I have been getting a MAF circuit error code on my 94Z. It will be running fine and all at once it will stumble (as in loss of time, bog type stumble), and then the check engine light will pop. When it pops, the car goes back into open loop and drives fine. Sooner or later the light will go off (after a few cycles I would imagine) and it is fine. There is no predicting this, as it happens whenever it feels like it (not certain RPMs or specific engine temp). My question is this...When the car goes into open loop and is running in speed density mode, how does the car make fuel calculations (injector pulse/width modulation, etc) and to what can I attribute an incorrect reading from the MAF? This is a brand new Granatelli MAF?!

Thanks!

Charlie

 

Why is your question not this: Why is my car stumbling? We would respond with a question: What codes are being thrown?

 

By using the VE tables, rpm, manifold pressure, and IAT.
Why did you change the MAF?
Put the stock MAF back in as thats what the MAF tables are dialed in for.

Get Datamasters so you at least know whats going on.

 

First of all, if you're referring to DTC48 then it goes into speed density mode, but not open loop. The only failure that will put the PCM into open loop mode is an O2 fault.

Open loop is just that, no closed loop control.

Speed density is one type of closed loop control.

Last, it doesn't matter how new the sensor is if the wires or connector going to it are poor.

 

I had a problem similar to this. I have a 97ss. It would run in speed density mode due to loss of the MAF power. The problem was T_shot to a faulty heater circuit on 1 of the four O2 sensors. The heater circuit would short and blow the 20amp fuse, but, not intermittant like your prob. I found the problem and cut the suspect O2 heater curcit wire on the sensor. Then, no problem. The O2 sensor took longer to achieve op temp, but still good. I re_wired my MAF power circuit. (Not stock now.)

I had to isolate each sensor and measure the resistance of the heater circuit since they are very low resistance, and, will always ring as a short with a digital meter on continuity test.

HTH. B.

 

I was forced to buy a new MAF due to OEM failure, so I went with a Granatelli. I have since picked up a stocker, thought it fixed the problem, but has not...I will try datamasters, have not heard of it but will see if I can get my hands on it.

 

Thanks Speedy, it is DTC48. Checked connectors, they look great. I am going to try to pick a new weather pack connector for the MAF and wire that in, trying the cheap route first.

 

Interesting. I will check the O2s, I have homemade extensions on them due to the long tubes, so maybe they need inspection...anyways, I appreciate the lead!