I'm thinking possibly a cat, I got a new pcm and according to my code reader, my pcm has completed all tests with the exception of the o2 sensor and the cat monitor. These two tests require a whole variety of driving conditions to occur before completing the test. It's running good enough that I'm putting ball joints on tonight and going fishing in the hills tomorrow. Hopefully after the hour and a half round trip drive, these tests will complete and i'll know more. In the meantime, I got my hands on a vacuum tester, it reads liquid pressure too so i'll be checking for vacuum leaks and my fuel pressure tonight, if nothing else I can eliminate some more possibilities. Just need to find out what kind of pressure/ suction everything should have.

 

15-16" at idle seems to be the norm. Seems low to me but I've read it in manuals. My vacuum test points to cat.

 

Just hooked up the vacuum test, according to the instructions, I'm right in the norm. 17 at idle, drops to 5 then shoots up to 22-23 if you pump the accelerator once quickly. Getting really stumped on this, worn timing belt? I'm considering starting to think back to the basics. It's begining to seem like I'm going to feel really stupid in the end, as if I didn't already!

 

You don't have a timing belt, you have a timing chain. Your vacuum readings are perfect.

 

Took it out fishing this morning in the hills, some fairly good grades on the

 

Took it out fishing this morning in the hills, some fairly good grades on the way up and the motor seemed to do just fine. No difference in this random putt from the exhaust at any rpm's or under any load, I even cranked on the ac full blast at one of the steepest grades and took it slow in a lower gear, no change. I apparently met all the driving conditions for my computer to complete the monitor on the o2 and cat, both are reading good. Still running a little rich, average mpg's are at 11.1, was about 10.4 around town. Completely stumped at this point, any new ideas?

 

I was thinking it may be a dirty injector(s), so I filled up the tank at Chevron and added a 20 gallon fuel system treatment, my mileage has improved decently, up to 12.0 now, but no difference in this "putt". Really getting frustrated because it's running so great otherwise. Please tell me something new I can try/test, I'm losing my sanity!

 

Injectors don't really get "dirty". There are so many detergents and cleaners in the gas these days that there is hardly any gasoline in a gallon of fuel. Intake valves and the inside of the intake manifold are the things that get pretty grungy.