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Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

yesterday sat at the lights with engine at running temp....the car began to misfire.

at first was just a few times....
but today on the journey into work...it was getting progressively worse...to the point of embarrasing.
it's only really apparent on idle at the lights....and when i try to pull away its lousy hesitation and judder until i get up above 2500 rpm.

i gave it a good rev at the lights, with the autobox in "park" and it was alright for about 15 seconds...and then started again.

am wondering what should i check first when i get back tonight?

thanks for your help once again folks

tiny
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*****1981 - 924 - Auto - London, UK******

Stu2j · Posted: Sat Jun 24, 2006 12:59 am Post subject:

Bad plug?
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Stampedetrail · Joined: 29 May 2005 Posts: 274 Location: Fairbanks, Alaska

I'd second that one, analyze the plugs & go from there.
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1977.5 924 "Martini" head / New Old Stock rebuild
1985.5 944 Why? Because I can.

Joes924Racer · Posted: Sat Jun 24, 2006 2:20 pm Post subject:

it sounds like a fuel delivery issue could be a filter..
or an injector or maybe the WUR.
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gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

It's an 81. Could be the Bosch breakerless module inside of the distributor is failing, as many do when approaching and passing 100K miles.

Paul · Posted: Sat Jun 24, 2006 3:07 pm Post subject:

Other things worth a look:

Spark plug wires?

Leak in the intake tract?

Cap or rotor?
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
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Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Yeah, it might be smart to look for a vacuum leak. On a 81 or later with electronic idle stabilization, you get all kinds of problems with vacuum leaks, especially if you have tried to correct idle speed or mixture problems with the mixture or idle speed adjustments in the past.

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

OK, I checked the spark plugs, cap and rotor and have found nothing wrong there.

Thanks for all your replys guys.

I am now wondering where to check for the troublesome vacuum leaks.

Even though it only happens when the engine is warm....I read other posts saying it could also be the WUR, but i'd need to get this professionally diagnosed, right.

And this is the same for the breakerless module in the distributor. I'd have to get a replacement distributor to see if this is the prob...

According to another poster with the same prob, it was the wiring/earths around the IGN module and it was always running on choke. He paid a bosch specialist to diagnose in the end.... I'll check the earths, but wonder how to know for sure if its always on choke?

normally idles around 800/900 rpm

The inside of the exhaust is a little sooted....but not really showing signs of running rich. Mostly greyish there.

Is there anything else I can check while the weekend is here, or test for a manual diagnosis to further my elimination process?

thanks for eveything folks...i'd be lost and broke without the guys on here!
tiny
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*****1981 - 924 - Auto - London, UK******

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

whats happened?

i identified the misfiring cylinder as the 2nd, by pulling the spark plug lead and noticing no change to the poor idling.....so i pulled the injector by first undoing the banjo end...and then pulled the injector from the seal....did the banjo end back up again....and now when i crank the engine, it doesn't fire and theres no fuel coming through, even when i unscrew the injector from the fuel line and crank the engine!?

why is this?

tiny
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*****1981 - 924 - Auto - London, UK******

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

i put the injector back in, and started it up...and it was fine for a little while...so i took it for a 5 minute drive, and it was ok...but then it started misfiring again.

went to watch the england v ecuador...then

i decided to jack the car up and locate the point where the the exhaust is blowing.

it's cracked around the weld line, where the exhaust pipe meets the entrance of the primary muffler. my question is would this crack.... which goes half way round the tube.....cause the car to misfire??
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*****1981 - 924 - Auto - London, UK******

Stampedetrail · Joined: 29 May 2005 Posts: 274 Location: Fairbanks, Alaska

I dont know but it will definitely cause you to pass out while driving. I'd fix that first, for certain. Dirty job but well worth it.
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1977.5 924 "Martini" head / New Old Stock rebuild
1985.5 944 Why? Because I can.

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

Hi, I think I'm the other poster who had the 'always on choke' problem and got the bosch dealer to sort.

It sounds like the same symptoms I had - I'd imagine that the exhaust is just an additional issue. The bosch guys checked the voltage to the cold start equipment, as its this that determines whether the cold start gear is used. i.e. the bad earths caused no circuit which caused the car to run on choke.

If you're handy with a multimeter, warm the car up to the point where it does the fault and then check the voltages. if they vary from the reading when cold, I'd rule out bad earths. if they're the same then it could well be the same fault!

bit vague, but hope it helps.
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Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

brilliant, thank you very much

i have a small muffler on the way, so i'll get down and dirty this weekend....instead of up and high on fumes when i drive...

i'll get my multimeter out and look up which points to check the voltages to the cold start gear.

thanks again

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*****1981 - 924 - Auto - London, UK******

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Hi everyone,

After doing a service she definitely drives smoother but the problem that i mentioned in my first post is still apparent.

Just done:
Cambelt
Fan belt
spark plugs, leads
Distributor cap, and rotor arm
Fuel filter
Air Filter

I have taken out and tested the auxilary air valve, and that is working OK. However, I only get the unsmooth idle once the engine is warm and the AA valve is closed. The spark plugs look fine.

When i rev up hard from idle, it's juddery and reluctant at the lower revs of the "range". Plus....And I don't want this to sound gay, but it does it really bad when it's pouring with rain outside...and with the engine at running temp.

I am wondering where exactly to check the voltage to the cold start equipment? (as mentioned in the previous post)

Or.... if there is anything else you guys think could be the dasterdly culprit?

Again, thanks for your help guys. It is much appreciated.
Tiny

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*****1981 - 924 - Auto - London, UK******

Paul · Posted: Mon Oct 23, 2006 12:50 am Post subject:

Is it still cylinder #2 that's missing?

Have you tried to swap injectors to see if the problem moves with the injector?

Have you done a compression check to see if #2 is low?

Have you done a vacuum check to check your valve springs/cam?
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.