1990 928 GT with chronic 4 cylinder mode issue

928mac;6003 wrote: Oh man that is a pisser. it still must be an electrical problem and you may have to inspect the entire LH/EZK to engine bay harness.
Sean or Malcolm maybe able to say which circuits, but at this point if you dont find anything behind the CB panel, you may have to visually inspect every inch of harness looking for any scraping or bulging in the wires/harness.
sounds like you have done everything else.

www.tmworld.com/file/4479-6436546.pdf?force=true

A key question is whether it is one or many problems. I am thinking it is more likely one problem than many, and as John suggests, a ground is a good candidate. Of course they were all checked by professionals at least once But we know that doesn't mean much.

stepson;6004 wrote: I checked the main engine ground (the one under the car on the passenger side)and it was hooked up and tight and everything, but not one electron was getting throught the braided cable. I removed the cable, cleaned it (and the engine mount and the frame mount) checked continuity and reinstalled. It has run great since. I did clean and tighten the coil grounds and both grounds at the back of the "V" just for good measure.

Your airbag and PSD warnings are probably related to ground issues as well.

My thoughts are that the computers and the car would work just fine as long as they could find a ground, but when they had to search for a ground, all kinds of wacky stuff would follow.

Good Luck

It is the direction I am going in, certainly easier on the back, then R&R the panel, although it has many grounds near it as well and I wonder about those too

There is a quick easy way to check this ground issue as well Stan.

Man I hate throwing stuff at you,

you just have to tread through all our suggestions and do what you think is best.

OK
you can take a roll of wire, connect it to the battery, run it to the fuse panel(just across the seats), throw a connector on it and stick it with the rest of the grounds.
Then do the same but run it through the fire wall and connect it to the engine at any head bolt.

This is a quick test for bad body grounds.

BTW completely removing and checking continuity/resistance of those heavy ground cables will tell weather they are corroded in the connector.

I wish I was there to give you a hand rather then just blab away.

Brad

928mac;6012 wrote: There is a quick easy way to check this ground issue as well Stan.

Man I hate throwing stuff at you,

you just have to tread through all our suggestions and do what you think is best.

OK
you can take a roll of wire, connect it to the battery, run it to the fuse panel(just across the seats), throw a connector on it and stick it with the rest of the grounds.
Then do the same but run it through the fire wall and connect it to the engine at any head bolt.

This is a quick test for bad body grounds.

What gauge wire do I need to use?
I actually have a spare used battery ground cable, it is really long, so can probably do this.

928mac;6012 wrote: BTW completely removing and checking continuity/resistance of those heavy ground cables will tell weather they are corroded in the connector.

Someone suggested off forum that I would really need to do a load test to know anything. What test are you suggesting?

I could just ask one of the 928 vendors to price a set of ground cables, swap them, rather then check them. A 21 year old car could probably use new ground cables. I can't easily find their cost on the 'net

928mac;6012 wrote: I wish I was there to give you a hand rather then just blab away.

Brad

The moral support helps quite a bit. Knowing that others will offer suggestions rather than me simply guessing on my own, is quite useful.

Stan.Shaw@Excell.Net;6016 wrote: What gauge wire do I need to use? (Just 14-12 G would be lots, its just assisting to help locate if that is where the problem is)
I actually have a spare used battery ground cable, it is really long, so can probably do this. (a 12-10 G would be good for sensor controls at the engine, its not being used solely for cranking)



Someone suggested off forum that I would really need to do a load test to know anything. What test are you suggesting? (resistance test should read no more then .3)

I could just ask one of the 928 vendors to price a set of ground cables, swap them, rather then check them. A 21 year old car could probably use new ground cables. I can't easily find their cost on the 'net
(You can go to any auto store and by ground cable pre made)




The moral support helps quite a bit. Knowing that others will offer suggestions rather than me simply guessing on my own, is quite useful.

Here are some examples

www.lawsonproducts.com/webapp/wcs/stores...reId=10001&langId=-1



www.eastcoastterminals.com/battjumpgr.pdf

www.grainger.com/Grainger/GROTE-Ground-Strap-Braided-2FFT3

www.oreillyauto.com/site/c/search/Batter...trap/N0848/C0061.oap

I am nearly positive I replaced the battery ground cable, after reading about Landseer's plights. If someone has the specifications on the other straps, length, gauge, connections, I would pick them up and replace them, otherwise I will pull them and bring them to the napa store for replacement.