Bill Ball

The bypass relay is a simple double jumper. The system has characteristic behavior when it trips. Colin has not observed anything to indicate it is tripping - all the injectors are firing, for example.

Bill Ball

So, what caused it to now "run better"? The CPS? Pretty strange. It had all the fueling anomalies before. Most appear to be gone, except for cold behavior and some idle drop issues. Weird.

What about John's tank vent question. Other than it being a possible vacuum leak that is often overlooked (George Suennen - are you reading this?), I'm not sure what he is getting at.

ptuomov

I know nothing about any of this practical stuff, but that won't stop me from speculating.

Hydrocarbons up, CO up, and running rough says misfire. Vacuum dropping dramatically without the injector pulse width and MAF voltage getting commensurately longer and higher might say lean misfire due to vacuum leak. If it's not surging, it has to be a big vacuum leak to immediately cause lean misfire. Because it's on and off roughness, it's probably some part that can switch state.

Is it possible that idle adjustment controller is somehow broken? That has moving parts. Do you have a way to freeze that in one position?

Is it possible that any of the crankcase breather hoses is letting air into the manifold? If you have eliminated the IAC as a potential problem, then how about plugging the second port in the throttle body element and the one port on the driver side plenum cover?

I am sure someone has already suggested all the sensical parts of the above in this thread, no new stuff here.

AO

IAC is a good point. It is the only item that is dynamic in operation and yet has no way to diagnose except visually. But would it also cause the strange MAF readings?

the flyin' scotsman

certainly seems that way and that the part is switching through erroneous input.

The IAC can simply be frozen.......unplug it

AO

Ok.... I went back and re read the first post in this thread. I now have doubts it's the IAC. It sounds more like a grounding or a harness issue.

Remember there are two ground straps that could cause issues. I've seen both go bad before. A simple test is to use a set of jumper cables and run from the - post to the block. Would allow you to illuminate this as the cause.

One other thought... Is there any kind of "funny stuff" going on behind the CE panel? Maybe a mouse, extra control module, etc. I've seen crap like that before that can be well hidden.

the flyin' scotsman

was the issue resolved......interested in the outcome