Ive read that the load from 4 tpi injectors wired in parallel is similar to a single tbi injector, but i think theres a problem with the firing. The tpi is batch fire, so each bank fires every 180 degrees..right? How often does the tbi fire, and does anyone think each injector firing ever 180 degrees would work.

 

I bet the dynamic behavior of the injectors would be different, but you should be able to adjust the PROM for that. This would be cool, HAS anyone done it? I bet Bruce has...

 

Im looking at how feasible it would be to adapt a 91-92 tpi ecm to my xfire engine. I've worked out most of the wiring, theres a few more i have to figure out, and also add a mat sensor. but the main interest is getting the 8192 baud rate, and better tunability.

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1984 Z51 Auto, Ported and polished intake, K&N, MSD, Ram air/Cold air intake, no cat, no AIR, no egr, no swirls plates

 

I thought of an alternative to using the TPI computers, how about the later TBI ecms that came from trucks like in 95. My dad's suburban has a really fast update but Grumpy pointed out that the ecm wasn't designed for a 3500lb car and that it would be really difficult to adjust.

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, Jon (350 TBI!)
91 Red My website

 

GMECM and DIY, have my notes on the subject.
The matter of differences in styles of injector is an issue. Once ya figure out the injectors using ohms law things fall into place better.

 

The TPI fires all 8 injectors at once.
My dad tried to run a 7730 TPI computer on his 92 RS before he converted to TPI. The TPI computer was in single-fire mode, while the TBI runs in double-fire. The car wasnt getting enough fuel to even idle. He put in 454 injectors and cranked up the fuel pressure, and then it would idle, but it would die when you revved it up. So he gave up and switched to TPI. I dont know how to convert the TPI prom to double fire, otherwise it could work now. He is going to try again when he switches his 87 El Camino to TBI.


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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Nick and I were talking about this - TBI uses 10PSI (approx) as the working fuel pressure, where TPI uses 45?PSI (approx? I don't know) for working fuel pressure, so I can only assume that the PW would be substantially shorter for the TPI injectors.

If that proves true, then you'd have to increase PW (BPW?) and pressure to compensate.

Sorry Grumpy, DIY-EFI is down, otherwise I'd go back through those notes in a heartbeat.

Ken

 

Kevin, can you explain single-fire mode vs. double-fire? I'm not sure I understand.

My TBI system (well, my old ECM at least) fired both injectors at the same time, not alternatively.

Ken

 

I am guessing this double fire mode fires the tbi's once ever 180 degreed while the tpi single fire is every 360. Did your dad try altering the prom at all?

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1984 Z51 Auto, Ported and polished intake, K&N, MSD, Ram air/Cold air intake, no cat, no AIR, no egr, no swirls plates

 

Ive done some reading since diy-efi came buck online. Lets see if anyone can help me out. Ive read the 7730 7727 have 4 modes, that can be selected via a different cal-pac, 4 cylinder, 6 cylinder, 8, cylinder and tbi mode. With activation of tbi mode does this initiate double fire? Could someone explain the different modes to me.

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1984 Z51 Auto, Ported and polished intake, K&N, MSD, Ram air/Cold air intake, no cat, no AIR, no egr, no swirls plates

 

Missing some important points.
The 730 was used in a TBI application, BUT it was a single injector. Like I said use ohms law and you'll see the current ratings are way off. You need a 730 type that was used for a ***Similiar*** injector loading.

Using a 730 for a twin TBI will make for very sluggish, injector firing, and be very battery v sensitive.

 

how about if the 7727 from the 4 cylinder application was used to trigger and external driver which in turn triggered the pair of tbis

I also read this in the archives

"When running in TBI mode, the hardware doesn't need to know the number
of cylinders - but it does need to be set to TBI mode. Pin 56 does
that. It has four possible values: 4 cyl, 6 cyl, 8 cyl, and TBI.

Once the hardware is set to TBI mode, you still have to make sure the
software is told the number of cylinders (possibly through an EPROM location)."

What is the tbi mode? is that double fire?

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1984 Z51 Auto, Ported and polished intake, K&N, MSD, Ram air/Cold air intake, no cat, no AIR, no egr, no swirls plates


[This message has been edited by nsimmons (edited October 09, 2001).]

 

I've been looking into something similar. Grumpy is right about the impedance of the injectors, trying to use the 730, or 165 would way overload the drivers using TBI style(low impedance) injectors. If you dig around on the DIY-EFI site, you can find injector drivers that are basically cusomizable(set current limits, etc) so you could make a driver baord that is fired from just about any computer, and the number of injectors is also open(hmm...dual tbi's anyone?). As far as batch firing, if a single plane intake is used, having the injectors fire alternately would not be a problem, but there might be some tweaking necessary for a dual plane(which feeds multiple cylinders on either bank per throttle blade.) Maybe bigger injectors or something.

 

Might look around for an ecm with the drivers you want already in it.

 

I measured the resistance of 4 TPI inj. and one TBI inj. and found only a small difference. So each driver would batch fire aproxamately with the same resistance with 4 TPI or 1 TBI.

------------------
Chronologically challenged. But still kicking!
'92 CAMARO RS
305 TBI 5/spd (now TPI)
B4C Alt.
14.94-92.00 mph
'69 camaro-BB/Lenco,1050 dominators, /Pump Gas/no drugs 8.97-150+/3200lbs.
SoCal Thirdgen F-Bodies

 

Based on Grumpy's recommendation, I have been looking at the potential of converting from a 7747 to 7749 for my Xfire. So I'm real interested in this thread.

 

TPI P+H= 2.4 ohms
TBI P+H= 1.2 ohms

That's a huge difference. The TBI draws twice the current of a port P+H injector.

 

My '94 Fullsize TBI pickup has the same PCM as my '95 S-10 TBI pickup (16196427). The S-10 weighs in 1000 lb lighter than the fullsize at 3700 lb. After prom tuning, they both run great. This PCM has the 8192 baud rate and CPI mode. The $0D mask has been hacked and is supported by TunerCat, TunerPro, and Datamaster. To make it run a twin TBI Xfire setup would probably require an extra external injector driver, but that has been done by the guys running the Holley 4BBL TBI unit. HTH

 

Sorry for the repost. For some reason, the thread did not update with my post.