surfbp

My 1994 4.3l z code truck is back firing through the air filter on top of the engine. I was told it was the timing chain and with 170,000 mile on the orginal I didn't quetion it. Now after doing all that work it still does the same thing. The timing is right zero so I know thats not the problem. Gas keeps pooling up under the fuel injector on top of the engine. Also it only backfires when I am on the gas and the engine is warm. I was now told it might be the cat and to pull the pre oxygen senor and leave out to see if it runs better, if the cat was clogged. i don't want to replace the cat if thats not the problem. Does this sound right to anyone? Help I am out of ideas?

KEVINS800

i know that the vortec 4.3 had issues with the egr valve and gassing up the engine and backfiring! i bought a 94 gmc jimmy with the 4.3 for 800.00 and 70,000 miles! the owner said that the mechanic said the engine was junk! well after new egr valve the truck was bought from my boss and now has 195,000 mile on it! he also has had the egr valve replaced twice !

rrousou

Check the egr to see if its sticking open. Worn camshaft lobes will also give you that problem.The 350 and 305 had lots of issues where the rear lobes would wear down, very common problem. I dont know if other Gm engines have or had that problem though.

acewelderman

I totaly agree!!A bad egr can do this & also if your cam has packed it in & its not opening the valve (intake)the gas will stay in the intake then backfire when it gets hot enuf.Just ck one thing at a time & good luck!!!

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JUST WELD IT !!

surfbp

I replaced the EGR valve already and that wasn't the problem. The problem ended up being a spark plug wire. The boot from the wire on the #1 cylinder, had a small crack in it. I only discovered it by mistake. the wire are only a 1000 miles old too. I am so pissed because the original diagnois was, that the time chian needed to be replaced, and spent two days doing that. It sucks! It took me 5 mintues to repalce the wire.

Cadillakin'98

Damn that sux dude. Atleast you aint gotta worry 'bout that timing chain goin' out @ the wrong time!

KEVINS800

been there> done that! lol