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Username Post: 91 5.7L TBI Timing procedures?
Posts 33
02-29-08 04:58 AM - Post#1377209    

I have a chilton manual on my 91 GMC Sierra 5.7L TBI and it doesn't give me much info on timing procedures. I just put a crate engine in this truck, followed the procedures on installing the distributer properly, and got the engine running. I haven't took it out on the road yet to test it. Put the timing light on it and it's set at O degrees right now. I saw in a past timimg subject that a guy had to pull a wire off of the ECM when timing?? Can someone give me a little more info on which wire/wires to pull off and where? I believe I found the ECM behind the glove box. Is it a silver box with two wire harnesses connected to the front of it?
Fishngame1 - 1991 GMC Sierra 1500 4x4 Ext cab 5.7L TBI/Auto

Posts 986
02-29-08 06:52 AM - Post#1377244    

The brown wire connector on your truck should be near where the main engine harness goes into the cab, on mine it's about 12 inches away. It can be hidden inside the loom.

Almost when timing your truck should be warmed up and running in closed loop before disconnecting the timing wire.
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Subject Matter Expert - Senior Member
Posts 3747
02-29-08 08:45 AM - Post#1377340    

To set the timing you must unplug the set timing connector, which is a single Tan wire with a black stripe/tracer on it. On some years the set timing wire is tan with a white stripe/tracer.

For your 1991:
The set timing wire is located, under the hood, on the main harness that goes from the engine to the firewall, on the passenger side, sometimes underneath the black plastic cover (if it’s still there) that covers the junction block, relays & fuses. It’s near the top usually on the back side of the harness. Doing this will set a code 42 in the computer. Clear the code after you are done checking or setting the timing.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.

Posts 33
03-01-08 09:32 PM - Post#1378420    

Thanks! I found the wire and got the timing set. Runs great!
Fishngame1 - 1991 GMC Sierra 1500 4x4 Ext cab 5.7L TBI/Auto

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