Fuel Pressure Test

[Jason_25]

Bump

So would it be safe to say my problem is the MAF?

 

[SteveVB]

yep

The idle voltage is high, .7 is max at idle, so yes looks like it could be part of the problem. My 91 service manual gives voltages as follows:
idle .6v
20 mph 1.10v
40 mph 1.70v
60 mph 2.10v
Yours nmay have different specs but close I would bet.

Check ohms between the signal terminal and ground to check the MAF element. Open is bad.

May try cleaning the MAF element again see if that changes the readings before you replace it.

You need a FSM for the excellent diagonostics they ahve a bunch of tests for the MAF and related circuits.

 

[Jason_25]

Steve, does the high voltage cause it to run leaner or richer? I'm thinking leaner. The MAF tests good on the reistance test (there is a connection).

I've gotta go to work soon, but tonight I'm gonna see if I can get some longer cables and test voltage of the MAF as I drive. I'll also clean it and see what happens.

 

[mosinman]

Hey Jason25, I'm assuming you've done all the simple things? Fuel filter, plugs, wires, air filter, fuel injector cleaner??? Seems like you have your other bases covered.

 

[Jason_25]

mosinman, yepall that stuff is new within the last 10K miles or so.

 

[Jason_25]

Ok cleaned the MAF yesterday. Put it back in, voltage stabilized perfectly right at .6 and the truck ran fine. Now today it has gone back to it's normal crappy self. Checked voltage at idle and what do you know? Back at .82........

What in the world is happening here? I even changed back to the stock filter to make sure the oil wasn't contaminating it. Is there some sort of anti-sludge coating that I have burnt away?

 

[Jason_25]

Ok problem fixed it seems.

The air filter wasn't seated perfectly causing it to leak unmetered air around the seam of the MAF housing.

Oh and ya know what? I didn't close the boot back while testing the maf so that was drawing in unmetered air as well...........DOH!

It only has a slighly rough idle and performance is ok now. I'm thinking this may be normal.

Thanks for everyone's help!