924Board.org

[Iwan]

I recently bought a 924 (1980 std -European model). I have the car starting first turn of the key and, through the hot start 'button fix' posted on this site, 1st time when hot. There's just one problem which is.

On a cold start (very cold) it starts 1st time. If I blip the throttle and drive off - no problems. However if the car is allowed to idle for about 30 seconds the throttle response disappears - it just turns over and no amount of throttle will get the engine to rev any higher. After about 2-3 minutes I get full throttle and no further problems. This problem doesnt exist when the car is hot or even luke warm. Ignition components are all fine; there are no leaks in the rubber inlet 'hoses'. The Air auxilliary valve has been replaced.

Does anyone have any clues? I'm new to K Jetronic (am OK on Motronic & Trionic) fuel injection

Iwan[/b]

[Mike924]

Hi, Iwan, welcome to the board.

It sounds as though it could be the WUR (warm-up regulator). When you first start your car the CSV (cold start valve or 5th injector) squirts more petrol in to enrich the mixture for starting. Once started, the WUR then reduces the control pressure which makes the mixture richer and, as the car warms up, increases the control pressure and hence brings the mixture to normal.

This fits the symptoms you've described - apart from the first 30 seconds, because a dead/siezed WUR will make the mixture weak from the moment the car starts until it's warmed up to close to normal temperature. But I still think it might be the WUR. Expensive new (~£120) but resonable (£10 - £15??) used on E-Bay.

Or perhaps a vacuum leak when cold - not very likely.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[chris24]

Hi
I think Mike is right, sounds like the WUR. My first 924 had similar problems, but there wasn't any wiring to the WUR. My understanding is that if it isn't getting voltage then it would make the car run rich all the time, so the fuel mixture on my fuel distributor was weakened down to compensate. This was fine when the car was warm, but not when cold, similar symptoms to you. Check there are wires to it and it is getting voltage. Mine didn't have the good stage for the first thirty seconds though.
It could be that it is good in the first thirty seconds cos the 5th injector is still throwing fuel in, but usually it isn't on for quite that long, normally about 10-15 seconds?
Good luck.
_________________
1983 - 924 (185K miles) - not mint
1985 - 924 (148K miles) - mint
1990 - 944S2 cab (52K miles)

[Iwan]

My understanding is that the WUR controls the fuel supply to the 5th injector? So if it wasn't functioning then the additional fuel wouldn't get there - am I wrong, please correct me. The car is also running rich - when I got it someone had turned the mixture to very rich and adjusted the idle speed (throttle bypass) to compensate. I've now turned the mixture down and idle speed up. When my exhaust gas analyser arrives I'll sort it properly (dont want burnt valves).

I was wondering whether there was something special about the fuel relay - is there a timer in it anywhere?

Iwan

I look forwards to being corrected

[Mike924]

The WUR doesn't control the 5th injector (that's done by the thermo-time switch). The WUR adjusts the control pressure to the fuel metering unit, which controls the fuel flow to the main injectors.

All the fuel relay does is turn the fuel pump on; it doesn't play any part in controlling the mixture.

(BTW - running too lean causes burnt valves)
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[Smoothie]

[Iwan]

Have just set the mixture/slow running speed. have checked functionality of WUR - is working fine. However.... I have now verified that the engine is slightly advanced for the use of UK 'regular' petrol. Filled with Optimax and - problem dissapeared completely. So the choice is - use expensive petrol or retard slightly.

Thanks for your ideas everyone - they helped

[Ozzie]

Forgot where I got this.

_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Iwan]

That was very kind of you -most helpful.

Thanks

Iwan