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SilverGhost

Problem #1
There is a valve on the side of my fuel distributor which does not seem to be described in Haynes or other documentation I have.

Line "A" goes to the middle port on the top of the fuel distributor.
Line "B" goes to the WUR.
Line "C" goes to the return line to the fuel tank.
Seems to me that when this valve is open, then control pressure on top of the control plunger drops to zero as it is effectively open to the tank.
Can anyone tell me what this valve is for please.

Problem #2
The engine is running so rich that its barely running. Plugs are wet and black. Oil smells strongly of fuel. Adjusting the mixture by means of the 3mm hex socket screw has no effect, even 2 turns changes nothing. (Cam timing and tappet settings are OK).
Haynes describes on P75 how, after pressurising the fuel system, there should be slight but even resistance to lifting the air sensor plate as a result of pressure on the control plunger. I can feel no such pressure - is it really, really subtle?

Seems to me that if the valve described in problem #1 is always open then this would cause problem #2.

Help appreciated please.
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"Priscilla" 1981 924 NA RoW auto, metallic blue

Harm · Joined: 02 Apr 2009 Posts: 1376 Location: Holland

SilverGhost · Posted: Mon Apr 11, 2011 8:17 pm Post subject:

Many thanks Harm.
That's it alright. It all makes sense now.

My Haynes says "20 Electric Solenoid (1979 models only)" and mine is a 1981, so I hadn't even bothered to read that section, and Fig 3.27 escaped my notice for some reason.

I've not done the fuel pressure test yet, as I don't have the pressure gauge. I am checking out the things that don't require the gauge as best I can first.
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"Priscilla" 1981 924 NA RoW auto, metallic blue

Harm · Joined: 02 Apr 2009 Posts: 1376 Location: Holland

Is your CSV (Cold Start Valve) functioning propperly?
It should only provide extra fuel during cold start.

Did you check the System pressure regulating valve, attached to the Fuel distributor body?
(#13: page 73 Fig. 3.1 Component of the CIS)

Mixture settings.
Half a turn on the mixture adjustment screw should make quite a difference, so your mixture is way off I guess. One procedure is to unplug one of the injector lines at the fuel dist. or lift an injector out of the head, activate the fuel pump and watch (the injector spray pattern (should be evenly shapped)) or fuel coming from the opening at the fuel dist. Turn the mixture screw CCW untill the flow stops and take it a quarter turn back. Fine tune from there, or;
Remember the amount of turns when completely returned in (just in case) and return IIRC six(?) turns CW would be close to normal, depending if there are any false air leaks between air intake and manifold, and the TB setting.

My regular setting if the mixture screw is about 10 turns CW.
The maximum of turns you could give is about 30.

From there:
— What is the “air” setting on the TB?
— Replace the oil ASAP!

Reading the FAQ is a must

Cheerio!

Edit01: replaced in/out by CW/CCW.
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Porsche 924 NA 1982 LY7A/A3A3 _ Greater driving pleasure never harmed anyone.

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

No resistance on the air sensor plate could indicate a stuck piston in the fuel distributor or a lack of control pressure from the WUR. Check the WUR to make sure the metal screen on the input line isn't plugged. Have you checked the control and system pressures with a CIS test gauge?

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

Harm · Joined: 02 Apr 2009 Posts: 1376 Location: Holland

SilverGhost · Posted: Tue Apr 12, 2011 7:38 am Post subject:

Thanks Harm and Dennis.

Harm the CSV opens correctly and closes completely. I've just changed the oil and will change it again once I get the engine running. Thanks for the suggestions for initial setting of the mixture adjustment screw - I'll need that.

Dennis I'll take out the fuel distributor and and give it and the WUR the cleanup described at
http://z8.invisionfree.com/ClubNARP/index.php?showtopic=3471
This should allow me to ensure the system pressure regulating valve and other parts are clean, ports are clear of obstruction and the control plunger is free to move.

This should cover the all possibilities suggested by each of you.

I don't know what is meant by the “air” setting on the TB? Mine is an NA if that's relevant.
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"Priscilla" 1981 924 NA RoW auto, metallic blue

Harm · Joined: 02 Apr 2009 Posts: 1376 Location: Holland

rkn · Joined: 01 Apr 2007 Posts: 176 Location: Copenhagen

Harm · Joined: 02 Apr 2009 Posts: 1376 Location: Holland

Hi Rkn,
Your remark does make sence;
It should only spray fuel when the air plate is lifted by the rotating engine.
_________________
Porsche 924 NA 1982 LY7A/A3A3 _ Greater driving pleasure never harmed anyone.

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

SilverGhost · Posted: Tue Apr 12, 2011 5:16 pm Post subject:

The metering valve piston was completely stuck, gummed up with fuel varnish/residue.

It now runs, if roughly, and I have been able to drive it back and forwards a few meters.'

'

I expect I'll be able to plod on through the other documented procedures to get it running well.

Many thanks for your help folks.
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"Priscilla" 1981 924 NA RoW auto, metallic blue

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Now you should try readjusting the A/F mixture and add fuel system cleaner. BTW the A/F mixture will change as the system is cleaned out, so recheck it periodically until you see no more changes.

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

SilverGhost · Posted: Fri Apr 15, 2011 1:09 pm Post subject: