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Old 06-01-2005, 10:58 PM   #1
TexRex2002
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Default fuel trim gurus: stalling right after reaching operating temp.

ok master tuners:

I think I have a fuel trim problem. when I start the car up in the morning it runs just fine. By the time I get to my first stop sign though, my engine has reached normal operating temparature, and when I push the clutch in and let off the gas my rpms plumment to like 300 (for a split second), rebound to 750 and I get a CEL.

a minute or later everything is peachy. When I let off the gas the needle drops quickly until about 1500, where it's fall slows noticably and it settles into idle nicely.

Every single morning it is the same thing: CEL at my first stop sign.

My guess is that the ECU learns one set of fuel trims when the engine is cold, and when the motor is warmed up those fuel trims cause the engine to stumble (upon letting off the gas) for the minute or so it takes for the trims to re-learn.

Anyway, that's my hypothesis. Anyone have thoughts or advice on how to fix? I do have deltadash and a TXS tuna. I should mention that this is on a hybrid WRX/STI motor with modded stock injectors.

The problem is especially bad if I let off the gas right after the car being under load (i.e. hauling ass before stoping at the first stop sign).
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Old 06-01-2005, 11:06 PM   #2
mcowger
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So what kind of EM are you running with this? UTEC?
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Old 06-01-2005, 11:46 PM   #3
Uncle Scotty
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Try this.....

In the am when the car is as cold as it is gonna get.......do an ECU re-set.

Get in the car and start the car WITHOUT TOUCHING THE THROTTLE AT ALL.

Let the engine come to operating temp....the fans will come on when it is at temp.....Shut the car off, and take the key out.
Start the car and drive it normally.

See if that helps.
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Old 06-02-2005, 12:03 AM   #4
TexRex2002
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yes UTEC


Uncle Scotty:
Are you suggesting that as a permanent fix?

Thanks
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Old 06-02-2005, 12:33 AM   #5
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....I'm suggesting it as a potential cure for the current issue.......if you have not reset the ECU for a while, it may just work wonders for ya.
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Old 06-02-2005, 10:14 AM   #6
x99percent
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If you have DeltaDash, then check what your fuel trims are once the car is fully warmed up.

Air/Fuel Learning #1 <-- The important one
Air/Fuel Correction #1 <-- This should be oscillating at/about 0%. If not, wait longer.

Report back with your results.
Also, exactly what CEL are you getting? (read this using F4 in DeltaDash)
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Old 06-02-2005, 02:59 PM   #7
TexRex2002
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the CEL's are MISFIRE 1,2,3,4

I'll check the fuel trims and report back.
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Old 06-02-2005, 05:16 PM   #8
x99percent
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Quote:
Originally Posted by TexRex2002
the CEL's are MISFIRE 1,2,3,4
What *exactly* are you doing when you start the car?

Many people are noticing that if you turn the key to the "ON" position and then WAIT for a few seconds before actually starting the car, most "cold misfire CEL" issues go away.
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Old 06-02-2005, 07:35 PM   #9
TexRex2002
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I start the ignition, let the fuel pump prime and start the car. the cels are n't when it is cold. it throws the cel right after it gets warmed up.

the problem is worse if I am on the brakes, by the way.

I have quadruple checked every single fitting and hose already looking for a vac leak, by the way...
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Old 06-02-2005, 10:38 PM   #10
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Quote:
Originally Posted by TexRex2002
I start the ignition, let the fuel pump prime and start the car. the cels are n't when it is cold. it throws the cel right after it gets warmed up.

the problem is worse if I am on the brakes, by the way.

I have quadruple checked every single fitting and hose already looking for a vac leak, by the way...

...how about the brake booster hose.....?????
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Old 06-03-2005, 11:36 AM   #11
x99percent
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Quote:
Originally Posted by Uncle Scotty
...how about the brake booster hose.....?????
Good call.
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Old 06-03-2005, 01:49 PM   #12
TexRex2002
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I know it's not leaking coming out of the intake, but it may be leaking by the booster. I'll check tonight.

Thank you very much for the help everyone.

I'll be sure to post the cure once I figure it out....
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