Ok, I'm hoping someone can help because I'm about to "accidentally" light my brothers truck on fire. I will try to make this short.
My brother bought a 94 suburban, 5.7 tbi, auto, 4wd. Ran really good but ended up having a bad head gasket. Pulled it apart, did the head gaskets, valve seals and everything that goes with that. Also did cap, wires, rotor, plugs, oil change, water pump, radiator and a coolant flush.
Went to do the timing, found the connector to bypass the computer. It took a long time to get started and once it was running we pulled out the light and the timing was sitting at probably 20 degrees. Tried to bring it down to bring it down to 0 and it just runs way rough to the point of after about 8 degrees it dies and won't restart. We tested the module, it's good. Fuel pressure is good. Checked every ground. Checked all the vac lines and tested the tbi base gasket with a propane torch. Didn't even have one left over nut (rare).
I'm out of ideas and I'm pulling my hair out. Any ideas you guys can give me.
Thank you.

 

Only suggestion I have is to double and triple check that your plug wires are coming from where they should be and going to where they should be. Sounds silly but with frustration comes a lack of concentration, you may have just misplaced a wire or two. I've been there and was puzzled for almost two days just trying to get the dang thing to start.

 

Thanks for a reply. I did recheck them and they are going to the right places. They follow the firing order stamped on the intake.
I'm going to pull the plugs and verify gap. Its the only thing I didn't check and I'm not sure if my brother checked them when he put them in. Maybe one is crushed shut?
I got advice from a guy that owns a shop in town and he said to ignore the timing marks and try to time it by using a vac gauge. See how it runs that way.
One thought is could the distrib be off by one tooth? Would that cause this? I don't see how when at tdc the rotor is pointing to 5 o'clock and the #1 pole on the cap lines up to it but ???
If you have any other ideas shoot em at me. Lol thanks.

 

I've had instances where the firing order on the intake was wrong, and tdc was also, it can definitely be frustrating, but as a last resort, you did say it runs when about 20 out. Does it run good or bad that far out??

 

It idles fine and will warm up to operating temp. If you try to give it gas it stumbles a little bit. I can get that to go away too if I leave it alone at around 20 degrees. And that's with the wire disconnected.

 

When your setting the timing, do you have the tan/black wire to the ecu plugged in or not?? If its plugged in, when you set the timing and drop it down from 20, the computer registers the adjustment to be far below zero as you drop it down, causing the engine to sputter out and die as the ecu tells the TBI when to allow fuel to flow through the injectors, and if it thinks its too far off, it will be going with your adjustments and eventually the fuel and air ratio will be all out of whack, thus the engine can't and won't run.

 

The whole time I have the wire disconnected.
Little update, the truck will run and idle good but will not stay running if it is put into gear. That's with it at about 20 degrees out and the wire unplugged. Once in a while it will drop idle and try to die. About half the time it will actually die. I tried to time it based off the vac. The problem is it will not hold steady. It will fluctuate about 2-3 inches. I have gotten it to about 15 1/4 inches tops. The IAC looked a little grungy so we replaced it. No change.
I did go to re-check the fuel pressure because we found out the gauge we used was broken. I ran into a bit of a problem. I can't pull the line to put the test fitting in because the gas just keeps siphoning out of the tank and will not stop. I crack the lines and it becomes a river. I did pull the pump fuse and pulled the gas cap.
I've never had a car that would keep pulling gas from the tank without stopping. Is this normal for this truck?
Also checked TPS, that was fine and threw a new temp sensor in it for good measure.
Anyone know how much explosives you can pack in a suburban?