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02-23-2013, 10:32 PM #1
94 Chevy 350. Back fire through TBI
Okay guys. I'll go ahead and list what I've not done. I've not replaced the crank and pistons. Other than that. Everything from the Camshaft to the TBI itself is new. Brand new. Coil, plugs, dizzy, fuel relay, fuel pump, filters, cam, lifters, cam bearings, push rods, spark plugs, all plugs for the wiring harness. Fuel line, fuses, Throws no codes, shows no check engine lights. When I'm driving, around the range of 40MPH in 4th gear the motor will back fire through the TBI every now and then. I hit 50MPH, throw it into 5th and it will do it literally every 3 Mississippi seconds without fail. I changed the valves first, then bought entire brand new heads not rebuilt, still did it. Replaced cam shaft/lifters and push rods next due to believing it had a worn lobe. Did nothing to help. After that I basicly restored the old rust bucket with replacing every single little thing that has anything to do with the way the motor runs. And still does it. I love this truck. Truly do. But I'm at the point I'm about to take it to the beach, put it in 1st and 4 low, throw a brick on the gas and drop the clutch and tuck and roll. Then enjoy watching it go for a very deep swim. I've dumped enough money into it that I could have just bought a crate 350 and been done with it. Only thing I could possibly think of is taking off the converter because it might be clogged *though seein as it's hollowed out, I don't see why it would be* Help me please, before I start to think it's getting thirsty.
02-23-2013, 11:17 PM #2
I cannot remember the exact details but another member had a sympton like yours and eventually found a screw that had come loose in his distributer and was bouncing around and causing a missfire. Check the mechanical and vaccume advance mechanisms along with the timing. Thinking more about it, definitely check your timing or just retard it some and see if it improves.2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear
02-24-2013, 12:32 PM #3
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Just swapped out the vaccume advance, didn't do nothing.
02-24-2013, 05:37 PM #4
As a last thought, at least from me, I have been cautioned about running plug wires to close together without crossing them at least once because if you do then there is a chance that the firing wire will induce a current in the other one to fire its plug. I have never had a problem but in theory it is possible. Heavy loads require a healthier spark than light loads so maybe a correlation? Please let us know what the problem was when you find it.
02-24-2013, 08:32 PM #5
Last edited by James4012; 02-25-2013 at 09:14 PM.94 Chevrolet K1500 4x4. 5.7L 350, 5-speed (AKA Betty) Or Rust Bucket...depends on if I'm mad at her.
02-25-2013, 04:47 PM #6
OK, it was not my last thought. There is an aftermarket distributer cap that will allow you to put the plug wires in order of the cylinders. All right side plugs on right side of cap and left hand plugs on left side but still maintains the correct firing order via routing internally in the cap. I cannot remember how to tell them apart or if you can without using an ohm meter. Go ahead, ask me how I know!
Last edited by dpeter; 02-25-2013 at 05:03 PM.
02-25-2013, 06:44 PM #7
Na I know the firing order perfectly, and never had a problem with setting the time. I went ahead and cut a hole in the convertor to see if it's clogged, but we got like 55MPH winds here right now and I don't want to take a chance of my rusted ass bed flying off down the road. I cranked it a min ago and one of the damn rocker arms is tapping again. I installed the cam and let it break it in for over 30 mins *more than required* opened em up and readjusted them again. But seems one backed off. Idleing rough wanting to die. It was seizing up bad on my way home in first and second gears when heavy accelerating. *sigh* if not one thing, it's always another.
03-08-2013, 02:23 PM #8
i know im late on this one,just looking to see if you got an answer to the issue.once i had lifter trouble,too tight,didnt prime properly i guess.went thru 2 times,once backing them off,2nd final adjustment.
03-10-2013, 09:33 AM #9
03-10-2013, 12:31 PM #10
many chevys ago,i had a carbed monte,same issues,tore it down,found nothing wrong,took a bit of thought,swapped some parts and wound up being alternator,cant remember all thoughts but do remember car kept starting and running,so alt was not even concidered in begining,just a thought for you,possible module in distributer?good luck,keep me informed
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