How about this:

Two ECU's (7747)
One MAIN harness
One "partial" harness
Two identical PROMs

Now, can you just tie/share the sensor wires of the ECU's together (same-wire-to-same-wire?) so that you have, essentially, the two ECU's just to drive the injectors:

- (1) TPS Sensor: Connect the (3) wires together so the feed/ground/data are shared and identical to both ECUs

- (1) O2 sensor, shared data ok with (2) feeds???

- (1) Temp sensor, shared wires

- (1) MAP sensor, shared wires

- (1) Knock sensor, shared wires

- (2) IAC motors, run by individual ECUs (or (1) ECU???)


I don't know if this is possible as I am not that electrically inclined. If possible, it would be a rather inexpensive way to do it, no???

 

Probably much better to just use the injector driver from the second ECM, then it does not even have to be the same type. You could probably get a faulty ECM for free. As long as the injector driver is working it will do.

Use the internal injector driver signal from the first ECM and connect that signal to the second ECM injector driver too. (the original signal wire in the second ECM must be cut first)

With a simple interface you could probably use the injector cable as source too. Then you could leave the first ECM compleatly stock.

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Jonas Bylund


[This message has been edited by JoBy (edited November 06, 2001).]

 

Joby, that's what I plan on doing when I get to money for a larger TB unit.
The signal is digital and so you can just tap into it and the injector drivers will work no problem BUT you need to build a powersupply, I don't know for sure what the pinouts are for the injector drivers but it isn't just an "in", +12v and ground, there are some other pins I'm not exactly sure about.
I wouldn't go as far as to hookup 2 ecms. Each ecm would look for things like vacuum drop, VATS!, other crap that would be kind of messy and a PITA to get around. I'm sure it could be done but I think it would take less time to figure out the injector drivers from a spare ecm and hook em up.

 

That's my point. I don't/didn't want to cut/chop inside/outside an ECU and/or use non-OEM parts for replacement/breakage purposes. I thought that the (parts of the ) harnesses could simply be spliced, two exact BIN PROMS made and the whole thing would work flawlessly... Is there a reason it won't work the way I suggested??? Won't cost more than a couple hundred bucks...

 

Sounds like a fun project. But which ECM do you scan from?

 

It shouldn't matter which ECU to scan from. They'll essesntially be doing the exact same thing(s) together at all times, or taht is my thought/understanding. Main point is that if the sensor data is the same and the BIN is the same, they should act the same way, I guess??? Cheap cheap cheap

 

If you connect two ECM's to one sensor it will not work.
One example ... To measure a recestive sensor the ECM could drive a current to the sensor and measure the voltage. If you connect two ECM's paralell the the current will be doubled, and the voltage reading will be wrong. If the ECM works the other way the result will be the same. If you heve a fixed voltage over the sensor then the two ECM's will share the current ... false reading again!

TPS might work
O2 might work

Temp - not
MAP - probably not
Knock sensor - not

Even if you get the sensor problems worked out I still don't think that it is possible to get them to run the same. The programs will not be in sync, so they will sample at differnt times. The internal A/D converters will not be identical. One ECM might think that it is a tiny bit rich, the other that it is a tiny bit lean. One starts to increase the injector pulse the other will decrease. Then you will end up with some cylinders running very rich, some very lean, and the O2 samples from the exhaust mix thinks that all is well ...


The easiest thing would be to have one stock ECM. The splice into the injector wires coming from the ECM and use that signal to drive an extra injector driver. A second ECM could be modified to act as a slave injector driver. Then you know that all the injectors use the same pulse ...


------------------
Jonas Bylund

 

As long as you were doing all this anyways, you could remove the injector drivers from both ECMs and combine them into their own external array. Then you could have a switch between one ECM set up with a stock or mild chip to run only one tbi for economy and the hot ECM could run both ?? You guys got me interested in this now...

 

I'm with you now, JoBy. thx

 

BTW, if you wanted to run 2 ecms you could do it pretty easy.
I see where you're coming from Joby but listen to this solution and tell me what you think.
2 TB units have 2 TPS sensors, problem one solved. 2 TB units can have 2 map sensor ports, problem solved. 2 TB units have 2 IACs, 2 ecms with IAC drivers, problem solved. 2 o2 sensors, one for each header, 2 ecms, problem solved. Knock sensor is the tuff one but even that isn't too hard since only one needs to control the ESC. You can just hookup 1 knock sensor and leave it since the ecm only adjusts timing if knock is detected (not sure about this).
The obvious work around would be the extra work to install all the extra sensor and wires. You just need to think of the v8 as being 2 inline 4 engines sharing a wetflow manifold! I'm pretty sure I could get that to work but I would just not want to run the extra wires.
Oh yeah, about the extra CTS, no problem, there are multiple holes for 2 CTS sensors.
lol, if you do ALL that you'd have a pretty original setup. I would only do it if I had all those extra parts. Running the wire is no problem for me, the hard part would be controlling the IAC but I think that might not be as tuff as it sounds.

 

If you can read a wiring diagram and make a printed circuit bored, I can send you the plans on how I made my duel TBI setup for the 427 I had. The circuit bored I'm talking about is nothing but a switching amplifier that allows one computer to run all 4 injectors. Also, you only need one TPS, but I had to do some more custom work to use both IAC's, and it would not idle without both. One's not enough.
I did have an idea though. If you removed one IAC from one TBI unit and replaced it with some sort of a screw, you might be able to get away with just one IAC.

E-mail me with any questions joe69_10@hotmail.com

Joe

 

One MAP sensor also.

 

chalk me up another reason to build my 2.25" unit.

I made the suggestion to try this a while back and it got shot down in like 4 posts, whats going on here.

I think people are learning to love tbi, and therefor learning about it more. Good.

 

Not shooting anyone down. The thought of two TBI units on a big manifold just sounds good and HAS to look good. Running good is the only other MAJOR consideration.

 

Hi Joby. What going on w/ the CFI forum?

Fast broker, let me get this straight. You want to do all this just so you can get the power and looks of a "dual quad"?

If so why not just get a dual quad intake, throw in two 454 injectors for more fuel flow. One in the front TB and one in the rear. Then just drive the two 454 injectors and adjust FP accordingly.

 

Got this info from Ken:

Go to http://www.crossfire.webhop.net/cfforum and sign up. The old board is
GONE.



------------------
Jonas Bylund

 

Just some "mocking up" that I've done - it really hasn't gone any further than this...

That's an Edelbrock Dual Carb intake that I got off of Ebay for $80.

Steve


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Steve's Trans Am Temple

 

Geesh. I was just thinking out loud. I thought it MIGHT have been possible to make dual TIB work easily with two ECUs and some splicing/brains. Sounds like the EE smart people here think that is not the case. Idea done for me...

MPFI conversion is probably the way I will go, with a 454 TB for air control.

 

I HAD SEEN THIS DONE BEFORE.IF YOU CAN FIND A POST THAT TAZ HAS RESPONDED TO,IT WAS IN HIS SIGNATURE AT THE END.HOLLEY OR OFFY,HAD A KIT THAT YOU COULD BUY AND IT ALL RAN OFF 1 ECM.THEY SPLICED THE WIRE TO THE TPS AND RAN AN AFPR ON THE SECOND UNIT.THEY SAID YOU COULDN'T USE OEM HARDWARE BECAUSE THE INJECTOR'S MAY NOT FLOW THE SAME,BUT I THINK YOU CAN.LATER

------------------
"Let's get to it,well let's do it!"

 

Grumpy (one of the more knowledgeable people in the ECM/EFI arena) has tried running four injectors off of one ECM before and it gets flaky at 3000rpm. Apparently there is no way around using another set of drivers for the second set of injectors - or rather, it's the easiest way to get things done.

Steve

 

Edelbrocks MPFI system simply uses the drivers in the OEM ECU, each driver running 4 injectors run in parallel. OEM TBI injectors are about 2ohm each in resistance and the injectors in the Edelbrock MPFI kit are 16ohms. So, with four injectors run in parallel, they act like a single 4ohm injector/resistance, which is more than an OEM TBI, double the resistance, to be exact... I am told the GM ECU tolerates this MPFI operation very well up through 6500rpm without a problem whatsoever. On a test bench AND in vehicles, themselves.

Sounds to me like MPFI is in my future. Need a 454 TB for air control... Steve, you out there?

Only difference I will have is that my injectors are 28pph while the Edelbrock MPFI conversion injectors are 19pph, I believe. BPW change only?????? 28pph injectors should be enough to support 450hp easily. so, HotCam, FastBurn heads, 1.6 rockers and Weiand Vortec Single-plane MPFI conversion should get me 400hp... I sense a dyno workout in the future. As usual, carb first with the MPFI manifold to get things (A/F ratio/spark) close, then EFI!



[This message has been edited by fast_broker (edited November 09, 2001).]

 

fastb, if you look at 4 ohm and 2 ohms, the 4 ohm is less of a load on the ecm. If you have to, think of it in car stereo systems. A sub with an 8 or 4 ohm load is "easy" to drive. If you load the amp with 2 or even 1 ohm you can easily destroy the amps.
A sub is a driver, just like injectors, the ecm is an amp.
TBI has one advantage over TPI ecms, we have 2 drivers. Each is able to drive a 2ohm injector where as TPI can only drive 2ohm total (all 8 batch fire, once a rev). TBI fires twice a rev, TBI injectors are also for peak and hold, not saturated. peak and hold injectors are harder to drive and require more power, this is why they get flaky over 3000rpm (when 4 injectors on 2 drivers), they see only half the volts, it's simple physics.
Hopefully I'll be able to get my hands on a bunch of peak and hold injector driver ICs from school. I talked to a guy that works with the school project cars like the electric F1 and the honda autocross car etc.

 

I am rather excited about getting MPFI working with the 7747 ECU and 454 TB. Should be neat!!! the WINALDL program will help me a lot, as will the Edelbrock MPFI BIN. But, the MPFI BIN is for crappy TBI OEM heads, I was warned, and will need some spark/fuel changes but the BIN will get me started/operational...

Later, maybe, I could rig the (normally "off") TB injectors with a driver to supplement nitrous input? That'd be cool.

[This message has been edited by fast_broker (edited November 09, 2001).]

 

HOLLY !!!!!!!!!!!!!! I was just thinking about this idea too!!!!!!!, i just posted the question on nethirdgen. Damn, thats increadible, i was looking at the edelbrock in summit catolog, wow!

[This message has been edited by snflupigus (edited November 11, 2001).]

 

scauffiel
Instead of the inline carb manifold I was thinking about the Offy cross ram thats similar to the old Z28 cross ram.

Build a new lid and mount 2 two barrel TBIs.
Not being a computer wiz I considered running two complete 7747 ecms. each one running a tbi with O2 sensor in opposite header. That sure would make for a large bundle of wires.

 

Well that would work as well, it just depends on how much you're willing to spend. I personally wouldn't run two separate computers - too much hassle. Run two extra injector drivers, halve the signal going to the IAC's so they both open and close the same amount, run a single TPS on one of the TBI units, halve the fuel going to the injectors... and then learn how to tune said animal via programming. If you're set on being able to run two (or more) separate programs, then burn separate chips that you can swap in whenever you feel like a change...

That's the part that will make or break this type of project - the programming/tuning. Until I get another daily driver, I can't even consider having my car down for the amount of time I could see this taking.

Of course, once that is worked out, you could make yourself a nice big bonnet and turbocharge the whole shebang...

Steve

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Steve's Trans Am Temple

 

heres one to keep this one going. im tired and this is when i get those crazy ideas.

imagine.

2 sbc tbi's.
2 of the largest injectors you can find.
stick one in each tbi, and two other junk injectors in the other side of each pod.
using the computer etc you have now, run 2 injectors with 4 barrels. one injector firing on and oposite side of the one in the other tbi. now crank the pressure, use a vafrp on both, split the iac, and have one tps.

ok these tbis are gona have to be on a tunnel ram so the fuel distribution isnt screwed up by having only one injector firing in each of the tbis. but that way you tune and program the chip normally, and dont have to mess with the wiring etc, except for the iac. I would actually only run one iac, and drill holes in the blades of the other tbi to let in the air for that one, and plug that iac. i think it would work fine.

there is your cheap fix, let me know what you think.

 

why can't you wire in resitors in paralel to each injector the wire 2 injectors per drive with resitors on a series arivving back at the correct ohm rating?

 

9177, that's a good question, but I have a feeling the answer cannot be that simple. It would be nice, though.

[This message has been edited by fast_broker (edited November 13, 2001).]

 

You can do that and fool the ECM that the injector has the right ohm. The problem is that the injector will not get enough power.

------------------
Jonas Bylund

 

Aaah, always a catch...

 

Hell, why not make a triple TBI using the 6-pack intake? I'm not sure the TBI's would all fit, though. Linkage could be tricky to setup, too. What would really be cool is a quad-TBI set-up, then you could probably use the bin from the edelbrock multiport chip as a template for programming, and could use smaller injectors. Geez, imagine all the fuel line that you would have to use.

 

scauffiel what manifold is that in the pic? Will that one fit a 305 or are we talking about a 350?

 

Jim, I'm pretty sure the 350 and 305 manifolds are the same size. If it fits one it fits both.

 

ive heard this wouldnt work, but do to my custom chip and need to flow alot more air than stock(the thing soulds like a friking vacume) i had to opt of a tpi computer. so maby since it can run 8 injectors you can run 2 tbi's of the some unit, just by taping into the wires with new ones. but then again iwas told it wouldnt work

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90 RS 305 tbi, 4 3/4" cowl Hood, Edelbrock TES headers, Flowmaster exhaust, Crane roller cam, comp roller rockers, vortec heads/intake, ported tbi, w/new injectors, MSD probillet Distributer/ coil, 1 inch tbi spacer, air foil, 14x4 k&n flat base air cleaner, Rebuilt 700r4 w/ B&M shift kit, B&M Megashifter, 3.23 posi, 2 12 RF's with mtx amp, top of line alpine cd player, soon to have 90-91 gfx, z-28 wing, new paintjob, rims, and all new lowered suspension.

 

good lord this is like reading some of my friggin engineering mechanics text books..i have to read each post like 4 times to get the idea...

but, this is interesting...

-brian

------------------
1991 Camaro RS
GMPP 350 HO crate engine - 454 TBI, MSD ignition, SLP exhaust, everything is new
700R4 - 2,400 stall converter, vette servo, shift kit
My car's webpage - z28boy.cz28.com
President - Central New York F-Body Association
Email - z28boy@twcny.rr.com
AIM - "Z28 Boy"

 

btw, there is a company on the net that makes an adapter for tpi injectors to mount above a throttle body unit. that would solve all your problems, batch fire 4 of em, with the right ecm, skip the rest of em, and run a high pressure. Then all you have to worry about is tuning, and finding enough money in your couch to afford 50pph tpi style injectors.

 

You're talking about that Accell unit right? If so, I wonder how the injectors would react to being fired twice as frequently. Just wire the TBI inj drivers together so that the TPI injectors batch fire but twice a revolution. I bet it would get flaky after a certain RPM. Besides, the cost of the Accell unit is WAY too much considering you can just get the edelbrock EFI kit or some injectors and fuel rail. Make your own for the price!

 

Keep this discussion going! PLEASE!

------------------
Cheston Phillips
'96 BBB Impala SS "ADIOSS" & '91 white Caprice 'n0n 9c1' w/L03
GM_TBI list

 

Before jumping onto the more is better routine, how about figuring out what EXACTLY you want to do.

Is about the cool look?
If about HP what level do you want to run?.

It's alot easier to define your goals and then look how to acheive them.

You can get to 350 Honest HP, with a Weiand 7525 and a BBC Throttle body. 350 dun right is a fun ride, since with much more then that you over whelm the suspenion anyway, without lots of work. Also, on the street the tracion isn't as great as at the strip, so there is alot about what the chassis will handle Correctly.

You can tear the drivers out of one ecm and add them to another, so long as you have enough heat sink area (BTW, and ecm can get flaky at over 130dF operating temps).

Anything you do to drop an injectors operating voltage, just screws it's operation up. If anything you want to raise it's operating voltage (on my own car, I raise the charging voltage to 14.8 at WOT). It helps both the ignition (alot), the injectors response time, and fuel pump output.

Going with multipul TBs is also going to mean all the Acclerator Enrichment stuff will need work. The idea of two throttle bodies from a pair of 180 HP engines supporting 360 is correct, but remember, the wet flow area is 1/2 of what two 180 HP engines is.

Also, the IAC stuff will be totally wrong. You can run with just one IAC if sharing a plenum for two throttle bodies, but on a dual 4 manifold you'll need to use both. If you look at the IACs from a Xcross you'll see the difference in Pintles.

Can it be done,
Certainly.
The other questions are why?.
and at what lenghts are you willing to go to get it CORRECT.
Can you tune one?. It takes alot of work to understand the IAC strategies, and AE stuff. It's nothing you going go get right on a TBI in just a few attempts.

If your going for HP, and High RPM, then you might as well go with a SD port type of set up. The TBI's basic strategies are for truck applications (yes, they were used in cars, but based on truck stuff).

To get the most out of this also means using a 8746 with the IAT.

The higher the level of tune for the street the more sophistication you need!!. It's not the opposite, unless you like buying lots of gas and tuneup parts.

Cheers

 

Oy! The mighty Bruce has spoken! If there is a guy that knows his ****, it's Bruce! This is why I say, until I get another daily driver there is no way I can learn to program/tune said beast.

Steve

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Steve's Trans Am Temple

 

well it was fun while it was hypothetical .

anything can be done, i just enjoy talking about it when i cant do it right now.

 

Here's a thought. I've seen several times mentioned the ECU is designed for only 2 injectors, not four. Well, i've been doing research for the laste 2 weeks ever since getting my car and if i remember correctly the Haltech comp has drivers for four injectors... wouldn't that work?

------------------
Hondas get all the girls.
Camaro's get all the women.

'89 Camaro RS T-top L03, no mods.... yet.

 

haltech = $

 

Yeah, my original idea/point was to make it cheap and real easy to get parts with no modifications of anything so you could replace failed parts anywhere/anytime. Got shot down, I guess.

 

OK, this may seem kinda ghetto, but why not just use one ECM and splice into the injector wires so that you are firing one injector on each TB at the same time? You would only need one IAC valve, right? Just block off the second one. You would only need a TPS on the first TB as the two throttle blades would be linked and should be at the same position at all times. Basically, I'm thinking one fully sensored TB linked to one with only the injectors wired. This is how I would speculate that it could be do. Anyone know if I'm way off base or not?

 

You are thinking right. Why complicate things .... Only one problem, the ECM's injector driver doed not have the power to drive two more injectors when you get the RPM's up. That is why you need an extra injector driver. The extra driver should tap into the existing wires to the ECM driven injectors so they all fire at the same time with the same pulse length.

 

Cool! I might just do this mod! Yeah, I agree, the simpler the better.

 

i am learning to love TBI actually...i was really really close to sticking a carb on my car awhile back...definetly decided against that...running 2 TBI units would be badass...tho my 305 will never see the need for that much fuel...i was thinking about swapping in a holley TBI after getting a new cam and intake...would probably get things moving...if i ever needed a ton of fuel dual holley TBIs would probably run nice before i started checking out this board i was on camaroz28 and getting bashed for having TBI...not im kinda glad i have it...yeah its on a crappy motor but it seems like TBI is WAY easier to mess with than TPI and much more reliable than a carb...

 

I'm starting to respect my TBI more and more. However, my TPI 305 was awesome! And, despite what most people think, they aren't that hard to tune. I had an '85 Z28 with the pre-peanut cam, MSD-6A, Accel Super coil, trans cooler, Flowmaster cat back and Random tech high flow cat. After removing the A/C and smog stuff, adjusting the fuel pressure, and playing with the timing, that car flew! I got it to run smooth as glass about a month before I had to sell it. If I can get the same (or better) performance from my TBI, I'll be a happy camper!