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After a bunch of trips to mechanics, my car engine is hesitating/missing intermittently, and I would love a second opinion.
September 14, 2012 3:08 PM   Subscribe

My 1998 Nissan Sentra GXE (1.6L) has been acting up for the past few weeks, in decreasing degrees of severity. After a varied set of problems and repairs, the engine now hesitates at random, more often when idling than when driving. It sounds like it's about to die completely and then returns to normal in a second. What the heck is going on?

A bit of backstory. A few weeks ago, my fiancé and I were leaving the East Coast to move to Chicago, and as luck would have it, my car died at an intersection the day before we were to leave -- no warning, no check engine light, nothing. The engine would start to rev but wouldn't turn over. We tried jumping the battery to no avail. We pushed it across the road from where it died into a mechanic's lot, who promptly replaced the distributor, as he mentioned the engine wasn't getting a spark at all.

Upon taking the car for a spin, we noticed that the engine would intermittently dip out and back to normal, causing the car to buck slightly. As we drove, the problem got worse. We brought it back to the shop, and the mechanic checked the ignition wires and spark plugs, noticing that the ends of the ignition cables had been wrapped with electrical tape at some point (?), and so he elected to replaced them with new wires.

Unfortunately the problem persisted, and so he adjusted the engine timing a number of times to see if it would help, to no avail. He checked the spark plugs, which all looked pretty good (he showed them to me, and I agreed) and decided it might be worthwhile to replace them. After the plugs were replaced, the car ran just fine. I left, went back to my parents' house with my fiancé, we packed the car up, and hit the road.

The first leg of the trip went fine. But, after waking up in Ohio the following morning, I noticed the engine hesitated once (sort of a 'dip' in the engine sound despite no gear change and consistent acceleration) but didn't worry about it. Later that day, while driving through western Ohio, I noticed it happening again at highway speed. Sure enough, it started to happen more frequently (maybe three times an hour). Given that we had a lot of driving left to do, I began to experiment with things to see if anything else in the operation of the car had anything to do with it -- I tried turning the A/C on and off, turning cruise control off, releasing the accelerator, and turning other various electronic components on and off, but nothing seemed directly correlated to the problem. Fortunately we made it to Chicago without the car breaking down/catching fire/exploding.

While here in Chicago, I tried replacing the fuel filter on my own, as a guy at an oil change shop in CT had recommended it. Part of me hoped that would finally take care of it, but to no avail.

Here in the suburbs, I brought it to another mechanic who hooked the car up to some scopes to measure the electricity output of the car. He noted that while he had difficulty getting the car to reproduce the problem, he did experience it several times. Looking at the output of the testing machines, he noted that during those moments he saw the electricity dipping during several occasions, which was likely responsible for the issue.

In response, since most of the electrical system to the engine is brand new, the mechanic cleaned a number of the circuit connections between the battery and the engine, and also topped off my transmission fluid as it was relatively low. He noted that this didn't entirely address the issue, but it seemed to improve it.

Unfortunately, it hasn't. The engine is still hesitating randomly, and it seems to be worse during idle than while driving. The mechanic assured me that the car likely won't break down again, but I'm not sure if I believe him. He noted that, at this point, it could either be that the distributor was faulty or that, worst case scenario, the car computer needs to be replaced. I'm going to try and get in touch with my mechanic in CT on Monday to check about how to replace the new distributor under warranty, but I'm at my wits end here.

I guess I'm looking for a second opinion, or third, fourth, etc. Is there something we're missing? I have some Seafoam fuel injector cleaner -- would that be worth running through the engine? Part of me is concerned that the reason the distributor blew out in the first place is still lurking somewhere in the car's electrical system, but that may be off-base. If it relates (and I told this to both mechanics) some other odd electrical things have happened with this car, particularly in the weeks leading up to the distributor blowing out:

- A few times, the turn signal slowed down to a crawl, and would speed up again eventually. It seemed to help to manually turn it off and back on again, but still it's weird. May not be related.

- Sometimes the dashboard lights would turn off and back on again at random. This would happy maybe once every few months. Also may not be related, but figure its worth mentioning.

Anyway, the latest mechanic may very well be right and I may need to just replace the distributor again under warranty, but the original mechanic seemed to think that that was unlikely. If any of you folks have a second opinion that you think might help. I'd appreciate it. The car has about 135k miles on it, and has been quite the workhorse for me over the years -- I'd rather not get rid of it as I may be working in the suburbs and would need a car to commute most efficiently. Thanks!

TL:DR -

Car engine is hesitating intermittently. In the last four weeks: it died, had its distributor replaced, started up but was bucking and misfiring, had ignition wires and spark plugs replaced, was driven from New Haven, CT to Chicago in two days, started missing/hesitating while driving with no traceable cause, had its fuel filter replaced by me, had its ignition circuit detailed, and still hesitates, mostly while idling. Mechanic recommended returning the distributor under warranty, and if that doesn't work, replacing the car's computer. I would love a second opinion!
posted by summerteeth to Travel & Transportation (12 answers total)
 
It could be a bad distributor cap and/or rotor. These are pretty cheap and easy to replace so it is worth checking out. (parts are 17 buck for the kit at rock auto)

You may have a bad voltage regulator, which is built in to the alternator. You fix this by replacing the alternator. however you should have the alternator tested off the car, and a lot of auto part places can do this. You can also have a bad belt that is slipping, this is easy-if you have any ear splitting high pitched noises coming from the car when you start it up, it is likely a bad belt-but the this model may have a serpentine belt and those are different but still need replacement every so often, your owners manual will tell you and the perfect time to change it is when you are getting a new alternator. If the replacement part is cheap and you need to change the belt it might be worth just changing it out anyway as this is one of those items that just goes bad after a while-and ten years might be enough. (new alternator is about 160 for one you want at rock auto)

Do you have any corrosion around the battery terminals? you don't have a bad battery but you might be getting screwy voltages from bad connection on the battery that is messing up your computer (this is a long shot btw)

You could also have a bad sensor somewhere, like maybe the mass airflow sensor(but if this is the case you will likely have a check engine light) or the crank angle position sensor (part is cheap, labor usually sucks for this-a great time to get some other work done usually like timing belt/water pump but not sure on this model sentra).

BTW you don't adjust timing on these cars-no idea what the mechanic was claiming with that one. That is all set by the computer and you CAN'T physically change the timing without remapping the computer which you DON'T want to do.

I don't think you have a fuel problem at all. Generally a fuel problem only shows up at high loads (like max acceleration or climbing a hill) and then gets progressively worse. When you have a problem at idle it is likely an electrical problem.

You should really buy the haynes manual for the car and check out a nissan sentra forum for help on this as well. But don't trust a mechanic that told you he adjusted timing on this car, that kinda went out about 1990 or so on most cars.
posted by bartonlong at 4:09 PM on September 14, 2012 [1 favorite]


I'd bet it's electrical, not fuel. Almost certainly.

I suspect it's something like either a voltage dip (that causes the ECU to go fruit loop momentarily) or briefly losing an essential signal trace (like the crank sensor or cam sensor). Either would take some hunting down. The other big options is corroded terminals on the battery or a loose or corroded earth (or even power supply to the fuse box or similar). I think you'd see more than an engine miss if it was main battery leads or one of the more important earths, though. Weird dash lights during the misses, for instance. You do mention that, but not at the point of the engine misses. If they were at all close together, or the lights came on at the bigger misses, then it's much more likely a voltage supply/earth issue.

1: Voltage dip = voltage regulator which is part of the alternator. It sounds like the second mechanic may have seen this when he saw a voltage drop, but maybe it's not clear if the voltage dropped because the idle dropped or if the idle dropped because the voltage dropped. Without knowing the drop and what happened at the same time its hard to guess. This could also cause the weird lights and miss as the same fault.

2: Signal trace. This should be easily diagnosed with a proper scanner. Just connect it, run the engine, watch/log the trace from the sensor and start wiggling things until the problem occurs. Check all the wires and each sensor individually. Crank sensor, cam sensor, throttle position sensor that kind of thing.

3: It may be the ECU (computer). They can get dry joints or corrosion inside that mean they get very confused and falter occasionally. They are damned expensive, so I'd be making sure the other things were discounted before I got one unless they have a trial one of another (breakers yard?) car just to see if it goes away.

4: It could be the distributor, but I find it unlikely I think. It just doesn't mesh with the symptoms for me. I may be wrong, but the dash flashing and other symptoms make me lean more towards voltage supply issues.

Either way it will be hard to pin down. You need to find a mechanic with some patience and a dogged attitude.
posted by Brockles at 5:21 PM on September 14, 2012


Hmmm.

If it was electrical, or sensor then the car would show a code (here's how).

This will tell you if there's any problems which the ECU has picked up. From what you describe any answer here will be guesswork I'm afraid. Seeing what codes the car has thrown should allow you to narrow it down a bit.

There are a couple of things you could try; disconnect the battery for a couple of hours. This will allow the fuel injection to relearn what it should be doing. It may be that the recent electrical problems have confused it. (Unlikely)

Check your ignition key; if the electrical contacts worked by the barrel have become worn, this could make the car turn off momentarily. Look for signs of burning/scorching. (unlikely)

I wonder whether you have got some water in the fuel? This would make sit at the bottom of the tank and can cause exactly the symptoms you describe as it runs through the fuel system. (This can be particularly pronounced at low revs/speeds as the fuel apertures are much smaller and easier blocked). The easy fix for this is to put half a cupfull of methylated spirits into a full tank. The meths absorbs the water and runs through the engine without affecting it. Make sure it's a full tank though so it's well diluted.

Hope that helps, let us know how you get on.
posted by BadMiker at 6:05 PM on September 14, 2012


As it turns out, the turn signal issue and engine missing issue may be tied together, I just hadn't experienced both at the same time before. However, I was waiting to turn into a parking lot, earlier, and the engine starting to dip more rapidly AND the turn signal began to slow down, simultaneously. Hopefully that sheds some light?
posted by summerteeth at 7:07 PM on September 14, 2012


An easy thing to check for distributor problems is to get your battery voltage tested.
posted by rhizome at 7:36 PM on September 14, 2012


I know absolutely nothing about cars but FWIW, a couple years ago my 97 Nissan Altima was doing something vaguely similar (hesitating, sometimes stalling at lights IIRC) and I needed a new alternator. I guess if that were your problem, someone would have figured it out by now, though. I also have the same problem with the dashboard lights going in and out (mostly out). Honestly my Altima just runs funny in general (although it has <70,000 miles), the engine (?) vibrates like crazy, especially on the highway, and I'm always convinced it's going to break down any minute, but my mechanic who is a trusted friend can't find anything wrong with it.
posted by désoeuvrée at 7:51 PM on September 14, 2012


Shoot, is it the alternator that handles battery charging while driving? If so, then forget my use of "distributor."
posted by rhizome at 7:59 PM on September 14, 2012


Yes; alternator.

Theoretically you should have enough of a store of electricity (battery) that you dont run out like that. Any leak big enough to drop power like that should blow a fuse so check your fusebox; make sure all the fuses are the correct rating and there's no sign of damage. Look for obvious previous 'repairs'; if someone has bypassed a fuse then this could be causing the problem.

Are there any other common factors to when this happens? Only when the indicators are on? Only when the car's getting hot?
posted by BadMiker at 4:31 AM on September 15, 2012


No, unfortunately I can't really trace it to any other factors. Part of me wants to say that the air conditioning being on makes it happen more frequently, but I don't know if that's valid.

To answer some other questions: The battery is maybe a year old, and the battery cables were replaced at the same time due to significant corrosion on the terminals. The fuses look ok (no hack jobs, anyway, and I pulled a bunch last week just to see; they looked fine) but I may just check them again, to be sure.

Also, after speaking with my brother in law about this, he mentioned that around the time we drove out here there were some BP stations between Ohio and here that we're serving up 'bad gas' (so to speak). Apparently they have a site set up so that folks can get reimbursed for repairs. It's kind of a small chance that I filled up at one of the listed stations, but it's not out of the question. Wondering if running methylated spirits through a full tank, as you'd suggested, would be a good idea.

Also, it would appear that the problem is more pronounced later in the day, as opposed to the morning when it's been sitting cold all night. I cant prove that, scientifically, but it appears that way. Grain of salt.

Thanks again for your continued help, folks. This has been seriously helpful. I've been trying to find a sentra forum for my year and car that seems relatively active, but haven't had much luck. Needless to say, you've given me a lot to think about.

Strongly considering getting the alternator tested at an auto parts place, soon. I had no idea that the voltage regulator was inside of it. I would assume that one of the two mechanics would've checked that out, but maybe I'm wrong?
posted by summerteeth at 6:16 AM on September 15, 2012


If it was electrical, or sensor then the car would show a code

Not always, unfortunately. You'd think it would, but sometimes intermittent, very short term, faults get ignored. The systems sometimes need confirmation of a fault (ie repetition within a certain time frame) before registering it to avoid logging false positives.

Any leak big enough to drop power like that should blow a fuse so check your fusebox

Don't agree with that logic. Cutting power supply won't increase or spike the current necessarily, which is what would be needed to blow a fuse. So, essentially, no blown fuses isn't a data point in the diagnosis.

the engine starting to dip more rapidly AND the turn signal began to slow down, simultaneously.

This does make me lean more towards voltage reg/alternator. I wonder if it starts breaking down when hot? I had a weird intermittent issue with the car throwing codes at odd times and dropping to limp home mode that kept sending us in the wrong direction and turned out to be voltage regulator. An intermittent voltage reg problem won't necessarily show up in an alternator test but it's worth (at this point) replacing it as a precaution if it is cheap enough.
posted by Brockles at 7:19 AM on September 15, 2012


How about a bad coil?
posted by Mr. Yuck at 1:23 PM on September 15, 2012


So, I called the mechanic to ask about the voltage regulator/alternator potential issue, and he said that when the car was on the scopes he didn't recognize and sort of dip in the voltage going through the system, except after the distributor. So, that brings us back to the distributor again. Unfortunately, my CT mechanic isn't entirely sure how to go about replacing a part through them under warranty, particularly with me being 900 miles away.

Will continue to update when I see progress. Thanks again!
posted by summerteeth at 12:13 PM on September 18, 2012


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