obrigado

Had a second run-in this weekend with a power loss / hesitation issue on my 1987 944S with ~100k miles on it.

Basically, the car starts losing power (feels like you've lifted off the accelerator) and then eventually dies and shuts off. Trying to restart right away gives you a few seconds running rough before dying again at idle. If you let the car sit for 20–30 minutes, it will eventually restart successfully. (Waiting this out on the side of the highway is... not ideal.) This seems to happen on warmer days (80°+) after an hour or two on the highway.

The first time this happened, I replaced the DME relay, fuel filter, crank shaft position sensor, and speed reference sensors. Apparently these weren't to blame. This time, the power-loss drama was accompanied by a loud whine from the fuel pump. Now I'm suspecting the pump or the FPR according to some reading on Clark's.

So a few questions for the Rennlist brain trust:

1. Does my suspicion towards the FPR seem reasonable?
2. Technically, I should test the fuel pressure to confirm that it's an issue with the FPR, but would need to source a gauge and an adapter. Worth it?
3. FPRs for the 944S are ridiculously expensive, looks like the Bosch part is NLA. OEM PN is 94411019804... I believe the Bosch PN is 0280160263. Uro also makes the part at 1/4 the cost, but I'm nervous to trust them with something mission critical. Does anyone have a lead on the Bosch part, or a kind word to say about Uro?

Big thanks for any assistance, I realize I'm piling on the questions here.

SC924S

Hey Obrigado, my understanding is a quick, easy way to check the FPR is to run the car for a little while and then pull off the vacuum line connecting to the FPR and give it a sniff. If the FPR is failing, I've heard that you'll get pretty strong smell of gasoline. That being said, you may be able to rent a Fuel Pressure Gauge from your local auto parts store for nothing, so long as you return it. Some have it, some don't, but would be a pretty easy check.

If it is the FPR, I have heard that those are nuts expensive. Having considered that route before myself, I would suggest going all in and getting a Lindsey Racing fuel rail kit. They come with their own FPR, no damper, braided SS lines, regulator, etc for like $550. Considering the OEM damper is $350 by itself, might not be a bad deal.

Hopefully this helps.

Zirconocene

I don't know if it will work for the pressures that 944 needs but because the 928 is also afflicted with terrible prices for FPRs, there's a Rennlister that has made new FPR units for those cars. I believe that he has made them somewhat customizable so you can probably get it to work for the 944. If you're interested, contact Roger at 928sRUs (no affiliation) and he can set you straight with things.

Good luck

obrigado

Thank you SC924S and Zirconocene.

The Lindsey's an interesting option, hadn't considered it — I already replaced the fuel lines with OEM, so I'll probably see if I can source just the FPR. I reached out to Roger at 928sRUs and he graciously pointed to Delphi and URO manufactured FPRs on Rockauto. He suggested that he hasn't seen much warranty activity around the UROs which means they're likely fine, but I will probably give the Delphi a try.

I'll probably just buy a cheap pressure testing kit from Amazon with an M12 x 1.5 adapter instead of dealing with a rental.

Thank you again — I'll post an update if it's a fix or a fail.

Cyberpunky

have you tried jiggling the wires at back of the motor from the speed and reference sensors? I had similar issue and it was the harness going from that connector back to DME. The heat causes a poor connection but when it cools they tighten up. I roll started the car so many times till i read of the jiggling and realised it was the harness. Replaced the harness and never had a drama since

SC924S

I wouldn't think the S&R sensors would have an effect when the car is driving around, they are only used for startup as I understand it.

Breakaway944

Why are you talking about the FPR when you have not taken care of the bad fuel pump? If you are having a fuel problem and your fuel pump starts making strange noises, start with the fuel pump! Fix the known bad part first.

obrigado

Thanks all for your input.

Cyberpunky — I will double-check the harness, but the speed and reference sensors were replaced after round one of this issue so the connectors (at least on the sensor side of the equation) should be relatively fresh.

Breakaway944 — It could definitely be the pump, but my current hypothesis is that it's a symptom and not the source. From what I'm reading the FPR tends to fail "open", causing pressure at the rail to spike, which means the pump makes a racket trying to keep up. Reasoning's based on posts like this and Clark's troubleshooting page. Regardless, a new pump's on the way along with the FPR just in case.

Minispeed

Even though the website is still showing ot the 16v rail kit is NLA. I ordered one last year with ss lines and they said they can't get them anymore. I got an s2 rail on ebay as they allow all 4 lines to be replaced as the s has the fuel rail to damper lines non replaceable. I got one of their adjustable fpr and a gauge kit for it too. They say you can leave their gauge kit on for future diagnosis but since they warn of it maybe hitting the hood i took it off. I didn't have your problems and didn't smell fuel as described above but the car did small really rich. One mistake i made was ordering all lines for the s2 rail after i had ordered an S FPR as the line from the FPR to the tank return are different for s and s2.

I do hesitate to recommend lindsey racing as they still never refunded me the difference in price ($236usd) between the billet rail set i ordered and stock style ss lines i got however in terms of quality fpr that bolts right up it worked well and is serviceable if i remember correctly. Just be careful if they call you and say they don't have any item in stock cancel the whole order then re order.

obrigado

Thanks again for all the feedback. A quick update on this... didn't get around yet to R&R'ing the pump or the FPR. Same issue happened on a trip this weekend with pump noise, hesitation, stalling, and delayed restart again after about an hour of driving. Was a bit cooler this time, ~68°F ambient. In any event, water temp never goes above the high-side tick mark on the gauge.

After letting it cool off and getting home, I measured the fuel pressure and it was a little off of the specs listed on Clark's, but not massively so:

• Pump only: 42 PSI vs. 55±3 PSI spec.
• Idle: 50 PSI vs 48±3 PSI spec.
• Leak Down: 25 PSI vs 29 PSI spec.

Anyone think these numbers are far off enough to be of concern?

Now having some doubts about the FPR theory — if it is an issue with the FPR, then it's only going haywire when the car's warmed up after an hour or two on the road. (I've yet to take a measurement in the midst of the actual symptoms. Not exactly what I want to be doing on the side of the highway.)

Possibly just an issue with the pump itself as Breakaway944 suggested. I don't really understand how pressure could be higher when then car's idling vs. engine-off with just the pump jumpered. Maybe a difference in power off the battery vs. alternator?

Still leaning towards just replacing both the pump and the FPR, but it's definitely a strange issue.

Also if anyone's looking for a cheap fuel pressure tester, I can report that worked fine and included the right fitting to get it onto the rail — though I had to "borrow" an O-ring from another adapter in the kit. Hard to argue with $26.

I replaced the wires and the plugs while I was in there today, haven't driven far enough to see if these are involved in the issues. The plugs looked a little rich — I don't know how long they've been in the car, it's the first time I've replaced them in my ownership. The Boschs I took out were old enough to be "Made in Germany" instead of Russia like the batch I swapped in.

SC924S

After re-reading your initial post, combined with this new one, I would bet my lunch money on it being the pump or the fuel filter. I think your note that it only happens after a while of driving is fairly convicting: the heat generated by the transaxle after a long driving period is enough negatively impact your pump or the electrical connections near by. The pump is close by that transaxle and an hour of highway driving is certainly enough to bring that gear oil up to temperature, which takes much longer than warming up the coolant or the engine oil. Replace the pump + filter and while you're in there, check the wiring and clean all the connections up. This may be a simple hypothesis, but it makes sense that the only heat the fuel pump sees is from the transaxle, so a longer period of driving will radiate more heat to the pump.

obrigado

Thanks SC924S, that makes sense — I already replaced the external fuel filter, but just ordered the in-tank strainer filter (928 201 081 04) to replace along with the pump. 🤞

obrigado

Quick update on this:

The most recent round of intervention involved replacement of the FPR, fuel pump, and in-tank fuel strainer filter. So far, I've put about 1000 miles on the car without the spontaneous shutdown issue resurfacing. I won't be 100% confident that it's resolved until I put on a few more miles in different conditions, but for now...🤞.

The in-tank strainer was clean, but removing it turned out to be a major ordeal since the threaded insert spun out of the tank during removal. (This part from 928sRus saved the day.)

Since the strainer was fine, it's likely that the issue was either related to the fuel pump or the FPR. A differential diagnosis is impossible since they were replaced simultaneously, but just wanted to offer to anyone else experiencing similar issues that in my case one or the other was likely the culprit. (Other items previously replaced which did not resolve the issue: Plugs, wires, DME relay, fuel filter, crank shaft position sensor, and speed reference sensors.)

Thanks again to all who helped in this thread.