MAF problem with supercharger

[JChalfan]

I posted this in here instead of the power adder forum because I believe it's more of a MAF issue than a SC issue.

I recently installed a Paxton SN92 on my 1990 5.0 5-speed, and I am having some trouble that I think is MAF related. The engine is stock with the exception of shorty headers, 24lb injectors, and a Pro Flow 75mm MAF (the chrome bullet one). The MAF is calibrated for a '93 cobra, which I believe just means 24lb injectors. I am using a Paxton red Fuel Control Unit.

When I go WOT and the rpm's hit around 3500, the car falls flat on its face. It completely loses power like someone yanked the coil wire off. When I back off the throttle, it starts going again. I originally thought the SC might be blowing out my spark, so I closed the gap to .025-.030 and it still does it. When I remove the supercharger belt, the car will pull to redline no problem.

I borrowed a C&L 73mm MAF (calibrated for 24lb's) from a friend and tried that. With the C&L the car pulls fine to 6000 rpm's, but I have a problem with low-rpm part-throttle pinging with the base timing set anywhere above 4 degrees. The pinging happens with the SC belt on or off. Has anyone ever had a similar pinging problem caused by a bad MAF? The pinging does not occour with the Pro Flow MAF.

My MAF is a drawthrough setup.

What could cause the Pro Flow to work fine naturally aspirated, but cut out with the SC belt on? I asume it has something to do with the increased airflow through the MAF. Is it possible that once the air flow gets to a certain level, the MAF gets confused and sends a bad signal to the computer?

Also, is it possible (although unlikely) that my computer has a problem?

Thanks a lot for any suggestions.

Jeff

 

[vristang]

I posted this in here instead of the power adder forum because I believe it's more of a MAF issue than a SC issue.

I recently installed a Paxton SN92 on my 1990 5.0 5-speed, and I am having some trouble that I think is MAF related. The engine is stock with the exception of shorty headers, 24lb injectors, and a Pro Flow 75mm MAF (the chrome bullet one). The MAF is calibrated for a '93 cobra, which I believe just means 24lb injectors. I am using a Paxton red Fuel Control Unit.Jeff

I have very little knowledge of superchargers, but I am somewhat familiar with using a 93 Cobra MAF on an A9L (I assume you are using the stock computer, and not the Cobra X3Z?).
Because the tube on the 93 cobra was larger in diameter than the 5.0 HO tube, the voltage output of the MAS (the sensor) is different for these 2 meters.
Long story short, you can't interchange these 2 sensors and expect the car to run well.
Here is more info.
http://www.freewebs.com/vristang/faqs.htm

If you run better with your friends C&L then I would suspect this is your issue.

The pinging you mentioned could be caused by removing the egr?
Have you removed the egr system?

 

[JChalfan]

vristang,

That's good to know about the cobra MAF not working with a 5.0 HO computer. I am using the stock HO computer.

The EGR system is intact. I actually just replaced the EGR Valve Position sensor because it had failed. It was pinging a lot worse at part throttle before I replaced the EVP sensor.

The fact that it still pings some with the C&L but not with the Pro Flow makes me wonder if there is something wrong with the C&L. I wonder if it is not calibrated properly, and it is making the computer run too lean and causing the pinging.

I would like to try another 24lb calibrated MAF, but I don't have access to another one.

Thanks for the info.

Jeff