Motronic Injector Signal Testing

[rusnak]

Feel for the second click in the dme relay (you changed it, right?), indicating that the dme sees the reference signal from the crankshaft sensor.

[vreference]

Originally Posted by rusnak

Feel for the second click in the dme relay (you changed it, right?), indicating that the dme sees the reference signal from the crankshaft sensor.

I've not replaced the relay since it runs the fuel pump and DME very reliably (at least when not cranking... I've decided to take a closer look at power and ground today since I haven't done that lately) I did feel for a second click upon cranking and realized the clicking I'm hearing (that I thought was coming from the Ignition) is actually coming from the relay. Click once for every trigger of the reference sensor; although it's as though it's momentarily losing signal; a test light on the pump output stays lit despite the clicking. (I can never hear the pump running while cranking but I think that's more about how loud the starter is - the fuel rail is always pressurized after cranking.)

[Tippy]

This crap will drive you batty, hunh?

I can't wait to hear what you find.

[rusnak]

There is a reason for my question. You should only feel two clicks. Once when turning the key on, and a second while cranking. The second indicates that the DME is getting a signal from the crank position sensor.

I would get some starting fluid in aerosol form, and try it next. It sounds like you are getting spark (did you pull a spark plug and do a spark test)? It sounds like there is no reason for it not to run.

Please just put away the 'scope. It's time to get to more basic things. If it does not start with ether, then I would try it again with the cht grounded to eliminate that.

[vreference]

Well it was indeed very simple. I've used the #1 intake runner as a ground for lots of stuff but apparently not a big enough load to make it fail.

Bad #1 Runner intake ground.

*edit, let me add that I lovingly serviced that ground point and had it perfectly clean with dialectric grease even. It's the intake itself that wasn't grounded sufficiently. It was painted and I never cleaned anything off for any of the studs to ground too.

[Tippy]

So it runs fine?

[vreference]

Originally Posted by Tippy

So it runs fine?

Yep. Lot of wasted effort but I'm quite a bit more familiar with Motronic now I suppose. I guess if I had been using a better meter I might have been tipped off, I was showing 0 ohms. Not sure how much amperage is being pulled through that intake... enough to float the ground I had anyway.

[rusnak]

Well that's just weird then...