safulop

Oh God, the grounds on either side of the bell housing? You have to get to these from underneath I guess. Well, at least I have something to tell the shop to do.

soontobered84

The grounds for the computers are on either side of the V at the back under the air cleaner. Remove the air box to access them. They are under the fuel lines and vacuum lines, but you CAN do it from the top. I took the opportunity to clean the grounds above the CE panel as well as the coil grounds while I was at it.

And one more: remove the main engine ground (the bare multi-strand copper cable) at both ends and clean the ground points and both ends of the cable. This is done from underneath the car and takes about 5 minutes total. But it's worth it.

Good Luck!

Landseer

I'd also consider bypassing the battery shutoff system, replacing it with a standard ground strap from Mark or Roger.

Don't worry too much about being able to exactly describe the solution at the end of the day. Attack all of this as preventive/corrective maintenance and hope it solves itself.

Even if the electrical stuff seems to fix it, consider it to have simply gotten you to the minimum baseline to support troubleshooting, I'd then immediately run thru the Dr Bob list, no matter how good it seemed to run. His troubleshooting is artwork and these cars are so fickle, with layers of intermittent problems, that it could have great value.

safulop

^^^^^^^^^^^ I already took the kill-switch out of the equation just to make sure. I connected the 6-gauge wire (serving as ground strap) directly to ground, bypassing the switch. This had no effect in particular. I'm assuming that if the ground strap is sufficient to run the battery and the accessories of the car, it should run properly at idle at the very least. I feel like at least now there is some explanation for the behavior of continued richening, because in the standard documentation there is no way to produce this effect from a good LH. This is why the shop was so baffled, they aren't all over Rennlist reading our "TSBs" as it were. Porsche no longer issues official TSBs on the 928 I figure, but this business of the LH behavior with a weak ground circuit should certainly be added to all the documentation on the car.

Landseer

Well, in the troubleshooting documentation, ie the test plan, at least for the LH 16V and the LH 32V 85/6, it is the first item on the list IIRC. Grounds.

Its been really interesting to see, over my 8 years here, the emergence of issues that are common across the platform --- at the 20-30 year mark in the life cycle of the cars. The stock plastic ground covered groundstrap has been seen to fail on both ends.

Alan and Dr Bob, again from memory, both saw them fail on the battery side, hidden under the plastic,with speculation that offgasses from the battery caused the corrosion. Mine have failed on lesser examples of the cars.. due to water and/or mouse pee where the strap wingnut attaches to the cars, as the moisture got under the plastic strap. Failure was intermittent, and sometimes so bad the car was dead as a doornail 5 minutes after a flawless ride, due to touching the strap with cargo removal in between driving.

I'm not certain yours is solved yet. Expect multiple issues.

TSBs are in the documentation from Morehouse. 20-30 year mark TSBs are buried in postings.

The beauty of these cars is that normal guys give up on them and bottom feeders like me buy them cheap and make them run more or less. You've hung in a long time, don't get frustrated, don't give up.

drwhosc

you got an 88. it has a primitive diagnostic port. You can look at the lh and ezk readings. get theo's tool. UDT999 http://jenniskens.livedsl.nl/diag/Diag.htm

It will tell you what sensor is bad and if you are getting the proper voltage. Again. it is the simple stuff.

Also you should get a bottle of deoxit and put some on your terminals. that stuff is mazing in these cars.

Still have to say feel your pain, but love your persistence. I bought a temp2 sensor that failed within a year and half, but it sure does sound like you are battling a fuel delivery issue.

safulop

Yeah I'm not giving up yet without a fight. As I explained to my wife, this is a problem I can't just run away from. Fixing it is the only option to preserve the value of the car. If I give up, even if I decide I am fed up with it, I would have to sell it for a song because it is not running. And that won't do, not until I've exhausted everything I can do. I will tow it to L.A. for an appointment with a real expert if I have to.

safulop

My crystal ball told me when I bought this car that this day would come. I have tested the limits of what can be done with limited mechanical abilities on my part, together with no one but an intrepid local German car shop to serve as "experts". We will see how it turns out.

John Speake

These are the two engine electronics grounds...

Mongo

One of those was loose on mine and it caused years of running nightmares until one day I found it on a troubleshooting adventure.

safulop

^^^^^^^^^ Years? Wow, that hurts. Mine first became an obvious problem this past spring, then was OK from August until now, although mileage was down possibly indicating rich running from the problem being present only slightly. Now it requires a towtruck

Mongo

If you did a search on me, you would find at least 3-4 threads on the issue. I had changed everything from LH, to MAF, to a CE Panel cleaning. Then one day, I started cleaning grounds, and found the LH ground loose. I cleaned both the LH and EZK at the back, then used a little bit of blue loctite on the bolts to hold them down and have not had a problem since.

soontobered84

It took me a full year to figure it out. Rebuilt LH, MAF, Timing belt, etc. It was running good at the start of the trip from DFW to SITM, then we were radioing back and forth about fuel levels and mine was on empty while everyone else was 1/2 full. I was asked about making it to the next town in Arkansas (Hope) and I thought I should make it. I didn't. Basically averaged 4 mpg for that trip. As I got into Tennesee, it became necessary to turn the car off and restart, which for some reason would reset the fueling. It would always crank right back up at this point and run fine for a bit, then the computer would decide that the engine needed more fuel. It would add more and more until the engine would die from too much fuel. Restart and everything was good again for a while. I thought while at SITM, that the best and brightest minds would figure out what was happening. We replaced LH computer there, MAF, EZK. None of which did anything different. Checked the engine harnesses and kinda thought it might be a problem with the engine harness. When I got home from that trip, I was ready to run shorts and grounds in the harness, when my uncle tried to test the test light. Alas, the test light would not work because the engine showed no ground.

Since I cleaned and tightened the grounds, I have had zero issues with the car's ability to run. YMMV

safulop

Yeah my mileage in city has always been below spec, (like, since in bought the car in 2010) but I had always put that mostly down to the Autothority chips. Recently it fell by an additional 1 mpg and I started to get faltering idle (probably due to flooding), then most recently I started to get this hesitation at wide open throttle I started the thread with (again, probably due to flooding). Now, like you say it starts up just fine but is bogged down to 0 rpm in about 30 secs.

Mongo

Sounds like it stalls when the O2 loop closes. On a cold start, the oxygen sensor is ignored for about a minute I think. This makes me believe it could be something related to grounds. The O2 sensor shares the LH ground by the way.