MicroSquirt.com read only forum (Jan.15,2018)

I am trying to convert a 96 Toyota Tacoma 2.7L 4cyl to spark only, no fuel yet. I am using the stock distributor and a 2 pole VR crank sensor. I am V3 MS1 using the VB921 to drive the coil direct.

So far I have spark and it tries to run but the stock ECU is shutting down fuel after just a few revolutions. I think it is looking for some feedback on the IGF line confirming the ignitor has delivered a spark signal to the coil. Now that the MS has taken those duties it no longer sees it and shuts down fuel delivery.

Does anyone know how I can fool the stock ecu into thinking it still has control of the spark?

Does anyone know what the stock ECU is looking for on the IGF line from the ignitor?

It's late and I will go at this tomorrow again. I might try hooking another coil to the ignitor and see if that fools it. Maybe I can come up with a resistor or something later.

While on this subject, do you think I can trigger the ignitor itself with MS? Can I do it thru the VB921?

Todd

I got this running just by 'T'-ing into the IGF line and using a 1K resistor before it reached the 'squirt IIRC. This shared the signal with the original ECU and all were happy. You may have to tweak the resistor size to get the right compromise, big as you can go without the MS losing signal.

The igniter is looking to charge a coil. You can add a coil for the igniter to play with and it will send the IGF back to the ECU. MSD makes a "tach adapter" specifically for this, but just using a spare coil with the output grounded should work also. The signal itself, if I recall, is about +5v with spikes to ground at each discharge. If you fake that with a tach output from the MS to the OEM ECU, that might work too.

Dr Hess - you sure its 5 with a drop to ground? I used it as a tach input signal to the MS and im 99% certain that on mine it was a 0-5v digital pulse upon spark.

I went ahead and installed another coil and this worked to fool the ignitor to send a signal to the stock ECU so it would not shut down the injectors. I'll try to come up with something cleaner later.

I scoped the IGF line and it is a 5v square wave. It looks to me it is going 5v on each firing of the coil. The 5v line does not change duration with engine speed but the 0v line does. (Just because I own a scope doesn't mean I know how to use it ).

The engine will now start with some difficulty but runs extremly bad. Hard to even keep running long enough to check timing. Backfires and misses. I will have to research this as I think others have had this problem with VB921 setups. Thanks for your help!

Todd

BTW, does anyone know for sure how many teeth the stock Toyota crank wheel has? I scoped it and I think I count 36-2 teeth. Does this sound correct? they are difficult to count on a DSO when you move the time width up far enough to get an entire revolution in the window.

It uses a VR sensor. Do you think this could be shared with MS to run the ignition?

Todd

Big Creek wrote:BTW, does anyone know for sure how many teeth the stock Toyota crank wheel has? I scoped it and I think I count 36-2 teeth. Does this sound correct? they are difficult to count on a DSO when you move the time width up far enough to get an entire revolution in the window.

It uses a VR sensor. Do you think this could be shared with MS to run the ignition?

Todd

32-2

ares650 wrote:

Big Creek wrote:BTW, does anyone know for sure how many teeth the stock Toyota crank wheel has? I scoped it and I think I count 36-2 teeth. Does this sound correct? they are difficult to count on a DSO when you move the time width up far enough to get an entire revolution in the window.

It uses a VR sensor. Do you think this could be shared with MS to run the ignition?

Todd

32-2

Do you mean 36-2?

Yes, I think you can get the crank wheel to count. That is what we have been doing.

yea....sorry 36-2

Big Creek wrote:I went ahead and installed another coil and this worked to fool the ignitor to send a signal to the stock ECU so it would not shut down the injectors. I'll try to come up with something cleaner later.


Todd

Why don't you drop the vb921 and use the factory ignitor to fire the coil? The factory ecu will still accept the igf signal from the ignitor irregardless of the fact the megasqirt is triggering igt or the factory ecu is triggering igt.

This works quite well since I have used megasquirt as kind of piggy back fuel controller that controls fuel and spark and the factory ecu is still present for idle control and other vehicle computers that it needs to communicate with.

Ryan