Performance flat spot
Thread Starter
Drifting
Joined: Mar 2002
Posts: 2,213
Likes: 1
From: Westlake Village CA.
Performance flat spot
I recently noticed a bad flat spot in my engine. If I put her in 3rd gear at 3000 rpm and then floor the gas, as the revs build there is a big flat spot as it goes through about 4800 rpm and then clears back out above 5400. Its very noticeable and the car actually shakes a bit. And it occasionally farts loudly.
The CEL is not flashing.
The reason I noticed it was because I was goofing around after I put on the bypasses to see how much sooner I was getting boost.
I ran two tanks of gas mixed with techron through it to no avail.
I always mix 4 or 5 gallons of 100 or 103 octane with each fill up.
If I run the car normally to redline through all of the gears, it does not happen. It almost feels as if the turbo's are stalling out or blowing off or something.
The ECU is FVD as are the so-called hybrid turbos.
The car has an Andial intercooler and an S oil cooler as well. Basically the only changes are the cat bypasses.
Any ideas?
The CEL is not flashing.
The reason I noticed it was because I was goofing around after I put on the bypasses to see how much sooner I was getting boost.
I ran two tanks of gas mixed with techron through it to no avail.
I always mix 4 or 5 gallons of 100 or 103 octane with each fill up.
If I run the car normally to redline through all of the gears, it does not happen. It almost feels as if the turbo's are stalling out or blowing off or something.
The ECU is FVD as are the so-called hybrid turbos.
The car has an Andial intercooler and an S oil cooler as well. Basically the only changes are the cat bypasses.
Any ideas?
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Thread Starter
Drifting
Joined: Mar 2002
Posts: 2,213
Likes: 1
From: Westlake Village CA.
You know what? It pretty much just healed itself.
After running two tanks of gas mixed with some techron, it was still doing it. I quit going to McVally oil for my 100 octane and only go to the 76 station. Eventually, it just quit doing it on it's own, so I'm guessing bad gas, even though it hung on for about a month of two tanks of gas per week.
For good measure, after it cleared up, I disconnected my battery for 15 minutes to let the FVD ECU unlearn any bad gas behaviour.
Not a very satisfying solution, as I never really nailed it down.
After running two tanks of gas mixed with some techron, it was still doing it. I quit going to McVally oil for my 100 octane and only go to the 76 station. Eventually, it just quit doing it on it's own, so I'm guessing bad gas, even though it hung on for about a month of two tanks of gas per week.
For good measure, after it cleared up, I disconnected my battery for 15 minutes to let the FVD ECU unlearn any bad gas behaviour.
Not a very satisfying solution, as I never really nailed it down.
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Former Vendor
Joined: May 2002
Posts: 6,849
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From: Tampa
Guess with the bad gas, the knock sensor was cutting down the timing and boost, and then when it stopped it readjusted at the higher RPMs. I noticed some of the 996TT guys have had some of these issues after modified ECUs from various manufacturers, turbos, etc. From what I could tell most seemed to throw more money at it until it was better. Glad yours cleared up without any undue expense or damage.....
Thread Starter
Drifting
Joined: Mar 2002
Posts: 2,213
Likes: 1
From: Westlake Village CA.
The only problem with the bad gas theory is why did it take a month to clear up?
I'm still considering getting it on a dyno so I know where I'm at. This weekend at Buttonwillow, I seemed to be able to hang around in the vicinity of Ed Kramers 996TT that he said was putting out around 500 horse so maybe it's all okey dokey. (Not very scientific though huh.
I mean I don't know how hard he was trying and what not.)
I'm still considering getting it on a dyno so I know where I'm at. This weekend at Buttonwillow, I seemed to be able to hang around in the vicinity of Ed Kramers 996TT that he said was putting out around 500 horse so maybe it's all okey dokey. (Not very scientific though huh.
I mean I don't know how hard he was trying and what not.)
Lifetime Rennlist Member
Joined: May 2001
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From: KC
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by ScottMellor:
<strong>The only problem with the bad gas theory is why did it take a month to clear up?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">What could have happened is that you were running on low octance fuel for all that time. I assume that the two stations are generally close. The independent could well be buying 76 100 octane, thus you might have been using the same batch even though it came from 2 stations. A blending or labeling problem could have gotten the station's tanks filled with 91 or worse.
<strong>The only problem with the bad gas theory is why did it take a month to clear up?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">What could have happened is that you were running on low octance fuel for all that time. I assume that the two stations are generally close. The independent could well be buying 76 100 octane, thus you might have been using the same batch even though it came from 2 stations. A blending or labeling problem could have gotten the station's tanks filled with 91 or worse.
Thread Starter
Drifting
Joined: Mar 2002
Posts: 2,213
Likes: 1
From: Westlake Village CA.
Mark, McValley in Oxnard sells 103 Octane from some company in whose name escapes me. BUT their 103 tank was down for about three months. It could have turned to onion water by the time they got it fixed. I quit using McValley immediately upon noticing the problem.
It's almost like the catastrophic shaking, car dying, flashing check engine light issue. It just healed itself.
It's almost like the catastrophic shaking, car dying, flashing check engine light issue. It just healed itself.