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

wrongear wrote:with 5 volts applied to Techselect I have .017 volts on both sides of R12.

Check the resistance from the right side of R12 to TachSelect. It should be zero.

Yes, the resistance between the right side of R12 & Techselect is zero.

What is the resistance between the left leg of R12 and ground?

20 K ohms

This is weird, but I'm guessing you have a dead optoisolator.

"This is weird"

Does that mean that's it's checking normal & you don't see the problem. OR the trail is lost?

No, that means that you have a weird problem. And said weird problem appears to be a bad optoisolator.

optoisolator U3 replaced. No change.

Do you have continuity from R12 to the optoisolator?

Yes. From the left side of R12 to pin 1 (top left) of U3.

Ok. But running voltage through the optoisolator doesn't pull its output to ground?

Matt; I'm unsure what your asking me to do. Please re-phase your request. thanks

If you apply voltage (at least 5 volts) to the input to the optoisolator circuit (TachSelect) does the output of the optoisolator (at TSEL) go (from 5 volts) to ground (0 volts)?

I took 5VDC from the center post of U2 (vac manifold sensor). YES , TSEL goes to .09 volts. At the some time, I lost the IG light on the Stim & the center LED on the board lit & stayed on until power was removed.

So the answer is Yes; goes to 0.

Check if that makes it all the way to pin 14 on the U1 socket. Also, please post a copy of your current MSQ.

.2 ohms from TSEL to U1,14. With 5 V jumped to TSEL, I get zero volts at 14. With no voltage jumped, I get 5 VDC at pin 14 of U1.

wrongear wrote:.2 ohms from TSEL to U1,14. With 5 V jumped to TSEL, I get zero volts at 14. With no voltage jumped, I get 5 VDC at pin 14 of U1.

Did you mean TachSelect? If not, you've got some sort of REALLY weird problem somewhere between TSEL and the U1 socket.

Ya, I ment Tachselect.

So, what do you think Matt ???

Signal's making it to the socket. Try reloading firmware and see if that has any effect.