Engine shutdown
 

I have a 74 2.0. The problem is an electrical shutdown of an intermittent nature. Imagine driving down the road, car running great, no missing, etc., and all of the sudden the tachometer will go to zero. Dead engine. This will be either very temporary (a studder) or will cause me to pull off to the side of the road. The car will restart after fiddling with numerous wires. The problem seems to be power to the coil. But....New coil, new ignition switch (to solve my starter problem). I had a timing light at my side for awhile but the problem is too elusive. I guess the question is: What steps would you take to solve this. I can't read a electrical diagram worth a damn.
No other problems to speak of. Thanks for your input.

Scott S.

If your harness is clean, try to duplicate the failure by systematiclly isolating and moving sections of your harness. You may discover a cracked wire intermittently grounding out, or a connector that is loose from age. Heat at a wire connection will cause the additional loss of tension and a connections ablity to stay connected.(what ever) I bought a pretty nice BMW that way once. Some one had replaced a female spade connector on the coil with the wrong size. It kept viberating loose. I got a pretty good price from the P.O. when the car left him on the side of the road one time too many. check the main power lead where ever it passess through a metel bulk head. a grounded main power wire will shut the system down or eventually melt it down! Good luck

You might also try disconnecting the tach lead. That's the thinner black wire (with a purple stripe that can be hard to see) on the same coil terminal as the green wire from the points. If that wire is grounded or the tach is bad, it can keep the ignition from firing.

Probably lots of other stuff to check. There are a lot of things that it could be, but in order to check many of them you need the car to be in the failed condition.

Not sure what to tell you...

--DD

Something similar to this happened to me not too long ago. I was driving then it died on me... had to pust it home, lucky i was only a block away.. You might want to check the fuel pump, relay, and fuse for the pump..
I replaced the pump about a week before the incident, so a new pump can give out..
Hope this helps!

Back in the bad old days( Pre 6 ), I had an intermittent failure similar to the one you describe; running fine then dead .Dead time would be anywhere from 1 to 20 sec. then it would run fine.
It was driving me nuts.
First clue was it happened at the same place(approx) in my morning commute. Huh? Maybe the alignment of the moon , Venus and the nuke plant.... naa.
Let's see same place, same distance from home, same lenght of time = same temperature...Ah Ha.
The experts at AA said it couldn't be the cylinder temp sensor, but they were wrong.
Thus began my education on my teeners FI.If that's not it it could one of about 10 other things.

J P Stein

I had a 914 die on me, a PO used masking tape and an uninsulated bus bar to bypass the "interlock-relay". The wires chafted on the seat track and killed the car. When this happened the "G" light came on, but nothing, not even the hazards, worked.

So if the G light comes on I "guess" it is a short (of the +12 volt variety) if the car dies but the rest of the electrical system works, it may be the tach wire or a bad interlock relay.

Also, when the car dies, can you still hear the fuel pump? If yes it is probably the ignition system grounding out. If is dosen't work then it may be the ingition switch, or interlock relay.

No free lunch here, sorry. You will probably be spending some quality time, upside down and bent over, under the dash and buried in the engine compartment.

Thanks for all the input. I have been through all the wiring and connectors. (At least they are all clean and /or new now). I didn't even consider the tach causing the problem. I have the interlock relay by-passed. I know one of the primary functions is to disable the starting of the car when the seat belts aren't latched, but what elso does it do; what circuits are run throught it? Thanks again.

Scott S.

The seatbelt interlock relay has a lot of things that run *to* it, but not much that actually goes *through* it. Most of what does relates to the specific seatbelt-warning related systems.

The only thing the seatbelt relay gizmo does that is of any interest to the running of the car is that it allows the current to go from the ignition switch to the starter motor. That's it. It acts as a big switch in the big yellow wire from the "crank" position on the ignition switch to the starter solenoid.

I suspect that the unsheilded bus mentioned by JP was also shorting out some of the wires that go to the relay but not *through* it.

The tach doesn't have anything to do with the interlock system. The tach signal wire goes from the tach, to the relay board, through the board (doesn't connect with anything else) to another wire that runs to the (-) side of the coil where the green points wire connects. The tach can fail and internally short its input to ground, which means the points have no effect and so no spark.

The fact that the tach goes straight to zero indicates to me that you are losing spark. It probably isn't the tach causing it, but unplugging the tach signal wire from the coil is VERY inexpensive and easy to do.

One thing that often gets overlooked: Check the ground braid inside the distributor. It should go from the points plate to the distributor body, and provides the ground path for the points. If it disconnects, you will lose all spark. See if you can move it and disconnect it.

Someone on this forum just recently reported this problem.

--DD

Dave, There is no ground wire in my distributor. There hasn't been one since I have owned the car (two years). I realize there should be one, but it has always run fine w/o. By the way I am running a Pertronix. Thannks again for this input.

Thanks to those that dared reply to such an ambiguous topic. The problem turned out to be a positive lead from my Pertronix pulling away from the sending unit. Very intermittent.. Very frustrating. What's new !