Keeping your Protec EFI with a DUI system

Disclaimer - I no longer have my 1994 Supra Comp with the Pro Boss 351 EFI. It has been replaced by a 1995 Supra Comp with the GT40. The 1994 was still running great, with the full Protec intact, when I sold it last year. And also, I know supposedly "EFI cant be kept without the ignition"

My brother and I took a Protec system and did some work identifying what is required from each module for the EFI to function. We hooked it up to an oscilloscope and determined the following.

Starting point was the thread on planet nautique containing this info
"7) The EFI module and the Pro-Tec module communicate with each other via the green/purple wire connected to terminal "C" of each module. No signal from the Pro-Tec module, then the injectors will NOT operate (check continuity of this wire). "

Both the ignition and the EFI module share the signal coming from the trigger connector terminal B. The shared wire is green/purple. This signal is a 4 volt (confirmed not 5 volt) signal that drops to near 0 each time a tooth on the trigger wheel goes past the hall effect sensor. From the oscilloscope we confirmed it's a 4 volt square wave. The trigger wheel has 8 teeth.

So, remove the ignition module and all the EFI module should be looking for is this 4 volt square wave.

The DUI distributor/coil puts out a 12 volt square wave from it's tachometer wire. This information was obtained from DUI. I don't know how this signal works as I don't have a DUI setup. Does it drop to 0 during each pulse and how many pulses per revolution?

I can't find the information but I recall reading somewhere that the EFI is looking for >300 rpm from the trigger to start firing the injectors.

It seems to my brother and I that a simple electronic device could be used to create a 4 volt square wave from the 12 volt square wave provided by the DUI. Feed this into the EFI module via terminal C and you should be able to have EFI without Protec ignition.

I'm the mechanical engineer and my brother is electrical, so I'll have to wait until my brother gets back to the USA to add what electronic device he had come up with. Just wanted to share what I've learned and get others thoughts.



Reference threads

- Protec conversion to DUI
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=34338&title=protec-ignition-swap

- Protec wiring diagram on first page
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=33526&PN=1&title=protec-ignition-replacement-question

- First thread I started on this topic
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=37481&title=pcm-protec-pro-boss-efi

0v would be my expectation from the tach wire in a conventional distributor ignition. You’ll get 8 pulses per revolution of the rotor (4 per revolution of the engine since it’s a 4stroke v8).

2001Sunsport wrote: I can't find the information but I recall reading somewhere that the EFI is looking for >300 ton from the trigger to start firing the injectors.

What does this mean? Or what's it supposed to say?

Sorry, was writing while on the plane, believe it autocorrected. It's supposed to be 300 rpm, I'll correct the other post.

I think it's unwritten site rule #7 that says if you bring up something like this and get people interested, you have to do the testing you're talking about

So...........get that EE brother of yours involved and see if this will work even if it's only a bench test

How's the new old transplanted Borg Warner treating you?

what kinda of holley injector upgrade was done for efi? is that a SEFI or Batch fire? Im guessing still speed density back then. I would have done FAST efi when I took my protech off but bridge I didn't want to jump off just yet and splice a bunch.

One bit of advice might be to do some reading on marine carburetors if you end up going with a carburetor

2001 Sunsport is around fairly often so maybe he'll see this and update it.

Otherwise I think it's worth a shot

And..............make sure you update with your results

So today I installed the DUI. I then used a voltage diving circuit (2 resistors one through ground one through the 12v wire) going into the green purple wire going into the efi box. I tried starting it and was getting no spark. I assumed the problem was a lack of 10.5 v at the distributor. I charged up the battery and even ran a second battery with voltage just going to the 12v side of coil. Still no spark. Then I tried unplugging the tach wire from the distributor and the engine started and ran for a few seconds. It turns out the with the tach wire attached, I’m getting the fuel injectors firing, but no spark. When the tach wire is disconnected I get spark, but no fuel.

I’m assuming this is because the tach wire is essentially connected to ground with just a resistor between them as that’s how my voltage dividing circuit work. I am not an electrical guy, so I need to figure out if there’s such a thing as a 1 way valve for electrical current. If that’s the case or I figure out a different way to reduce the voltage, I might be in business.

Well Google didn't lie to ya".

That's the function of a diode.

There are a large number of different sizes so you should have some idea of the current going through the wire you're going to install it in when you go to get the diode.

If in doubt go big

The diode wasn’t backwards was it (obviously they are directional)?

The diode was the correct direction.

It runs! Without a diode and with just some different resistors. I have a hand drawn diagram, just need to figure out how to post pics

Mikewolf wrote: It runs! Without a diode and with just some different resistors. I have a hand drawn diagram, just need to figure out how to post pics

CCF, making it possible to keep older boats running, one solution at a time!

Awesome!!! Glad we could prove PCM otherwise. They were the first ones to tell me this would be impossible.

Mikewolf wrote: It runs! Without a diode and with just some different resistors. I have a hand drawn diagram, just need to figure out how to post pics

I tried 10k and 5k and also 8.2 and 4.7 ohm

With the 10k and 5k, there was no signal getting to the ecu. With the 8.2 and 4.7 ohm, the ecu was getting signal, but the distributor was being grounded out.