I know all the books say that all even and odd cylinders fire from the ECM. Does it mater if the front 4 and back 4 cylinders are wired together, and what would be the effects of this? Do all 8 fire together or 1 set of 4 and then the other?

 

i BELIEVE that 4 fire then the opposite bank of 4 fires

and judging by the schematics i have, it looks like they are wired in 2 groups of 4 like you mentioned

 

From what i have gathered from people who have actually checked and dissassembled the TPI ECMS, there is only 1 injector driver in it. And considering we don't have cam/crank sensors on our car, there would be no rhyme or reason for the banks to fire independently anyway

 

If you look at the GM wiring diagrams, they show that once the two banks enter the ECM, they are tied together, not to mention what Ed said, there is no way for the ECM to time which bank needs to fire next.

 

wow, thanx Ed, you answered one of my main questions on how sequential fire systems differeniate from cylinder to cylinder

(and i didnt even have to ask )

 

they fire bank to bank

 

The banks may be seperate outside of the ECM, but once inside the ECM, they are tied together. All 8 injectors fire at the same time.

 

You could wire all 8 to the same set of 2 wires, it wont make any difference. I can say I have seen the banks fire alternately timewise though, on the only car Ive ever seen it checked. If it had to do with grounding or wire length, I dont know, but both were not firing at exactly the same time.

 

If that was the case, it was not on purpose. There is no way the ECM would know which bank it needed to fire. There is a digital signal (square wave) sent to the ECM to let it know that the engine is running, and how fast (Reference signal, circuit 430). All it does is pulse on and off with varying speed in relation to engine speed. It gives no indication whatsoever as to which bank needs firing next. And even if it wanted to simply just alternate the banks back and forth, it would quickly loose synch fast as the cylinders do not fire in alternating banks. The firing order is 1-8-4-3-6-5-7-2. So the injectors would have to fire: Left bank, right bank, right bank, left bank, right bank, left bank, left bank, right bank.

 

Exactly. The right and left banks were not firing at the same time.

 

Yep, clear as mud! I have a digital multimeter. When I get the time, I'll connect it between the 2 wires at the ECM and check to see if they fire together.

 

Definitely post your results. Everyone says they are wired up the same and off the same driver, and so they must fire at the same time. I've seen different with my own two eyes, so if your results vary from mine...

 

Guys, when Corvette went speed density in 1990 it also went to sequential fire I believe. This would be 1 injector at a time. Did the F-bodies also do this? Something to consider maybe.

 

Nope, the only difference was that the 1990-1992 Corvette ECM part # 1227727 was the same as the 127730 except it was designed to go under the hood. Sequential firing did't start until the late 92's went to the LT1 intake.

 

vettes didnt get SFI until 94

92-93 LT1's were still batch fire

 

Whoops my bad, 1991tealRSt-topGuy, has it right. 1994 was the first sequential for vettes. I got the LT5 mixed up in my head for the ZR1, that was SFI in 1990. Should of pulled the book out before opening my mouth.

 

i didnt need the book

heh, i wanted a vette since i was 12 and i have countless books on them

 

The 1227165 (and clones) uses a single unijunction transistor (Q1) to simultaneously operate both banks of injectors once per engine revolution. The injector output is a sinking output, in that the load is powered from a bus and the circuit is completed to ground via the transistor. The fact that each bank of injectors is powered from a separate fuse is what generally starts the confusion. they are still connected at teh harness before pin D15 at the ECM and switched together. I'm not positive that all other ThirdGen TPI ECMs operate in this manner, but the TBI engines use teh same scheme. The 1227730 and 1227749 have separate output connections at the ECM (D6 and C13) but join those outputs internally to be operated by a single transistor (Q2) in the same manner.

I used to get all screwed up on that one, too. Then again, I'm a dope sometimes....probably now, too.

 

Thanks VADER, that answers my original question. We can close this sucker now and end all the fun.