Hi All,

I had something weird happen yesterday and as I start trouble shooting I wanted to get your thoughts.

68 coupe. 496, Holley Sniper EFI, all new wiring harnesses, and Tremec 5speed. Been going for 2 years now except for the EFI which was installed almost a year ago (1000 miles or so).

Yesterday I started it and warmed it up. Cold day (42 degrees) which I don’t usually drive in but it was a beautiful sunny day so I had to. When I went to pull out of the garage, I always put it in 1st first to sync the gears, then shift into reverse. As soon as I shifted into reverse, it died. Even then fans. I turned the key off and back on and it immediately roared to life. Again to reverse and it died. Hmm.... One more try and all was fine. I drove to the store, backed into the spot, no problem. Got home and decided I pulled a little too far forward so I hit reverse to back up, it dies. 3 times. I go inside for a minute and come back out to try it again and no problem.

Before yesterday day it had happened like twice over that year. So intermittent I didn’t really chase it. But this was too often to ignore. Like I said, it was cold outside so that might play in. I have verified in the past the reverse lights work normally,so the reverse switch from the tranny does work.

Two questions:
1) Anyone seen something like this before?
2) I am assuming that the fans stopped because the ignition power was interrupted making them think that the key is off. Does that make sense or am I barking up the wrong tree there?

Any help is appreciated!

 

Just curious about the power locations of the backup switch and the ECM/ignition module. Are they sourced/tied together somwhat closely where an intermittent connection to the ECM/module would cause them to source voltage/current from the backup switch source, and then cause the ECM/module to shut off when the "leached" current was diverted to the backup lamps?

 

The ECM goes back to the neg side of the battery (+ and - are both directly to the battery). The ground for the reverse switch is wherever stock location is. I would have to look that one up.

 

I checked the wiring diagram. The wires INTO the trans connection come from the fuse box. The other side runs to the reverse lights which grounds on the other side of the light.
I just don't see how that could be killing the ignition. Ugh.

 

I can understand that wiring, if that is the keep-alive memory power supply leads. But I assume there's an additional + lead to the ECM to tell the ECM you are going to start cranking the engine over, and also to let the ECM know to stop triggering the injectors when you are wanting to shut the engine off. Is there another Bat/Ign line going to the ECM?.

 

Gotcha.
Yeah here you can see the wiring of it.
I took it from the fuse box for the wire they show coming from the key..

 

Okay, if I understand your posts, both the Switched ignition input to the ECM and the Reverse light switch both get their power from the fuse block. My original question remains: Are they connected close electrically, where possibly the reverse lamps can drain current from the Switched Ignition point, if the original/correct/desired connection feeding the Switched ignition line gets itermittent or resistive? What happens if you temporarily add a battery 12v jumper wire to the ECM Switched ignition line (to provide an additional/redundant power line)?Does the engine continue to run when you put the trans in reverse? (Remember to unhook the wire to stop the engine.)

 

unplug the back up switch.

 

I would jack it up so the wheels are off the ground then start it. Remove the little link bar from the shift linkage and manually move the switch so it would think you put it in reverse with the shifter. See if there is a short some where with the reverse light wiring and the ECU.

If that isnt it, does it die before you let out the clutch or as you let out the cutch? maybe the torque going on the other direction is breeaking the gound to the frame. If it was a positive short you would have totally different poblems

 

Interesting theory. I was planning on adding a remote fuse box in a few weeks and move the ECM and fans to that box anyway. Now I really think I will.

 

But then i have no reverse lights......

 

It dies as soon as I move the shifter into reverse. Clutch completely in.
The Tremec transmission has everything internal. You cannot access the shifter rods like on a Muncie.