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red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

Hi guys, ive gotta bit of a problem with my 924, when i first drive it everything is fine, well for about 20 minutes, then it starts to missfire and run on 3 cylinders, it doesn't do this over around 2k rpm. Its just had another service, oil, oil filter, plugs... I was think of changing the fuel filter as i dont know the last time it was changed.

Any ideas?

Also the volts stay at about 11 during night driving with the lights on, what volts do you guys see?

One last thing, once the cars warmed up the oil pressure at idle drops to around below 1 bar?

Thanks

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924RACR · Posted: Sat May 22, 2004 9:28 am Post subject:

If I were looking for a common thread I'd be hard pressed to avoid saying... bad ground! Or grounds!
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Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

Did you replace the distributor cap and rotor? I would change the fuel filter because its good PM, but most likely it would not cause a problem when the engine warms up. Usually the fuel filter would cause a problem warm or hot.

A thought would be the WUR. I would do a CIS pressure check. Although I dont think it would take 20 mins for the problem to show up.

I would also check the thermo vacuum switch. It only controls the EEC system, but if there is a vacuum leak in that circuit it might only show up when the engine is warm.

I am thinking that it could be an electrical problem. Either the relay or the fuel pump is overheating and having a resistance problem. Try jumping the fuel pump relay when the engine is hot and see if the performance improves. Also do the electrical test on the fuel pump when hot. I cant remember what the current should be it may be in the Haynes. If not I can look it up for you.
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red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

Thanks for the replies!

Ok guys i think ive pin pointed the problem a bit, when the engine starts to miss, the volts do drop!
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Click on link 4 pics! http://www.924board.org/viewtopic.php?t=12422

924guy · Posted: Sat May 22, 2004 11:48 pm Post subject:

Roger might be onto something..ive had dizzy cap issues with every 924 ive owned, they tend to develope micro fractures after time that arent readily visible and will develope intermittant misses as a result. If yours is older, it might be a good idea to replace it just in case..theyre fairly cheap and it certainly cant hurt...
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ltgland · Posted: Sun May 23, 2004 2:12 am Post subject:

£10 at halfords for the cap and a rotor arm

red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

im goin to get a cap and rotor today hopefully that will sort the problem, as it doesnt even start now, i tried to move it from the drive to the garage engine was warm as i had just been out(was a bit juddery on the way home) and it went pop and turned off!

Any ideas?

Could it be a fuel pressure problem?
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1980 Red 924 CARRERA GT(rep) with custom leather interior + GT goodies!
Click on link 4 pics! http://www.924board.org/viewtopic.php?t=12422

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

Check to make sure the alternator belt is not slipping.
Some times even with a belt that looks and feels tight... there could be slippage... ouch.
Anyway ... car not running... reach down and push on the alternator pulley fan. If with a good amount of force you can move the pully fan and thus pulley with out the belt moving... you need to tighten it up some more... and or replace the belt.

The car should be putting out around 13-14V not 11.

At least that is what I remember. Each time my car would begin to misfire and run poorly it was due to the belt.

If it was just changed it could definately be the issue since many of the cheaper belts stretch quickly and need to be adjusted again.

Eric
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red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

hopefully that might be it as the car running rough seems to coincide with a voltage drop down to 11
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Click on link 4 pics! http://www.924board.org/viewtopic.php?t=12422

78porsche924 · Posted: Tue May 25, 2004 2:31 am Post subject:

I had the same problem as you. Gas tank was rusted out and the fuel filter was clogging. Take off the intake side of the fuel filter and look at the fuel coming out. If it looks like a muddy red color, congrats, your tank is rusty. When my fuel filter clogged it would run for so long and then the engine would run very rough. Does your engine cut off at an earlier rpm when you floor it as opposed to giving it a little bit of gas? Also when you start the car, let it sit for a few minutes, then start her up again, does it run better? Also if u are brave, richen your mixture a little bit and see if it will start/run better. If so you are not getting enough fuel to your engine most likely. These were all symptoms of what happened when my fuel filter clogged. Also get like an 8 or 4 gauge ground wire from a car audio store and add an aditional ground from the battery to the frame, it did wonders for my 944 and i assume it would at least help out your 924.
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red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

well it was running sweet now all of a sudden this, im gonna give all these ideas a go as im sure its bound to be one of them, it has progresivly got worser, then the bang and pop now it wont start up again!
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1980 Red 924 CARRERA GT(rep) with custom leather interior + GT goodies!
Click on link 4 pics! http://www.924board.org/viewtopic.php?t=12422

red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

well i didnt get time to change the dizzy as i got home from work late but thought i would try start it anyway, and guess what, it started up first time no probs!

What the hell is goin on?
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1980 Red 924 CARRERA GT(rep) with custom leather interior + GT goodies!
Click on link 4 pics! http://www.924board.org/viewtopic.php?t=12422

924RACR · Posted: Tue May 25, 2004 10:15 pm Post subject:

This just screams odd electrical issue to me, starting with the grounds...
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

welder · Joined: 16 May 2003 Posts: 158 Location: cumberland,maine

I also agree that sounds very much like the all to common ground problems. I can see how inexperenced new owners would jump and replace parts instead of checking these very simple, but poorly wired grounds. Also check the wire harness where it runs along the block under the exhaust manifold, between starter and the alternator. Chech to see the insulation is still intact,(probably not)
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red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

hi all another update, ive now changed the dizzy and roter, also cleaned up the ground on the battrey, and checked alternater belt all is fine, the car starts up, BUT when the heat gauge goes to a quarter it turns off and wont start until it is cold again, Any ideas cos im really stuck now, also i cant get it to a gargae without towing it there, so i want to check what i can now before i give up and get to that stage,

I hear talk of grounds can someone tell me where these are located and the best way of sorting them please.

Thanks in advance

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1980 Red 924 CARRERA GT(rep) with custom leather interior + GT goodies!
Click on link 4 pics! http://www.924board.org/viewtopic.php?t=12422