924Board.org

alanf_uk2002 · Joined: 31 Oct 2005 Posts: 31 Location: England, UK

Hello all.

My 1982 n/a 924 used to run fine until I swapped the engine. Since then it will start first turn and idles sweet but it only revs to 2,000rpm then coughs and splutters.

If I keep the throttle open while it's coughing then lift the metering head up manually it makes no difference therefore it's not a vacuum problem. I have also squirted Cold Start in the throttle body and that too makes no difference therefore I presume it is getting enough fuel. Also fuel is pumping OK and squirting out of the injectors.

So far I have changed:-
- Ignition control module
- Coil
- Distributor
- WUR
- Fuel metering head
- Spark plugs
- Ignition leads
- Fuel filter
- Injectors

The only questionable area is the fuel pump relay and wiring to the starter. When the engine turns or runs the relay clicks in tempo with engine speed. Also when the engine went back in the loom that runs to the starter was fried so I replaced it, therefore there may be something wrong with the wiring - can anyone confirm how many wires and where they should be going to?

I'm flat out of ideas and things to swap so any ideas would be gratefully received.

Alan

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Hi, Alan.

I would suspect your fuel pump relay. I don't think it should click at all when the engine is actually running, so it could be an intermittant wiring fault to the relay.

Try removing the relay and connecting the 30 and 87b terminals (I think) with a jumper wire. If the engine revs OK with this in place, have a good look at the relay itself or the wiring between the ignition switch and the relay.
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1993 Porsche 968 Coupe, Midnight Blue, 6 spd

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Ozzie · Posted: Mon Jan 23, 2006 7:28 pm Post subject:

I also suspect fuel.
Check that both fuel pumps are running also.
The car will starve of fuel with only one.

I replace the same wiring last March. I'll see if I can find the diagram.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Ozzie · Posted: Mon Jan 23, 2006 7:33 pm Post subject:

Found it - changed the wiring color to red brown and blue.

_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Tim Hancock · Joined: 06 Oct 2005 Posts: 9 Location: NW Ohio

Alan, I had a similar occurance with my '77. My problem actually was that my fuel pump was shot. Unfortunately, I first replaced injectors and wasted a bunch of time screwing with the fuel system before I found the problem. My pump would pass the quantity flow test, but I did not have a CIS pressure tester at the time so I assumed the fuel pump was fine. When I finally found the problem, I found the fuel pump had tiny bits of aluminum flakes in it. It obviously had started chewing itself up inside.
A new fuel pump was installed and the cutting out at 2500 rpm problem was cured.

Might be worth checking the pressure if you have not already.
_________________
Tim Hancock
'77 924
'87 951
'79 911 SC
'92 325i

alanf_uk2002 · Joined: 31 Oct 2005 Posts: 31 Location: England, UK

Thanks for the response guys, it's most appreciated.

The next thing is to suspect the fuel pump (s) but I want to investigate why the fuel pump relay is continuously clicking first? Any suggestions?

I will bypass the relay tonight but I think in the dim and distant past (it's been 3 years since the problem first appeared!) I have done this without any change to the problem.

Cheers

Alan

Benino · Posted: Tue Jan 24, 2006 4:16 am Post subject:

This is probably a fuel problem, but I just thought I'd add this because the symptoms are similar to something I'm seeing on my car. I always run with about 6 degrees of advance. The car runs fine, but I set the timing back to normal for a smog check recently and the car did what you said yours did. Something is wrong with my distributor's advance/retard mechanisms. I haven't fixed the problem yet so I'm not sure exactly what's wrong, but it is a timing issue. Just thought I'd bring up that possibility in case it turns out not to be a fuel problem on your car.
_________________
1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

If your fuel relay is clicking continuously it's probably only delivering half the power to the fuel pump, so the sysmptoms may look like a pump that's dying. Sort out the relay first then see what's left to do.

Cheers and happy hunting.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Paul · Posted: Wed Jan 25, 2006 11:37 am Post subject:

Check for air leaks in the intake system.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

alanf_uk2002 · Joined: 31 Oct 2005 Posts: 31 Location: England, UK

I've put a jumper wire across the fuel pump and it didn't run any better - worse in fact. The relay only clicks when the engine rotates so maybe it's something to do with the wiring from the distributor...hhmmm I'll have to think about that one.

Thanks for the replies anyway. Benino - if you get your car going let me know what the problem was!

Alan

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

i had this 2000 RPM limit too...my car idled fine and went ok until 2000 RPM or i pressed on the gas pedal harder...then it stumbled and died....i also replaced some parts...but i found two distributors and i replaced mines with one of them and since then the car runs ok.
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Min · Posted: Thu Jan 26, 2006 2:57 am Post subject:

alanf_uk2002 · Joined: 31 Oct 2005 Posts: 31 Location: England, UK

Now you've got me thinking about the distributor again. Maybe the second dizzie was knackered as well?

The timing is spot-on and I've even had the engine running while the dizzie is turned through 360 to see if it made any difference. I also suspected the timing advance was out but by rotating the dizzy by hand it would have had the same effect so I don't think it's timing or advance problem.

I'm now thinking there is a short in one of the wiring looms but I really don't fancy breaking in to all the looms to find out....gulp!

Alan

chris24 · Posted: Thu Jan 26, 2006 6:05 pm Post subject:

On my 924 the the fuel pump relay (FPR - I'm lazy) cut off wire comes from the coil, measuring the engine going round, and if it isn't going round the FPR cuts off to stop the 924 turning into a possible fireball if you have a problem/accident.

If you bypass the relay using the jumpers this safety feature is avoided so the car should run well if jumpered if you see what I mean. As long as the contacts are clean at the FPR I would put your original FPR back.

Then test what the current is going to the main fuel pumps by putting an ammeter in line with it. See what the current is, then see what the current is when it gets hot. It shouldn't rise too much, but this is a qualitative thing I suppose. Thing is, I can't see how knackered pump would cause a clicking at the FPR.

How old is your fuel filter. I suppose it is unlikely to be the culprit too.

Good luck.
_________________
1983 - 924 (185K miles) - not mint
1985 - 924 (148K miles) - mint
1990 - 944S2 cab (52K miles)

MunkPuppy · Posted: Fri Jan 27, 2006 8:33 am Post subject:

I had the same problem, turns out I had the #2 & 3 plug wires swapped, so it was running like a wasted spark.
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