Thread: How Crossfire TPI really works

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This is a series of emails between me and someone at speedscenewiring about how TPI works. I inverted the order of the messages so that you can read it top down.

Does anyone know the answer to my original question?

Can anyone translate his response into english for me?
Some days it feels like I grabbed the coil wire once too often and fried the last 2 brain cells...

Help!
Mark

-----Original Message-----
From: Mark Leigh Hein [mailto:mlhein@sbcglobal.net]
Sent: Thursday, June 30, 2005 5:45 PM
To: Info@speedscenewiring.com
Subject: How group fire fuel injection works


To Whom It May Concern:

I’m trying to educate myself about TPI, and I just keep getting more confused.

http://www.speedscenewiring.com/fuelinjection.html

Your web page says:

"The firing order of the common V8 TPI is the same with the TBI fuel injection / crossfire fuel injection which is 18436572 rotating clock wise on the distributor. On all Speed Scene Wiring fuel injection wire harnesses, the right side (passenger ) intake manifold injector bank 2, 4, 6, 8, evens will have a Green wire controlling the pulsed ground to the injector. The left side of the intake (driver) injector bank 1, 3, 5, 7 odds, will have a Blue wire controlling the pulsed grounding of the injector. In this form of fuel injection there are only two (2) drivers that fire the odds and evens."

And:

"The two drivers Blue and Green are again batch fire and fire the fuel injection system in batch intervals left right left right, bank one bank two, so on so forth."

If all this is so, it seems that the injectors would be firing at the wrong time, since the firing order is OEEOEOOE (184366572) and the banks would be firing OEOEOEOE..

1 8 4 3 6 5 7 2

O E E O E O O E

O E O E O E O E

1 2 3 4 5 6 7 8

Is the thing so sloppy, firing at closed valves anyway, that it doesn’t matter? Does the controller actually fire OEEOEOOE? Or am I just confused?

Your assistance would be greatly appreciated.

Mark.

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zac <zac@speedscenewiring.com> wrote:

1843

6572

You will see the adjacent cylinder configuration taunts the firing order, just split in 2, thus the reason that batch fire should really be considered bank fire. But in truth, the computer is only receiving a hi and a low signal from the distributor, a 4x and an 8x signal, so there was no way to get any more precision at that time. Once the crank shaft sensor was added to the modern engine as we know, it became economical. You are correct in the theory of sloppiness, this series of computer is just dumping fuel. Most of the inaccuracy in fuel usage, can be corrected on a dyno or a rough tune.

Enjoy
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-----Original Message-----
From: Mark Hein [mailto:mlhein@sbcglobal.net]
Sent: Tuesday, July 05, 2005 7:54 PM
To: zac
Subject: RE: How group fire fuel injection works

Does your system actually fire Even-Odd-Even-Odd or not?

If it does, it would probably work better if you had the blue wire hooked up to 1,4,6,7 and the green wire hooked up to 2,3,5,8. At least then it would be firing on one open intake valve every time.

Mark

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We wire the system factory, due to engineering and liability of damage, we usually never stray from factory schematic suggestion. Since this system was designed as batch fire, all the injectors on the right 2,4,6,8 fire all at once and the left the same way, if you mix it up you may or may not have lean issue, firing order is dependent on camshaft design. The idea you have is essentially how sequential fuel injection works, this system fires in batches, you may find it uses the same amount of fuel. Try it out and let us know what you come up with.

In reading about fuel injection, I remember some info about batch fire vs. sequential fire injectors. The batch fire stuff (including Tuned Port Injection) was far superior to the Throttle Body Injection (per Fuel Injection Specialties web page, the improvement was on the order of 30% in torque).

The sequential injection is theoretically better since the timing of the pulse can be tailored for each port.

For your question (as I think you are asking), the batch fire sequence really doesnt matter because the intake air flow is not coming to a stop....it is continuous, especially at higher rpm. If the injected fuel is atomized, it mixes with the air fairly well.... certainly better than it does in a carburetor.

When the OBDII standard arrived with all its additional checking and the new emissions standards, sequential injection offered a tad more precise control.....mainly for emissions.

So.....to answer your question.....it doesnt matter. AND, they chose to fire banks because the wiring was mucho simplified as opposed to having two circuits on each bank....saved them a few pesos.