924Board.org

Porver9two4 · Joined: 22 Jan 2004 Posts: 104 Location: United Kingdom

I am trying to resolve some issues with an unknown history 924. It has had literally everything wrong with it but I have been working through the problems and it actually runs nicely now...... until it just.... dies

Whereupon it will not start unless left to sit for a while

Once it has 'rested' it will fire right up as if nothing was ever wrong......

So what on earth could be causing this?

It only does it when up to temperature, having been running for a while and whilst driving - for example you will pull up to a junction, put your foot on the gas to pull out and it bogs the engine, which stutters and dies and you cannot catch it..... You can replicate the symptoms at rest when idling if you crack the throttle wide open - it bogs and stutters before revving. Open the throttle smoothly though and its absolutely fine. It will also sit and idle fine for hours, cycling the fan on and off.
There is some background in this thread here:- http://www.924board.org/viewtopic.php?t=42929&sid=9bbdfe7f95c645ba4ec2ea39faffe6e7 and since this I have fitted a fuel pressure tester gauge.

To summarise what has been done.

New spark plugs.
Ignition timing verified, together with vacuum and centrifugal advance operation
Ignition system gone through (spark also checked when the motor dies - spark still present and correct)
DME relay bypassed so I know the engine is getting pump fed fuel pressure all the time
Fuel system pressure checked - 5bar from the pump
New fuel filter
New injector seals
Injector spray pattern checked
WUR rebuilt
Control pressure (warm) reset to 3.5bar
AAV checked (working correctly)
CSV checked (working correctly)
Fuel metering head overhauled, stripped, cleaned, new o-rings etc. and mixture set (by feel, no gas analyzer yet)
Inlet tract checked for air leaks etc.
Fuel tank checked for vacuum

I am really running out of ideas as to what might be causing this problem.... it is like it just runs out of fuel, although checking my pressure gauge when the engine dies shows control pressure is spot on, so the fuel is there.
I would be happy to listen to any ideas anyone might have as to what could cause an engine that normally runs absolutely fine to randomly bog down and die on application of throttle. Like I said, once the engine has died it will not start on the key unless it is left to rest for a few minutes. It can be coaxed into running again with a bump or tow start whereupon it runs rough for a very short while before returning to running and idling absolutely fine. Help!

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Fuel pump volume test? System pressure at metering head? Electrical ground system renewed (cleaned or replaced)?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Grenadiers · Posted: Sat Feb 25, 2017 2:01 am Post subject:

Could be the fuel Accumulator in the back, unscrew the little screw, see if gas drips. If so, bad.
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'83 944 Track car.
'88 924S Track car.
'89 944 Turbo
2004 Winnebago Vectra monster RV
2012 Jeep Wrangler
2014 Kia Soul
2001 Ford F350 powerstroke

Ozzie · Posted: Sat Feb 25, 2017 7:24 am Post subject:

Get a gas analyzer and also check fuel flow rate
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

pmcaya2 · Joined: 24 Nov 2005 Posts: 191 Location: Scio, NY USA

Swap fuel pump relay. Fairly cheap and available. Had similar symptoms on my car. Will post more later. Peter

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Fuel pump Fuse.
Known to melt and/or have poor connection over time.
Located at position 2 on the mini upside down fuse panel.
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*****1981 - 924 - Auto - London, UK******

Porver9two4 · Joined: 22 Jan 2004 Posts: 104 Location: United Kingdom

Thanks for the suggestions, I had checked pretty much all of these at one time or another.....
Pleased to say this is now sorted and the car is running great! Has been in daily use since licking this issue and it is going like a champ.
Turned out there was a split in the rubber elbow pipe that connects to the throttle body at the join between the elbow and the feed pipe for the AAV. Found it by luck when I took the pipe off to realign and pull the injectors. You couldn't see the split with the elbow fitted or hear a leak, but it was there and it was big enough to make a difference! Swapping that part out and tweaking the mixture has cured the running issues and it starts, sounds and goes like it should. Hot start bypass fix also applied which has taken care of any remaining issues.