94 yukon ran bad, then quit, now won't start at all

[98_k1500]

Buddies truck, 94 2 door yukon 4x4. Lifted on 37" boggers. TBI 350. He started complaining of a lack of power. Then it got to where it was sputtering and backfiring. The problems would last for a few miles then clear up. Over time it got worse until it never would clear up and run right. So he started replacing parts thinking it would be something simple. Fast forward 4 months, and EVERYTHING sensor wise has been replaced to no avail. From the knock sensor to the fuel pump, its had everything we can think of. Last night, it finally quit. Cranks but no start. We put a distributor in it last night (the whole thing), made no difference. It came with a new ignition module on it, and that was the last electrical part that had not been changed. It is firing, and it is spraying fuel. It will not pop or backfire or anything now. I know the distributor is in it correctly, I have changed 1000's of them. Now comes the decision. Does it need a ECM, or a timing chain? I realize it would have been smart to put a timing light on it BEFORE we pulled the old distributor, but we were both 99% sure that had to fix it and did not think to check it before we pulled the old one. Anyone have any ideas before we spend any more money on it and still can't fix it? Im usually pretty sharp on this kinda stuff, but this one has got me stumped unless the ECM is just bad. Pouring gas in it makes no effect. If you advance the ignition time, it does start kicking back on the starter, but if you pull it back enough that it turns over smoothly, it just spins and does not start. Anyone have any input?

 

[skylark]

Check the plugs to see how it was firing and do a compression check. Have you cleaned the ground wires at the thermostat housing?

 

[98_k1500]

Doing a compression check tonight. It is firing fine on all the plugs and the ground has been cleaned multiple times. Im seriously ready to pull my hair out on this one. I usually don't post up problems for friends, but this has really got me stumped.

 

[98_k1500]

Just out of curiosity, what does the ground at the rear of the passenger head actually ground? I don't think it has been cleaned.

 

[skylark]

It just grounds the engine to the frame. It beats somehow randomly grounding through something stupid like the fuel lines or the drive shaft and rear suspension.

 

[98_k1500]

Maybe the TBI trucks don't have it, but the vortecs have a wire that splits out of the harness back there and grounds there too. This is the ground i was referring to.

 

[sewlow]

Check ALL the grounds & the condition of the cables while you're at it! Those braided ones can corrode over pretty good. If it's green or rusty, replace it. Cheap!
My '98 gave me nothing but ignition/firing probs till I replaced all the power & ground cables. That too was a last resort, after a complete tune-up that didn't cure the prob. A mindfvck!
Upgrade...Big 3!

 

[98_k1500]

I'll get a couple of sets of jumper cables and hook up as some temporary grounds tonight. May fool around and fix it, but i am pretty sure grounding is not the issue. The ones at the thermostat housing are spotless. May have to get a test light and probe some ground wires. Could be corroded internally i suppose.

 

[98_k1500]

OK, Grounding is not the issue. We found the fuel pressure regulator cracked. Replaced the TB with a known good one off a wrecked truck and BAM, she fired right up. Ran about 15 seconds and then died again. REFUSES to start. I can see the injectors spraying. I know it is in time, and it is firing plenty hot (fat blue spark). As it spins over, the injectors spray for a second, then stop. Should they be spraying the whole time it is spinning, or is this to keep it from flooding? I guess this is leaving us with a fuel pressure or ECM problem. What are the chances that we changed the fuel pump, filter, and whole TB and still have the same fuel pressure issue? (we did replace the rubber hose in the tank) What are the chances the metal line inside the tank is cracked and pumping fuel back into the tank? Im really running out of ideas here without just finding a good ECM and plugging it up.

 

[skylark]

The pick up coil and ignition module control the pulses of the injectors. If you are losing injectors while cranking then you are most likely losing the signal for them to fire. A long time ago I did see one that had spark but no injector pulse and we swapped the ignition module and pick up coil and never had another problem.