Planning on doing -749ECM swap.

Can the -749 drive 8 low imp. injectors without beeing modifed? I know it can handle 4 but 8?

Found 57lbs 12 ohms injectors at racetronix. So if the 730ECM can handle those I dont have to change to -749ECM, right?

Is low imp injectors better than high imp injectors? it that case maybe I should change ecm after all............

/N.

 

The stock 749 will fail with 6 port, Peak and Holds.
Both the 749, and 730 can handle 8, 12 ohm injectors.

If you can get a clean idle with your combo at idle, then your OK. It's when you need a shorter PW then the injectors will operate at idle that's typcially the problem. For some really high RPM applications there are other concerns, but that's only at really high RPM.

 

Thx..

So why change to -749ECM if they cant drive 8 P/H inj?

I mean, you still have to change the drivers but maybe you cant change the drivers in the 730ecm?

I will probably be using 57lbs high imp. first with the 730, and see how it goes...Its the £58 code that makes it goes quasi not the ECM right?

BUT if I cant get the idle good then I should change to -749 with modified drives and low imp injectors?

 

No stock GM ecm can drive 8 P+H's.
There is a known way to fix that in the 749s. (It's in the archives)
And a guy in Canada doing the driver swap.

Define Quasi.

Yes.

 

Found it.....

Quasi-asynchronous pulse injector fire one time/cycle....

So low imp injectors are better when it comes to tuning big injectors, why?

 

But don't all injectors fire but once per cycle?.

The lower resistance allows for a faster developement of the magnetic field to move the pintle, ball, disc thingie, and thus allowing the fuel to move.

 

Yeah, you are probably right...

I read in some post that the #58 changed to async mode when the pulse width got to low....cant remember exactly what is was

/N.

 

Sync
Async
Quasi

Sync, in relationship to a DRP. Distributor Reference Pulse.
Async, every 12.5 msec.
Still waiting on a good definition on that one. So far just know what it's not.

 

Well bruce according to the docs ive read the following cn be defined as such.

sync. firing every ref pulse.
asynce firing every x numbers of ref pulses typically half of a complete combustion cycle on a given engine. IE 2 on a 4cyl and 3 on a v6 or I6 or 4 on a 8cyl.

Quasi synchonos fires every 12.5 msec of whenevr a minmum firing pw is acehived. IE it will hold and add up sevral small PW events until the minimum async is acehived.

 

Might try the DIY-EFI archives, and the name Spoonmore, and see what you get.

And like we went thru before, spin up a 749, and actually look at the PWs and see how applicable you now Asycn is, at least according to your last defintion about how it works at high RPM.

BTW, I've noticed you've swapped your Quasi, and Asycn definitions.

If you've been able to get the Q-S to work at high RPM, please let me know under what circumstances.

Just like the injector constant (in the Sy Code), not always what you read is the truth when it actually comes to what's implimented in the code.

 

I switched to some 36# svO injectors, at 55psi (injectors were flow tested 2 weeks ago at 35.9 @ 43.5psi)

Believe it or not, i'm running WICKED lean at idle. I gotta drive around with the laptop and get an idea of how far off my VE is..
I'm still on $8d, but gonna repin this weekend to $58.

Why 55psi rail pressure? I was talking to Rich at cruzin performance about fuel pressure. He was telling me that a lot of guys like to run the lower pressure on big injectors. He said "But if they saw what that looked like on the flow bench, they wouldnt do it!" 55 is a safe medium. 60 is about the max you wanna run on these (though the LS1 guys like 58psi).

The dox I read on the $58 stuff agrees with what funstick said. Which is nice if you need really large injectors.

-- Joe

 

Try and get the car to jump pulse widths by a factor of 2 and try and actually see Quasi function as he discribed. As discribed, it say that the injectors will go to a every other normal firing routine. And in his original explaination he said it was at higher RPM to increase the injector flow.

All I can say is I never got the PWs to give any indication of that actually happening. After alot of time looking for it.

If someone can tell me how to get it to happen as he discribes, please let me in on the secret of what conditions it takes for it to happen.

There's lots of reading material, even from GM that's wrong about EFI. They claimed for years the 165 and 730s fired the banks of injectors alternatively, and it wasn't true. EGR operation has some errors. GMs a large co and weither do to revisions, or miscommunication, or making something just easy to understand at their service schools, things happen..

Like I said, if you can get the PW to double on a given set of conditions to indicate Q-A, do to rpm please let me know, I'd like to see if I did miss something.

 

Both banks fire at once??

What about on 749?

wtf..

-- Joe