I have been fighting with a code 1178 for a while now. I have replaced numerous parts,serviced and cleaned numerous things,only for it to keep coming back.

This is going to sound stupid and crazy, but I've found something that affects it. If I change my oil and run a straight lightweight, like 5w-30 or 10w-30, the CEL comes on every other day with an 1178. If I put 10w-40 or 20w-50 with some Bardhals no-smoke/stop leak(really thick goop), the CEL has stayed off for up to a month.

What condition could this be masking? That I can tell, I'm not burning oil, but I do have a nice build up of black soot at the tailpipe that I passed off as running rich. Could the valve seals if worn bad enough cause enough of an air leak to set off an 1178? I was going to replace my valley pan gasket, thinking I might have a vacuum leak there(all other vacuum leak sources have been eliminated). Could the thick oil stuff be masking a vacuum leak at the manifold gasket? Does the oil even make it up there?

Any,at all, ideas,suggestions,thaughts, etc would be greatly appreciated

 

What does that code mean? I cant find it.

 

As for what I've tried so far, I have replaced both pre-cat o2's, maf sensor, plugs/wires, fuel and air filter, all vacuum lines, cleaned t-body, induction cleaning, two bottles seafoam through the gas. Think that's about it.

 

P1178-Maximum Positive AMFR Correction Fault. What I've been told by many, it's the engine running lean, the ecu is trying to correct by richening the mixture to the limit it can try to correct.

 

The 1178 is one of the dreaded 4, as I like to call them.
It is a code for,"Maximum Positive AMFR Correction Fault".
I have always felt it was vacuum related and suggest inspecting all hoses, especially the PCV as well as the entire intake manifold gasket for leaks. If you find a leak, great, if not go thru a Rave CD and see if you can find help.
Let us know what you find.

 

Yeah that sounds like a vacuum leak then, the valley pan gasket can leak and suck air as well as oil into the engine.
That would explain why the heavier oil stops/slows the light from coming on, it is plugging the leak.

 

O.K., thats what I was wondering, if the thicker-oil could be temporarely masking a leak at the intake gasket. Think I'll go ahead with replacing that and see what happens. I've gone as far as plugging all vacuum ports on the intake to see if that helped, and it didn't. I've been told that 99% of the time its vacuum leak related.

 

Have you tried spraying carb cleaner all around the intake whith the engine running?
You can also use a spray bottle full of water, if the engine rpms change then you have found your leak.
If it is buried deep you may never find it this way, but it is worth a shot.

 

Use the water any time, but only use the carb cleaner when the engine block is cold.

 

I tried the carb cleaner trick, but I didnt get towards the back of the intake real well. Between stuff in the way and not wanting to spray the injector harnesses and other wires I didn't get it real well.