MAF Problem

[LightningWhite]

Here is my situation: I have a 91 GT, that already had a descent motor in it with an intake swap, shaved heads (believe they're stock), and new cam. I decided to twin turbo the car. The car still had the original 19# injectors in it, thought that was a little small for what power the car had, it seemed to hit a wall around 4500-5000 rpms.

For the first part of the turbo build I bought 38# injectors, matching maf, and adjustable fuel pressure reg. Both the injectors and maf were used. I put all the parts on and it couldn't idle or run. Since it was big injectors, I turned the fuel pressure down to about 20-25 psi and it still wouldn't idle. I then decided for whatever reason to try the stock 55mm maf with the bigger injectors, I had to turn the idle up to about 1,000 rpm but it would idle perfectly fine. I drove it around the block like that, but couldn't get above about 1700 cause it would run terrible. So then I decided the used maf calibrated for the 38#s must not be any good. I put it back on to make sure and it again wouldn't idle, but out of curiosity I gave it gas and it would run smoothly higher in the rpm range, around 2000, where the stock one wouldn't.

So with that description, do you think the new (used) maf is bad? Note: The injectors, maf, and fuel press reg. are the only things I have done to the car.

Also what is the significance of changing the fuel pressure when the car is on as compared to when the car is off?

 

[vristang]

If the car is off, then the pump isn't running... you won't get any fuel pressure.

What brand is the MAF?
What part numbers are on the MAF?
What ecu are you running? we need the catch code...
When you purchased the MAF, what vehicle was it previously used on?
Where did you buy it?


We don't have enough information to say if the parts are defective or not, but it does sound like you have a parts mismatch...

Why are you running twin turbos without a tune?

 

[Maryland Stang]

You do know that you can't just throw parts at a car and hope they will work right. The difference between adjusting the FP with the motor on and off is you can't read the fuel pressure with the motor off. You need to get a FP gauge and know what the FP is. How was it you picked the 20 to 25 pound range? Do you know for a fact that it's 20-25 or are you just guessing? You shouldn't try to use the stock 55MM MAF with 38 pound injectors. What is your ignition timing set at?

 

[Maryland Stang]

And that "wall" you were running in to at 5000 RPM. It wasn't the injectors. The heart of power in an engine is the cylinder heads. With stock, unported heads you will get stock performance.