924Board.org

[Danski]

Okay so recently my car has not been liking the cold starts. I understand that the main items that can cause issues are the CSV, AAV and WUR. Basically my car starts, runs ok for a couple of seconds then the idle drops right off to virtually nothing. I started the car the other day stopped it once it got to this (usually 5 secs) and pulled the plugs out. They were wet with fuel. Once the car is warmed up after like 10 mins of driving she idles stable and fine and drives well. Sooooo I checked the AAV (which is working) and the voltage to it is 10.5 volts when the engine is turned on. I don't think it is the CSV as doesn't this only work for a second or so? And anyhow I don't measure any voltage across it. Any ideas? I am keen to get this problem sorted before winter as I don't think she'll even start when it get properly cold! What does the WUR do again? Could this be a fuel pressure problem? As I said after 10mins the car is absolutely fine. At the moment I have to start the car and give it some revs for it to run for the first 10 mins. Any help would be greatly appreciated The car is an 924 NA and doesn't have an O2 sensor or lamda system.
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1985 Porsche 924 NA

[Danski]

I will go for a long drive soon and then pull the plugs to see if they are still over rich or correct. I suspectt
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1985 Porsche 924 NA

[Ozzie]

The CSV only works when cranking and would flood pretty quick if it was faulty.
They can leak so to test would be to remove it from the manifold leaving the fuel line connected, bypass the fuel pump and check.
The AAV could be working but is it open far enough? There is an article somewhere that shows how to adjust.
The WUR adjusts the control pressure to enrich the mixture for cold running.
Not really adjustable.
From the sound of it the AAV is not open far enough or closing too soon.
Leave the plug off it and try a cold start.

If your normal running is over rich this will cause poor cold starts
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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

[ideola]

Not sure the history on your car, but many of these cars end up with completely wonky fuel enrichment settings from previous owners who didn't understand CIS, changed one thing, then another and started a downward spiral of ill-advised adjustments to the idle and mixture settings.

In my experience, the only way to get it right is with an exhaust sniffer or wideband O2 setup. Others here have used the dwell meter method, but that only works on 1980-onward North American cars with the Lambda equipment, so no good for you (judging by your location).

In any event, if you have wet plugs, there are a variety of potential culprits:
- leaking CSV
- leaking injectors
- malfunctioning WUR
- malfunctioning fuel distributor, specifically deteriorating o-rings around the metering slits

The AAV has nothing to do with mixture beyond the warmup cycle, and shouldn't have anything directly to do with wet plugs. It's nothing more than an automatic choke that lets in more air for cold starting.

To properly diagnose the issue, you need a sniffer and a CIS pressure tester. The CIS pressure tester will confirm proper functioning of the WUR and other components, but won't help you get the mixture correct. You should do the pressure tests first, as outlined in this post. Get a proper CIS tester, and do ALL of the tests exactly as outlined. Don't skip any of them, as you could have multiple faults contributing to the problem.

Once you've ruled out any malfunctioning CIS components, you can then turn your attention to proper mixture adjustment, which is where the sniffer or wideband setup come into play. I've used a Gunson Gastester with pretty good results. Not sure if you'll be able to find one, but if you can find something similar, it's a pretty good DIY solution for getting the mixture pretty damn close to where it should be.

The other thing that can cause wet plugs is weak spark (leaving unburned fuel on the plugs). If you eliminate all of the CIS components (by confirming they are functioning correctly using the method described in the above-referenced link), then you should verify all of the ignition components:
- fresh plugs in the proper heat range
- no faults in the plug wires, including the main coil wire
- strong, blue spark at all four plug leads + the main coil wire
- proper voltage to and from the coil
- dizzy rotor and cap in good condition
- ignition timing properly set

The problem is most likely something amiss with the CIS. Hopefully it's just adjustment, but you should start with the CIS tests FIRST and go from there.
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erstwhile owner of just about every 924 variant ever made

[Danski]

wow, cheers for the huge replies! I am increasingly thinking that it could be poor injectors so I'll check those and then take it to a K-Jet specialist about an hours drive away to get the pressures checked. Thanks again for the info.
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1985 Porsche 924 NA

[Danski]

Yep, you guys nailed it! Dodgy wires, producing poor/no spark on no. 4 cylinder!
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1985 Porsche 924 NA