michael_grayson

I got my car going today and the thing runs rough, and way rich. I unplugged the maf and it runs alot better so I tried another maf sensor and it did the same thing. Should I send the ecm off and have it redone. The guy I bought it from had it done but I dont know where or if he even gave them the right information when he had the ecm done. Fuel pressure was 42lbs so that seems alright, O2s are working fine. Also at what rpm should it start to make boost. It seems like im not getting any boost. I revved it up to 6000 rpm and nothing. so I unplugged vacume to the bypass valve and revved it to 5000 rpm and the boost needle moved.

flusz28

could be your map sensor acting up or your computer needs a tune badly..

boosted-lt1

You wont see any boost revving the engine in neutral......only when the engine is under a load. You'll have to drive it and get on it. You should have positive pressure by +/-3000rpm and WOT.

The bypass will be open when there is vacuum.

-Scott.

94 NO TOP Z

Is the MAF before the blower? If so, do you have the bypass valve plumbed where the air will re-circulate?

Sean94Z

If you unplug your MAF and the car starts running correctly, then it sounds like you have a vacuum leak somewhere after the MAF. Check all your plumbing after the MAF, including at the throttle body and the intake. Where is your MAF, is it before or after the blower? It sounds like you are getting a lot less air into the engine than the MAF thinks you are, so it is running pig rich.

SMOKNZ

Your blower is making boost, it's just that the boost/vacuum gauge is plumbed into the intake manifold, and you aren't holding the throttle wide open to get it to rev in neutral, did you? If your boost gauge was hooked up before your throttlebody blades, i'm sure it would register some boost in neutral. A blower is RPM dependant, unlike a turbo whick is LOAD dependant. You can see this first hand if you ever remove the blower discharge and rev the engine. The air that thing moves will move small animals out from under your car, yet a turbo just lightly blows because there is no alot of exhaust produced in neutral with no load on the motor.

CALL911

It is highly unlikely that 2 MAF's are bad. If you are unsure of the computer tune then I would definatly start there. You must have at least a decent base tune setup to your car and its mods to run correctly. For example, if he was running a 350 LT1 with a hot cam and 24# injectors, and no boost, that computer is going to be WAY off from a 383 with a blower cam, and a D1SC pulling 15# of boost with 60# injectors! If its running rough, and rich, it is obviously compensating for something not being right, and adding fuel so you don't have any detonation. My 2 cents would be to get your car to a dyno tuner, and figure out exactly whats going on.

mzgp5x

I had a similar problem. Ran very rich due to most air being dumped to the outside, and, not recirculated. I ran a HKS blow-off valve. Then, I went with an evolution motorsports bypass valve(s). Returned air back to the blower intake. My MAF was up stream of the blower, so, any air that was dumped to the street, caused a rich afr condition. This solved my problem.
Also, check the injector constant in the fuel map. If you changed to a larger injector, and, the calibration constant is lower, the PCM will cause the engine to run rich. I use LT-1 edit ver. 2.2 (obd-2).

Sean94Z

Everyone is missing the simplest thing.. .. I posted above, check for a vacuum leak first. Like mzgp5x said, if your blow off valve is not recirculating air, you have less air in the system then the MAF says. Where is your MAF located???????????????

michael_grayson

Thanks for all the info fellas. The maf is on the intake side, I talked to a tuner and he said I need to move the maf to the boost side and do a tune on the computer. I talked to Bryan at PCM for less. there are no vacume leaks. The bypass valve is plummed going from the boost side with a tube down to the bypass valve and through the valve to the intake side. Once again I really epreceate all the input guys. If theres more I need to look into please let me know!