1982 Corvette with the crossfire injection running off '7747 w/ Prominator Pro. I have made several modifications to the car including SY-1 intake, 2" throttle bodies, 228x228 roller cam w/ 1.6 ratio roller rockers, auto to manual conversion, sidepipes etc. Been reading and studying posts for about a year now trying to get ecm tuned - making slow progress. I am currently stumped and can't seem to find a post addressing this problem - maybe I'm searching for the wrong thing. Anyway, the front injector flows noticably more fuel than the rear injector. I have checked fuel pressure and the compensator and it seems to be working (not stuck). Even changed the injector. Any thoughts on what would cause front injector to dump fuel - causing the left bank of cylinders to run nasty rich?
Thanks in advance!
Gene

 

The injector flows are staggered from the factory. This was done due to the accumulator/FPR set up. Best thing to do is to parallel plumb the TBI units, block off the accumulator and AFR, and run an external FPR.

Then use two of the same injectors.

The injector connector on the rear TBI unit may be intermittent.

RBob.

 

Thanks for the quick reply RBob! You're one of the experts I've been following on the forum. I am familiar with the injector issues and plan to install the 454 (90 lb/hr) injectors. At that point, parallel plumbing and VAFPR would be required. I was trying to learn tuning before tackling any more challenges. I was concerned I may have a bad ecm or something because it is dumping significantly more fuel at idle. Your suggestion on the rear injector connection is one I had not considered and will make sure it is making good contact.

 

Can't run a VRFPR with the '7747 ECM.

RBob.

 

Why not? The ECM doesn't care what the mechanicals are. There would be some tuning needed to make sure that fueling under different loads is correct.

If you're getting so much more fuel from one injector over the other that you have overfueling issues on one bank, there's a problem that needs to be fixed. Even if GM staggered the injector sizing (which is something I have not come across) they wouldn't be so drastically different that you could see the difference, let alone have actual fuel delivery issues.

The only time I've seen that so far with a Crossfire system is when the injector pods were reversed, so that the FPR was first inline. This also caused a no start condition, since the crossfire system was all stock sizing, and didn't deliver enough fuel to light the engine. I could see with larger than stock injectors that and engine could start even with the injector pods reversed.

 

Not enough range in the VE table, BTDT.

RBob.

 

I think the people that have done it would disagree with you.

 

Yep, but ask them why they end up using check valves and restrictions in the vacuum line to the FPR. Take a look at the VE tables, and drive the vehicle to see how it runs.

RBob.

 

I have not come across any reports of restrictions or check valves, when using a VAFPR with a '7747.

It's far too much of a blanket statement saying that "it won't work", when it can work, with proper tuning and proper reasons (mechanicals) why it is used.

 

I used a Marine TBI regulator with vacuum reference years ago on a 230/230 roller cammed 305 vortec. Ran just fine with a VAFPR and 7747. It actually HELPS the limited VE table range by allowing a WOT fuel increase. With that much cam the restriction that needed to be added was in the MAP sensor vacuum line. The 7747 did not appreciate the erractic vacuum signal. What I used was a TCC delay valve from an earlier application. It slows the vacuum signal one direction, but has a check valve that allows a freer flow the other direction.

I ran a 350 TBI with a 204/214 cam and 081 TPI 305 heads on it as well with the marine regulator and a stock 350 chip for quite some time. 255 RWHP at the time and was running the STOCK 350 chip. Had the timing set at about 8-10*BTDC as well.

 

Fair enough, a VRFPR shouldn't be used with a '7747 ECM. It can work, but there are a lot of things that can be done that shouldn't be.

RBob.

 

I agree with you on that. I have used both the 7747 and 7427 with boost, using a vacuum check valve to vent boost pressure above atmospheric away from the MAP and a FMU to increase fuel pressure at WOT. Used a split second auxiliary injector controller to add fuel via two additional 80 lb/hr injectors and a MSD 6BTM box to retard timing with boost. It sounds like alot, but it all worked fairly seamlessly when combined and properly dialed in.

 

As usual, the folks on thirdgen provide more that expected and I thank you for that. I may need to back up and reconsider the way ahead.
I'm going to list my mods to solicit advice to move forward;
'91 fuel pump
228x228 roller cam
Edelbrock Smokey Yunick cross flow intake with custom lid to accomodate a Crossfire Injection
2" throttle bodies
4sp manual trans
200cc Dart Pro1 aluminum heads

I would really like to get the car tuned and start enjoying it. Would you recommend a modern ecm and parallel plumbed injectors?
Thanks,
Gene

 

Yes a modern ECU like the one at dynamicefi.com!

Sounds like a set up similar to mine a few years back. I started with a 7747 that was Ham'd for connection to stock ECU connection(s).