I read somewhere that tpi is supposed to be batch fire, it fires the injectors a little on one bank of injectors while the opposite side valves are openining and when the valves are about to open on the side that is firing the injectors fire the rest of the needed fuel. Is this true?? Would sequential port fuel injection be that much better if it is? Would it make the car any faster?? I thought spfi was better. Thanks for any info.

 

Yes, its batch fire but it doesnt work like that, it fires once, whether or not valves are open or closed. Alot of the time the fuel sits there before the valve opens up.

Sequential is better, but not enough to make any considerable power difference. Usually they get a little better mileage and low rpm driveability, but thats about it.

 

hey thanks a lot max. Also so i know exactly what is going on. when you say they fire at once do all eight injectors fire at the same time, and when the last cylinder has fired they all fire again. Just trying to have an exact understanding of what is going on.

 

it fires 4 on one side of engine and 4 on the other side. THat is what I was told and made sense to me.

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89 Iroc 350 TPI,
Forged pistions
Comp roller Cam .510 lift 230dur
Flowmaster exhaust
Dart Iron Eagle heads 200cc runners 64cc chambers
MINI RAM SOON!!!!!
stock TPI for now 24# inj
87 Trans Am GTA 350 TPI
had engine fire hope to get running soon
Flowmaster exhaust

 

According to computer experts on this board, they are wired together inside the ecm. One of these days I'll check it again and see but I seem to remember alternating flashing lights when me and a friend were diagnosing a car years ago...

 

Madmax is right. They fire all together.

But you have to understand the dynamics of a moving column of air to understand that just because the injector fired, that the gas hasn't hit the back of the intake valve.

It is constantly firing while the column is constantly moving (accelerating and decelerating) in "pulses or waves". So the fuel is actually very well mixed. Much better than a wet intake.

When you note the "injector pulse width", this it the amount of time the injector fired during one revolution of the engine. That is why there is a limit on how short of pulse width you go until you encounter driveability problems. Somewhere around .9 ms is the shortest you can go. This is becuase the actual "pulses" are very close to .1 which is the close to the smallest measure of time available to fire the injector from opening to closing.

There is minimal HP gain from Sequential when compared to Batch Fire. The biggest advantage of Sequential is extra fuel economy and even lower emissions.

The key to fuel injectors is to get a fuel injector of the right size so that it does not exceed 80% Duty Cycle @ WOT, yet does not require too short of a pulse width @ idle.

 

I can verify what Glenn and madmax are saying...the ECM circuit show's only one Quaddriver...going to two fuses in parallel to each bank of injectors.

 

There is another reason that small pulsewidths result in poor driveability and idle. I read an engineering report from Bosch regarding this subject and their injectors. At very small pulsewidths, the fuel exiting the pintle does not have time to stabilize into a nice atomized spray pattern. In addition if you look at the data for flow volume, the consistancy falls off quite noticeably at low pulsewidths. So from the engines point of view, it is getting poor atomization and an inconsistent amount of fuel from one injector opening to the next.

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Dave Zelinka