I've got codes 24 (VSS) and 33 (MAF high signal). I'm trying to address 33 first. I've got the Bosch MAF.

The problem is intermittant. She sometimes drives fine. But sometimes she stumbles, drives like crap and won't do more than 30mph.

I've got 5 volts at the green signal wire with the truck 'on'.
Both grounds on the black and blk/wht wires are good.

My book says I should see 12 volts at the purple wire with the engine running. I don't see a 'purple' wire. But I do have a red wire and it's showing 13.98 volts. Is that too high? Could this be causing the code 33? Or should I just order a new MAF?

Input please, thanks,

 

Well, I just blew $200 on MAF and got code 33 again.

I don't see how it will help but I just ordered a new MAF power relay and a new MAF connector.

And I'm not really understanding how the MAF works. If the green wire is providing 5 volts to the sensor from the ECM (b12), how is the signal getting back to the ECM?

 

BTW, It's an 87/88 5.0 TPI and 700R4 swapped into a 67 truck.

 

Your circuit is probably like this:



The red wire (terminal E) should have system voltage when the engine is running. 13.98V is good, and means your alternator is working properly.

Check the voltage on the dark green wire, or 'C' terminal to read MAF output voltage while running. Expect to read something about like this:

 

I was getting 1.12v when I first started the engine and it would increase with throttle.

But once it warmed up and the idle dropped, voltage went down to 0.05 and wouldn't change with throttle.

I guess the replacement MAF I bought is bad too?

 

What voltage should I see at the D' terminal of the MAF with the engine running?

I'm thinking it should be 0.0v.

Thanks,

 

I have a 89 350 tpi but anyways my problem is close to the same.

ive got a code 33 and so i looked it up on iroczone.com

So it says to test voltage at the green wire by back probing at the maf plug while its still all plugged in.

Your supposed to see .5v with the key on and throtle at idle position and 4.7v at wot

Well im getting 4.7 with the throttle at idle.

This is explaining my code 33 so does this mean my maf sensor is bad?

Thanks

 

In both cases, suspect the MAF burnoff relay and circuit. You can remove the relay while the engine is running if you suspect a problem.