for suggesting part replacement on guess work, yet you trust internet folk’s remote intuition/guess work based on limited personal experience and blindly replace parts based on … guess work. hmm.”

    Ha! I haven’t committed to pay one of you to repair the vehicle for me, have I? Where the code-enslaved mechanic offered an $1,100 repair as the only thing to try. I’m not putting “trust” into anything anybody says. I’m gathering data and checking it for myself.

    Some people’s opinions get weighed more highly than others. But blind guesswork? Not!

  19. Claire
    Claire June 5, 2015 2:16 pm

    Kyle — Supposedly the wiring has been checked. But there’s so much of it and it would be so easy to miss a crack in a piece of insulation or some such. Will definitely explore this, especially because it seems like such a nice, low-impact solution.

  20. KiA
    KiA June 5, 2015 2:20 pm

    i just read

    The sole reason he concluded that the distributor didn’t fix the problem was that the service engine light didn’t go out.

    the lite going out (on its own) has different criteria for different codes. some codes may be checked for and cleared on each startup. others may require multiple startup cycles, or multiple cycles + miles driven, etc.

    without knowing the specific criteria for the code, i think it’s generally better to reset the lite with an OBD2 diag device and see if it comes back.

    so it is possible that the problem was fixed, however the service lite remained on (if the mechanic did not manually clear it).

  21. Claire
    Claire June 5, 2015 2:21 pm

    And the people here are working from the actual symptoms, which the Blind Mechanic was not. That’s huge.

  22. Kyle MacLachlan
    Kyle MacLachlan June 5, 2015 2:21 pm

    Just read your last post:
    I don’t know if he did, but the “check engine” light will not go out by itself after a fix, it has to be reset with the diagnostic tool. I have my own (bought from Harbor Freight for $100) and it has a line in the diagnostic menu specifically for that.
    Also, with advanced dia. tools like garages usually have, you can get all kinds of info on the condition of the engine at the time the “check engine” light came on. It’s like the computer takes a snapshot of all the sensors at that moment and stores that data for later use until you erase the trouble code.
    My tool will let me see some basic info; the one my shop uses will actually “talk” to the computer and can tell them a whole lot of other details (it also costs about $2,000 !).

  23. UnReconstructed
    UnReconstructed June 5, 2015 2:22 pm

    Failing crankshaft and or camshaft sensor sounds believable if they are failing gradually.

    So do a LOT of other things. The ECM might or might not solve the issue.

    It could be a loose wire, too. They have taken the entire engine and turned it into a black box.

    This is largely because of the fedgov, you know. Mandating ever higher fuel economy and lower and lower emissions (by fiat) have forced the car manufacturers to get more and more exotic in their pursuit of those ever changing goals.

    Now it is commonplace to have cars with double overhead cam, turbocharged, fuel injected motors….things that in the ’60s were strictly super race car stuff.

    Yeah, I like the economy, but this is the price we pay.

    Give me a carbureted big block ’69 chevy . I’ll pay the 14mpg gladly.

  24. Karen
    Karen June 5, 2015 2:23 pm

    Darn Claire! did you ever want to know this much about cars? Gone are the days when you could raise the hood and actually see the engine and all it’s various parts.

  25. UnReconstructed
    UnReconstructed June 5, 2015 2:27 pm

    A crankshaft position sensor is pretty cheap….around $30.

    It could be that. Probably not horrible to replace.

  26. EJ
    EJ June 5, 2015 2:28 pm

    It your fuel pump is tank mounted I bet it has a sock filter on the inlet. Good chance this is gummed up or at least catching gunk and temporarily starving the pump. After you drive a bit it may shake the blockage loose for a while thus the intermittent nature.

    Drop the tank. Dump the gas, flush it thoroughly and if there is debris in the tank or on the sock replace the pump as it will soon die as a result of the fuel starvation.

  27. Claire
    Claire June 5, 2015 2:37 pm

    UnReconstructed — I hear ya. In fact I’m off to begin a riff on that theme.

    EJ — Another good thought, and a new one, too.

    I was thinking at first that the continuing roughness after the repair might just be some gunk working its way out of the system. Increasingly I’m thinking not, but something like you describe seems possible.

  28. Scott
    Scott June 5, 2015 2:44 pm

    This sounds like a lack of fuel. Have you checked the fuel pump relay? Volvo 850’s wil die because of bad capacitors in the relay, mostly when temperatures get below 40F. Might be something similar.

  29. Rusty Miller
    Rusty Miller June 5, 2015 5:29 pm

    I’ve experienced similar problems in the past with motorcyvles where the culprit was a gas cap that had a clogged vent. Once the engine used enough fuel, it pulled a partial vacuum in the gas tank and the engine would starve. I don’t know if such a problem is possible in newer cars with fuel vapor emission controls, but I think that it’s worth unscrewing the gas cap the next time that you have the problem. If the car runs well with the cap off, then you know something in the evaporative controls is causing the problem. On the other hand, maybe my car experiences are too old to apply to modern vehicles…

  30. Iwoots
    Iwoots June 5, 2015 7:18 pm

    Funny, what you described sounds like what happened every year to my mom’s ’79 Camaro, with the small V6. Every year like clockwork the EGR valve (pretty sure that was it; this was years ago in the early ’80s so I may not be remembering correctly, and its now too late to call her) would have to be replaced because of rough idling, the engine suddenly dying but restarting OK.

    At this point I’ll just shut up; and let someone more knowledgeable say if such may be applicable to your XTerra.

  31. Tom W.
    Tom W. June 5, 2015 8:26 pm

    Have the mechanic load test the battery. A bad cell caused the same symptoms on my 2002 Xterra. In days of old, once the car was started the battery was not REALLY needed. Not the case anymore.
    Remember Occam’s Razor!

    Good luck!

  32. Tom W.
    Tom W. June 5, 2015 8:33 pm

    P.S. On the 2000-2004 V6 Xterras, they always throw a engine knock sensor code. It costs over 1k to fix I hear, but mine has 197K on it and has thrown the code for around 60k miles that I know of. It is so common they reprogramed the computer so the MIL light would not illuminate when it throws the code.

    Tom

  33. jolly
    jolly June 6, 2015 5:25 am

    Did that car get its 100,000 mile maintenance? I believe you’re supposed to replace the timing belt. If I recall correctly, if that goes, the engine is one of those that self-destructs.
    On our Xterra, we did all required maintenance through 120,000 miles. At this point, however, parts are literally falling off the car, and we’re just hoping for it to last one more year ( we’re at 280,000 miles ).

  34. Claire
    Claire June 6, 2015 8:46 am

    KiA — Thank you again! I missed your comment about the distributor and the light. But I’m absolutely glad to know that’s a possibility.

    And UnReconstructed — I missed your comment, too, about the crankshaft position sensor. I’ve been hanging on to that as the #1 culprit based on my research of the symptoms. The fact that it’s an easy, inexpensive fix helps, too. I was wondering why nobody was saying anything about that part.

  35. Claire
    Claire June 6, 2015 8:52 am

    Jolly — Yes, the car did get its 100,000-mile maintenance, including a new timing belt. I didn’t buy the car until it was already 10 years old and had 115,000 miles on it. I have none of its maintenance records before my purchase, but it had obviously been impeccably maintained. I’ve done everything I’m supposed to since then.

    Also, the SES light in this case doesn’t seem to indicate a catalytic converter problem (though this is something several people have suggested). The code associated with the light is P1320, which indicates things inside the distributor.

  36. Claire
    Claire June 6, 2015 8:52 am

    Tom W. — Thanks for the suggestions. The battery is new (got it last year, a month or so after the original SES light appearance. What symptoms is the Xterra having that make you think bad battery? That’s pretty funny — sad, but funny — about the engine knock codes.

  37. Claire
    Claire June 6, 2015 9:00 am

    Karen, Scott, lwoots, Rusty Miller — Thank you. And Karen, yes, I’m coming to hate having to get all this education. I’m grateful for it. But OMG! Information overload.

    If mechanics can’t learn this stuff in entire careers, how can I possibly figure it out, even with all this wonderful help?

  38. kevin mullis
    kevin mullis June 6, 2015 11:03 am

    Like Kent was saying there might be more than ONE fuel filter. Sometimes car makers hide one on ya somewhere. I know they have one that is like a mesh bag that surrounds the fuel pump in the gas tank and maybe one on the fuel pump itself [in the tank]. Plus the fuel pump might be getting weaker as it warms up providing less fuel as you drive it. Or it could be one of ANY of the things others have suggested. So frustrating cars are when they don’t run right.

  39. mark
    mark June 6, 2015 1:05 pm

    had just this type of problem on an amc pacer. mesh screen filter in the tank at the fuel line intake clogging. side of the highway fix drop the tank and remove the screen problem solved.

  40. Dan
    Dan June 6, 2015 1:20 pm

    It’s all witchcraft….. I have a dodge 3/4 ton diesel that started surging on the way to a horse show with horse trailer in tow….!@#%##! Surging in diesels is ALWAYS a fuel problem right? Checked the filter, it’s clean no water. ?? Surf the net, find an answer. The ground cable from the alternator to the controller picks up “noise” from the alternator that confuses the computer..!! The cure ?
    Wrap aluminum foil around the cable to shield it from the noise….and it worked ! 1/2 hour later we’re on the road to the show, surge free.
    I also have an ’03 grand Cherokee with much the same problem as your’s and even the boys with the big computer engine analyzers can’t find the problem.
    I swear, it’s WITCHCRAFT.

    Dan
    P.S. Never let your trailer brake controller get out of level on a bumpy road.

  41. The Freeholder
    The Freeholder June 6, 2015 1:57 pm

    I’ll second the EGR valve. Sounds suspiciously like a bad one I had, and at least it’s normally a relatively cheap part to replace.

  42. MamaLiberty
    MamaLiberty June 6, 2015 2:36 pm

    And just think! Once you’ve replaced all these parts, you’ll have a new car… or something.

    Very, very frustrating. Hope you can take a break from it all and have a quiet day tomorrow.

  43. Claire
    Claire June 6, 2015 3:10 pm

    LOL! Yes, a whole new car built out of spare parts. Now, I just wish I could accomplish it all by witchcraft — though putting tinfoil hats on any random car part would also work for me.

    And … sigh, I’ll add EGR valve to the list of things to be checked.

  44. Paul Bonneau
    Paul Bonneau June 6, 2015 8:27 pm

    [Ever wonder how the cars managed to run before there were all those “sensors?” LOL]

    Poorly. It is possible to make crude engines work, as in the “good old days”. They won’t have much power, they will pollute, and will waste fuel. And it was a rare car back then that made it even to 100,000 miles.

    When sensors stop working, the CPU realizes this and assumes some average value for the thing to be sensed (if possible), and keeps the engine running. It’s called “limp home mode”. In the old days, the engine was always in limp home mode. 🙂

    Claire, is your car ever running well? Or is it only either 1) stalled or 2) threatening to stall? If it SOMETIMES runs well, that suggests a bad connection, or some other electrical problem. Keep in mind you are near the ocean I think. Corrosion happens. I have at times opened and closed connectors just to break any corrosion in them, and maybe applied di-electric grease to the contacts (although some people disagree with this almost violently…)

    Has anyone done a compression test on that engine? How do the plugs look when they are pulled, tan and dry or oily or wet?

    What is the color of your exhaust pipe. Really, really black (sooty)? Or too light? If too light then it might be the fuel starvation thing (plugged filter) or an air leak in the intake manifold (look at all the rubber hoses, they do tend to crack over time and let air in). If the exhaust looks normal then maybe you can eliminate those causes.

    I’m just grasping at straws here…

  45. Claire
    Claire June 7, 2015 9:11 am

    Well, Paul, that’s some pretty decent grasping at straws.

    “Claire, is your car ever running well? Or is it only either 1) stalled or 2) threatening to stall? If it SOMETIMES runs well, that suggests a bad connection, or some other electrical problem.”

    It runs absolutely brilliantly — flawlessly — until suddenly it doesn’t. It’s good probably 90 percent of the time.

    “Has anyone done a compression test on that engine? How do the plugs look when they are pulled, tan and dry or oily or wet?”

    No compression test, but the fact that it runs perfectly most of the time seems to indicate that’s not the problem, yes? Pulled plugs are dry and normal.

    “What is the color of your exhaust pipe. Really, really black (sooty)? Or too light? If too light then it might be the fuel starvation thing (plugged filter) or an air leak in the intake manifold.”

    Neither sooty nor too light as far as I can tell. (But then, I admit I never gave much thought to what a “normal” exhaust pipe looks like.)

    My thought is that the problem is electrical. Maybe the electrical system is causing a fuel shutoff. But dollars to donuts, the initial culprit is in the electrical system.

    I’ll explore that angle first. Then if that’s not the cause, will check the fuel system (or have it checked). After that, the emissions system. After that, other stuff.

    Would be nice if somebody could just check all these things at once, but I can hardly even imagine the expense of that. I think the first thing is just to have a couple more sensors replaced — the ones that seem most likely to be producing these symptoms aren’t horribly expensive or hard to swap out.

  46. Thomas Knapp
    Thomas Knapp June 7, 2015 11:33 am

    I am NOT NOT NOT a mechanic. However, based on a recent experience I had with an older Volvo, I think that crankshaft sensor you’ve mentioned might be a place to look at.

    We had the “suddenly dies for no reason, a few minutes later starts back up and runs like a top” problem someone mentioned above with their old truck). Our shadetree mechanic instantly narrowed it down to 1) fuel pump, 2) fuel pump relay or 3) crankshaft sensor that tells the fuel pump whether or not to be pumping. A few quick tests that involved 1) bypassing the relay and 2) listening for the pump narrowed it down to the sensor. It makes sense to me that in some cases, the sensor might be messed up in a way where it starts a quick on-off-on-off thing that could cause the rough idle because the fuel pump is getting the signals on-off-on-off.

    But like I said, I am NOT NOT NOT a mechanic.

  47. Paul Bonneau
    Paul Bonneau June 8, 2015 6:10 am

    Agree, it really sounds electrical. The intermittent nature completely eliminates problems like plugged filters. Also, now that I think of it, the fact it sometimes runs poorly and sometimes doesn’t run at all eliminates everything past the distributor, and everything that has to do with a single cylinder – because a v6 should be able to at least run on 5 cylinders if I’m not mistaken.

    Maybe pull the computer and then put it back in, just in case there is corrosion at the connector.

  48. Thomas Knapp
    Thomas Knapp June 8, 2015 10:09 am

    “The intermittent nature completely eliminates problems like plugged filters.”

    Not sure that’s the case. I had an old Mercury that would run great for a few minutes, then start grumbling, then die. A few minutes later it would start right up. Got it to the shop and it turned out there was some sediment in the fuel filter that would settle (letting the car start, etc.) and then over the course of a few minutes get stirred up enough to block the fuel line.

    Of course, they may have come up with better fuel filters since 1978 🙂

  49. Kel
    Kel June 10, 2015 6:42 pm

    Having just popped in and only skimmed the comments, my first instinct is fuel pressure intermittently dropping off. Ignition problems or a cam/crank sensor won’t usually cause the loss of power that you are describing. They would usually cause a definite miss or die all at once then maybe re-start. Not much experience with Nissan stuff specifically, but most modern pumps are controlled by the ECM on a duty cycle, cycled on/off quickly to maintain a specific pressure. Sometimes the pumps get stuck. Could be a bumpy road, temperature, or even the presence of chickens that causes it. If the problem is repeatable, having a manual fuel pressure gauge on it and watching the gauge while the problem is happening will either confirm a fuel problem or rule it out pretty quickly. Symptom to system to component to cause is the way I was taught to hunt these things. Hope that helps.

  50. Kel
    Kel June 10, 2015 6:51 pm

    Oh, and the idle air control valve can cause low/rough/dying idle, but won’t cause any noticeable symptoms above idle. Won’t lose power or kill the engine going down the road.

  51. SW OR John
    SW OR John June 10, 2015 10:00 pm

    Sorry for your car (and ankle) troubles.

    I am not a mechanic. However, I do have an unusual and hopefully interesting story about ghost troubles. Several years ago the owner of the company I worked for bought a brand new, ultra expensive luxury car. He loved it. About 6-8 months after he bought it he was cheerfully flying down the interstate at, ahem, 65 and the engine quit. He lost everything, lights, power brakes, power steering, everything but barely managed to get the thing over to the side of the road. The car was towed to the dealer and upon arrival started right up, worked and tested in perfect condition. This happened several more times.

    Each time the car got to the dealership it was perfect again.

    By accident one evening, they noticed that right before the car died this time the oil light blinked on. Turned out that they had a connection or sensor problem with the oil pressure sensor.

    The Car’s ECM was programmed to shut down the motor instantly whenever a complete loss of oil pressure was sensed to prevent the motor from becoming a pile of scrap.

    A new oil sensor and connector were installed at a cost of about $20 and the problem disappeared. They were still happily driving the car when I went on to greener pastures.

    You may have a similar intermittent connection / sensor failure of a more uncommon sensor.

  52. Claire
    Claire June 11, 2015 6:30 am

    “my first instinct is fuel pressure intermittently dropping off”

    Bumpy road or the presence of chickens? Oh my. This makes me more than ever wish I could get by with a nice, simple quadracycle instead of a vehicle chock full of sensors and computers.

    I’m still going to explore/swap out some electronic parts first because it’s easy and cheap and because there is that diagnostic code. Next up if that doesn’t fix the problem is investigating fuel system problems. But that’s so freaking terrifying! Could be sensors. Could be dirt. Could be wires. Could be, as you say, the pump. Could be anything. Sigh. Appreciate the insight, but oh my …

  53. Claire
    Claire June 11, 2015 6:33 am

    SW OR John — OMG. Makes me really glad there are no freeways around here. That is just weird — and infuriating that such a problem would strike a nearly new luxury car.

    But yes, I’m also betting that the Xterra’s mystery problem is caused by some $20 sensor (or its wires) glitching out. Alas that it might take thousands and lord knows how much time to FIND that $20 sensor. Or that bit of inconvenient grit. Or whatever it is.

  54. Dan
    Dan June 13, 2015 6:48 pm

    Witchcraft part 2
    It was a sensor wire melted & making intermittent contact with the manifold. And, finally, the mechanic was in the car when it happened.
    Been on any bumpy roads, Claire ?

  55. Claire
    Claire June 13, 2015 8:07 pm

    Bumpy roads R me, Dan. I’m on logging roads all the time. Still … latest failed fix (this week) involved nothing but smooth roads and the Xterra was behaving worse than ever. I thought I’d cry when the mechanic said it was all fixed and perfect … then it went haywire after I’d driven less than half a mile.

    Sensor wire melted, eh? Interesting. Wires on the Xterra have supposedly been checked and re-checked. But since we’re dealing with voodoo here …

  56. Dan
    Dan June 14, 2015 12:58 pm

    Glad I only had witchcraft, that voodoo is nasty stuff.
    Every thing I “fixed” would work for a bit, then come back worse than before…and I’m a fairly good mechanic, having grown up on a car lot fixing everything. It was simpler 50 years ago, tho.
    As a parting shot, see if there is a crimped connector in a ground wire from the battery that might be corroded.
    And, unless you are totally mechanically declined, take whichever tool is required and loosen & tighten every ground connection you can find. On both ends. They are the ones attached to body & engine parts for no apparent reason. You are in the Northwet. Contact points do corrode.
    You didn’t crack that ankle kicking the Exterra, did you ?
    Dan

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