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BC77-924 · Posted: Thu May 11, 2006 12:26 pm Post subject: 77.5 update

Well the car is still in the shop. The mechanics are stumped!!! I'll throw this one out again and see if there is a simple fix. Car seems to run ok on the flats and downhill. Under load it is missing. No vacuum leaks, new plugs, new distributor, new fuel filter. The fuel pressure is good. Injectors are in good shape as well. It seems to run better when cold.
Seems to really protest at about 3000 rpm in 3rd gear for some reason.
The mechanic seems to think it is running too rich. Everything else checks out 100%. Any words of wisdom appreciated.

Thanks

D
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Silver/Grey 77.5

Lizard · Posted: Thu May 11, 2006 2:37 pm Post subject:

I would recommend 1 of two things, either install an air fuel mixture guage and install it on its OWN O2 sensor, or 2 hook up the cold start valve to a switch, when it happens hit the switch if it corrects the problem then you know it is too lean, if it makes the problem worse then you know it is becoming too rich, if it has no effect then you know it is ign system. but in all honesty a plugged fuel filter would have been my first suggestion
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Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Check the fuel pressure right through the rev range. If it loses pressure at higher revs, then a blocked fuel filter (as Lizard says) is a very likely cause.
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Ozzie · Posted: Thu May 11, 2006 6:00 pm Post subject:

Does this car have points or hall sensor in the distributor?
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BC77-924 · Posted: Fri May 12, 2006 10:11 am Post subject: Rough Running

There is a Hall Sensor in the distributor. The mechanic is still stuck with the problem. Everything checks out 100% but still wont run. On his test drive the car died and the battery went dead today. Just more time and money needed I guess. I'll go on holidays next week and leave it for more testing. Any other thoughts???? Might be up for sale a little sooner than expected!!!

D
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Silver/Grey 77.5

Ozzie · Posted: Fri May 12, 2006 10:48 am Post subject:

My guess would be electrical fault.
It could be any module/sensor or coil or anything like a break in the wiring or faulty plug.
I have seen break in wires where the insulation is intact and occasionally the wires touch.
(They always touch when you put a test meter on them, Murphy's law.)
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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

BC77-924 · Posted: Sat May 13, 2006 3:04 pm Post subject: New thoughts on the Problem

Well after trying just about everything else, I am starting to suspect it may be the gas cap. The seal appears to be leaking and as a result I think it is not building up enough pressure in the CIS system to get it to work properly. It is a bit of a long shot.... any thoughts????

Thanks D
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Silver/Grey 77.5

Ozzie · Posted: Sat May 13, 2006 3:11 pm Post subject:

Have you pulled the injectors and checked spray pattern?
If so then you have fuel pressure.
If the tank needs air to stop it going into a vacuum it should get it from either the charcoal canister or gas cap.
The tank otherwise is not pressurised and excess pressure goes to the canister.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

BC77-924 · Posted: Sat May 13, 2006 11:49 pm Post subject: Yup it all checks out

The pressure is well within the specs and the injectors are in reasonable shape. The gas cap is still leaking however. The shop has gone over the car for the past several days but cannot find any specific problem. You are probably right saying that it is some little wire shorting out.
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Silver/Grey 77.5

Eturbo924 · Joined: 09 Nov 2002 Posts: 2212 Location: Londonderry NH

This is very unlikely since you said it happens going down hill... but some thing struck me when you said the battery died.

It ... on a very off chance be that the alternator belt is slipping. A long time ago I put a post on about this. What happens is that the pulley gets kind of glazed and no matter how tight the belt is... it still slips. There is a very easy check for this. ENGINE OFF!!!! Reach down to the alternator and push on the alternator fan. The aluminum fan on the alternator. Push relatively hard. If you can rotate the fan... then the belt is slipping. Thus it is not charging your system once the car gets up to speed. Normally what this means is that the car runs ok at the lower rpms but once it starts spinning up... the belt slips and you loose spark power.

Check that out. The next thing I would suggest is testing and or just replacing the coil. A weak coil (or one that is about to check out) will begin randomly dying and or causing misses.

Anyway those would be my quick suggestions if the other things suggested do not check out.

It is simple... either fuel or spark

If only it was that simple. Good luck

Eric
eturbo924@yahoo.com
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1992 968
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Paul · Posted: Sun May 14, 2006 12:45 am Post subject:

Any chance your motor mounts are bad and the motor is rolling over causing the distributor cap to hit the hood?
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Eturbo924 · Joined: 09 Nov 2002 Posts: 2212 Location: Londonderry NH

Oh oops ... I just read it again. You said it runs well on flats and down hill. Not that it is bad going down hills... haha

Ok so I would definately check the alternator then. Sounds exactly like the belt is slipping when the engine is trying to make power.

Remember... do not tell them to check the tension. It could be very tight and still slip. Tell them to see if they can rotate the pulley on the alternator yet the belt stays put.

Eric
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1982 924
1992 968
2003 C4S
Parts Parts Parts and More parts.
E-mail me for parts you need!
Drive Fast!

seanski44 · Joined: 13 Mar 2006 Posts: 532 Location: Nottingham UK

also, check condition of alternator/starter loom - it wears near the alternator and can short out under bizzarre conditions - mine did this and would sometimes short and cause engine to run rough, sometimes would cause it to not shut down at all. check you haven't got some bizzarre short.

Also, can't remember if you said you'd checked the alternator earth strap - poss this is intermittent. Add an extra strap?
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seanski44 · Joined: 13 Mar 2006 Posts: 532 Location: Nottingham UK

also, did you try fresh leads like I mentioned last time? - still think these can have a great effect - when the leads start to break down over time they can be shocking!
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1998 BMW Z3 2.8 arctic silver & red

1981 168HP 931 S2 blue/tan leather - SOLD

1985 121HP 924 2.0l na modded - SOLD!
1992 968 lux SOLD
1989 944 2.7 lux SOLD

BC77-924 · Posted: Mon May 15, 2006 1:51 am Post subject: taking a break from it

I have dropped the car off this week for body work and a paint job. After that is done it will be taken to another shop (Yikes!!!). This new guy figures it is a burnt valve(s). I'll have to see how it all goes when I get back from holidays.

It is off to Cuba this week. It is a pretty interesting place with lots of old 40's, 50's and 60's American cars.

Time will tell I guess

Thanks for the responses

D
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Silver/Grey 77.5