924Board.org

[alanf_uk2002]

Hi guys

Can someone help me identify the function and operation of a part of the fuel system please (2.0 NA)? I'm having trouble with my car and I've replaced everything I can think of apart from one item because I'm struggling to work out what it does! You need to know your engine really well to answer this question...still interested then read on.

Bolted on to the air metering unit is a small bracket which holds a cylindrical unit that has 3 fuel lines going to it and 2 wires plugged in the bottom. The fuel lines are from; the control plunger, to the WUR, and one going indirectly back to the tank. Note this is not part of the fuel metering head as I thought it may have been the control pressure regulating valve, but this is shown in Haynes as being inside the metering head and I have seen where this is. I am interested to know what the wires are activating - a solenoid? It can't be temperature - any ideas?

Cheers

Alan

[Mike924]

Hi, Alan,

the part is the 'hot-start' solenoid valve. It reduces the control pressure to the metering valve (thereby enriching the mixture) whilst cranking when the coolant temperature is above a nominal 45°C. The temperature sensor for this is in a short length of hose coming from the back of the cyclinder head.

It's easy to miss because the Haynes manual incorrectly states that this device is only fitted to '79 model. In fact, it is fitted to all models from 1979 onwards.
_________________
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

[alanf_uk2002]

Nice one Mike. Makes sense. This could be the culprit then....

Cheers

Alan

[Mike924]

Are you having a specific problem, then...?
_________________
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

[alanf_uk2002]

Yes Mike. But I've had the car for over 3 years and I've still not got it to run properly yet!! In a nutshell, it starts on the button, albeit slightly rough, but won't rev much above 2k. It sort of bogs down. The plugs are black and wet. I've changed the ICU, WUR, AAR, coil, dizzy, fuel filter, metering head, injectors, checked for pump flow (OK), jumped the ignition relay, changed the timing a million times and so on.

Everyone, including myself, seem to believe it is the timing that is out but it has been checked loads of times. The latests theory is that the timing marks on the cam and flywheel are a load of crap and you should set it up by eye. So I'll be doing that tonight.

Regards

Alan

[John Brown]

Geez. 3 years is a long time!

It's pretty straight forward to check the timing marks against TDC. Then confirm the cam is properly indexed. (A stretch, but I guess stranger things have happened)

A modern timing light with advance function only needs a TDC mark to work from.

No mention of checking the fuel system pressures. Yes, no?
_________________
John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

[Rasta Monsta]

[Chrenan]

[alanf_uk2002]

Hi guys

3 years IS a long time. I checked when the road tax ran out and it was 07/03 - yikes! It's kind of a running joke that lost its humour a long time ago. For me anyway. Everyone thinks its frickin hilarious.

The timing has been set many times, including checking for TDC manually, but I've always used the mark on the back of the cam for reference. It seems to be right (as I check with the cam cover off) but if it's not at all accurate then maybe that's my problem i.e. it could still have number 1 valve closed but be 4 teeth further advanced.

The system pressure has not been checked for one very good reason - I haven't got a CIS tester. And you can't find one in the UK - or I can't anyway. All the internet searches I've done have come up with kits in the USA - you guys have got loads of them - what gives?

I have got a whole rack full of parts and when I'm done (!) I'll need to set up a shop on E-bay to get rid of them!

The plugs are carbon'd up - it's not oil. And they're wet because of the fuel. Hence why it would be a good idea to check the system pressure which is on the top of my priority list (after I've done all the free things - like cam timing).

I've told this story loads of times on 924 forums over the last 3 years so it probably sounds familiar.

I'm going to hang out in the garage with my 924 for a bit.

Cheers

Alan

[Rasta Monsta]

I think the factory shop manual describes a technique for testing that involves running fuel into a container, and measuring the amount that comes out in a specified time? I'll check this evening. . .
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[Mike924]

CIS pressure testers are available in the UK - if you don't mind paying £600 for one! On the other hand, they're about $50 in the States... Rip-off Britain!

Alternatively, you can make one yourself out of 30 quids' worth of plumbing bits. You need quite high pressure seals if you don't want the thing to pop off when you turn the fuel pump on. Ask me how I know...

The volume test is supposed to supply 750 cc of fuel in 30 s. I think this is measured after the fuel filter...? There's another volume test for the injectors to make sure they're all within 20% of each other.

You never mentioned adjusting the idle fuel mixture, Alan. Presumably you've eliminated this as a cause of your wet plugs...?
_________________
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

[alanf_uk2002]

Hi Mike

Yeah those CIS testers inthe USA are cheap and plentiful. The prices varied from $50 to $200 but there were lots to choose from.

I'll have to sort something out if I'm ever to get to the bottom of this. I did the volume test about a month ago. No problem with volume being pumped. The injector volume test hasn't been done but they have all been checked for spray pettern etc.

The idle mixture was a last resort type thing and it didn't make a massive amount of difference, not the extent that I'm seeing anyway.

It's a real PITA that's been driving me nuts for so long. Keep on sending the ideas in to me!

Alan

[Jaf]

Hi Alan,

Did you put a new fuel metering head on? Or second hand? Just that your problem sounds the same as I had. My fuel meter was stuck fully open so it would start but not run or rev as it was massively overfuelling. All the fuel was going down the bore into the oil too so watch out! She's still not entirelly happy. When I first was checking for spray pattern it looked good but of course there was just too much of it (took a while to realise that).

Other idea is don't suppose the exhaust is bunged up or leaking? When my car was bought the exhaust was loose at the downpipe so it was not happy. Made for a lot of noise though so I guess you'd know. When I eventually got the car going there were a lot of chunks coming out the exhaust.

Jaf
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1978 924na

[alanf_uk2002]

Hi Jaf

Yes it does sound like a similar problem. The metering head was second hand - new ones are hellishly expensive. However the control plunger moves up and down real sweet so I can't see it being stuck open. Which is why it may be some other part of the fuel system that is causing the same type of overfuelling problem.

Alan

[Lizard]

Try removing the injectors and put them into there own little bottles.

Then jumper the fuel pump relay and make 100% sure that the injectors arent leaking with the relay jumpered and the engine off, then lift the metering plate manually and verify that the spray increases with the metering plate movement.
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3 928s,