88 S4 wont start

LummoxPG · LummoxPG's Garage

Ok here's one...hopefully someone can chime in...My 88 S4 always started up great when cold, but when warm would start hard so...I replaced the fuel pressure regulator with the corresponding Bosch part...and now it wont start at all...all the lines are hooked back up...i cannot see where I missed a step...is vapour lock possible?

LummoxPG · LummoxPG's Garage

I have just checked the 15 amp fuel pump fuse and it's good, also I only just replaced the fuel pump relay a month ago. Bit of a head scratcher...last night I even removed the fuel lines off the old regulator and then hooked it back up again and it started up fine, first try...and now with the new regulator...nothing. Admittedly, since installing the new part today I have not installed the old regulator to see whether or not it starts, in order to see if the new regulator is faulty.

LummoxPG · LummoxPG's Garage

Ok...so I put the old fuel regulator back in...guess what....fired right up...hmmm thinkin that Pelican sent me a faulty regulator...that or..and i'm not sure it matters but on the original
bosch part was the number 752 and on the new one the number 519, although the part was identical looking in every way....either way...someone's got some splainin to do...freakin me ouit pullin fuses and relays...grrrr

Mrmerlin · 08-16-2015, 11:27 AM

you probably got a fuel damper instead of a fuel pressure regulator

LummoxPG · LummoxPG's Garage

Mr Merlin...I suspect you are right sir...the part number on the Bosch box is 0 280 160 297 which is suspiciously close to other dampers sold by Bosch...although the receipt I got says 928 110-198-04-M14 fuel pressure regulator.....arrrggghhh

Mrmerlin · 08-17-2015, 04:02 AM

quite possible both were opened and then put into the wrong boxes as they both look quite similar

LummoxPG · LummoxPG's Garage

The FPR saga continues... so I returned the FPR that Pelican sent me...no worries there and spoke to a
knowledgeable service rep. I explained that the part number on my original Bosch FPR was 0 280 160 034 and the part number on the replacement the sent me was 0 280 160 297, he figured that the 297 was the part number they were using now and that the one that I had received may well have been faulty so they sent me another...same thing...no dice car starts with the old 034 part but will not start with the new 297 part...curious thing is that the aperture in the bottom of the new part where the fuel comes inti the regulator is way smaller than in the old 034 part. I am not sure if the FPR in an 88 Euro is different from the North American model...but that is what I beginning to suspect...that or 297 is a damper.............any thoughts?

LummoxPG · LummoxPG's Garage

Okay...I am starting to think that I might be a moron...and despite the PET that I am following suggesting that the FPR in a 1988 928 is located at the front of the engine just to right of the oil filler cap...that this is in fact the damper location and that the FPR may be located at the right rear of the engine where they suggest the damper is....is this correct?

Mrmerlin · 03:34 AM

Ahh I see your path.

So here is the layout of the dampers and the FPR.

There are two dampers on the S 4.

There is one fuel pressure regulator.

NOTE the fuel pressure regulator is at the back of the fuel rail on the right side of the engine,
just above the #4 cylinder.

The dampers are at the front above the water pump and the left side rear fuel rail above the #8 cylinder

The FPR looks just like one of the dampers so care must be taken to not mix them up

LummoxPG · LummoxPG's Garage

Thanks Merlin...correct again!...I pulled the air filter shroud and saw the FPR in question...I was able to see the numbers 297 on the part and that cinched it for me. I have ordered 4 new fuel lines from Roger so I will wait until they arrive to switch out the regulator.

S4hounddog · 09-07-2015, 08:14 AM

Yes, I had the same confusion when replacing the fuel Pressure regulator on my '88 S4. The Damper is in front above the water pump (part 034), the regulator is at the back of the motor. I found a great website from the 928 Porsche Club of France that details every component on the motor (use Google translate to convert to english).
Club Porsche 928 - Détails de moteur

LummoxPG · LummoxPG's Garage

Thanks Ray...That site looks like a good one...many thanks

LummoxPG · LummoxPG's Garage

So I received the four fuel hoses I ordered from Roger at 928srus and was able to replace the 3 of the four lines and the fuel pressure regulator...and that has solved the "hot start" issue...great success...the only thing that kinda sucked beside lining up the two rear hoses with the regulator and the rear damper was that I was unable to use the short hose that roger sent that runs between the regulator and the damper as it was way too long and would tend to kink when in place. I noticed in the pic that accompanied the hose that the regulator and the damper were way further apart than in my car which are only about 4 inches apart. So I had to reuse my original hose....it looks ok, but it's not an ideal alternative. So I was wondering whether not to attempt to shorten the braided hose from 928rus or just send it back and build one myself from 8 bar hose...any thoughts?

LummoxPG · LummoxPG's Garage

Alrighty...I had thought that by changing out the Fuel Pressure Regulator that that would resolve my problem with reluctance to start when the engine was warm...but apparently not. The car still starts up great when cold, but it takes much longer to fire when restarting after it is warm...any thoughts?

harborman · harborman's Garage

Sounds like your problem is electronic not pressure related. There is a temp sensor on the front of the engine which might be the problem. At least there is one on my 86. Have you investigated that?

LummoxPG · LummoxPG's Garage

hmmm...thanks harbor, I'll look into that...is that the same sensor that registers your engine temp on the dash gauge? If so, I have long suspected that it reads too high, at least according to my IR gun...how would a faulty temp sensor effect starting?

LummoxPG · LummoxPG's Garage

Hey Harbor...I just read an article written by Wally and I think that your hunch about the temp sensor number two may be spot on. Thanks much I'm gonna order one ASAP. One question...is there an o-ring that precedes the sensor and does it generally come with the part?

harborman · harborman's Garage

Quote:

Originally Posted by LummoxPG

Hey Harbor...I just read an article written by Wally and I think that your hunch about the temp sensor number two may be spot on. Thanks much I'm gonna order one ASAP. One question...is there an o-ring that precedes the sensor and does it generally come with the part?

Off hand I can't recall. I don't remember any "O" ring. I did replace mine how ever, Temp II sensor, up by the front of the engine.

LummoxPG · LummoxPG's Garage

Thanks Harbor...bty I did order a new sensor and the attached image shows a small aluminium crush washer to be inserted ahead of the sensor...I wasn't sure if the part would come with one so went ahead and ordered one separately...just in case

harborman · harborman's Garage

Quote:

Originally Posted by LummoxPG

Thanks Harbor...bty I did order a new sensor and the attached image shows a small aluminium crush washer to be inserted ahead of the sensor...I wasn't sure if the part would come with one so went ahead and ordered one separately...just in case

There is a way to test that sensor with an Ohm meter. It is a variable resistor that is temperature sensitive so the resistance changes with engine temp. I am sure there is a write up on here or Rennlist.

Yes there might have been a compression ring to seal it. When I think of "O" ring I think of a rubber type. Take care in removing the connector as it may be a little brittle from heat.