Dual quad tbi setup? Start from mid 80's cross-fire ecu?

**lionelhutz** · 01-29-2016

I posted that the Crossfire is useless because it's wrong for this application and the stock computer is too simple and badly supported to bother with. You can use the manifold and throttle bodies for a swap with success and even make a stock system work if you want, but the throttle bodies and ECM are completely wrong for this application.

Trying to run progressive on the throttle blades and/or 2 ECM's is over-complicating things for no good reason. Carburetors used progressive linkage secondaries to help correct various issues caused by their mechanical operation. EFI systems use the software to take care of those issues so a mechanical fix isn't required.

On a separate note, you can try to create a more progressive response in the throttle linkage between the throttle pedal and the TBI units. For example, make it so the first part of the pedal travel moves the blades slowly and then have the blades go faster as the pedal moves more. The amount of progressive really depends on how sensitive you want the pedal to be in the "cruise" range.

**Keithnh** · 01-30-2016

Wow got some good info here, not sure I mentioned I would not be running an electronic transmission just a simple turbo 400, and the intake I have looks like it has 2 isolated sections with a rectangular hollow connector ( I call it the "warehouse") connecting the 2. The sections fuel the front 4 and the back 4 respectively ... it is not interlaced. Although no expert I believe progressive is not the ticket and would cause uneven fuel distribution and a very rough running engine. Would prefer to run a single computer if possible with only the basic necessities to keep the engine running as well as I can make it. WAS thinking I might need 2 computers and sets of sensors as the sections appear to be very distinct, but would like to have a s few components and variables as possible. Will have individual header tubes to locate oxy sensors in and since this is an experiment, don't mind adding connection spots to manifold for other sensors if I have to. I was worried about throttle likkage but do have machinist buddies luckily :)

**dave w** · 01-30-2016

I wonder about the option of using a Dynamic EFI EBL Flash system, which can operate 4 TBI Low Impedance injectors with the 4 injector upgrade?

http://www.dynamicefi.com/EBL_Choice.php

http://www.dynamicefi.com/EBL_Flash.php

dave w

**Keithnh** · 01-30-2016

I used to be an electronics tech and think of this as a bit of a challenge. I wish I had a diagram with computer inputs and outputs to start with. Just helps me collect my thoughts as I am used to them. Would like to know what exactly the computer is saying to the tbi. Understand there are adjustable fuel pressure mechanisms that enable tuning but I don't believe they are computer controlled. So if the computer is just saying "squirt" and "stop squirting" to the injectors according to the sensors and the throttle position they will be delivering more fuel in between the "squirt and stop squirting" instructions at a higher fuel pressure. The computer makes it possible easily most likely to respond to its inputs thousands of times per second, probably far faster than an injector has the capability to react. Was wondering however how injectors alone could respond as accurately to changes as the multiple systems of a carb idle,primary,secondary,accelerator pump,power,choke without all the mechanisms ... will be interesting to see this project through and find out. It appears the computer is possibly modifying the spark advance in some applications, not sure if it needs to in my application, don't know whether there is a sufficient advantage over vacuum and centrifugal advance and complexity would probably be far greater for computer program most likely.

**uncabob** · 01-30-2016

Keith: Welcome to the forum. Best info you will find on Fuel Injection. The Crossfire system was originally used on the L83 engine in 82,83 and 84. The Corvette crossfire was on the 1982 and 1984 Corvettes. (There was no 1983 Corvette). I feel the crossfire was much maligned because of tuning difficulties. You should know injectors on the crossfire were not identical and were plumbed in series. The fuel was supplied to the first injector which used an accumulator and the excess fuel went on to the second injector which had the regulator. This was the reason for the mismatched injectors. The L83 Corvette engine in 82 was rated at 205 horsepower. The manifold is rather unusual and I understand some machining is required to fit up to a later block. The computer is very slow and I don't think you would find any up to date source. You could however use a later computer and plumb the TBs in parallel by using blocking plates instead of the accumulator and injector mounted regulator. You would need to regulate fuel pressure with an external regulator. My setup is as suggested above using a 1227747 ECM and treating the the separate TBs as a dual truck throttle body. I have higher volume injectors than the original and a RV cam. The horse power I can get is less than 300. You may get more fuel by using BBC injectors but there would be some machining. I also believe the cast iron heads may be a limiting factor. You are in the right forum for the info you're looking for. Good luck. Bob

**ScottP** · 01-30-2016

Great to see another Pontiac on its way to getting EFI! Mine is a 455 with a port intake manifold
from Professional Products being run from a 12200411 PCM. I swapped in a 4L80E at the same
time as the EFI conversion.

The dual-quad Offy setup will look great with the TBIs on top, and was something I seriously
considered before I got a great deal on the Professional Products kit. As others have alluded,
running dual TBI can be done with a GM ECM, but there are a few considerations. You can
run the injectors in series, which means both injectors on that driver see the same peak and
hold currents. You can also run them in parallel (this is what I've done in the past), which
requires the injector drivers inside the ECM to be upgraded and the current sense resistors
to be swapped out. I believe this is what Dynamic EFI does when you select the 4-injector
upgrade.

One thing you might want to track down soon if you're going to go the GM ECM route is a
distributor. The distributor used on '81 Pontiac 301 & 265 applications is a drop-in on your
400, and has all the correct interfaces/signals to feed a variety of C3 and P4 ECMs that were
used from the early 80's all the way up til '95. They're getting a bit scarce in the junkyards,
but make the swap to a GMECM on a Pontiac a bolt-in affair. The one you want is casting
number 1103453.

-Scott

**dave w** · 01-30-2016

Originally Posted by Keithnh

I used to be an electronics tech and think of this as a bit of a challenge. I wish I had a diagram with computer inputs and outputs to start with. Just helps me collect my thoughts as I am used to them. Would like to know what exactly the computer is saying to the tbi. Understand there are adjustable fuel pressure mechanisms that enable tuning but I don't believe they are computer controlled. So if the computer is just saying "squirt" and "stop squirting" to the injectors according to the sensors and the throttle position they will be delivering more fuel in between the "squirt and stop squirting" instructions at a higher fuel pressure. The computer makes it possible easily most likely to respond to its inputs thousands of times per second, probably far faster than an injector has the capability to react. Was wondering however how injectors alone could respond as accurately to changes as the multiple systems of a carb idle,primary,secondary,accelerator pump,power,choke without all the mechanisms ... will be interesting to see this project through and find out. It appears the computer is possibly modifying the spark advance in some applications, not sure if it needs to in my application, don't know whether there is a sufficient advantage over vacuum and centrifugal advance and complexity would probably be far greater for computer program most likely.

**Keithnh** · 01-30-2016

Wow , more great info ... will have to hunt a Pontiac 301 distributor ... now I have an excuse to go grab the whole engine that has been sitting on a shelf at a local junkyard with the factory turbo on it if its still there think they want 250$. That crank is supposed to have rolled fillets though the turbo setup was not exceptional. Will have to print out those 9 schematics and study them ... didn't find a legend for the abbreviations ... may be able to figure out with some brain burning :) Have to speed read my tbi book that's coming ... get my feet a little wetter :)

**Six_Shooter** · 01-30-2016

The park input on the '7747 does not negate the benefit, or need, of a VSS on the '7747. EVERY '7747 swap, or equipped vehicle I have worked on has ALWAYS benefitted from a VSS being used, and most other people have seen the same results.

Also the '7427 does indeed have a park input, it's just not a simple on and off single input. There's a set of 3 pins, that depending on which ones are grounded at any one time tells the PCM which gear is manually selected.

**lionelhutz** · 01-31-2016

In case you have missed it, there is a forum dedicated to bin files, definition files and wiring diagrams on this site. Just search for the ECM you want to use. Some appear multiple times due to having multiple applications and bin definitions.

http://www.gearhead-efi.com/Fuel-Inj...ams-Tuner-Info!

**dave w** · 01-31-2016

Originally Posted by Six_Shooter

Also the '7427 does indeed have a park input, it's just not a simple on and off single input. There's a set of 3 pins, that depending on which ones are grounded at any one time tells the PCM which gear is manually selected.

When the '7427 is "seeing" park input, would this default the '7427 to Near Idle Fuel / Spark tables? Would setting maximum TPS% for Near Idle to ZERO default the '7427 to use Off Idle Fuel / Spark tables when it "Sees" park input?

dave w

**Six_Shooter** · 01-31-2016

Not likely that simply, and that's not how the park input of the '7747 works anyway. The '7747 uses other variables to switch between the Idle tables and off idle tables, one of those parameters being vehicle speed.

I don't know why you continually want people to not use a VSS with the '7747 or say that it's not needed. you're the ONLY person I've ever seen that suggests that this is even a good idea. Even on a boat there can be a VSS signal, either from engine output speed (which would be tied very directly to RPM, obviously) or ouotput shaft speed to the prop, which depending on the boat could differ from the crank speed.

The fact of the matter is, claiming that the '7427 doesn't have a park input is just factually incorrect, it's just not as simple as grounding a single input.

**dave w** · 01-31-2016

Originally Posted by Six_Shooter

Not likely that simply, and that's not how the park input of the '7747 works anyway. The '7747 uses other variables to switch between the Idle tables and off idle tables, one of those parameters being vehicle speed.

I don't know why you continually want people to not use a VSS with the '7747 or say that it's not needed. you're the ONLY person I've ever seen that suggests that this is even a good idea. Even on a boat there can be a VSS signal, either from engine output speed (which would be tied very directly to RPM, obviously) or ouotput shaft speed to the prop, which depending on the boat could differ from the crank speed.

The fact of the matter is, claiming that the '7427 doesn't have a park input is just factually incorrect, it's just not as simple as grounding a single input.

It might appear that I advocate not using a VSS. Quite often members are looking for the absolute lowest cost / simplest / bare bones system. It's unfortunate that JTR has "back ordered" (for over a year now) their affordable 2K VSS ($85). http://www.jagsthatrun.com/Pages/Spe...eedometer.html

I welcome your Technical Write Up on connecting a Park input to a '7427.

dave w

**Keithnh** · 01-31-2016

ScottP was wondering how many injectors on your 455 Poncho and how does it run compared to a carb'd car? I know my 90 Z71 tbi seems like it stumbles if I do a quick to the mat stab ... something I used to test quadrajets I rebuilt with. Beyond the stumble it runs very nicely and buries the speedo quickly if I let it as long as the sensors are working and exhaust is tight. Is the fuel economy much different than a carb'd 455? The 6000lb p/u gets a solid 15 mpg with a computer tranny I believe. My 444 is a custom short stroke (4.040) 455 basically with a punched 400 block and modified 428 crank. Was planning on it being located in a 71 Formula 400 and being a summer cruiser and occasional strip attendee. Not sure I can afford the electronic transmission at this point, maybe down the road apiece. Was thinking I might gain an average of 5mpg or more with it. Would love to make the car a worker bee since my miles to work has decreased from 110 round trip each day to about 20 ... was thinking 20mpg avg (probably impossible or at least miraculous with my current thought process) and some serious weatherproofing. I got 15mpg with my 400 some years ago in a 64 gto with 3.23 rears and 780 Holley 3310. I also have a sbc project almost done that might make use of a single tb with 2 injectors on a GMPP RPM 2-plane manifold with 314 ci to feed. It also is short stroke (3.074) and meant for an expanded operating range to 7500 with fastburn heads. The donor engine is an 89 350 I have the entire electrical/sensor setup for untouched on my parts p/u.

**ScottP** · 02-01-2016

My 455 uses a port fuel injection manifold specifically for Pontiac engines, so there's a total of (8) injectors (one per intake port/runner).
The difference in driveability over my old Quadrajet is simply night and day. My carb was setup well and ran nicely, but the EFI setup has
simply transformed the car. Keep in mind, I went EFI and electronic trans at the same time, so some of the driveability improvement
also came from the 4L80E (was previously a TH400). I can't report on fuel economy improvements yet, mostly cause I've only had the
swap running for the last year, and in that time I didn't have a working speedo. As part of the 4L80E install, I lost the provision for my
stock cable driven speedo, so I didn't have a means to keep track of mileage for the season. I've since fixed that this winter with a
mechanical cable drive box from Dakota Digital, but won't be able to get mileage results til the spring.

BTW - can I infer from your screen name that you're somewhere in NH?

-Scott