VAF sensor CEL problems; NEED HELP!!!

[littlecar]

My '91 keeps throwing VAF sensor codes. It's a 1991 festiva L EFI 5spd. I did a full tune up, and a new VAF sensor. I've checked all the grounds and all are fine. I've hooked up a voltage meter to the signal wires from the VAF and all of them have normal operating voltage, until the CEL comes on. I'm thinking it's a bad CPU or an intermittent short in one of the wires.

Any ideas? You guys are the experts, I'm new to these little cars.

[mechanicaldj]

exactly which codes are present?

[littlecar]

Airflow code. Thats it.

[ejp2fast]

what about taking the VAF apart and cleaning it with contact cleaner.. i haven't done it for festy, but on toyota, and it worked great.

[littlecar]

No good. I tried that with the old one, then just got a brand new one.

I've narrowed it down to the ECM or a short in the wiring. It hasn't been acting up to determine which.

I hate intermittent problems!!!

[jglutz]

Possible leak in the air inlet ducts.....engine is getting combustionair from somewhere other than the VAF.

It could be the ECU but I would doubt it they are pretty roboust.

Most likely the reference voltage form the ECU to the VAF is dropping because of a bad/dirty connection. This is the green wire with a black trace. It should be a constant voltage at the VAF. I'm not sure what the voltage is but it should be the same at the VAF as at the ECU.

[littlecar]

u sure its the green wire?

I was told white by another mechanic.

[SIBladerunner]

ok for starters, ive never heard of a intermittent ECU problem, unless there was damage to the ECU, such as water corrosion etc. the ECU on these is so hard to get to, real pain. I had a rich running condition when I first got my festy and it was the signal wire grounding out. double check your signal back at the ECU, make sure that you're gettin the signal back at the ECU, I know its a pain to get at, but if you can confirm all the wires goin back to the ECU, then you can replace the ECU. try all that, otherwise I have a known good ECU you can have for $35 shipped.

[littlecar]

Update

I have checked all the wires heading into the ECU. All have good signal and are not grounding out.

I have ordered a ECU and it should be here later today and installed late tonight or tomorrow.

[littlecar]

Almost there

I've replaced the ECU. It solved my problem. I guess its the ultra moist North East.

Do however have a new problem with my Coolant temp sender. I've got one on order. Should be here tomorrow.

[littlecar]

update 2

I've replaced the coolant temp sensor...


...and all is well.

It took me long enough to do it, but it is well worth it especially cause my truck just broke yesterday.