924Board.org

[MikeDanger]

Well I had the car running "ok" (never perfect; as usual) and managed to get a few long, 100+/- mi. drives in, up to the mtns.

this last time, I almost got stuck 100 miles out. that was kind of stressful.
I had been driving from denver, down south, for almost 2hrs. between 65-75mph almost the whole way right around 3k rpms. OAT around 70F*

I stopped and got out to take a picture (with engine running) probably about 3 minutes, when i get back in, and try to leave, the car start running rough, A/F bouncing between 11-16 and the car is bucking badly.

I make it just up the road to the nearest gas station. It was barley drivable, but would "idle" drive, any time I touched the throttle it would start bucking.

Funny enough, I went in to the gas station and when I came out, a lady parked next to me and said "my husband has a couple 944s!" She called
him over and a couple hours later, we checked what we could, pulled out and injector and a spark plug(2 diff cylinders) watched the injector spray)

Couldn't see anything that would make it run that bad. No major vac leaks,

Now Im starting to think something major happened....but after letting it cool off for about 4hrs(hood open) and the temps dropped to the 50's.

started it up, and it ran "ok" gave it a little test drive in the parking lot, seemed ok. so I decided to give it a try and head home, and it made it all the way, but it was a really tense 2hr drive, staring at the A/F gauge the whole time. it held around 12.5-13 the whole time at cruise, would drop to 10 when I came to a couple stop lights, but made it the whole way with out to much trouble


So now im trying to figure it out, since either time/ or temp and it seemed to run ok, so probably not a burned valve or bad plug or something like that.

what other things would get better by waiting?? (I have a couple thoughts but Ill wait to see what you guys say first)

81,S2 version.
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It was either this or a giant box of legos

[Cedric]

The ignition amplifier on the front wing is always a suspect when it comes to misfire, cheap to change aswell.
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1980 924 Turbo
www.instagram.com/garagecedric/

[MikeDanger]

[!tom]

Ignition modules are notorious to being temperature sensitive.
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78 924 NA
5-lug

[MikeDanger]

[Cedric]

They break anyway, and newer ones seems to be much worse sadly, even the more expensive brand ones. Had one that lasted only 1.5 years before it started misfiring. The old one was probably 35 years old when it gave up, i originally took it from an old scrap volvo to get my car running:)
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1980 924 Turbo
www.instagram.com/garagecedric/

[MikeDanger]

Im wondering if it was a missfire, as in ignition/electrical or a fuel/air issue.

as when this was happening and the car was bucking, I could see the A/F bouncing way lean. But wouldn't an electrical miss, make it go rich, due to not burning the fuel?
I don't know.

also what about the timing sensor? could that be a possibility?

or possibly failing coil?
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It was either this or a giant box of legos

[924RACR]

A missed cylinder causes a crazy lean reading, actually - due to all the O2 NOT burned.

We're used to thinking we're reading mixture from the WBO2 sensor, but of course we're reading the EFFECT of mixture, the O2 left over... but that assumes there actually is combustion.

Have far too much data from both racecars this past season showing just this... thanks to cylinders dropping then recovering...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[MikeDanger]

[MikeDanger]

can anyone clarify is the S2 need a resistor on the coil?
and what ohm range?
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It was either this or a giant box of legos

[MikeDanger]

anyone? can't find much info on it
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It was either this or a giant box of legos

[72rallye]

The '81 manual doesn't show an inline resistor and my 81 S2 doesn't have one either. The 0 221 122 023 coil, which is the correct coil for this car has an internal resistance of 0.7 Ohm.
The M31/03 engine, which runs more boost than our US-cars uses the same coil. So, unless you are increasing the boost level by a lot the stock coil should be fine.
Thomas
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81 931 currently being resurrected after a 22yr hiatus
86 951, 86 928 5spd, 75 911S coupe

[MikeDanger]

[Cedric]

Yeah, bosch stock coil is good, i put a new on there while chasing a misfire (it was my fairly new hella ignition amplifier, replaced it with a beru unit). Then it worked great over 1 bar of boost, 14.5psi.
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1980 924 Turbo
www.instagram.com/garagecedric/