Intermittent Problems with my Olds

oldsmobile

#1

I’ve got a 1996 Oldsmobile Cierra 3.1L. About a month ago it wouldn’t start in the morning, but then started right up when I got it to a mechanic. This happened a handful of times in the following weeks. Also, it stalled out once when I was driving it (and then started right back up about 10 minutes later). Another time after driving it about 40 miles I was waiting to make a left turn at a red light and the entire car started to rock and bounce rather violently. I got it off the road and had it towed about an hour later, and when it got to the shop it started right up.



The mechanic changed the crank position sensor and it ran real well for about 200 miles and a week’s worth of driving without any problems. This morning, I went out and tried to start it and it wouldn’t start again. The fuel injection definitely kicks in, but while the engine cranks it will not fire. I’m sure it’ll start up as soon as I get home.



I’m bringing it to the dealership tonight as a last resort (before buying a new car, of course), but do you folks have any ideas? My next guess is the ignition module and possibly the computer, but this has become such a hassle since I’m not capable of changing out parts myself. Any ideas?


#2

If you know you have fuel pressure and spark is the missing element, I guess I would suspect the coil and maybe the module but intermittants are really a problem to find and could be a number of things.


#3

I too suspect a problem in the ignition system. It could be the ignition module, the cam position sensor, or the crank position sensor. I know you have replaced the crank position sensor but you can still suspect it and its wiring. The problem with diagnosing intermittants like this is that part replacement is about the only way to progress which can get expensive. Unless the problem appears while a mechanic is available to troubleshoot, there is no sure way to find the faulty part. Usually ignition modules fail completely or have heat related problems. It is unlikely to be the coil as you have three and the engine would still run (poorly) with 2 cylinders misfiring.

Good luck on this. Post back if you find the culprit. We can use the feedback.


#4

In perusing Alldata, I noticed your engine has two crank position sensors and one cam position sensor. There is a course crank position sensor which looks to be inductive that goes directly to the igntion module which is probably used only during starting. The Engine Management Computer gets its timing information from a hall effect crankshaft position and a hall effect cam position sensor. Once the engine is started and running the computer switches the bypass switch to send the computer derived ignition timing to the igniter.

The ignition coils are indeed a coil pack of three firing two cylinders each using the waste spark method. An open collector transistor is dedicated to fire each coil.

So the mechanic is going to have to determine whether the signels to the ECM are intermittant or the ignitor is fouling up.

Again hope that helps.


#5

All of this, and no DTCs (Diagnostic Trouble Codes) set in the engine computer!? I would expect some P030X, or something.