88 Repair misadventures

[KDirk]

About a week ago the factory original harmonic balancer on my "good" 88 started to separate (at around 67,800 miles). Had to buy one (did have a spare on  hand for the 91's, but is a different part) from the local parts purveyor, which was Dorman branded. Also bought an aftermarket crank sensor (this was a big mistake) as they didn't stock it in Delco/Delphi and had too long a lead time to get one in.

 

Swapped both out and upon starting the car, it ran terrible. Engine speed was all over the place, almost semi-random on the tach. Acceleration and power were piss poor, and while the car ran (barely enough to drive on local roads, but not on the highway) it was obvious the new crankshaft position sensor was bad right out of the box. Went online and ordered a Delphi crank sensor and swapped it on last night, and that solved the aforementioned drivability problems.

 

Well, almost. Was just out on a drive in it, and it had an intermittent miss/shudder on acceleration between 65-75 on the highway. This behavior is somewhat reminiscent of  problem I had with a faulty ICM (Delco ignition setup, I ditched the Magnavox ICM and coils years ago) and yet slightly different. So now I need to swap the ICM and see if that cures it, or if something else. No codes set, so won't know if the ICM is the cause until I change it. Worth noting that the ICM is the only system on the car that sits beyond the scope of OBD, so a fault there will never set a code, because there simply are no ICM codes. 

 

I'd like to point out that the aftermarket crank sensors appear to have a very bad track record of reliability. Sometimes OEM is the only way to roll, and thankfully we do still have that option for this particular part. 

[EmTee]

Possibly a coil failing?

[KDirk]

Possible, certainly. I have spare coils to try, but past experience with a similar issue has me leaning towards the ICM being at fault. I'll probably try coils first since they are easier to swap, and then change the ICM if that renders no relief. I also have an intermittent issue with what feels like late shifts, and am wondering if the vacuum modulator on the transmission may be suspect. I had to replace one of those in my 91 coupe years ago.

[KDirk]

As a quick update, I started by changing the ICM. This seems to have cleared up the stutter/stumble at highway speed (60-70MPH) but I still get intermittent low RPM at idle where the engine will stall out. Going to check IAC, MAF and then TPS in that order. No codes being set, but this is really bugging me. 

[KDirk]

I guess I spoke too soon. The issue with the stumble and stutter at highway speed has returned this evening, so it obviously wasn't the ICM after all. In monitoring ECM data for the MAF, IAC and TPS, so far I can't catch any one of three in the act of screwing up, so to speak. I guess my next step is to swap the MAF, since that's easy, and see where that gets me. This is a real pisser trying to nail down the source of the issue. 

[samakijoe]

Any progress??