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Mr Bitey · Last edited by Mr Bitey on Mon Nov 21, 2011 12:15 pm; edited 2 times in total

Hey everyone,

I've been reading so much of this Forum and Workshop manuals that i thought i could solve this problem.
However I am now stumped and need some advice.

My 79 924 that i rescued had previously been sat undercover for many years without use. guessing 7 or 8 years.

Steps i have taken so far:
1. put in new oil and oil filter.
2. put in new coolant.
3. drained fuel tank of old fuel (oh man did it smell !!)
4. new fuel filter.
5. new fuel pump
6. new starter
7. new HT leads
8. new dist cap/rotor

Now when i try to start it. It starts pretty much first go.
however it will only start first go.
Problem is, second time starting i found the spark plugs saturated in fuel.
All four of them.

And after all my times trying to start it (over many weeks).
My oil became was more fuel than oil. Oil has now been replaced.

When it does start it will not idle. I have to keep the engine well above 2000rpm.

I have pulled the injectors and bypassed the fuel relay to get the pump running.
The injectors sprayed lots of fuel. and when i lifted the air-flow meter, it didn't seem to make any difference.

questions:
1. Are the injectors meant to spray when the air plate is closed?
2. When you lift the air plate by hand, can you feel the fuel value in the distributor move up and down. or is very balanced.
3. What is the difference in the fuel flow when the air plate is open compared to closed. should you visually notice it?
4. could putting in a new fuel pump increase the fuel pressure so much that would cause my problems.

I'm hoping that the answers to my questions will determine if my fuel distributor is faulty or not.
As in constantly providing too much fuel.

Cheers
_________________
Tom
___________
1979 924 NA
1979 924 NA - Parts car

!tom · Posted: Fri Oct 28, 2011 2:26 pm Post subject:

Your fuel distributor isn't working properly. No fuel should be flowing when the air plate is closed.
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78 924 NA
5-lug

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

+1 piston is probably stuck
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1980 924 NA
1982 931

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

One thing missing from your list. . .injector service. Might they be leaking?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Agree with the above statements, but adding a little more context:

Fuel distributor piston may be stuck as indicated.
Springs in the injector may be weak and not staying closed under the tiny amount of fuel pressure that should be present with the air plate closed. (Point being, when the air plate is closed, there should be insufficient pressure to crack open the injectors).
One or more of the o-rings on the slits to the individual injector ports may be cracked, disintegrated, or otherwise malfunctioning such that the fuel distributor is allowing indiscriminate fuel pressure to reach the injectors.

Have you confirmed that the wet fuel condition is on ALL of the plugs, or only some of them?

To me, it sounds like the fuel distributor is not functioning correctly, but be aware that you could have ALL of the above problems!!! (i.e. don't assume once you fix the fuel distributor that you don't have leaky injectors!!!).
_________________
erstwhile owner of just about every 924 variant ever made

!tom · Posted: Sat Oct 29, 2011 6:13 am Post subject:

Leaky injectors, although a serious problem, wouldn't stop the air plate from returning closed with fuel pressure.

Sounds like a stuck piston or busted o-rings to me.
_________________
78 924 NA
5-lug

SilverGhost · Posted: Sat Oct 29, 2011 10:11 am Post subject:

+1 piston in the fuel distributor is probably stuck fully open, or one or more of the O rings around the piston assembly is leaking.

Your question #2. "When you lift the air plate by hand, can you feel the fuel value in the distributor move up and down. or is very balanced."

The force exerted on the air flow sensor plate by the control pressure acting on the top of the control plunger (a.k.a. piston) is small but noticeable.

Depressurise the system by loosening a connection, then lift the sensor plate by hand.

Retighten the loosened connection, run the fuel pump to pressurise the system, then immediately lift the sensor plate by hand again.

If the piston is free and the control pressure somewhere near what it should be then you will notice that it was slightly harder to lift the sensor plate the second time.
If the piston is stuck then you'll notice no difference.
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"Priscilla" 1981 924 NA RoW auto, metallic blue

Mr Bitey · Posted: Mon Oct 31, 2011 12:01 pm Post subject:

Thanks guys, appreciate all the input!

Yes it was indeed a stuck piston

So spent quite a bit of time rebuilding the distributor.
Just requires patience and steady hands.

Put it all back together and instead of all four injectors spraying lots of fuel, only two do it now. With the air plate closed.

So I'm assuming that those two injectors can't hold the pressure.
_________________
Tom
___________
1979 924 NA
1979 924 NA - Parts car

!tom · Posted: Mon Oct 31, 2011 1:15 pm Post subject:

Swap injectors to isolate the problem. It's possible some O-rings tore during reassembly.
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78 924 NA
5-lug

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

Don`t assume anything Tom, check it logically & diagnose. Simply swap over the 2 injectors or lines with the other 2. Then deduce if it is the same 2 fuel dizzy ports or indeed the injectors. It`s very easy to nick or dislodge any of the O rings while reassembling the FD. BTDT! Faulty injectors will only dribble and not spray lots with the flap down.
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World`s quickest 924 2L slushbox

Mr Bitey · Posted: Mon Oct 31, 2011 1:25 pm Post subject:

Excellent info guys, thanks.

Will swap the lines around and see what happens.

Not looking forward to rebuilding the distributor again.
Will have to clean off all the gasket sealer I used.
_________________
Tom
___________
1979 924 NA
1979 924 NA - Parts car

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

Hope you don`t, but most likely will I bet. Used a loctite sealer some times, seals so well but PITA to ever remove. Then on one rebuild made 2 gaskets from very thin paper and worked well. So well had mates with MBs & Saabs calling round with cartons.

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World`s quickest 924 2L slushbox

SilverGhost · Posted: Mon Oct 31, 2011 2:31 pm Post subject:

If the mating surfaces are really, really clean then a very thin layer of ordinary grease seals perfectly, creates no risk of obstructing fuel passages and makes subsequent disassembly (should it be necessary) a breeze.
Wiping the O rings with oil makes assembly easier and reduces the risk of damaging an O ring.
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"Priscilla" 1981 924 NA RoW auto, metallic blue

Mr Bitey · Posted: Mon Oct 31, 2011 2:48 pm Post subject:

I have a feeling I will be rebuilding this.
Just ordered a 400 pack of mixed metric O-Rings.

And when I pulled it apart the small O-rings looked a little dry.

@SilverGhost - not sure about how clean I'll be able to get the surface after cleaning out the liquid gasket. But I will certainly be oiling the o-rings next time.

@RC - If i fail again i send it over with some Little Creatures beer

_________________
Tom
___________
1979 924 NA
1979 924 NA - Parts car

SilverGhost · Posted: Mon Oct 31, 2011 3:06 pm Post subject:

Make sure the O rings are petrol resistant, eg nitrile. In time, some materials swell and soften in petrol.
My box of assorted O rings are of an unspecified material, so to be safe I bought the following in nitrile from CBC Australia (sizes are in mm):
4 off 8x2
2 off 14x2
1 off 25x3
1 off 19x1.5
for the princely sum of $5.50.
I think Goldfields Bearing Supplies Pty Ltd in Perth are a division of CBC, so may help.
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"Priscilla" 1981 924 NA RoW auto, metallic blue