I am not well versed on the 4.3 engine, but i am working on a project and i have just swapped in a low-milage motor (2003) from a junkyard. I have it running and it will run just fine if i have the MAF unplugged. If i turn off the motor and plug in the MAF, it will start right up and run fine for a few seconds and then start bogging and chugging and choke itself out. So far, here is what i have replaced:
Cap/Rotor/Plugs/Wires
MAP Sensor
IAC sensor
TPS sensor
New MAF sensor.
I have tested the voltage at the MAF and have 12v and good ground. I have also tried to eliminate any vacuum leaks and have done the propane test around the intake with no noticeable change in engine speed.
Where should i go from here? Since it seems to run fine without the MAF plugged in, can i just run without it? What would be the consequences of doing so?

 

1. Do you have codes?
2. When you checked the reference voltage to the maf did you do so in reference to thr maf ground at the plug?
3. If you have a scanner with live data, what is the maf reading at idle and if it runs well enough, at the moment of full ecceleration into the 1-2 shift?
4. What are your fuel trims at idle and at 2500 rpm?
5. Make sure that you dont have an intake air leak after the maf
6. Can you look at a graph of O2 sensors?

George

 

Thank you for the reply.
1. I do have one code, but it is for EGR.
2. I did not check reference voltage using the ground at the meter, i checked voltage on the wire and ground on the engine/exhaust manifold. I will check that using those wires.
3. I think i should be able to get live data. I cant really drive the vehicle at the moment because it doesnt run well enough with MAF plugged in and also, i have the body off of it and am trying to make sure i have the engine running normally before dropping the body back on.
4. I will see if i can check this. I have several scan tools, seems my Otofix Autel doesnt want to give me much information on this motor
5. I will double check for air leaks between MAF and bonnet. I do not have a hose plugged into the bonnet, but have it taped closed. I will double check there for a vacuum leak.
6. I will see if my other scantool software on my laptop will give me O2 readings.

I was trying to be as vague as possible, as this isnt a normal setup to what most people will be asking for. I am actually putting together a project out of a bunch of different parts.....1995 2dr Blazer frame, 2003 4.3 out of a van, custom standalone wiring harness from Howell EFI to run the 411 PCM red/blue computer, 4L60/NP233, 1964 Scout body. Like i said, i have everything running great as long as the MAF is unplugged, just trying to chase down this last demon. Thank you for your input, i will see what kind of data i can pull.

 

This is what i just captures

 

If it will go into closed loop when it warms up then grab that screen shot.

George