93 suburban 350 tbi issues

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93 suburban 350 tbi issues

Post by nowforever13 on Sat Nov 11, 2017 8:39 am

in my 93 burb it has a 350 TBI with 270k miles.. no engine mods outside of the cats being removed. on cold start and even when its warm ( but not as bad) the truck will stumble and get really choppy until a certian RPM/speed and then its not as bad. and sometimes it will back fire out the throttle body/ intake. ive replaced the fuel psi reg, one injector filter, rotor, egr, egr solenoid, IAC valve, TPS, and CTS. i dont know what else to do.... i know its kind hard to digital diagnose but maybe somebody has had this issue and fixed it.. what are the chances ive jumped time, burnt a valve, or streched the chain.any other ideas would be great..
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Re: 93 suburban 350 tbi issues

Post by nowforever13 on Sat Nov 11, 2017 8:41 am

ive even tried spraying brake parts cleaner around my intake to find vac leaks. but nothing
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Re: 93 suburban 350 tbi issues

Post by Podor on Sat Nov 11, 2017 9:29 am

It could be a fuel pump. It sounds like a lean backfire. Newer multiport injection engines won't run at all if the pressure or volume is slightly off, where a TBI system will start and run poorly with only a few PSI. The hard part on those systems is there is no pressure tap to check pressure. They make adapters that go in where the fuel filter goes, or one that would go between the fuel line and throttle body. If memory serves me, it should be 12 PSI. I would start here first.

With that many miles, you could be right about it needing a timing chain as well. A simple check would be to pop the distributor cap off and rotate the engine clock wise slightly to tighten the chain, then rotate it counter clockwise and watch the rotor. If it doesn't rotate back words until you rotate the crank 5 degrees or so, you need to replace the timing set. A burnt valve would cause a consistent missfire.

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Re: 93 suburban 350 tbi issues

Post by nowforever13 on Sat Nov 11, 2017 9:39 am

okay.. that makes sense. its a random misfire. but i last changed my plugs about 10k miles ago. so one of them could be fouled.. but that doesnt account for the choppy take off. but i just replaced the fuel pump this year.. back in april or may. its car quest brand from adv auto, but the back fire is unpredictable. does it randomly but only when i try to take off. itll pop and then cut out for a second and then pick back up and go
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Re: 93 suburban 350 tbi issues

Post by Podor on Sat Nov 11, 2017 9:44 am

Aftermarket pumps can be iffy sometimes. I've learned in my years of working on cars not to assume a part is good.

Something else to try, spray the wires and cap with water to see if there is arcing. You could have a bad plugwire.
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Re: 93 suburban 350 tbi issues

Post by nowforever13 on Sat Nov 11, 2017 10:01 am

i didnt think of that... see the other day i replaced my Inj filters but i put the bottom o rings in the wrong spot.. and it caused my injectors to go into roid rage and filled up my bowl about 3 times before i caught it and some had spilled over onto my manifolds. and caught fire either way THIS issue im writing about came immediatly after. i wonder if gas couldve melted one wire just enough to not make a good connection
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Re: 93 suburban 350 tbi issues

Post by nowforever13 on Sat Nov 11, 2017 10:08 am

correction.. it filled up 3 times before i figured out what id done.. the first time i tried to start it and it arked and caught fire, but i had to run 3 bowls of gas through my intake. cleaned the whole thing out including my plugs Laughing
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Re: 93 suburban 350 tbi issues

Post by pila on Sun Nov 12, 2017 11:17 am

All the TBI units I've worked on on GM cars & trucks, spec'ed the fuel pressure as 12 to 15 PSI. Sometimes it's worth the effort to cut the fuel line someplace in the engine compartment & put a TEE in it, for a port to check fuel pressure ...
Or, there is a simple gauge with hose fittings, to use in a cut fuel line. That one I wouldn't leave installed, since it's plastic & I don't trust it to be in there permanently, so a short Fuel hose & clamps go in there when the gauge doesn't need to be there...

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