Issue with power falling off early

2007 gt stock heads cams kb 2.6 @13psi on e85

Took it to the dyno awhile back and got some results. I am having issues with power falling off around 5700 as u can see in the dyno graph.

Any idea what's going on here? You can see it kinda comes back for a second at the end of the graph.

Air fuel stays at about 11.5 and timing right around 19 degrees

how does the boost curve look?

what throttle body?

boost falling off or tb closing was my first thought

stkjock said:

how does the boost curve look?

what throttle body?

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It's got a boost gauge, and I'm almost certain it did not fall off, and have never seen it fall off before and have taken many videos of the gauge during pulls.

The throttle body is stock

Is the problem new, or are you sorting a combo?

RocketcarX said:

Is the problem new, or are you sorting a combo?

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Combo isn't really new. Could have been there forever as far as I know, never noticed it laying over like that while behind the wheel on the road

How far into the RPM range should stock cams and a TB be going against boost? 5700 is a lot of RPM when you consider how many stock parts you're actually running.
Is the 2.6 over spun or in it's upper range at that point?
What is it doing at the drag strip?

On a side note, I would think 11.5:1 would be too rich, but then again I'm working on a 2JZ deal the tuner has set to 11:1

13lbs of boost on a stock 07???

Do you think the clutch started slipping?

Is the VCT still functional?
Do you have any datalog info to look at for the VCT?
Just a thought.

RED09GT said:

Is the VCT still functional?
Do you have any datalog info to look at for the VCT?
Just a thought.

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Not sure how to multi quote on this forum..

The motor has a built shortblock, I suppose the clutch could have been slipping, would be new news to me.. and no the blower is not being
Over spun.


Now the vct deal I'm not positive but I think it's still active and not really messed wiTh

94_cobra said:

It's got a boost gauge, and I'm almost certain it did not fall off, and have never seen it fall off before and have taken many videos of the gauge during pulls.

The throttle body is stock

Click to expand...

so you have no boost curve to go with the dyno chart?

94_cobra said:

Not sure how to multi quote on this forum..

Click to expand...

bottom right corner of post

stkjock said:

so you have no boost curve to go with the dyno chart?


bottom right corner of post

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I have the datalog from thAt dyno pull, can't remember exactly what I logged, but don't think I can log boost. It pretty much goes straight to 13 psi and stays there.

Yea that's the multi quote button, but it does not exist on my screen. Only the edit, quote, and reply buttons are there

94_cobra said:

I have the datalog from thAt dyno pull, can't remember exactly what I logged, but don't think I can log boost. It pretty much goes straight to 13 psi and stays there.

Yea that's the multi quote button, but it does not exist on my screen. Only the edit, quote, and reply buttons are there

Click to expand...

If you are logging with LiveLink you will need to add an analog PID and use the boost gauge as the reference point since these cars don't have a manifold pressure sensor that the PCM can talk to.

With double digit boost, I would think the valve springs may be floating, if they're stock. As mentioned earlier I'd also check to see if the VCT is working as it should. There is a way to log commanded cam timing versus actual. If they vary then you know something is wrong with the VCT system.

46addict said:

If you are logging with LiveLink you will need to add an analog PID and use the boost gauge as the reference point since these cars don't have a manifold pressure sensor that the PCM can talk to.

With double digit boost, I would think the valve springs may be floating, if they're stock. As mentioned earlier I'd also check to see if the VCT is working as it should. There is a way to log commanded cam timing versus actual. If they vary then you know something is wrong with the VCT system.

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Thanks for the response. I am logging with livelink, and as you said, no boost PID.

I questioned the valve springs, but am looking into other possible sources. Ill look into logging the VCT.

What i DID just notice, is in the datalog, the SPARK ADVANCE pid drops off 3 degrees right in line with the rpm the dyno graph dips, but BORDERLINE SPARK does not dip so im thinking its not dipping like that because of the spark table.. what else could make it do that?


So you can see the BLUE line in the graph dip out for a bit toward the end of the pull which does line up with the dyno graph dip. Looks like its taking out 3 degrees of timing right there. I wouldnt think 3 degrees would do that much damage, but anyways.. what could be making it pull 3 degrees.. if thats even whats going on?

Did you log your IAT?
Been a while since I looked at an SCT datalog, is IAT the ACTB? If so, it isn't that high so it shouldn't cause it to be pulling timing.

The timing is probably the cause of the power dip as the power returns as soon as the spark advance comes back.

Any knock sensor activity?

I was going to say knock sensor too but he's running E85. But even that might not be bulletproof.

RED09GT said:

Did you log your IAT?
Been a while since I looked at an SCT datalog, is IAT the ACTB? If so, it isn't that high so it shouldn't cause it to be pulling timing.

The timing is probably the cause of the power dip as the power returns as soon as the spark advance comes back.

Any knock sensor activity?

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ACT is IAT.

The yellow line represents timing being pulled from high air temps. 0 timing being pulled for high iat during the timing dip in the pull


unsure about knock sensor activity. this datalogging process blows.. you have to choose what to datalog in the begging. so what you see on the left is all i have to look at during that specific dyno pull

Sometimes knock sensors get false readings from other noises or vibrations so it is probably worth investigating.

As much as datalogging can be frustrating it beats pulling plugs on a hot engine, or having to make a bunch of dragstrip runs and try not to do absolutely anything different from one run to the next driving-wise.
Kinda great that we have all these tools now to pinpoint where things are not working right rather than just a time and a MPH that we have to make a guess from.

Yea it def is nice to have the logs. Better than nothin!

I did a street pull to see if the issue is re-occurring and it did not pull timing like above, but the iats were enough to pull timing. I'll have to try and mimic the circumstances to see if it was a fluke deal or not

Is it pulling timing with IAT in the 140s even with E85?
What was your IAT during the street pull?