I wasnt sure what to search for to find this out so sorry if its been discussed somewhere, im trying to find out which injectors on a mpfi system fire at the same time, if any, or if its computer controlled and random, ive discussed aspects of my fageol supercharger project on here before so some of you may know its setup for tbi, im thinking of setting up the electronics for mpfi that fire 6 injectors to fire only 2 injectors that are on a tbi system, if they fire in groups of 2 or in groups of 3 ill make a 4 injector system, just need a push in the right direction, Thanks, BTW anybody interested in pictures of the supercharger? My g/f got a 4MP cam for xxx-mas which mean i got a 4MP camera for xxx-mas.

 

On your '91 all 6 injectors fire at the same time. The '730 ECM only has one injector driver. They fire once every revolution of the engine (every 3 spark plug firings).

Not sure what direction you are thinking of. Are you going to put a TBI on top of the S/C? (Sounds that way). If you do that the one injector driver in the '730 can only drive 1 TBI injector (different resistances: saturated vs. PnH).

A '7749 ECM is similar to the '730 and can drive 2 TBI injectors (it has two drivers). Some of your decision will ride on whether emissions is a concern.

Pic's are cool. . .

RBob.

 

I was thinking more of using the stock mpfi computer so i dont need to change any electronics besides those related to the fuel system at the injector level. I want to take a 2 injector tbi system and wire those 2 injectors with the electronics meant to fire 6 injectors used in mpfi, i was trying to see if i can wire the 3 injectors for the left cylinders to the left tb injector, and obviously the right cylinder injectors to the right tb injector. Depending on lots of things that may not be possible, So my next line of thinking now knowing that all 6 injectors fire at once is to ask if i can just wire up the 2 tb injectors with only 2 of the mpfi electronics and use injectors rated 4x what they are stock, meaning if there 15# i'd get 60# injectors, That should work right? I mean people on here are always complaining about clogged injectors, if the injector is wired up but unfunctional its not doing any good, so 2 injectors rated at 4x capacity should make up the difference in my proposed system, Right?

 

Also if the injectors work on different electronic signals ill modify the casing on the tbi system to accept mpfi injectors so thats not really an issue atm, The reason behind this line of thinking is i dont want to modify anything that came stock with the supercharger, just incase i ever need to sell it, i dont want injector bungs welded in the manifold anymore. Emissions arnt a concern to me, but i bet you mean the great state of Connecticunts concern.

 

Correction, there are actually two drivers on teh 7730 and 7749 ECMs, but they are bridged internally to both injector outputs.

 

No, there is not. As I stated the '730 has one injector driver while the '749 has two.

RBob.

 

To put a 2-bbl TBI on top of the S/C you can't use the '730 (or, you shoudn't use it). The one driver can be used for 2 TBI injectors but it isn't recommended. Can just wire them in series. Which cuts the voltage in half and makes the injectors open a lot slower.

One way to go is the '749 ECM with the $58 mask. This will provide 2 injector divers, one for each injector, along with boost capable code.

This ECM & mask is used on some of the GM turbo cars along with the Sy/Ty's. Down side is that it doesn't support the digital EGR and the CCP. The $8F mask (turbo GranPrix) supports a vacuum EGR along with the rest of the emissions stuff.

Need to make a chart of what you can do without, what you are willing to use for injector drivers, what additional functionality is required, and how much re-pinning you are willing to do. Then decide upon an ECM and a mask.

As for which TBI unit, the 4.3L, 5.0L and 5.7L 2bbl's have 1-11/16" bores. Big enough. The 5.0L has 55#/hr injectors with the 5.7L unit having either 61#hr or 68#/hr injectors. This is at 12 psi, which is stock for those units. These TBI units and injectors can also be run at higher pressures, up to 32 psi with out trouble.

That would provide more fuel then you'll ever require.

RBob.

 

Funny, the '7730s I have personally pulled apart and inspected used 2 drivers.

 

I really don't see why the '7730 would have any problems running two TBI injectors.

Doing a little math, the '7730 is commonly used to run 6 to 8 high impedance injectors, that equals 1.5 to 2 Ohms, at the driver.

Even if the TBI injectors are lower impedance, which I don't believe they are, that would still be about a1.5 to 2 ohm load, since most low impedance injectors are around the 3 to 4 ohm mark. So total wattage out put will be pretty much the same, in both cases.

Now I do agree that a '7749 would probably be the better start, due to being hacked for the Sy/Ty .bin. The TGP (A turbo 3.1 V6) .bin has also been hacked and will work in a '7730, but works better in the '7727, even though people swear the two are the same, there are differences, which do effect drivability and a few other factors.

 

ive always thought the 730 ran a batch fire system where it did bank 1, then bank 2.. alternating.

does the V6 use totally seperate code then the V8?

 

For once it would be nice to post on the V6 board without everyone wanting to argue about the posted information. So, I'll again state as fact: the 1227730 ECM has one injector driver. All 6 injectors fire at once. All of the GM V8 TPI setups along with the 2.8L and 3.1L MPFI V6 f-body engines are batch fire. All injectors fire at the same time.

The '90-'92 TPI engines and the '90-'92 MPFI V6 engines both use the 1227730 ECM. However, they each run completely different code within the ECM. It is the $8D mask for the V8 and the $88 mask for the V6.

As for the resistance of the GM TBI injectors, they are 1.2 ohms. For best results and proper usage of those injectors, they are required to be controlled by a peak-and-hold driver. Sure, you can hammer them with a saturated driver. Can also put resistors in series with them. Can also wire the two injectors in series and use the driver in a PnH mode.

However, best method is to use the proper driver. . .

RBob.

 

Can we start back at that thinking point? And let me apologize by saying im probaly confusing alot of you, my plan is to take a 2 injector tbi setup and modify it to accept the same injectors as my mpfi so i can use all the stock electronics,thats not changing no matter what, ill find away to do it, what id like to focus on (if everybody wants to join me in this conversation) is my therory that since all the injectors fire at once, that using 2 injectors at 3x stock capacity will deliver the same amount of fuel, and using 4x injectors should give enough fuel for the supercharger aspect, id also like somebody to confirm that electronics hooked up to a non functional injector ( clogged or just plain broke) would be the same thing as just capping off 4 of the injectors and not using the electronics. thank you for your time guys.

 

Yes, if you used 1/3 the number of injectors at 3x the flow, it will give the same anount of fuel. And using saturated injectors you will be able to use your current ECM.

As for using broken injectors, I wouldn't do this. Injectors can short out when they go bad which will prevent the others from operating properly.

RBob.

P.S. yes, I was confused over what you wanted to do

 

Thank You for your reply, and im glad i cleared that up, im deffinitly going to be capping those "extra" injector wires specificly to prevent shorts though i was thinking of using my currently functioning injectors not hooked to a fuel source before, i do have a slight problem now though, ive read a few places that the injectors each fire seperatly, not all 6 at once, is there anywhere i can confirm this either way? i tried looking on 60degreev6.com but couldnt find anything, and thats a very important piece of info in this project. i got the cam, pics soon

 

I was under the impression they switched sides below 3k, and above 3k it was batch fire.

But then I'm no ecm wiz.

 

Stop over on the DIY_PROM or the DFI & ECM board and ask there. Also, a search on either board with something like '730' and 'driver' as search criteria may bring some results.

Take an ohm meter and measure the resistance between the two injector output pins on the ECM (they are tied together inside of the ECM).

If you had a TTA then each injector fires individually as a sequential setup. Only 3rd gen f-body that does this. Note that this is also a MAF setup.

RBob.

 

this may not be even be true or have anything to do with reality but from what ive read i think this may be a valid question, can i run my car in closed loop permenantly and make it use batch fire? or is that something 4th gen and 3.4 related im thinking of

 

According to the ecm forum gurus the 730 ecm for the v8 and v6 are only capable of batch fire, I see no reason why this plan wont work now. If anybody sees a potential problem let me know.