Using the link provided to so many of us by agent 86 for code 33 troubleshooting, I have a question.

In step 4, option 3 it says "should read zero volts" when checking circuit 994

I am reading between .15 and .18 volts, that's a decimal in front of 15/18.

If I follow the "not ok" line to the next test I still get the same voltage on the circuit.

If I follow the "ok" line on to step 5 (thinking that voltage this low could be considered zero), I get 2.6 volts which tells me that circuit 998may have an open or the ecm or connection is bad.

My main question is: Is .18 considered zero for this type of test?

If so, where have you found an open in circuit 998 which runs straight from the ecm to the MAF sensor? Any rub points or should I just run a new line? I did wiggle the connections at the ecm and saw no change in the 2.6 volts.

If not to be considered zero, same question about trouble spots for circuit 994. It's also a straight run from the MAF sendor to the burn off relay and can easily be replaced.

Finally, any way to test the ecm voltage output at the ECM on this one circuit?

Thanks in advance for your replies, been chasing this for two years off and on and am finally getting serious about it.

I know they are only $100 but I don't want to but a new ECM if it's not necessary!

Thanks,

Mark

86 stock coupe
190,000 miles
new MAF power relay
new MAF burn off relay
new MAF sensor harness connector

 

Update to my post last night.

Went ahead and replaced the ECM today, now getting exacly 5 volts on circuit 998, there were no opens on the line. Perfect!

Still dies and throws a code 33 after a few minutes. Not perfect.

Still wondering about the 0.15 voltage on circuit D (994) and if I can consider this zero volts.

Checked for an open on 994 and did not find one. Chart also says if their is a "short to voltage" to repair it on this circuit, I don't know how to check for a "short to voltage" only have done "short to ground" and open testing.

Any ideas?

 

Code 33 is a plausibility check for the MAF flow.

Basically means that the MAF is reporting greater than 45 gm/sec airflow for 600 ms, under 2200 rpm with a throttle opening less than 14.8 %.

Likely cause is a misadjusted or malfunctioning tps sensor.

In my car for example, I see 45 gm/sec around 11% throttle at 2200 rpm, so the factory settings can be a bit tight, especially for a modded car. MAF sensors also vary in their output. Yours may be flowing on the high side.