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What went wrong??

 
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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Thu Nov 09, 2023 6:40 pm    Post subject: What went wrong?? Reply with quote

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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Cedric  



Joined: 27 Aug 2004
Posts: 2592
Location: Sweden

PostPosted: Thu Nov 09, 2023 8:59 pm    Post subject: Reply with quote

The ignition amplifier on the front wing is always a suspect when it comes to misfire, cheap to change aswell.
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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Fri Nov 10, 2023 9:02 am    Post subject: Reply with quote

Cedric wrote:
The ignition amplifier on the front wing is always a suspect when it comes to misfire, cheap to change aswell.

hmmm, ok, I have a spare, Ill carry that with me.
Would that be something that would work again after cooling period?
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!tom  



Joined: 28 Aug 2006
Posts: 1930
Location: Victoria, BC Canada

PostPosted: Sat Nov 11, 2023 7:13 am    Post subject: Reply with quote

Ignition modules are notorious to being temperature sensitive.
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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Sat Nov 11, 2023 7:13 pm    Post subject: Reply with quote

!tom wrote:
Ignition modules are notorious to being temperature sensitive.

yeah, I had that happen on a past vehicle, but that one was on the engine. these are on the fender, where air should be readily cooling it off, and at 70F, I would hope its more reliable than that?
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Cedric  



Joined: 27 Aug 2004
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PostPosted: Sat Nov 11, 2023 7:27 pm    Post subject: Reply with quote

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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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Sat Nov 11, 2023 7:34 pm    Post subject: Reply with quote

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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924RACR  



Joined: 29 Jul 2001
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PostPosted: Sat Nov 11, 2023 9:37 pm    Post subject: Reply with quote

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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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Sun Nov 12, 2023 6:02 am    Post subject: Reply with quote

924RACR wrote:
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...


hmmm, good point, ok I guess that makes the ignition avenue more likely.


Im actually considering replacing the coil with a higher power one, any feedback on that? (although I have read many of the after market ones MSD, etc are crap quality)
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MikeDanger  



Joined: 21 Nov 2002
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Location: Denver

PostPosted: Mon Nov 13, 2023 8:00 am    Post subject: Reply with quote

can anyone clarify is the S2 need a resistor on the coil?
and what ohm range?
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MikeDanger  



Joined: 21 Nov 2002
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PostPosted: Tue Nov 21, 2023 5:28 am    Post subject: Reply with quote

anyone? can't find much info on it
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72rallye  



Joined: 08 Apr 2023
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Location: San Diego, CA, USA

PostPosted: Tue Nov 21, 2023 9:00 am    Post subject: Reply with quote

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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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Tue Nov 21, 2023 1:58 pm    Post subject: Reply with quote

72rallye wrote:
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

im running 13psi.

was thinking about trying a MSD coil or something, some say with resistor and some with out and some same 1.5ohm would that be suitable?
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Cedric  



Joined: 27 Aug 2004
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PostPosted: Tue Nov 21, 2023 6:01 pm    Post subject: Reply with quote

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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