Did my H/C this winter and the car fired right up. It started to O'Heat so as a diagnostic tool, I removed the T-stat. It was stuck, and that cured the overheating. It hasn't been tuned yet but it smelled rich as hell so I pulled the no 2 plug and - pig rich...

Maybe it's just because it's got a big cam and has only been run at low RPM's, I dont know. Just wondered if this was normal, before I head off to the tuner.

 

very normal. the bigger cam holds the valves open longer and farther (so more fuel enters motor) and the computer cannot compensate enough. it's my understanding that all cam swaps end up rich before they are tuned....

 

That's what I was thinking but I am an idiot when it comes to computer tuning and all. I know in the old school iron motors I used to have to pull my plugs once a week if I drove the car on the street at all ( use to call it "loading up"). I was kinda thinking the computer might compensate a little though. Just hope I didn't mess with the open loop closed loop thing by removing the stat. New one is in the mail...

 

With a big cam the O2's will lie. They can't be trusted. They will tell the PCM you are lean, causing your trims to add fuel.

 

running the motor without a stat will make it richer as well.

 

yup! your on the right track, now get it tuned and all will be fine.

 

So I got my 160 stat in today. Installed it and started it up. I cannot believe what a difference it made.

Trex, Heads, 85mm TB and no tune. Idles at about 950...

http://media.putfile.com/Learning-to-Idle

 

Tune it quickly.

 

Next week, and it won't be driven until then...

 

Not only that^^^, but with more overlap, the manifold vacuum drops, the computer sees it as load, and viola!!, adds more fuel.