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tbi dumping to much fuel in my 383

91GMCSuburban

91GMCSuburban

1/2 ton status
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Dec 9, 2002
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San Antonio, TX
Just got my built 383 in my truck and it is dumping to much fuel and fouling out the plugs. I haven't put the custom chip in it, but I also have not driven it, just start it to move it. What do you need to know to help me out?
 
91GMCSuburban said:
it is hot for TBI standards. What should I do?
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Presumably you've upped the fuel pressure in anticipation of the new chip and larger cubes. This would overload the injectors, especially at idle as you've altered the base pulse width to compensate. If you're not doing your own tuning you'll have to wait 'till you get your new chip and just hope whoever is burning for you gets it pretty close.

If you haven't altered FP then check you've not trapped the return line. If it's doing it from cold, when the ecu is in open loop I don't 'think' it could be the cams fault as the VE tables are preset with no learn.
 
I did up the FP and added bigger injectors, but had way too much fuel and couldn't get it timed. Replaced the fuel pod with the original injectors and stock FP regulator, got it timed, and it is still dumping too much fuel. And yes, this is from cold; it has never reached temp.
 
Look for leaks around the injector housing and put a strobe light on the spray pattern at idle and see if you're getting a 'spray' or lots of big drops too.
It would be worth check the true FP too. If you're fouling plugs you're running REALLY rich and it's going to kill your bores.
 
I thought there were stories of the throttle bodies actually having been bored all the way through to internal passages at some point, may have been on this board or thirdgen.org.

No idea what the "real" story was though. Might be worth checking out.

Rereading your question, maybe I was wrong in my assumption. Are you using a stock TB, and you have a "spare" bored one that you could try?

Really doubt it's the TB if it's stock or aftermarket. (unbored) Leaks due to bad gaskets, injectors, or seals yes, bad casting that "just happened"? Highly doubtful.
 
What do you have the timing set at? With that larger cam you'll want to set the timing up around 8-10 degrees. I'll bet your manifold vacuum is low enough to make the computer think the engine is under a heavy load and fuel the heck out of it. Bumping up the timing will help get the vacuum up some and help. Have you checked the fuel pressure as suggested before? high fuel pressure equals rich. Is the MAP sensor connected properly and getting an actual reading? Low MAP reading also causes a rich condition. Last but not least what are the specs on your cam? If it's over 220 duration (@ .050") or under 112* lobe seperation it will cause the idle vacuum to go low enough that it will be tricky to get the chip right and have it idle right and consistent. Make sure you don't let it run very long in this condition as it will wear the motor out in short order. Make sure you change the oil as soon as you can to get all that fuel saturated oil out.
 
bigblock72 said:
What do you have the timing set at? With that larger cam you'll want to set the timing up around 8-10 degrees. I'll bet your manifold vacuum is low enough to make the computer think the engine is under a heavy load and fuel the heck out of it. Bumping up the timing will help get the vacuum up some and help. Have you checked the fuel pressure as suggested before? high fuel pressure equals rich. Is the MAP sensor connected properly and getting an actual reading? Low MAP reading also causes a rich condition. Last but not least what are the specs on your cam? If it's over 220 duration (@ .050") or under 112* lobe seperation it will cause the idle vacuum to go low enough that it will be tricky to get the chip right and have it idle right and consistent. Make sure you don't let it run very long in this condition as it will wear the motor out in short order. Make sure you change the oil as soon as you can to get all that fuel saturated oil out.
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If it is a MAP issue you could just put a false vacuum to the MAP and see if it suddenly runs ok. Small vacuum pump like the Silverline things would do.
 
Subscribing to this thread.

Just got a 383 as well and it will be installed soon. Havent gotten the bored out TB yet, hoping it will do ok on stock for a little while.
 
You've read the burned piston/383/TBI thread, right? (or burt(s?)4x4 454 thread)

I wouldn't run it anymore than necessary until I got fueling dead on.
 
Well, I replaced the bored TB for the original and no more dumping of fuel. I guess I will replace once I'm ready for a new chip...
 
Good news! Change your oil and give the truck a good run.
 
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