QuestionMy daughter is in the service, and drives her car around base at a low speed most of the time. It is a manual transmisson, and at around 20 to 30 mph or around 2000 to 2200 rpm she started getting some hesitation (maybe misfire). We rebuilt this car from a wreck when it only had about 800 miles on it and had another car we used for parts which had 15,000 miles on it. She was home on leave and said the problem was getting worse, I put in new plugs, put one wire on #2 cylinder, because it looked like it was burning a little rich, but in general all the plugs looked great. Swapped out the air flow sensor,throttle position sensor, all of the injectors and the fuel manifold they are connected to, which I think even has the pressure regulator on it (these parts were all taken from the car with 15,000 miles on it, they were not new) But bottom line none of these things changed the performance. My daughter called after a week and said it seems to be getting worse, now it's acting up at highway speeds and will die at stop lights. She has taken to a local shop with computer, they spent all day on it, agreed it was not running right, but could not find what was wrong. Appreciate any help you can give me.
Thanks
AnswerIf you really think it's a misfire, you should check the ignition system first.
I'll pause a minute and talk about the check engine lamp. The check engine lamp should illuminate when the key is turned on. If it doesn't, then you've got a computer or lamp issue. If it does light up in the bulb check, does it come on when the car is running? If so, I'd like to know what codes are present. In fact, I'll presume the shop checked for codes regardless of whether the lamp was on. Did they find any trouble codes? If so, what were they? A misfire without a check engine lamp on this car would be an oddity.
If you can feel a misfire at idle, try to track down which cylinder it is. Then you can concentrate on the plug/wire/coil for that cylinder.
Here's the things I've seen that I can recall off the top of my head:
- Split pcv hose -- causes poor idle, lean condition
- TPS readings erratic -- causes weird engine performance issues, including idle issues
- Fuel pressure low (fuel pump) -- causes loss of power, especially under acceleration, but if it's bad enough to make the car idle poorly, the acceleration performance is so bad the car is basically not driveable
- Idle control valve -- any sort of idle issue
- Poor contact in air flow sensor connector -- general lack of power/bogging
At this point, a *really* good driveability shop may be your best bet-- at least for diagnosis. Experience and knowledge of how the car's EFI system operates are the two largest keys to having the ability to diagnose your problem. I don't have a real good understanding of how the car feels when this happens, and that's usually the key to sorting out problems like this. I typically gather more information about the likely nature of a problem from a scan test and a test drive than I'd ever be able to glean from a book or a diagnostic tree.
If you can pin down some more specific information-- what you've given me so far is actually very good-- such as if the problem occurs only under accel, only when hot/cold, or anything else all the occurrences have in common, I might be able to tailor my guessing a little better. It may also be of assistance to know the mileage on the vehicle.
Hopefully, I've helped at least a little. If you need further advice on testing the ignition system or have further questions, let me know.
