924Board.org

91rocco · Joined: 20 Mar 2007 Posts: 10 Location: nottingham,uk

Took my 2.0 924 down to my wifes garage on saturday to get it on the ramps to do oil change,air filter etc,The car drove really nice on the way down,1st run its had for a while,Did all the work i wanted to then drove it home,On the way home it started to feel sluggish and produced a missfire under load which seemed to get worse the warmer the engine got,I managed to get it home in a sorry state,let it cool down for a while checked plugs etc and tried again,same problem got worse the hotter it got,I have checked the coil with a ohm meter and it seemed a bit high on the high tension side 880kohms,could this be the problem,I dont really want to waste money on a new coil!!

Many thanks James

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Check your alternator output first. A low battery / weak charging system will give the same symptoms.
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

91rocco · Joined: 20 Mar 2007 Posts: 10 Location: nottingham,uk

Funny you should say that,The battery on the car is crap and doesnt hold its charge long

91rocco · Joined: 20 Mar 2007 Posts: 10 Location: nottingham,uk

I also have problems starting the car (see new guy got a problem)I wonder if my mixture is set to lean,The car seems to warm up very quickly,I put a new air filter on it,Could it be getting too much air/not enough fuel maybe???

Smoothie · Posted: Wed Mar 28, 2007 6:44 am Post subject:

When you switch the ignition on, but before activating the starter, make sure the battery light comes on. The alternator needs to see 12v+ at its' D+ terminal in order to switch on and start charging - that 12v+ comes through the same wire that the battery light is on, so no light = no charging. See my little adventure here - http://www.924board.org/viewtopic.php?t=21642
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

91rocco · Joined: 20 Mar 2007 Posts: 10 Location: nottingham,uk

Checked the battery light,no probs there!

Smoothie · Posted: Wed Mar 28, 2007 8:11 am Post subject:

Well, a bad coil is a possibility - though I haven't had the problem with my 924T, I did have one go bad on an old '74 Dodge van years ago. Symptoms were similar to yours - it ran ok while cool, then sputtered and coughed once warm, and much worse under load. -Replacing the coil fixed that one.
According to my Haynes (with misprints corrected,) the 924NA up to 1980 secondary resistance should read 5.5k to 8.0k ohms between terminal (1) and the center post (4). Primary resistance between (1) and (15) should be 1.0 - 1.3 ohms. -So if your meter doesn't lie and everything else's been gone through - vacuum leak check, plug wire connections, dist cap, rotor, etc., it would seem there's a good chance the problem is indeed a bad coil.

Also check the running voltage at the battery connectors, then the battery posts - should be approx. 13V or more and the same whether measuring from the connectors or from the posts.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Also, when you say 'as the engine gets hotter', does this mean it's starting to over-heat? That could also be a cause of a misfire under load.
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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

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

Have you messed around with the ignition timing, or the camshaft timing belt lately? If so, you could have installed/adjusted it/them incorrectly, causing this problem.

You could also have a blown headgasket.

91rocco · Joined: 20 Mar 2007 Posts: 10 Location: nottingham,uk

The timing is spot on,it doesnt overheat,it doesnt use oil or water or blow any smoke out,I'm gonna have a fiddle at the weekend,gotta be something small and simple that I am missing,Its just one of those anoying things I cant put my finger on!!!

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

If you have a 1980 or later car, the other possibility is a failing ignition module (inside of the distributor), or is you have a 1981 or later car with an electronic idle stabilizer, you could have a have connection on the idle stablizer, or a failed idle stabilizer.

You could also have a vaccum leak, or a stuck AAV.

Do not play with the ignition timing, the idle mixture, or the idle speed, until after you find the problem or you will only create another problem.