Why do I have boost?

[1slow95]

I'm still trying to get my car running right with my AEM. I took it wide open for the first time tonight, and I noticed something strange in my data log....For some reason I'm seeing 0 to 0.5 PSI at WOT, and it hit 1.3 PSI once. I'm showing just below 0 with the engine off, like -0.04 I think.

So why would I see any pressure in the intake? The car was running pretty rough and it didn't want to rev over 4000 rpms.

Here's a screen shot of the data log. I left it at 1600x1200, so I'll just post it as a link.
http://www.mustangaddiction.com/aem/datalog.jpg
And with timing displayed
http://www.mustangaddiction.com/aem/datalog2.jpg

 

[revhead347]

Error in the sensor. You don't have any boost.

Kurt

 

[ThePumpkin]

Error in the sensor. You don't have any boost.

Kurt

thats what im thinking...

Either that or air was having a race to get into your engine

 

[Black Stampede]

How did you car go from running great track #s to running like garbage?

 

[1slow95]

How did you car go from running great track #s to running like garbage?

Simple....I removed the tuned SCT chip and installed an AEM that I'm tuning myself.


Could a backfire into the intake cause this? It was missing and running rough, so that's the only thing I can think of. Unless there's a problem with the MAP sensor or it's not set up right in the AEM.

 

[Stanger007]

If the vehicle is running rough then you could see a pressure in the intake from the aircharge reverting. Valve float will give you some interesting pressure readings as well.

Vehicle electrical systems are notoriously noisy, run the vehicle and pull the MAP from vacuum at idle and see what it reads there - make sure your fueling is sane for this test in the calibration so the vehicle will continue to run.

Just a couple thoughts.

Wes

P.S. I'll also add that an extremely lean mix will cause a popping in the intake. There are quite a few ways to see a positive pressure in the intake tract, especially if the vehicle is running "rough".

 

[Black Stampede]

Simple....I removed the tuned SCT chip and installed an AEM that I'm tuning myself.

Haha, yeah that makes sense.

 

[ThePumpkin]

Simple....I removed the tuned SCT chip and installed an AEM that I'm tuning myself.


Could a backfire into the intake cause this? It was missing and running rough, so that's the only thing I can think of. Unless there's a problem with the MAP sensor or it's not set up right in the AEM.

Wouldn't backfire create an outgoing vacuum instead of positive pressure?
Air is forced the other way, so that only makes sense.

 

[1slow95]

I sync'd the timing tonight, and it was off by a degree or two. I had the dizzy set at 10* with the stock computer, so I never thought to sync it with the AEM since it defaults to 10*. I also tried to adjust the O2, I connected my voltmeter to it while the car was running and matched the AEM as close to it as I could get. I think it was off by a good bit if I got it set right.

The car now runs up to 5500 at least, which is the highest I took it. It's making decent power, but nowhere near the 450rwhp it was making before....I'm low on cash, so instead of buying a new air filter I just stuck on an old k&n filter I had laying around for now. That could be part of my problem.

http://www.mustangaddiction.com/aem/datalog3.jpg
There's my latest data log with a WOT run from 2000 to 5500 rpm in 2nd gear. It seems like it builds pressure up to 3900 rpm, then it drops off instantly from 1.1 PSI to -1.6 PSI. There's not much of a change at that rpm in the fuel and spark tables...