Sudden loss of tach and no power

[bytes311]

This issue used to occur every once in a blue moon after I'd go out and start the car if it's been sitting in the sun for a few hours. The issue would resolve itself just by simply restarting the car, however, today it happened in the middle of a drive.

While driving, I noticed my tachometer jumping around and becoming "sticky" before quitting all together (within a span of a couple seconds) as if it was no longer receiving a signal. Immediately, the car had no power during acceleration and would stumble when given gas. I shut the car down and attempted to start it up again. Normally the tach would reset itself with the key in the "on" position, but this time it would not wake up, even after several on and off attempts and bumping the binnacle. I also observed that I wasn't getting an oil or battery light in the "on" position. My alt gauge was also bizarrely low. I had no issue restarting the car. It would run fine at idle, but it would not take any acceleration,

Another strange observation: When I turned my headlights on, there'd be a loud and repetitive "clunk" from the engine bay. I was not able to pin-point it exact, but it sounded like it was coming from the ignition distributor or thereabout.

After several attempts of key "on and off" and messing with the ignition ECU connector, and touching other various connectors, the tach went back to normal. The "clunking" noise with the headlights on in the engine bay also disappeared. Now I have no idea what that was all about and I can't reproduce it.

Everything ignition related on my car is stock, except for the alternator.

Any ideas?

Thanks!

[Bitsyncmaster]

Tach acting up could be ignition (ignition coil primary) was failing. Lack of power would also confirm that.

Now headlights causing a clunk makes no sense unless it caused a misfire which may also be related to the the ignition problem.

[bytes311]

Tach acting up could be ignition (ignition coil primary) was failing. Lack of power would also confirm that.

Now headlights causing a clunk makes no sense unless it caused a misfire which may also be related to the the ignition problem.

Thanks Dave. When you say ignition coil primary, do you mean something along the positive circuit is failing, or is the coil failing?

[Bitsyncmaster]

Thanks Dave. When you say ignition coil primary, do you mean something along the positive circuit is failing, or is the coil failing?

It could be the coil, the ignition ECU, wiring or even the pickup coil or it's wiring.

Make sure the two pin connector on the pickup wire is clean. Mine was corroded so bad I removed it.

The ignition coil does tend to fail with heat so replacing that next is probably the least effort and cost.

Then you may be able to find a used ignition ECU to replace yours or borrow one if your problem shows up often.

[Rich]

Check out Posts #1-4 in this thread (http://dmctalk.org/showthread.php?9304), too, plus the others there.

Same symptoms you report - jumpy tach and engine stumbling. 3 possible issues listed; pointing to the ECU or its wiring as Dave M. also mentions here.

The thread ends without the OP reporting a positive resolution so it's only a guess for now.

[David T]

Because you disturbed the problem it is hard to find again because it is intermittent. Makes it very hard to replicate and therefore difficult to know what it is and if you fixed it. In all likelihood it is a wiring/connection problem, not a part problem. Unless you can find a way to replicate it the "fix" is to go over every connection in that circuit.

[Ron]

Try checking that Auxiliary Relay 2 is working.
It feeds fuses 1,3,4,5 and the ignition resistor. If it is not feeding fuse 1 OR the ignition resistor, you will loose ignition. If it's not feeding fuse 5, you will loose dash instruments and indicators.
Check in order:
Its brown wire should have 12V at all times.
Its black wire should have ground at all times.
Its two white wires should have 12V when the key is turned to run.

[bytes311]

Thanks guys. This gives me a place to start.

[bytes311]

I pulled fuse #5, which is the fuse for the dash instruments, while the motor was running and it reacted EXACTLY like it did when I lost my tach signal the other day. I revved the engine and it sputtered and wanted to die. It would idle just fine though. I reinserted the fuse and everything worked again like normal.

The alternator light stayed on for a few seconds and then switched off, which tells me the car was running off the battery and not the alternator. Makes sense if the alt light is out in the dash.

My battery puts out 14v, however, it is coming up to 7 years at this point. I'm also using a 10 amp fuse for #5 while online it shows a 20 amp.

[Spittybug]

Listen to Ron and Bitsyncmaster, they knows their proverbial 'excrement'..... David, while good at waxing philosophic, is generally short on solutions.

CLEAN EVERY CONNECTION & GROUND. And I don't even own one of these things anymore....

[Ron]

I pulled fuse #5, which is the fuse for the dash instruments, while the motor was running and it reacted EXACTLY like it did when I lost my tach signal the other day. I revved the engine and it sputtered and wanted to die. It would idle just fine though. I reinserted the fuse and everything worked again like normal.

The alternator light stayed on for a few seconds and then switched off, which tells me the car was running off the battery and not the alternator. Makes sense if the alt light is out in the dash.

My battery puts out 14v, however, it is coming up to 7 years at this point. I'm also using a 10 amp fuse for #5 while online it shows a 20 amp.I can see the 10A fuse getting hot and causing the holder to get weak/bad connection.

I'd swap the fuse, and if it is currently working, do some shake & wiggle testing...

Next time it does it, while the gauge and warning lights remain dead, try not to disturb anything you don't have to and check in order:
12V @ Battery
12V @ Aux Relay2.Brown
Ground @ Aux Relay2.Black
Turn key to Run.
12V @ AuxRelay2.WhiteA AND AuxRelay2.WhiteB
12V @ Fuse1 AND Fuse3 AND Fuse4 AND Fuse5 {See * below}
12V @ Otterstat.Green
12V @ Cluster.Green {Terminals 3, 9, 20 }
Ground @ Cluster.Black {Terminals 13, 17}

A failed test means you just passed the problem.

* Gently probe from Battery(-) to each hole in the top of the fuse.
(You might have to use a piece of small diameter wire to fit down into the hole.)

[bytes311]

I can see the 10A fuse getting hot and causing the holder to get weak/bad connection.

I'd swap the fuse, and if it is currently working, do some shake & wiggle testing...

Next time it does it, while the gauge and warning lights remain dead, try not to disturb anything you don't have to and check in order:
12V @ Battery
12V @ Aux Relay2.Brown
Ground @ Aux Relay2.Black
Turn key to Run.
12V @ AuxRelay2.WhiteA AND AuxRelay2.WhiteB
12V @ Fuse1 AND Fuse3 AND Fuse4 AND Fuse5 {See * below}
12V @ Otterstat.Green
12V @ Cluster.Green {Terminals 3, 9, 20 }
Ground @ Cluster.Black {Terminals 13, 17}

A failed test means you just passed the problem.

* Gently probe from Battery(-) to each hole in the top of the fuse.
(You might have to use a piece of small diameter wire to fit down into the hole.)

Solid advice. Thanks Ron!

[bytes311]

Just to follow up for any future readers: The ground cable to the battery was barely hanging on. Apparently it had worked itself loose over time. I went ahead and replaced the 7 year old battery and tightened the leads nice and snug. I have not experienced a problem since. :thumbup:

[bytes311]

Last (hopefully) follow-up because this happened to me again. But I think I finally found the culprit!

Yesterday I drove my car to work where it sat and heat soaked for quite a few hours. When I went out to my car to start it... no tach signal. I could usually get it working again if I played with the ignition key, but this time it wasn't having it. The car started and ran, but it felt like a miss with piss-poor acceleration. And if I put any load on the electrical system (headlights or AC), I'd hear an audible popping/arching-type sound from the distributor area. Weird.

After working up the courage to limp my car home (I live just 5 minutes from work), I made it home safely and pulled out my multimeter. I went through Ron's testing procedure and passed ALL the tests. I even swapped Ignition ECU's, to no avail. Next, I moved on to the alternator. I found it wasn't putting out. So I messaged a buddy of mine and he asked if I ever inspected the printed circuit board behind the dash cluster. That got me thinking about the battery light. It dawned on me that I wasn't getting a light with the key in the "on" position. So I proceeded by smacking the side of the dash. Suddenly, my batt light and tach came back to life!

Today I am placing an order for a new printed circuit board.

[David T]

It could just be a bad connection of the plug to the PC board, the PC board may not be bad. Most of the time you can make it work just by cleaning up the connections. While you have it all apart change the light bulbs. Do NOT use an LED bulb for the alternator warning light (in case you are planning to change them over to LED).

[bytes311]

It could just be a bad connection of the plug to the PC board, the PC board may not be bad. Most of the time you can make it work just by cleaning up the connections. While you have it all apart change the light bulbs. Do NOT use an LED bulb for the alternator warning light (in case you are planning to change them over to LED).

I've had the dash out before (years ago), and swapped the lights for LEDs, minus the batt light. CA roads are not nice to our cars. The connector may have worked itself loose over time (or perhaps I didn't seat it properly).

[MrChocky]

I've had the dash out before (years ago), and swapped the lights for LEDs, minus the batt light. CA roads are not nice to our cars. The connector may have worked itself loose over time (or perhaps I didn't seat it properly).

Yeah. I think also after a certain age, the PCB just doesn't survive removal; the connectors get fragile; I've had to replace 2. One problem I had too was not putting the screws on properly - this caused my tach to jump around.