1990 928 GT with chronic 4 cylinder mode issue

Stan, I wish you luck. I see you have all the best people on this as is what I would do after 4 years.

Let me know if it is a standard and if it is for sale. Sorry,

I guess this is one of those stories that people ask when they say "I here the 928 can be a nightmare"
You can answer Yes! want to buy one

Still, you have to remember that it is just a machine.
If you put power to the end of a good wire, the other end will have power.

Speaking of which, I have come across wire that had been probed with a test light, looked good, showed voltage, but only had 1 or 2 strands left inside and would not handle current.
Pulling on wires helps find these ones.

Anyway, good luck.
Brad

Thank you both, I don't anticipate it being for sale, I have been a 928 owner for 20+ years, and getting a GT was a long term goal. (yes, Brad it is a manual, as always with a GT).

I don't expect to get to it until at least next week, as I have a day at Lime Rock Saturday with the M3.

I am nothing, if I am not persistent. I have never been beat by a problem, and don't plan on starting now. I have always claimed my greatest technical strength is problem determination, this will be just another one.

Hi Stan,

Sorry you are having trouble with your car. I'm not an expert, but if you have checked out/swapped out all major components, I'd strongly suspect the wiring harness itself. Is it possible to swap the IMS harness with another one? Or carefully inspect the wiring and determine it is able to carry the required voltage. Often, it's the simplest thing that is the culprit. Remember, that is 20 year old wiring in there.

Best regards,

Joe B.

After getting the 928 back, I was driving to a racquetball club @25 miles away.

In the first 3 miles of driving it went into 4 cylinder mode perhaps a dozen times while the IMR relay was swapped out and the bypass relay swapped in.

I had given up, and was almost back home when it no longer had the issue. I turned around drove to the club and back without it ever going into 4 cylinder mode again.

On the way down, I went off a random bump, and warnings that the anti-lock brakes and locking differential were disabled. This error did not reoccur on the way back.

On the way back, I did notice the alternator gauge dropped to @12 a few times. I recall this doing so before I brought it in the shop and testing the battery at such times showed 13+, so perhaps one issue might be a connection to the dash cluster. I do have a replacement pod to install too.

On the way back I stopped about halfway and swapped the IMR relay back in. I had no issues.

Like others have suggested, the shop suggested it could easily be a connection somewhere or even just a wire.

I don't expect to get a chance until after Saturday, but I will review the components Sean suggest first, and document what and when I check each.

Thank you all.

Stan.......by the last description the intermittent issue indicates wiring or the CE to me.

I'd completely remove the fuse/relay panel and all fuses and relays. Inspect thoroughly and replace anything suspect........I'd replace all common relays they're cheap.

Also inspect the back side of all the 'grey'wiring and the associated wiring harness.

good luck

Yes, sounds like bad ground, intermittent ground and I think I know which one it is.

Pull the air box and MAF. Right side in the V, under the throttle cable pulley is a block ground that is the grounding point for the EZK/LH. There is also the ground for the MAF and a CPS on the left side, in the V. Check those and ensure they are grounded.