924Board.org

[stevekat]

Just picked up my 1981 931 S with 56K miles. It is the red one that was available in Baltimore earlier this year.

The owner indicated it was hard to start when warm, but I believe it is generally hard to start, period. A few observations - please point out if any are issues or hints...

Fuel pump (not sure if in tank or external) runs continuously with ignition on...I had a 1981 931 S in the late eighties but cannot recall if this is normal for these CIS systems, or if it should stop when pressurized.

The fuel pump stops (humming) when the ignition is being cranked.

I noticed I can get the car started often with short cranks...in such instances the car does not start during cranking, but when ignition key is released from start position, the engine sometimes then catches...one cylinder at a time...very slowly, and eventually rising to idle...all after the key has been released, and with no sign of any success while cranking before the key release.

Occasionally on a long crank, it can gather momentum and fire, but not easily or frequently.

The ignition swtich was very recently replaced by the prior owner, for an unrelated problem, with the hard starting issue pre-existing this replacement.

Accelerator to the floor does not appear to make any discernible difference.

I am not terribly familiar with what aspects of the fuel system are doing what at what times, or what is supposed to be happening when warm, cold, etc. WUR, Cold start valve, etc. Personally I tend to suspect a vacuum leak, perhaps from the o-ring to the throttle body, etc., but that is pure conjecture, and the problem can be anything.

The car has a factory 937 intercooler.

Appreciate any epiphany from the 931 Columbo's out there.

[dpw928]

When the engine catches after cranking is stopped, is a sign that your low resistance wire from the starter (50 circuit) to the coil (15 post) is bad or making poor contact. i.e. you are getting low or no volts to the coil when cranking. You can check this by measuring the volts at the coil (15 post) while the engine is being turned over. IIRC you need a minimum of 6 volts to start.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[stevekat]

That's an interesting and straightforward idea based on the symptoms...I'll check that. This also begs the question on whether the fuel pump should be turning off when cranking - the humming of the fuel pump disappears when when the engine is cranking (as best as I can tell) - any experience whether this should or should not be occurring?

[Smoothie]

Yes, fuel pump should be running while the starter is activated.
Sure you just can't hear it over the starting noise?
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[stevekat]

My clear impression was that the pump stopped running while cranking, and that it was noisy enough that I should be able to hear it, though I'll double-check that just to be sure.

If the pump does stop while cranking, would this point to the fuel pump relay?

Also, since I just got the car, I am going to pull the relay and check the numbers on it - to make sure the correct part is installed.

[dpw928]

When you aren't cranking the pump will sound loud as the pressure is built up. When cranking there is less build up of pressure at the pump so it will not be as loud.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[stevekat]

I'll crank again and listen carefully, or put a meter on the pump.

I pulled the fuel pump relay. To confirm, the relay is at the end of the board, on the top most row or relays?

It does not say Porsche or VW, has a number 898340, 12V, says 2 x 25A and Made in Germany, and has a schematic on it. The pin numbers are 87, 30, 85, 86, A, B. If it is the fuel pump relay, it is non-standard.

[Smoothie]

FP relay should be the second one from left, top row.

[5 images of fuse-relay info starts here - http://www.flickr.com/photos/9754161@N02/739764940/in/set-72157600685476130/ ]
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[stevekat]

Thanks Smoothie. Jeeesh, the relay I had out was the fan relay. There were only three 'large' relays. I knew the other two were not the fuel pump so I assumed the one that was left was the fuel pump, but it was for the cooling fans.

Turns out in the fuel pump position (number II), there is a generic Bosch 'short' relay with the little plastic tab at the top (reference 0 332 019 150). Uggghh. I found this reference for it...a horn relay.

http://www.tessco.com/products/displayProductInfo.do?sku=79246&WT.mc_id=google_base

Wonder if I can get a cheap 944/968 relay locally (if it would power the pumps properly sans the other bits inherent in the 931 relay) to hold me over until I can order the right one. BTW, see you are in NJ. This car is in S. Jersey though I live in Los Angeles. I am this week visiting family and plan on using the car when I am here.

[Smoothie]

Ah, you're enjoying the rain and wind from tropic storm Hanna about now, right?

Don't know off-hand of a 924S/944 relay that'd work. -But a 16A or higher '79-up 924NA FP relay should work - only thing is you'd be on your own to avoid over-revving it (USA 931 FP relays have rev-limiting built-in).
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[stevekat]

Oh yes, lots of rain, but no wind down here so far. I am soaked as I write this, from hanging out from under the dash. Was hoping to find a relay that ultimately I could try now and then use as a spare, just to see if the funky horn relay that is in there now is the culprit to hard starting.

Seems like a 1984 VW Rabbit fuel pump relay might work - it appears to be 433 906 059. I though maybe PepBoys, Advance or Autozone would have one - no luck so far. No rev limiter but that would be OK as a spare in the glove box. I am heading back to Los Angeles on Monday and was hoping to make solid progress before then.

[Min]

Why not just make a set of jumpers you can put in there to run the fuel pump all the time? its alot cheaper to have a piece of wire in your glovebox than a expensive relay. Use the jumper to test if your fuel pump relay is the problem and then throw it in the glovebox to jumper your fuel pump relay later if for some reason it fails.

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[stevekat]

Probably going to do just that...the 433 906 059 is only $18 at a few places, but I think I'll just wire something up to check.

[stevekat]

Built a switch box with two wire leads and a fuse on one of the wires. Installed to relay sockets pins 30 and 87. Made no difference in starting. Continues to be difficult.

Found one bad vacuum hose so far and temporarily fixed. Boost now is up a little, closer to 7lbs, from 5lbs. The car has an adjustable boost but I have not made any changes to the setting.

Discovered Mahle fuel filter is installed backwards ughhh (arrow facing toward front of car.) Did not change this right away- waiting to install a new filter. There is no plug in the CIS air mixture hole - I'll add this - assume it does not effect starting.

Continues to sometimes start after ignition switch returns to run position, as engine is winding down from cranking. Have not yet check the voltage to coil during cranking.

[ideola]

The backward fuel filter can definitely have an impact on both running and starting.
_________________
erstwhile owner of just about every 924 variant ever made