TBI adaptations

[dyeager535]

I don't think tire size should matter that much. As long as you aren't into the throttle so far that it's in the "enrichment" mode during normally light throttle conditions (cruise), it's still going to be compensated for with the O2 sensor.

Yes, more load on the motor won't help, but that's a necessary evil on many peoples trucks.

AIR on trucks apparently just diverts (to atmostphere or air cleaner) under hot engine operation. If it's pumping into the manifold other than cold engine temps, it's going to be seen as LEAN, thus richening the mixture artificially. More oxygen introduced post-combustion=lean to the O2 sensor.

FWIW, in the TPI cars, since AIR was introduced even under hot engine operation, there was a voltage offset to the O2 sensor for those times.

 

[xCaliK5x]

I don't think I'm in enrichment mode. I accelerate to 15 MPH and it will richen up, but then as I cruise the HC's come down and level off. The load I'm sure isn't helping. Most of the cars are tested in second gear, mine is in first due to the tire size. I will pull the sheet out of the center console in a bit and get the RPM/MPH.

Well, I am getting divertion of air to the air cleaner when warm as I am supposed to. But if I pinch off the feed line to the exhaust manifolds when its hot, my O2 values jump to rich, then it starts to compensate. So I am getting a little air in the exhaust. I have vacuum from the scavenging effect on the tube if I pull the injection hose off completely. I think I should be getting no air injection at all when its warm correct?

I think I still have a vacuum leak somewhere since I get a rough idle still. I'm going to recheck the intake manifold, if the bolts on that are as tight as the rest of the ones all over the truck, I
could be in trouble.

 

[dyeager535]

How is that line "valved"? On the cars there was an actual solenoid...perhaps if your truck has one its not working correctly?

I *believe* you are correct on the AIR injection, as without a way to compensate for the additional air in the PROM (I looked before, didn't see anything) it would always cause problems, and GM wouldn't have done that.

 

[BGKYK5]

it would always cause problems, and GM wouldn't have done that.

One other thing to check would be an exhaust leak upsteam of the O2 sensor.

 

[dyeager535]

What? GM couldn't have had high HC and passed EPA certification, therefore it wouldn't have been sold.

 

[BGKYK5]

I just meant that in general, GM did plenty of dumb things that caused problems.

 

[xCaliK5x]

I think I have gotten somewhere. I noticed that the #1 position on the cap, is pointed to the drivers side rear of the truck towards cylinder #7. Isn't the TBI dizzy supposed to be indexed so #1 is pointing to the drivers FRONT corner (#1 cylinder)? From what I have read, this appears to be the case so the ECM knows where #1 is. This would also explain why the truck runs great at idle, but with RPM it doesn't?

 

[dyeager535]

Distributor cap position has no bearing on how it runs, *as long as #1 cylinder is getting spark when it needs*.

If yours is that far off, your timing could be all screwed up. But if the #1 terminal on the cap is getting spark on #1 cylinder at the right time, doesn't matter where the distributor is indexed.