TBI Set-up

Thank you very much for the info. I have a lot to learn about TBI and you have been helpful.

Jeffro G

Is it a Howell, CustomEFIS, Holley or homebrew system?

When the engine is warm it goes "closed loop" and tries to use the data from the sensors (map, o2, etc.) to adjust the mixture. A badly programmed chip could cause your problem, as well as faulty sensors.

When cold it runs in "open loop" mode, using a fixed fuel mixture table. One way of keeping it open loop after warming up is to unplug the o2 sensor. Yes, it will set a trouble code and turn on the check engine light, but at least it will give you a starting point to where the problem might lie.

The fact that it "runs great when it is cold" leads me to believe it's sensor problems. If he mounted the o2 sensor too far downstream and it is a one-wire unit, it may not be getting hot enough. Fix: replace with a three-wire heated unit. Although, there are many more people running TBI on

360's than 304's, meaning the chip might not be optimized for the smaller motor. If it's a homebrew system he might still be running a stock chevy chip. Open up the little door on the ECM and see if the chip looks tampered, aftermarket or stock GM.

BTW, fuel pressure for TBI systems is only about 11 - 14 lbs. so line pressure of 15 - 20 lbs. is fine. It's TPI that runs >35 lbs. If it runs fine cold I wouldn't worry about the pressure. Don't go cranking it up unless you have some spare injectors and a very good fire extinguisher.

Fuji,

Thanks, you seem to be very knowledgeable. As it turns out I may have been going the wrong direction thinking that the TBI was the problem. I was working on it earlier today and figured out that the vacume cannister was cracked so I got rid of that sucker. I also removed the EGR valve. That got rid of the hesitation but now it idles rough and sometimes dies after it is warmed up. I'm going to put a timing light on it tomorrow. Thanks again for all the useful info.

Jeffro G

Thanks everybody for the TBI info. As it turns out, I have a blown head gasket. Crap ! I should have checked into that a long time ago. Jeffro G

Thank-you, nice th hear the bottom line...Gene