Porsche Enthusiasts Club Forum

Ash944
Hello gents. I've just bought a 924 and it's got a cold start issue.

When I got it it ran but very lumpy on a cold start after 20 mins it would be fine a friend had a old fuel distributor and air box replaced that hoping it would sort it but not. I then got a cold start thingy 924 0438140 it came off the same engine as the air box which was a running engine but it's done nothing in fact it seems to be running worse.

What could the problem be????

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White 84 2.5 lux
Silver 77 924

Hi

Mine ran quite rough when cold when I first bought it. There are a couple of easy things to do first which are:

1) check for air leaks. Take the pipework off from the airbox through to the throttle body and check for splits etc. On mine the hard plastic pipe that sits between the two rubber ones had been over tightened and opened up an air leak. Everything needs to be air tight.

2) check the electrical connections on the warm up regulator (the second bit you replaced I think which is on the back of the inlet manifold and has 2 fuel connectors and an electrical plug) along with the auxiliary air valve\aav. Get hold of a multi meter and make sure they have 12v. By swappin gthe WUR over I'd expect you have totally wrong fuel pressure settings which would explain why its running worse - see part 4!

3) Check spark plugs, leads, rotor arm, distributor cap and fuel filter for condition.

4)*IMPORTANT BIT* Buy, borrow, rent a fuel pressure gauge which will allow you to check the fuel pressure from the pump and the pressures applied when cold, heating up, hot and residual pressures after shut down.

I held out on point 4 for quite some time but soon as I got one I realised how great they are. You can see exactly what your engines doing and helps loads!

You may need to clean the WUR out as they can get clogged up with rubbish over the years but the pressure gauge should give you a good idea of the WUR condition.

Good luck and let us know how you get on.

Wur??????

Warm up regulator. From your description this is the second part you replaced and controls the fuel pressure throughout the running of the car, not just warming up.

If its not calibrated you maybe running to lean when cold, to rich when warm or even both. If you Google Porsche 924 warm up regulator you should be able to confirm this is the part you replaced.

Got good pressure to all injectors. Took the wur off again and gave it a clean

Still the same. Any more suggestions

Can you confirm the cold and warm fuel pressures? Did you manage to get hold of a fuel pressure gauge?

Not managed to do it yet no but I'm getting a good amount of fuel coming from the 4th and 5th injector

It starts ticks over very grumpyly give it a little rev and it just wants to backfire. (Surly that's to much fuel)

Is it the air fuel mix????
Or could it be timing????

Hi

The fuel distributor (top part of the air filter box) basically consists of a plunger and when more air is drawn in, the flap in the air box lifts up which pushes the plunger up and allows fuel to flow to the injectors. The opposing force to the plunger (above it) is fuel from the warm up regulator so when the cars cold the warm up regulator lets less fuel through so the plunger can move up more and let more fuel to the injectors\richer mixture but as the car warms up the warm up regulator allows more fuel through, creating more resistance to the plunger moving and less fuel\leaner mixture. This is why the fuel pressure from the warm up regulator is so important as it sets the basic fuelling for the car.

As for setting the base mixture you should see a hole between the fuel lines and the larger rubber boot on top of the fuel distributor. With a long 3mm allen key you can adjust the mixture (left to lean it out, right to richen it up). A basic setting can be achieved by listening to the idle speed and tweak the mixture until the idle speed peaks then winding back 1/16th of a turn.

Hope that makes sense and is useful? let us know

Ok mate I shall give it a go later after work.

Dunno if it me being stupid but there no hole on the top. Do you mean the little tube just off the square distributor with all the fuel lines coming out.

It was the timing. Had my mate come out with his timing gun. It was way off

Run fine now

Great news it was a nice easy fix in the end.

There is one strange thing tho. The 5th injector and the wur. There connections are wrong the blue plugs goes to the wur. It doesn't want to run right if there plugged in the right holes ????