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post #1 of (permalink) Old 10-21-2003, 05:52 PM
427jimmy
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Any TBI knowledge out there

I'm having a bit of a problem with my 350 TBI. When driving down the hiway and I mash the throttle down it pulls very strong till about 4000 sometimes 4500 rpm it will crap out and kind of gurgle a bit and not want to climb higher. Let off the gas a little and it starts to pull but its hesitating. I'm thinking EGR valve (it moves freely but its kinda sticky)? Sometimes she'll kinda rattle like in the old carbed 350's when the timing is out. Again this motor is daamn strong in the bottom and mids, but it shouldn't die at 4 grand. The motor has about 5000 kms on it. .030 overbore. 9:1 compression. hedman hedders, aluminum edelbrock performer intake, throttle body spacer, new fireball coil, msd 6a box, MSD cap & wires, holley ignition module. Jet stage 2 chip and adjustable regulator. Chevy caprice fuel injectors. New TPS and TPS calibrator. new IAC. Anyone have any info would make me very happy. [img]images/graemlins/smile.gif[/img] Just can't wait to try these new 35's [img]images/graemlins/AR15firing.gif[/img]

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post #2 of (permalink) Old 10-21-2003, 10:19 PM
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Re: Any TBI knowledge out there

perhapes its the egr valve, i have a 350 with tbi, so yea id try replaceing the egr valve, or taking it out and cleaning it.
post #3 of (permalink) Old 10-23-2003, 05:43 PM
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Re: Any TBI knowledge out there

I agree, it might be the egr valve, but I'm not 100% positive. The minor modifications you have done to the engine help the engine breath better, so maybe it's time to check the block learn numbers and see what they are. The bad news about reading the block learn numbers is that it requires a GM scan tool called a Tech II. The GM engine control module, (ECM) has the ability to learn, but if the block learn numbers are at a min or max, then the PROM will need to be changed to correct the block learn numbers. Then again, you might have a minor vacuum leak that's causing the problem.
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post #4 of (permalink) Old 10-23-2003, 06:17 PM
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Re: Any TBI knowledge out there

Easiest way to see if it's the EGR valve - disconnect the vacuum to it. If it's electronic with no vacuum, plug the plug into another one so the computer "thinks" it's still there.

Your symptoms indicate fuel starvation - low pressure at WOT. Filter, weak pump, crimped line etc.

Easy way to check that is with the propane trick. Use a propane torch, take out/drill out the restrictor orfice, take off the torch head - you really just want the valve. Slip a long hose over the tube - tie the hose end into the airstream, take the bottle inside the truck with you.
Hold the bottle upside down in your lap (to get liquid rather than gas.) Run it to where it's starving, open the valve. If it "likes it," it was fuel.
Propane will burn very similar to gasoline - adding it under load is about the same as pouring in a little extra gas -- but far safer. If the engine was starving for fuel, it'll "like" it.
Some folks seem to think it'll make the engine run lean and be harmful like nitrous - but propane is fuel, not oxygen.
Good for finding vacuum leaks too.
A small vacuum leak will not cause your symptoms.
Could be a weak ignition too, look there if propane doesn't help.
Let us know what you find please - it's frustrating to never hear what worked.
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post #5 of (permalink) Old 10-23-2003, 11:26 PM
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Re: Any TBI knowledge out there

wonder if your valves are floatn at that 4-4500 range. thats alittle higher than most tbi motors are usualy ran.
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post #6 of (permalink) Old 10-24-2003, 05:12 PM
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Re: Any TBI knowledge out there

I'm going to be taking a good look at this thing tomorrow. I'll pull out the egr and clean it out good. Take a good close look at the vacuum lines and stuff, will let you know what happens
post #7 of (permalink) Old 10-26-2003, 10:28 PM
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Re: Any TBI knowledge out there

Well I took a good look at everything today. I changed the fuel filter and I turned up the fuel pressure a whole bunch. There is way more power and it goes a little higher now, but still the same thing. The problem definately is a WOT problem because when the throttle is squeezed, the truck sure does take off. Makes no sense, the only thing that makes sense is that the TBI is too small and not atomizing the fuel at higher RPMS. Maybe I should upgrade to the bigger 454 TBI base?
post #8 of (permalink) Old 10-27-2003, 11:22 AM
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Re: Any TBI knowledge out there

Turning up fuel pressure shows it's lean.
What happened when you added propane?

Seems odd that your throttle body must have shrunk - new they don't do that.
Going to a larger throttle body won't do anything unless the problem itself is/was in your TB.

I'd at least verify it's a fuel problem and not ignition before bothering swapping parts.
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post #9 of (permalink) Old 10-28-2003, 11:52 PM
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Re: Any TBI knowledge out there

I still think its just out of power in the upper rpms. to get it to feel like you want your going to just have to rebuild it with big cam so it doesnt idle, but its power rang is from 2000-5000 grand.
rioght now its idle to 3500

just my opion
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post #10 of (permalink) Old 10-31-2003, 09:49 AM
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Re: Any TBI knowledge out there

So what did you find?
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