Running on only 4 cyl?!

[Abrankod]

Hi all, long time no talk.

I've got a problem with a friend's 1993 Allanté with northstar engine. He states that he was driving home one day, and it started acting like it had less power, and then ultimately stalled on him, and would not allow a restart.

I pulled the car to my house with my suburban, and I pulled the codes. The major PCM codes set were a P095 stall detected (duh obviously...it stalled), P034 Idle throttle angle too high, and P085 MAP out of range code.

Now, for the oddness. With those codes set, the car would not restart. Once I cleared them, I could restart, however, the P085 (idle throttle angle too high) resets, and the engine now runs on only 4 cylinders. The right 2 (looking at the engine bay) coil packs never fire. I have tried swapping the coil packs around, and as long as you try to run off the left 2 coil "slots" the engine runs.

Is this engine running in limp home mode because of a TPS error? or something else? I've tried dropping the battery connection which did nothing, doing idle re-learn, which caused the engine to stall nicely when the CCP was engaged.

Any input would help. Cadi dealer is backed up for weeks and I'd like to return this car to service as soon as possible.

-Dan

[bigfoo]

Usually when a sensor is out of range, like a MAP sensor or something , the computers will engage the limp home mode but I don't think it disables cylinders (not sure on cadillc though). I'm just speaking in general Lots of newer cars do this. What happens is they assume a set of default values for the sensors which usually results in bad gas mileage or performance but doesn't cut off half the cylinders. Maybe cadillac does cut off half the cylinders in any type of limp mode, not just temperature related.

Could be a wiring problem. If you want to try something, i'd check the map sensor first. I doubt a tps error would cause limp mode. I'm trying to look this up but not having any luck so far. Have you had any?

[mike5514]

I would start by disconnecting the water temp sensor and drive the car. If no help then I would check the throttle position voltage not over 5 volts. after doing this I would have to look at the power control module. this is as far as my knowledge will take me. Hope this helps. Mike

[Abrankod]

Ok... update on the situation. I turned to the trusty service manual for my own 1997 STS, and pulled out some interesting info regarding the whole ignition system of the northstar. This allowed me to hang my o'scope on the cam and both crank sensors to make sure they were working right. Also, I probed the connections to the PCM and found that the ICM(Ignition Control Module) had been operating in IC mode and that the ICM was in fact the problem component.

This is the module that takes the cam and crank position sensor data and "creates" a distributor like signal for the spark coils. It can operate in a mode where the spark is dictated by the PCM or if a fault is detected, it can takeover the spark production but with severe driveability concerns.

I popped on down to my local cadillac dealer, and $358 dollars later, the engine is purring again.

HOWEVER...

I still must tackle the P085 Idle Throttle Angle Too High code. I've tried the "idle learn" procedure multiple times, but it refuses to learn the new "0" setting. I've watched the TPS output in the OBD system, and with my foot off the throttle, it reads "-1.2" or so. Is this far out of range for the TPS to handle the re-learn? Or could something else be wrong?

-Dan