Engine Stall Mystery

[Roger Beaudoin]

Just bought a 1988 928 S4 that was described to be in very good condition although some of the critical maintenance was due… so I had the timing belt, cam belts, water pump, thermostat, ignition wires, plugs and radiator hoses replaced. my capable foreign mechanic told me the car was overall in very good condition for an ebay find. Here's the problem: I first drove the car in city conditions and lower speeds for about an hour with two stops and re-starts. My first impression was that the car was NOT very powerful for a twin cam 32 valve V-8 (but I've never driven one before).. As I approached a stop sign and I applied the brakes, the car stalled and Would Not re-start after cranking it several times. After being stranded 15 minutes, it started as if nothing happened. I drove it back about 7 miles to my mechanic and cruising along about 40 MPH a half mile from the shop, it died again. Once more, 15 minutes later it started. I left it with the mechanic and he replaced the fuel pump and filter, oxygen sensor and temperature control sensor - he believed he solved the problem.. I drove it again for about 10 miles, came to a stop and revved it twice (maybe to 4,000 RPM)… on the second rev, it died again. I let it sit an hour and took it for a 45 minute cruise in variable conditions first city driving, then on the highway. I floored the car and it would Not exceed 70 MPH.. when I backed off the throttle and ran at a steady 50 or 60 MPH, it sputtered and alternated between surging forward and retarding in power… it felt like it was running on only 3 cylinders… then after a few miles of limping along, it died for the 4th time. 15 minutes later, it started as if nothing happened and I drove straight to local Porsche dealer… they are Now troubleshooting, are replacing manifold gaskets, they say are compromised and looking for further problems…(car's age prevents computer analysis they say)… Can anyone help troubleshoot this problem, before I spend a small fortune on further trial and error fixes? Thank you very much

[Danglerb]

Its very expensive to train a capable foreign mechanic as a 928 mechanic. Dealers are worse. You need to find an expert in the 928, posting your location will help.

Most issues the first place to look are relays, then grounds, then relays again.

Oh, and don't forget these.









Spaces between lines.

[Mrmerlin]

from your report you would be served well to replace the 4 running relays,
both knock sensors the crank sensor and the hall sensor.
also get the engine computer rebuilt.

Your manifold gaskets are just a money maker for the dealer,
take the car to a savvy 928 mechanic as they will be able to fix the car

[Roger Beaudoin]

Thank you for your helpful advice.. i will explore these areas

[Roger Beaudoin]

Thank you both for the advice

[JK McDonald]

Hey Roger, I realize that the car is new to you but you didn't mention if your poor performance problems were before or after your mechanic updated the timing belts, etc.... The newer 928's can be a little more complex to keep them running properly than the earlier ones.

Like several others have mentioned there are several relays, sensors and fuel pressure issues that could be the culprit but I've also seen where a new set of timing belts had been inadvertently installed a tooth off and caused some strange performance limiting issues as well.

Please keep us posted of your progress.

Michael

[Roger Beaudoin]

Thank you Michael for the reply… all I know is the car was delivered to me on a transporter from Florida. The driver told me that the car stalled for him either going on or off the truck. I was having preventative maintenance done with the necessary timing belt change and I never actually drove the car before this work was done. I had another car guy drive it to my mechanic as I was out of state. This person made no mention of it stalling on the approximate 10 mile drive to my mechanic prior to the timing belt change. I mentioned the first stall to the mechanic prior to them starting the work, but they had no experience with this car stalling in their test drives. The seller claims that the car was smooth and powerful on the highway with no issues when I bought it - But he also failed to mention that the odometer was not recording mileage and the title was signed that the mileage on the car was actual. He told me the timing belt was changed last year, but his maintenance records showed 8 years ago. So I have no reason to believe the seller. Its been a painful and expensive lesson in buying this car, as I took care to buy a car that came with extensive maintenance records. I was really surprised at the lack of impressive power in all four drives I've had in it so far.

In your opinion can a highly recommended Porsche dealer technician figure this out?

[Big Load]

A Porsche dealer must have all the necessary equipment to sort out your can. either they are just trying to mint money or the engineer they have does not know how to diagnose the car correctly. I'm not myself very good at diagnosing these issues so i will not lead you up the garden path with false information. but check what the car is idling at (low/high). leave her running and see if the symptoms a pair whilst idling. what is the oil pressure showing??

[Danglerb]

Porsche sold the last 928 19 years ago, and that last year they sold only about 100 cars. The chances of finding a dealer with a mechanic with any previous experience on a 928, AND for some reason that mechanic being assigned to work on your 928 is tiny. I doubt most dealers still have the diagnostic tools for the 928, maybe some manuals, but nobody that can do any trouble shooting.

Get in touch with some local owners, find out who in your area is expert on the 928, and save yourself a lot of money and grief.

[neil30076]

Give us a clue where you live and someone here might be willing to help you.

[Alan in AZ]

Originally Posted by Big Load

A Porsche dealer must have all the necessary equipment to sort out your can. either they are just trying to mint money or the engineer they have does not know how to diagnose the car correctly. I'm not myself very good at diagnosing these issues so i will not lead you up the garden path with false information. but check what the car is idling at (low/high). leave her running and see if the symptoms a pair whilst idling. what is the oil pressure showing??

A dealer probably does have the right equipment - but they may not have anyone who has any kind of clue.

Paying absolute top dollar to train someone at the dealership who knows nothing about 928's doesn't make much sense for most things. They will likely replace no end of things that are actually just fine... $$$

Find someone who knows 928's well and go there - even if you need to flatbed it for an hour or two to get there - it will still be cheaper AND much more likely they will (quickly) actually find & fix your real problem.

Alan

[Danglerb]

Originally Posted by Alan in AZ

A dealer probably does have the right equipment - but they may not have anyone who has any kind of clue.

Alan

I bought my Hammer, Bosch diagnostic tool, from a former dealer mechanic who owned it for years. All the early stuff was battery powered with proprietary batteries, chances of them still being good, about zero.

AFAIK the newer Bosch diagnostic box doesn't work or work well on the 928. Sharktuner is the way to go, and only independent 928 shops will have one of those.

[JK McDonald]

Hey Roger, Perhaps there is someone in your area who is a member of our 928 group that can come over and help. As others have correctly recommended it will save you a lot of grief and heart burn to seek help from an experienced 928 owner - operator.

Sadly the reason the previous owner may have sold this car is because he had 5th or 6th degree burns from paying an inexperienced shop to stumble through your current problem.

The down side of diagnosing an ailing 928 is knowing that there is a big difference between a parts changing Porsche service department and someone who is familiar with a fickled 928. In the Dallas/Fort Worth area there are several dealerships and any number of foreign car specialists but honestly in your case, I would take a 928 to an experienced and long time owner/mechanic before a high priced dealership. Even if a top flight service center knows Porsche, it doesn't necessarily mean they are current and (time wise) efficient when sorting out a 24 year old 928.

Good Luck and please keep us posted, Michael

[S4hounddog]

It almost sounds that your car is going into limp mode or the Ignition system is at fault. Are you getting any raw fuel coming out at the exhaust? My '88 928 had the same symptoms and it turned out to be a faulty ignition coil on the right bank. As mentioned before you could inspect the coils, ground points, relay but your best bet would be find someone who has the 1988 Porsche Diagnostic tool. I do have one if you live close enough.

[Roger Beaudoin]

Everyone's comments are super helpful and expected.. Thank you all for your care and concern. My first foreign mechanic was an old school guy and yes, I was paying him to learn on my car as he did excellent work on my '66 sting ray and '60 MGA (I know they are not German, but I had a track record with this shop). I originally hired him to change the timing belt, water pump and thermostat as preventative maintenance and go through the car to make sure it was reliable before I attempted a long trip. After the problem developed which he did not see in his test drive, he changed the temp control sensor, oxygen sensor, fuel pump and filter which he claimed was dirty. The problem persisted, but again in his second test drive, he didn't see it. I was in the process of moving to Ketchum (Sun Valley), Idaho and planned to drive the 928. I was forced to fly and leave the car at the local Porsche dealer with no other options. Their technician was highly recommended by a friend who used to work at this dealership. Ironically, the service manager told me that the tech has literally worked at this dealership for the past 40 years and has indeed worked on 928's. He was confident that the problem would be solved and they tell me it should be ready in a few days. I wait anxiously for their next report.

[Roger Beaudoin]

I failed to mention that the car is at the Porsche dealer in Portland (Falmouth), Maine but will be shipped to Idaho when they complete their work. I find the most recent post about the coil issue interesting and will query the service manager about this? thanks again to all of you.

[JK McDonald]

Hey Roger, It sounds like you are taking reasonable precautions before turning your "Sweet Thang" (always name your 928 for good luck) over to a competent mechanic. One comment though before you select a company for the planned shipment of your car - make sure to stress to them that you will closely monitor the odometer from the pickup points and that you have taken photos to verify the overall condition of the car. Even though you mentioned that the odometer is inop, this will at least cut down on the Joy Rides by the parking lot shuttle attendants. A friend turned his 911 Turbo over to a transport/storage company while he was overseas on a 6 month contract and when he returned his baby would barely run. He also found an assortment of new scuffs, dings and scratches on the body. After a couple rounds of threats and arm twisting plus a Better Business Report he was finally able to verify that it had been repeatedly used as a street racer by several employees at the warehouse.

Good Luck, Michael

[Roger Beaudoin]

Gentlemen: 3 competent foreign car techs including a Porsche dealer have failed to find the mysterious engine stall on this '88 S4. I bought the car for $15,000 and have spent another $10,000 on parts and labor including timing/cam belt change, water pump, thermostat, knock sensors, 02 sensor, temp sensor, crank sensor, ignition modules, ignition wires, fuel pump, filters, hoses, etc…
The interior is near perfect, the exterior is good - very good, the underneath is spotless with excellent brakes and lines… Can you advise on a fair price and do you believe a fellow enthusiast could troubleshoot this? I can't keep throwing money at it replacing parts that may be perfectly fine. Any advice would be helpful.. thanks

[stepson]

Roger, It sounds as if you have been paying a dealership to "learn" how to work on your 928. (Well actually, after I read the thread again, I find that you have been paying several mechanics to "learn" how to work on your 928.) You should probably now hire an honest-to-god 928 mechanic to fix what is wrong with it. I have no idea what 928 mechanic may be local to Maine, but I would certainly remove it from who has it now quickly.

Someone more local to Maine can assist you in finding a 928 mechanic.

There is a local to me 928 mechanic that has been known to fly to different locations to work on customers' 928s. I would think that would be pretty cost prohibitive, but it might be better than what you got.

[JK McDonald]

Roger - It's too bad that you are still trying to sort out this stall problem. After reading through your post again it still sounds like a fuel delivery problem/electrical circuitry to the fuel pump, etc... A review of the symptoms being - a lack of power, the sudden shut down and the delay in being able to restart the motor seems like fuel starvation. Surely the mechanics have verified and monitored the fuel pressure as the car shuts itself down. You can install a fuel pressure gauge in the fuel rail to check the pressure as you drive. Have you had the pick-up screen/filter inside the fuel tank replaced ?

One other thought - I wonder if there would be any recourse going back to Ebay with a complaint about the information provided by the seller. A buddy of mine actually got his money back on a Harley Davidson when he proved that the bike was not as described and the electronic odometer had been modified. It took quite a while to settle things up going through Ebay because the bike had been shipped across a couple of state lines but it was finally straightened out.

Good Luck, Michael