Problems With Tbi Unit

[klompster123]

Hey everyone! I have a 1990 C1500 and recently i have been getting 10mpg no matter how i drive it. Just tuned it up to. Plugs, Wires, Cap, Rotor, Timing, and did a TBI unit rebuild kit. about a month ago i was getting 14-16 mpg. Any ideas????? Thanks

[bill190]

How exactly did you adjust the timing? (I thought the engine computer did all the timing?)

[grampadirt]

How exactly did you adjust the timing? (I thought the engine computer did all the timing?)

 

 

You gotta set the base timing yourself.Look for a black relay box on the firewall and unplug the tan wire with a black stripe.This is from my Haynes manual

[klompster123]

How exactly did you adjust the timing? (I thought the engine computer did all the timing?)

 

 

You gotta set the base timing yourself.Look for a black relay box on the firewall and unplug the tan wire with a black stripe.This is from my Haynes manual

 

Thanks for the input! Yeah that is how i set the timing. I disconnected the cable and then adjusted it to 0 degrees. is that right?

[71GMC_3/4T]

For your low fuel mileage issue, I'd try shotgunning the O2 sensor, especially if it hasn't ever been replaced.

It could be giving it wrong information, causing it to dump too much fuel in, but still not throwing a code.

It should be fairly easy, assuming it isn't rusted too bad.

Good Luck!

[Cowboy09]

If it is the oxygen sensor, you'll need some heat shrink and a razor blade for stripping the wire with

[bill190]

Yeah that is how i set the timing. I disconnected the cable and then adjusted it to 0 degrees. is that right?

 

My 92 factory service manual (fuel and emissions) says to use the timing information on the emissions label under the hood.

 

And to place the EST (Electronic Spark Timing) system into bypass mode by disconnecting the tan wire, but gives different locations of that wire depending on the engine and in one case says to jumper two connections. But again this is for 92.

 

Do you have a label which gives timing information under the hood somewhere?

[klompster123]

Yeah that is how i set the timing. I disconnected the cable and then adjusted it to 0 degrees. is that right?

 

My 92 factory service manual (fuel and emissions) says to use the timing information on the emissions label under the hood.

 

And to place the EST (Electronic Spark Timing) system into bypass mode by disconnecting the tan wire, but gives different locations of that wire depending on the engine and in one case says to jumper two connections. But again this is for 92.

 

Do you have a label which gives timing information under the hood somewhere?

 

No i don't, but does it tell you what degree to set it at on yours? I have the 5.7L 350.

 

 

 

[bill190]

Mine is also a 5.7L and the label says set to 0 at "idle speed" and does not list any specific rpm's for idle speed. Maybe the exact idle speed does not matter? (Mine is a 92, so could be different as to this label business, I don't know?)

 

Anyway did you mark where the distributor was set before adjusting the timing?

 

If yes, might want to move it back and see if that gets it running better.

[Mike G]

Is there a problem with the way it is running, or just your gas mileage? If it's the mileage that's an issue, start with the O2 sensor, thos are relatively cheap and easy to get to. Then, you may need to have your throttle shaft bushings replaced. Those wear of course with time and get pretty abused. I am about to have mine done to my 92. For $100, I can put that problem or diagnosis to rest.

--Mike