TBI timing

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VIKING_MECHANIC

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Who needs proper timing advance?
[/QUOTE]

Not us.

All joking aside, I'm not to worried about the timing advance as this engine has a pretty serious rod knock. It's barely audible at idle, but under load, it's quite pronounced.
 

Schurkey

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A knock that loud could be picked-up by the knock sensor, which would retard the timing trying to control the "knocking".

The old-school test for the knock-sensor system was to whack something cast-iron--the intake or exhaust manifold, typically--with a small hammer. Watch the timing; or just listen to the RPM. When you ping the iron, the timing retards and the RPM goes down; then recovers if the system is working.

So I could see a rod-knock maybe screwing with your timing on a fairly regular basis.
 

langkg

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Why wouldn’t you top off the tank with fresh gas, set timing with EST disconnected and then go from there? That would be the proper procedure rather than chasing your tail. Set it at 0 degrees with the black/tan wire under the glove box disconnected. Reconnect it after setting 0 degrees and tell us what you have. If you’ve monkeyed around with distributor timing then your first step should be to set the engine at TDC firing stroke, reset dizzy and then do the above. Sounds like you’re taking a shotgun approach and don’t know where you are on timing. Stop and reset it properly using fundamental setup
 
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VIKING_MECHANIC

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A knock that loud could be picked-up by the knock sensor, which would retard the timing trying to control the "knocking".

The old-school test for the knock-sensor system was to whack something cast-iron--the intake or exhaust manifold, typically--with a small hammer. Watch the timing; or just listen to the RPM. When you ping the iron, the timing retards and the RPM goes down; then recovers if the system is working.

So I could see a rod-knock maybe screwing with your timing on a fairly regular basis.
It may not be rod knock like I originally thought. I drove the truck some more today and I heard absolutely no knock, even at high RPMs. But after driving it for about 10ish minutes it randomly came back.

I got curious and got under the truck with it running, and it seemed like the sound was coming from the flex plate/torque converter. The flex plate may be warped or out of balance as something was hitting the engine as it was running.
 

VIKING_MECHANIC

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Why wouldn’t you top off the tank with fresh gas, set timing with EST disconnected and then go from there? That would be the proper procedure rather than chasing your tail. Set it at 0 degrees with the black/tan wire under the glove box disconnected. Reconnect it after setting 0 degrees and tell us what you have. If you’ve monkeyed around with distributor timing then your first step should be to set the engine at TDC firing stroke, reset dizzy and then do the above. Sounds like you’re taking a shotgun approach and don’t know where you are on timing. Stop and reset it properly using fundamental setup
Well a few reasons:

The truck isn't technically mine yet. I'm just trying to get it to run good-enough to see how it behaves before I trade for it.

The fuel gauge may not work. Because last week when we were working on it, it was almost on "Empty". We put about 5 gallons in it and it magically shows "full" now. So I don't actually know how much it actually has.

As @PlayingWithTBI mentioned, the ICM may be on the fritz. Disconnected, it runs great, very smooth at idle and is very responsive. Connected, it runs rough, hesitates and would die multiple times. Most likely will have to replace the ICM/distributor in the near future.

And on the EST wire, it's not always under the dash near the glove box. In my case, this one is on the firewall a few inches from the distributor in the main harness.
 

Schurkey

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It may not be rod knock like I originally thought... ...it seemed like the sound was coming from the flex plate/torque converter. The flex plate may be warped or out of balance as something was hitting the engine as it was running.
Cracked/broken flexplates are very common on these engines.

I bought a "core" Vortec 5.7L short-block to rebuild for my '88. When I show up after driving hundreds of miles, the guy tells me that they took it out because of a "rod knock". I was crushed...I needed a good crank and rods. Then he tells me to look at the flexplate. The six bolts on the crankshaft flange were completely ringed by a larger, near-circular crack. The outer section of the flexplate could wiggle on the crack, but not actually spin. THAT was the "rod knock". I pulled that engine apart, the rod bearings had some wear, but not enough to damage the crank journals (I re-used the main bearings!)

The fuel gauge may not work. Because last week when we were working on it, it was almost on "Empty". We put about 5 gallons in it and it magically shows "full" now. So I don't actually know how much it actually has.
A fuel gauge "over-full" may indicate a broken wire to the sending unit.

As @PlayingWithTBI mentioned, the ICM may be on the fritz. Disconnected, it runs great, very smooth at idle and is very responsive. Connected, it runs rough, hesitates and would die multiple times. Most likely will have to replace the ICM/distributor in the near future.
Could be the ignition module, the EST module, the ECM, or the wire harness connecting them.
 

bahallig

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I had a similar issue with my 90 k1500, weeks of troubleshooting nothing worked , would run great with the timing advance wire unplugged but would barely idle with it plugged in. Ended up being a rusted out pickup sensor on the old distributor. I think you can teplace just the pickup but a new replacement distributor was like $100, been running great ever since
 
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