Have you succesfully put a bigger cam in a SBC with T.B.I.?

[mudseeker]

you need to get a new engine builder if he thinks drilling holes is going to fix your problem. sorry if he's a family friend or something but thats my opinion. it will act like a vacuum leak since you are allowing unmetered air in to your engine. your computer knows how much fuel to inject in to the engine at a given throttle plate position and engine load.

your injector pulse width needs to be adjusted for your engine to like that cam. advanceing your timing is also worth a shot and it's free.

have you pulled any readings with a scan tool? it will tell you how much vacuum your engine is pulling along with your pulse width and many other sensors.

[mudseeker]

a little more thought, incase you know how a carb works, this might help you.
a carb works off a venturi and use metering valves. as your pistons move up and down, they create a vacuum and suck the gas in. TBI works in the same way except it injects the predetermined amount of gas into the intake.

you put a bigger cam in a carb engine and you adjust your valves in the carb. same thing with TBI, you put a bigger cam in and you have to adjust your pulse width.

hope this helped make my thought process more clear. i can be bad with words some times.

[leolkfrm]

Hey give him the name of the place you ordered the reprogramed ecm, maybe they can tweak one to his needs

[mudseeker]

you mean nelsonperformance? not sure if they do obd1 but i guess it's worth a shot. they're located in texas and do mail order custom tunes.

[Chevy_Finatic79]

I am hesitant to drill holes thats why i made this post
from what i understand the function of I.A.C is creates a vaccuum leak based on info from the sensors the only reason i even thought he might be right about drilling is since my cam is opening at a later degree there is a loss of vaccuum at idle. I have no problems driving so i dont think the pulse witdh of the injectors is a problem.

i do have a scan tool snap-on mt2500 and the only thing i really see outta range is the O2sensor stays on the rich side like .966mv which is high it does flucuate but .966 is the highest reading i have seen.

on a nother note im starting to think i have a ground issue i notice my fuel gauge pegs to full then the idle gets crappy

[Chevy_Finatic79]

i am a mechanic in the field so i do understand hows theroy and engine components work so dont be scared to throw technical terms at me i hear them everyday i just work on imports now so i wanted to talk to some chevy guy's

[mudseeker]

Originally Posted by Chevy_Finatic79

from what i understand the function of I.A.C is creates a vaccuum leak based on info from the sensors the only reason i even thought he might be right about drilling is since my cam is opening at a later degree there is a loss of vaccuum at idle.

the difference is, the air entering the IAC is metered and is calibrated by the computer to be there. a unmetered vacuum leak will play havix with your sensor and make the problem worse. i'll get with you later a couple of stupids...i mean.... customers are at my counter.

[hotrodpc]

Originally Posted by mudseeker

you need someone to burn a new prom for you. drilling holes will not fix it and will only cuase problems due to more air entering the engine and your TPS staying the same value.

This is what I was going to sorta say. So drillign the holes MIGHT, and doubtful at that, fix this minor issue, but then what all else is going to be out of whack because of it. I don't buy it. I wouldn't drill the holes. Reprogam may be best. Not sure. I do not really have any suggestions, other then just to say, I don't buy the hole drilling method as a fix.

[Chevy_Finatic79]

once the butterflys open past a certain point the I.A.C has no more effect on engine performance until they begin to close again so it would be like i didnt even drill the holes once they open and the T.P.S. takes over. that high O2voltage = a rich condition drillin the holes would lean it out. i have tons of throttle bodies laying around i am tempted to just try it and see what happens

[Chevy_Finatic79]

i really hate to be admitting this (being a mechanic) but i thought i had a crack in my distributor cap cause it rained today and i had a backfire (headers no cat dual exhaust glass packs soon to be replaced by turbos) so i got a new borg warner cap and rotor replaced them and noticed i had a loose plug wire at the spark plug. plugged it back in and all my problems went away no surging no back fire so i dont think i need to drill any holes.
cant say for sure yet but i think the computer had no problem with the bigger cam. i will drive around the next couple days with the scan-tool hooked up and monitor the sensors but there is a night and day difference. the idle still isnt as smooth as i want so i might still drill holes i will keep you guys posted