I have a 5.0 with the Explorer intake, GT40 heads, RJM harness, E303 cam, and a A9M computer in a '68 Mustang.

When you let off of the throttle the CEL comes on indicating low voltage on the MASS air meter. I changed the MASS from the '89-93 5.0 Fox Mustang meter to a new '94 Cobra style meter, reset the computer and it does the same thing (immediately).

Current intake setup is the Explorer throttle body, an '89-93 Fox 45* elbow, MASS air meter and a double cone Spectra air filter mounted directly on the meter.

I don't really have room to go cold air unless the battery goes in the trunk and since this is my wife's daily driver, I am reluctant to.

Car is running open loop at 12mpg.

Any ideas?

 

Does your 55mm MAF from the 89-93 have the screen still in it? My car had issues without it. I also had some idle issues using the 94-up MAF.
I would also look for a vacuum leak.

 

Exactly what codes are you getting?

 

Screen is still in the MAF. I messed with it and put the 89-93 MAF back on with a longer tube between the air filter and MAF. I am getting a 12 (rpm low) and 26. Baffling the air filter from fan turbulence does not affect the 26 code.

I measured voltage on the MAF and have approx 1.5 vdc at idle going up to 2.6 at 4500 rpm.

The computer was showing a code for the MAP (newish) that seems to be related to the MAF low voltage that turned out to be a bad connection.

 

You do have a MAP/BARO sensor installed right? This computer uses the same MAP sensor as the trucks but it doesn't get connected to manifold vacuum that fitting is just left open to atmosphere so it becomes a barometric sensor.

 

I had the BARO sensor running as a MAP. With the thing vented to atmospheric it got rid of the CEL on deceleration and it began running closed loop and everything looked good on the code reader.

Two days later, PIP or TFI module starts dying and running like a fuel starvation issue. I replaced the distributor and it fixed it except for some stumble at around 2000 rpm during accelleration but not on steady cruise. No codes during test and fuel pressure good including new filter.

Replaced TPS and then my new Equus 3140 code reader died during the KOER test. I am waiting for it to be repaired or replaced. No appreciable change in the stumble.

Replaced IAT sensor as it was the last original sensor from the engine and I figured they probably have served their lifespan after 23 years. Haven't gotten a report back as to whether it still stumbles. She says she thinks she might smell raw fuel when it stumbles. Strange because it feels like lean condition to me.