350 TBI Flooding issue

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James Eufemia

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First real post beside the intro, what's up all? I'm having an issue and I can't find a single thread that will help so here it goes. I recently installed a bored out TBI from CFM Tech, as well as an injector spacer and a 14 psi spring from The Throttle Body Shop on my 1994 Chevy Suburban. The 'Burb has 125000 miles, 350 TBI, 4L60e, and 4wd. Now, when I crank the engine, it struggles to start, and when it fires it immediately goes to redline and stays there. Since I don't want to blow the engine up I don't leave it on for long but the amount of time I have left it running it stays right at 4500 rpm. After I ran into this problem, I've checked for vacuum leaks and found none. I've replaced the IAC and the connector since it wasn't seating right. I have a TPS with about 300 miles on it, and the throttle blades don't move and aren't open when it revs to redline upon startup. I took apart the injector pod and found it was flooded with gas, and upon watching it spray fuel, it's spraying it as if it's at WOT. I suspect the fuel pressure regulator is bad or I may have screwed something up, it wasn't doing this before the swap. I was just wondering if anyone has run into or heard of a problem like this. Any help would be a big help, and I'll update this if I find or fix anything. Thanks a bunch in advance.
 
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you need air AND fuel to rev that motor to 4500 rpm. You have a lot of air getting in somewhere. See if the IAC pintle is seating all the way.
 

98 Nitro

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When my 94 did that I had a bad IAC plug and I had replaced it, I originally soldered the wires wrong so check that 1st before you replace more parts.
 

joep88cheyenne

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Still have old throttle body? Try reinstalling it if IAC and tps are good. If if still floods the may be upline on fuel. If not the new TBI could have issues. IMHO YMMV.
 

magimerlin

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Biggest question really is?? Why the bored out tbi and 14psi injectors? You don't mention any engine mods that would warrant such an upgrade. That's waaaay to much fuel for a stock motor.

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James Eufemia

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98 Nitro what is the proper wiring for the IAC connector? The one on my truck was shot so I replaced it and copied the stock connector on the engine. What wiring did you go with?
 

James Eufemia

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Magimerlin I didn’t put in 14 psi injectors, I put in a 14 psi fuel pressure spring. The injectors are stock for the 5.7. As for the TBI it’s a modified one CFM tech. Bored out may be the wrong wording, it’s had the Ultimate TBI Mods done to it; ground down throttle shafts and ground down ridges on the throttle body. Everything else about it is stock, I’m just looking to get my truck back on the road and running.
 

magimerlin

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Magimerlin I didn’t put in 14 psi injectors, I put in a 14 psi fuel pressure spring. The injectors are stock for the 5.7. As for the TBI it’s a modified one CFM tech. Bored out may be the wrong wording, it’s had the Ultimate TBI Mods done to it; ground down throttle shafts and ground down ridges on the throttle body. Everything else about it is stock, I’m just looking to get my truck back on the road and running.

Sorry, yah I ment the pressure spring..i usually proof read my stuff first but must missed that....lol...

I was thinking it was actually bored out when you said that. But if it's just the tbi mods, that's understandable.

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DerekTheGreat

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I'll echo what joep88 said. Could be that when the bored out the TB they didn't match the job with correct throttle blades and so enough air is getting by to rev the thing that high. At idle/no load it won't take much air to do it. I have a 1992 F150 with a straight six, decided to redo all the upper gaskets and such and then when I got it running again decided to clean out the throttle body. Before I cleaned it, it ran perfect, nice low idle and the IAC wasn't closed all the way. Well, I took the throttle body off, cleaned it real well around the bores and throttle blades such that it looked new. Slapped it back on and when it fired up it wanted to idle around 2000rpm's and would only come down to about 1500 so says my scanner. IAC was at 20% or it's lowest allowable point per ECM when before it was around 24-29%. Base idle adjust wasn't much help as going to the lowest point put the TPS out of voltage range.. I had a dirty spare TB in the garage, slapped it on and the idle was fine again. Held the cleaned TB up to the sun and I could see light around the throttle blades- thing was worn out and also has air bleed holes in each blade when the spare did not. The schmoo in the original TB was essentially sealing it..
 
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