The wire going to the O2 has a bias voltage on it around .2 v from ECM unplugged. If you put a 3 wire on you probably got the wrong wire hooked to the signal on the O2. Only thing a 3 wire sensor is gonna do is heat up the O2 quicker if you have the heater hooked to 12v and ahve the other grounded. The ECM measures voltage against the bias. One way to check O2 responce is to spray some carb spray in a vacuum hose with engine running about 1500 rpm and watch your signal voltage, should go almost to 1 v. O2 should generate voltage independent of ECM. Are you checking voltage with scan tool or directly at O2? You don't want to check O2v in field service mode.

 

Yes, i was checking the voltage, directly at the O2, in the field service mode (the trouble shooting chart for code 44 indicates to ground the diagnostic terminal). I will have to double check my connections but, when I put the 3-wire O2 on, that was one thing i made sure of was to put the signal lead to the black lead on the O2 (it had 2-white & 1-black lead). I'll try your suggestion on the carb spray.

 

If you are only getting that low of voltage on the O2 with the lead unplugged, then try to fatten it up like I said. If it does, then your engine is running very lean. Terminal C off the MAF is the output to the ECM. Are you getting 12v on the power lead at pin E and a good ground on A? HAve to have 12v on the hot wire in order to heat it up to proper temp. I think you are barking up the wrong tree on O2 and the car is probably running exztremely lean, but the carb spray test will reveal that. [8D]

PS. Do you have MSN? If so PM me with your MSN addy.

 

I checked back you said code 33? That is a MAP sensor code, not MAF. That would also cause a 44 lean. Check your vacuum source to the MAP. If you have engine vacuum, check volts, should be around .5 v @ sea level, I think. I'll have to verify that. [8D]

 

Remember, this is an '86----as far as I know, its got a MAF not MAP.

Anyway, I went back and double checked all the connections on the O2---everything looked good.

I was then looking at the 44 trouble flows and one of them mentioned disconnecting the MAF and see if the lean condition exists. So I got the engine up to operating temperature, with the MAF connected, and verified I was still only getting the 44 code. I then cleared the 44, disconnected the MAF and ran the car. The SES immediately came on (which I expected because of the disconnected MAF). Went back and checked the codes. It only kicked out the 33 (which I expected). No 44 was generated. THAT LEADS ME TO BELIEVE THE MAF IS AT FAULT!!!

There was also a noticeable difference in how the car ran, especially when I was slowing down. I understand that when the ECM goes into a fault mode, that changes to rpms (when slowing down) are much more abrupt than under normal driving conditions.

Is my assumption right on the MAF????



TIA

 

"THAT LEADS ME TO BELIEVE THE MAF IS AT FAULT!!! "

I would conclude this as well.

 

mech359---would you know if a '85 MAF works on an '86? looks like everything i've seen goes from 86-87

 

I'm sorry, I looked up wrong info on the "33". Yes, the MAF has a "Limp In" mode, in other words the ECM has preprogrmmed responses to TPS position and I know it doesn't have a MAP. For some reason, I was thinking of a non TPI car. Matter of Fact, couple of tests include unplugging MAF to see if it runs better and tapping on it to see if you get engine stutter. Either one, replacement time. I don't think the 85 will work, but am not positive. Call your local parts store and get a cross to see if it does. [8D]

 

mech259---i really appreciate all the help you've given me.

Have a good one!!!!

 

Check this from Mid America Vette, MAF Sensor [8D]