When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
There is a factory diagnosis test plan manual for the fuel and ignition systems in the tech docs sticky thread. It would probably be better to methodically work through the systems instead of scattershot swapping and pulling things apart. That way you can figure out what’s good and what’s not. Because there are a LOT of variables at play, here.
Indeed, the factory test plan is critical to proper diagnosis. The diagnostic process begins in WSM Manual 1A around page 273. Here is the link to the consolidated WSM manuals
Also, here is a handy test matrix that allows you to filter for your symptoms and it will display which tests to perform and which page in the WSM the test is detailed. Hope you find this helpful.
In looking at the matrix, I would classify your symtom as "Poor Hot Starting"
Last edited by Michael Benno; 12-31-2023 at 08:39 PM.
Wasted most today putting the dash back in. Then the left power window motor died. Think the top part where the brushes sit failed. Is there a repair for that.
I found and cleaned 13 ground points but I couldn't find any ground points around the bell housing area. Anyone had pictures for the 87?
I got the 2 rear battery,4 brake harness, 2 coils, 2 engine block to chassis, 1 at igniters, 2 at CE
The heater control literally crumbled when I removed the center console. It glued and taped it back together it kinda worked.
I pulled a vacuum on all the FPR and the ally hold. However I'm beginning to doubt the previous mechanic actually changed them.
I don't think the central vacuum hose for the FPRs is connected properly. It runs under the intake manifold and when I suck on it there is nothing. No vacuum. Is that normal?
I'll check locally if anyone can repair the ECU. Doubt it so I'll probably send it out. I did find one locally for a 91 for the same price as a repair. Need to decide which to go with.
rob,
i believe the bell housing ground points sit under the intake system, which is a PITA to remove, but once its out, might as well restore the intake, hoses, etc..Also the knock sensors, change those while youre there, if you dont feel like testing them. the link i sent you shows you how to test pretty much a lot of things with a mutlimeter or oscilloscope.
clean those grounds till theyre shinyyyyy! i replaced my ground cable, got one from the local auto store and installed it.
Once the CE panel was removed and restored/cleaned, the car lit up like a xmas tree, after doing all grounds and CE panel and ground cable. I used a dremmel tool to clean the CE panel connectors, replaced ALL fuses and the important relays (55), the interchangeable ones for sure.
Most of the problems on those 928 are electrical. The rough running could be from the LH, typical symptoms of rough, then dying incidents...
A 928 guy burned his engine down because of leaking injectors.. be careful.
I think you're better off restoring your ECU, because they will upgrade the electronics and give you a warranty as well. I wouldnt intsall a used "running" ECU, as it will fail eventually. The 87 ECUs are known to fail, more than the earlier ones, which are sturdier... The controls, try to find used one from a junkyard or from Ebay etc... These are plug and play. easy to replace. not sure how much you wanna spend on the vehicle. i would get it running and idling first, then tackle the cosmetic parts, etc..
Hope that helps. Keep at it! Nothing like firing up and rescuing an old 928 that has been hibernating for years....sounds like you've been there before. Good luck,.
Here is the vacuum diagram for the S4. The vacuum source to the splitter and FPRs is generated by the plenum vacuum (engine running at idle or cruise). It is open to atmosphere with the engine off. So your test is not valid. If you want to see if it is connected to the plenum, put your vacuum gauge on the main vacuum hose from the plenum where the splitter is. Note the vacuum with the engine running. It should be about 18in Hg. Once you have verified the vacuum source is connected correctly, then validate there are no leaks on from the splitter side. Plug your vacuum pump into the splutter and if you have leaks, test each connection to the slitter for a vacuum leak
rob,
i believe the bell housing ground points sit under the intake system, which is a PITA to remove, but once its out, might as well restore the intake, hoses, etc..Also the knock sensors, change those while youre there, if you dont feel like testing them. the link i sent you shows you how to test pretty much a lot of things with a mutlimeter or oscilloscope.
clean those grounds till theyre shinyyyyy! i replaced my ground cable, got one from the local auto store and installed it.
Once the CE panel was removed and restored/cleaned, the car lit up like a xmas tree, after doing all grounds and CE panel and ground cable. I used a dremmel tool to clean the CE panel connectors, replaced ALL fuses and the important relays (55), the interchangeable ones for sure.
Most of the problems on those 928 are electrical. The rough running could be from the LH, typical symptoms of rough, then dying incidents...
A 928 guy burned his engine down because of leaking injectors.. be careful.
I think you're better off restoring your ECU, because they will upgrade the electronics and give you a warranty as well. I wouldnt intsall a used "running" ECU, as it will fail eventually. The 87 ECUs are known to fail, more than the earlier ones, which are sturdier... The controls, try to find used one from a junkyard or from Ebay etc... These are plug and play. easy to replace. not sure how much you wanna spend on the vehicle. i would get it running and idling first, then tackle the cosmetic parts, etc..
Hope that helps. Keep at it! Nothing like firing up and rescuing an old 928 that has been hibernating for years....sounds like you've been there before. Good luck,.
Sam
Thanks. I was afraid you'd say that. Guess Saturday is spoken for. I have to go back to work today and tomorrow.
Here is the vacuum diagram for the S4. The vacuum source to the splitter and FPRs is generated by the plenum vacuum (engine running at idle or cruise). It is open to atmosphere with the engine off. So your test is not valid. If you want to see if it is connected to the plenum, put your vacuum gauge on the main vacuum hose from the plenum where the splitter is. Note the vacuum with the engine running. It should be about 18in Hg. Once you have verified the vacuum source is connected correctly, then validate there are no leaks on from the splitter side. Plug your vacuum pump into the splutter and if you have leaks, test each connection to the slitter for a vacuum leak
Thanks. Guess when I go analog it's hard to go digital again. I need to sit myself down and read. Let's see how much I can get done at work without anyone noticing.
Btw I found a spare motor last night. I'll give it a try.
Based upon many of your comments and issues described, is it possible this s4 was in a flood?
I do love these cars. I marvel every time I work on one how advanced and high quality 90% of the material engineering. 10% Porsche shat the bed on.
I began to think that this car might have been about tub depth in water because of all the dirt and sand I power washed off the suspension especially the front sway bar mounts.
Dash done-ish. Tired to color match but it's hard to tell if it's grey or olive. Not to mention the sun damage. Still better than before. I put headliner material in to give it a bit of cushion but it looks puffy after I installed it. Think the glue is sit out gassing.
The 911"matured" closer to the 928 markedly with the 996. I've heard the 997 and 991s are even closer.
Cleaned it again. It starts and idles a bit longer but still no prize.
.
I agree with the importance of cleaning all the grounds. That is ALWAYS beneficial.
Another thing that I always check pretty early on in any diagnostic effort is the fuel pressure.
It's really quite easy to check, and it can be very revealing. If it's good, then you eliminate a bunch.
Check it at key on, while running, and at shutoff. It can help find a leaky injector(s), bad FPR, etc.
.
12-31-2023, 08:32 PM
