I hope my dad doesnt mine me posting this...

We tried on Wednesday to get the 7730 TPI speed density computer to work with the stock TBI induction. The car is all stock TBI except for a stock IROC cat-back, 55 PSI TPI fuel pump, and 3.27 9-bolt posi disc rear end. My dad converted the stock TBI harness to run with the 7730 computer (plans coming soon) and used a stock 305 5-speed TPI PROM to control it. Unfortunately, it wouldnt idle right, and was running very lean. So he swapped to 78lb (??) 454 TBI injectors, and it was still idling lean, and having trouble staying alive. He used a clamp over the fuel line to put a restriction in and up the fuel pressure, and finally it would idle and stay alive, but it wasnt quite correct. If you tried to drive it, it would die as soon as you let the clutch out. So we had a friend try to burn a custom PROM for it, but that didnt help a whole lot. Dejected, and not wanting to swap the harness back to the TBI computer, we went ahead and pulled the TBI intake off and switched it to TPI, on the stock 210k 305 block with the peanut cam. Now it idles and runs great, and my dad said he has no trouble now lighting the tires up. We had it dynoed with the TBI setup at 158 HP and 220 TQ at the rear wheels. We will get it dynoed again with the TPI setup to see the difference. Sorry guys, but we didnt have time to play with the PROM any further, my dad needed his car back right away. However, we can try again when he gets his 87 El Camino back from the body shop. It was already converted to TBI, and we will do everything we can to get it to work with the 7730 computer as easily and cheaply as possible.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
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why do you want to use the 730 computer so badly? the 7747 works great

 

Because my dad wanted to do the TPI conversion in stages instead of all at once. And he wanted to test to see if he can use the TPI computer with a TBI harness, eliminating the need to swap harnesses.

 

Well here's the fix: http://24.1.139.249/images/122000/DCP_0108.JPG

Just completed it last week.

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Chronologically challenged. But still alive!
92 CAMARO RS
305 TBI 5/spd (now TPI)
'69 camaro
BB/Lenco
1050 dominators
8.97-150+
Pump gas/no drugs

 

That problem was fixed quick with the removal of TBI. Hmm, makes u wonder a bit...

 

no not really, since the problem was caused by adding a TPI computer and TPI chip to a tbi system, its pretty straightforward actually

 

BAH!

 

Well if you think about the simple mathematics, the 730 ecm expects 8 injectors flowing 19#/hr for a total of 8*19 or 152#s. Where as the TBI has 2 55# injectors for a total of 110#s/hour. The pulse widths are entirely different to compensate for the higher flow of the TPI batch fire.

And, this does not consider the effect of the pressure differences of the fuel. You would have to modify the PROM to think that it had greatly reduced flow (like 12-13# injectors). I am unsure how the ecm would react to such a small injector size. I am finding there are upper and lower limits to how the PROM reacts. When GM designed the underlying code, they did it with certain constraints and limitation.

Such as a 160* T-stat, combined with a MAT relocation and TB by-pass really makes the PROM code do weird stuff and gives improper injector pulse widths when the temperature gets cold.

But if you insist on making the 730 ecm doing something it wasn't really designed to, try "tricking" the PROM by pretending the engine is much larger than it really is, combined with reducing the Injector Flow Rates to make the ecm increase the pulse width to compensate for the two larger but lower psi TBI injectors.

PS: I wonder what it does to the IAC? Bet that has a big effect in that area too.

 

Glenn has it, your TPI PROM was firing your larger TBI injectors with the same Pulse Width it would with the TPI injectors. A TBI injector has a pulse width almost triple that of a TPI injector.

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Hey Glenn:
Try this one on for size, when we put in the 78lbs inj. and increased the fuel pressure,and cut a special chip, the inj. pulse width would increase from 1.9 to 11.9 when you open the throttle but the inj.'s would reduce flow to almost nothing. Go figure.BTW the iac worked just fine, smooth idle at 750rpm.

[This message has been edited by Dyno Don (edited January 01, 2001).]

 

Whoa, gettin tooooo deep for me. I will just watch and read ur guys computer and TBI talk and see what happens.