nevermind, just was thinking since Dyno Don posted that TPI injectors and TBI injectors measured the same ohm load I thought it would be possible. Maybe it's a long shot but I just don't understand why it wouldn't work.

[This message has been edited by JPrevost (edited November 02, 2001).]

 

Well, the injectors all fire on tpi at the same time and most of the time tbi fire alternately. Simply stated, tbi has two drivers. I'm sure this could be overcome by adding external drivers but if going through all that work why not get rid of the tbi and go tpi. What advantage are you looking to get out of running a different ecm?

 

He needs a better ohm meter. I just double checked, on my group of 8 saturated injectors I read 2.5 ohms.

I also just checked a TBI injector, and it's 1.2 ohms. That 1.2 ohms is per injector. so the actual load fired thru a single injector driver is like .6 ohms.

Doubt me?.
Set up an ecm and actually try it, rather then just hoping to get a reply you like.

And again your ignoring the perferred operating ranges of the injectors.

 

Don't TRY and **** me off, I'm already hitting my head on the wall because of the darn fuel pump.
Notice I edited my post, I did a lot more research after posting so you guys are still not giving me any sound reasoning. The advantage of running a TPI ecm would be the use of an eeprom, having more complete tables in tunercat, a faster data rate, more goodies like AFR at WOT and at different coolant temps! The 8746 may have been "hacked" but it isn't anywhere near as far as the 7747 or the 730 and I like having more options. I'm one of those dogs that can't live on bread and water alone. Give me a bigger menu!
BTW Grumpy, I'm not trying to just post to hear an answer I like. I'm posting to hear answers "I" wouldn't have thought about.

 

No one can **** anyone off, if they don't want to be. If you want to act pissy that's on your head for being that way. I just write answers, reading anything into them more then that is silly and childish.

I've given you all the hints in the world for running a 2 brl TBI off of a particular P4 ecm. I've told you exactly where to look and you ignored it.

What will you consider sound reasoning?.
I've told you the resistances are different, and went to the trouble to 2x my readings before posting. I've explained the suggested operating times, and you want to ignore that. I mentioned the differences in manifold designs, and you've ignored that.

Even with you ignoring so much of what I said, telling you where to look, and then you tell me not to **** you off?.
Right...

If you want as much info on the 8746 as the 747 just takes work. You can follow Programming 101 and brute force it, or comment the code yourself.

You don't like any of the sound reasoning that you've gotten, well wire up an ecm, and go for it.

 

[This message has been edited by JPrevost (edited November 02, 2001).]

 

Since there is only (4) on each driver,what does that measure?
BTW,I haven't given up on this, I will endeavor to work it out somehow.

[This message has been edited by Dyno Don (edited November 02, 2001).]

 

4 on each driver? There is only 1 driver in the 730 ECM. The one driver in the 730 runs 8 injectors.

The 730's one driver can be set in the software to Peak and Hold for one TBI injector, but it won't fire two. Same problem with the TBI ECM's, each driver only supports one injector.

Even if you could run two injectors you lose the injector firing strategy the two channel TBI ECMs have. How critical is this? I don't know why GM used a different firing strategy, but I tend to think they had a good reason as it is more complex than batch fire.

Most of the time TBI fires both injectors twice a revolution in an alternating fashion unlike batch TPI which fires all injectors once a revolution.

Kinda like using a hammer to thread in a screw, no?

 

OK, no big deal as far as the resistance goes. A set of parrallel run TPI injectors gives you 2.5 ohms and one TBI injector gives 1.2 ohms so wiring the TBI injectors in series gives you 2.4 ohms. Now, what will they run like is anybody's guess. Also, this doesn't take care of anything to do with the firings per revolution which I don't know if there will even be a compatability issue. Now you say you want to use an eeprom. Doesn't the 2732 and 29256 have the same pins and i/o? A faster data rate can be had with lockers. Much faster than 8192 baud. I wish I knew what you referred to with the WOT AFR but I really haven't studied the 746/747 ecms as I will be using a 730. But if you like options then go with port fuel injection. TBI just doesn't cut it, especially at WOT. You don't have to use a GM TPI design. Hell, make your own. I plan on using a modded Vic Jr. and I already have a Holley for a TB, sans boosters and venturis and bowls. I like options too and when none are easily available, I make my own.

 

Wiring them in series effectively makes them 6v injectors, and they will be lazy. Looking at the PW correction via battery correction and you'll see how much correction is needed as the voltage drops. Firing them in series, and you can actually hear them get erratic on an ecm bench.

The injector firing strategies are a matter of using atomization (TBI) vs vaporization (TPI), in conjunction with wet and dry manifolding.

TBI uses the shearing forces of the butterflies to atomize the fuel so that it can get to the intake valve pocket. TPI just squirts the fuel into the intake valve pocket, and relies on the action of valve overlap to do all the work of vaporization.

Ultimately its the exhaust blowing across the fuel at overlap that gets the fuel ready for the reaction in the chamber.

2732 is 24 pin and the 128/256s are 28.

 

Jon, the CrossFire guys and I went through this same discussion. Stick with the '8746 or go with the '7747.

Here's why - 1st, as Grumpy mentions (and you already know) the impedance is different. Sure, you can make TBI injector drivers to cure that, but..

2nd, the firing RATE is different. They only fire every OTHER engine revolution, not EACH engine revolution. So, you'd have to figure out some way to change that.

3rd, you MIGHT be able to change the pulsewidth to get it close, but it's still going to be a half-assed solution and may never run right. (But don't let me stop you if you want to figure it out!)

4th, I'm working on a permanently installed internal EPROM emulator that requires NO battery backup and can be programmed via the parallel port. NO EXTERNAL HARDWARE WILL BE REQUIRED! It will be programmable while you are driving, so it won't be necessary (from a programming standpoint, not a safety standpoint) to pull over. I.e. you can have someone drive while you tune. (Yes, it's for the 2732/'7747/'8746!!!!) Don't sell your EPROM programmer just yet though, it's still in the design/testing phase. I'm trying to keep it cheap and maybe even DIY, for under $100.

5th, with WinALDL populating the tables nice and neat for you, tuning SHOULD be a hell of a lot easier with 160 baud now! (The jury is still out on that one of course, but it's a hell of a lot easier.)

The idea is that you install the EPROM emulator permanently in your ECM (it completely replaces the EPROM) and your ECM will have a parallel port poking out of it. When you want to program, hook your parallel port into it, and then your serial port into the ALDL port. Drive around, populate your tables, do a little tuning and upload the data to the EPROM emulator. Clear your tables in WinALDL and drive around some more.

Hopefully this combination will speed the tuning process, at least for the VE and spark tables - and make TBI cars a little less unattractive as far as tuning is concerned.

Also, Jonas has some software that does 1/4 mile time and he's figured out a neat circuit for using the Street Dyno software so you can even get a dyno graph! There's LOTS of tools out there.



Ken