TBI 454 Timing Questions

[BBslider001]

I know it's been discussed, but I am confused at some of the info and didn't want to hijack a thread.

I got a timing light yesterday to see verify before I started messing with the distributor. If I am looking at it right, wow is it off! The truck runs "pretty good", but at times, it idles like it has a cam, then it's smooth, then it's not, etc...The light showed the timing at the very left end of the indicator tab from the 0* hash mark....as in it was off by about 5 hashes. I am not sure how far off that is, but it definitely is not zero degrees. Also, the diagram on the air cleaner states that 4* is where it should be set? That is the part that kinda makes me wonder. So, before I go messing with anything, I just want to make sure I am reading the hash marks correctly.

What say you guys? Thanks.

 

[DerekTheGreat]

That's because the computer is controlling the timing. In order to set it or check where it is, you have to unplug the EST wire. It is located behind the cover on the passenger side adjacent to the coolant overflow bottle under the hood. It's a tan wire with a black stripe. Unplug or plug it back in with the ignition off.

 

[BBslider001]

That's because the computer is controlling the timing. In order to set it or check where it is, you have to unplug the EST wire. It is located behind the cover on the passenger side adjacent to the coolant overflow bottle under the hood. It's a tan wire with a black stripe. Unplug or plug it back in with the ignition off.

Well dangit, I never saw this info anywhere. Thanks a bunch! I'll report back. So pulling this wire and THEN checking the timing will give me true reading? Also, do we set timing on TBI engines by rotating the dist? I have been reading that it has to do with crank sensor on Vortec engines and rotating dist is NOT how it's done.

 

[DerekTheGreat]

Yes, unplug it, fire it up and check the timing. Be sure the engine is at operating temperature. To adjust, loosen the distributor and tweak it to the left or right as needed- usually doesn't take much. Have fun with getting it just right at 0 degrees. Seems when I go to tighten them back down the timing moves ever so slightly. Trick seems to be to leave the dizzy tight enough such that it takes a bit of effort to move it by hand. Advancing the timing beyond factory spec never did anything for me performance wise. Matter of fact, it just showed up more frequently as knock counts on my scanner. When the ECM detects knock, it retards timing. So while I had my truck that way I was probably down horse power.

 

[grampadirt]

And remember set TBI big blocks @4°BTDC and each of those notches on the crankshaft pully are 2°.Turning the distributor counter clockwise advances the timing,clockwise retards it.

 

[BBslider001]

I must be blind AF. Would someone mind posting a photo of that wire? All I see adjacent to the coolant bottle is a white ground wire.

 

[Schurkey]

The EST connector for setting timing has more than one location, depending on model-year. Maybe depending on engine family.

My '88 K1500 has the wire sort-of hidden behind a plastic cover at the right-rear of the engine compartment--near the A/C and heater-core area. Three plastic nuts hold the cover on. Remove cover (which also exposes a buss-bar of electrical terminals, the fuel pump relay, etc. The EST connector is in the wire harness.

Other trucks have the EST wire under the dashboard, in the passenger compartment. I don't know when they switched locations.

 

[BBslider001]

Ok, after for the reading, I think I found it. Another forum said it could be under the glovebox. I looked and there it was.

 

[BBslider001]

The EST connector for setting timing has more than one location, depending on model-year. Maybe depending on engine family.

My '88 K1500 has the wire sort-of hidden behind a plastic cover at the right-rear of the engine compartment--near the A/C and heater-core area. Three plastic nuts hold the cover on. Remove cover (which also exposes a buss-bar of electrical terminals, the fuel pump relay, etc. The EST connector is in the wire harness.

Other trucks have the EST wire under the dashboard, in the passenger compartment. I don't know when they switched locations.

You posted right when I did. This must be it. I'll find out and report back. Thanks!

 

[BBslider001]

Ok, update. Disconnected the wire and timing sits right between 2 and 4 degrees. Since that nut on the dizzy is not exactly easy to get to, I decided to leave it for now, do a good tune up, and revisit it in the near future. At least I now know what I have. Thanks for all the help here. Learned a lot.