Electronics Gone Wild - HELP!

[Big John]

Usually when the ballast resistor goes bad the engine cranks normally but won't start. I've had twp go bad. One on my '74 Duster when it was a few years old, and the other on a '65 Satellite I had after switching it over to electric ignition. I started carrying an extra and haven't needed them. So far at least!!

That's because you were using a double ballast resistor. One side is "hot" when the engine is cranking. That side has less resistance, so more current to the coil. When the engine has started and you let off the key, the other side is now "hot" and there's more resistance so less current to the coil.

With a single ballast resistor, there's full current to the coil, bypassing the ballast resistor when the engine is cranking and then when the engine starts, the ballast resistor is "hot" so less current to the coil.

So... with a single ballast resistor, if the engine starts, but won't run after you let the key off, it's a bad ballast. With a double resistor, it could go either way, depending on which side of the ballast resistor has failed.

 

[Roadcuda]

As I remember it John the instructions said that both resisters were needed and had diagrams on how to wire it up. I never had a problem with the car again after that.

 

[Ranger]

Pardon my stupidity, but mine looks exactly like this. Is it a single or double?

Also, can you tell if they go bad. I removed it and looked at the back side. All I saw was a coiled wire. It looked shiny (like new).

 

[Basketcase]

that would be a single.
here is a single and a double

 

[Big John]

Pardon my stupidity, but mine looks exactly like this. Is it a single or double?

Also, can you tell if they go bad. I removed it and looked at the back side. All I saw was a coiled wire. It looked shiny (like new).

Check resistance with a multimeter is the best, but a simple check for continuity works. The coiled wire in the back is what provides resistance for the current flowing through it. Generally speaking, it fails by the wire breaking or burning through. Sometimes you can see the break and sometimes you can't.

 

[Ranger]

Went to a car show today and I was running at about 2000 RPM when I noticed the tach bouncing again. It was jumping up around 3 & 4 thousand. Then it would settle down and hold steady at 2K for a while. Idle was steady at 800. This how it was acting when this thread started, but I have replaced the mechanical regulator with a Wells electronic (voltage is now steady at 4 -14.5) and have replaced the ECU (post #30) after it crapped out and left me dead in the water.

Also noticed it is taking much long crank times to get it started.

Going to a Mopar show tomorrow (Sunday) and I must admit I'm a little worried. Could the ECU be going again? It's only a month old and has maybe 400 miles on it.

 

[Ranger]

I noticed another piece to the puzzle if it will help anyone come up with any advice.

On the way to and from the Mopar show today the tach was erratically jumping around, though the engine seemed flawless, but on the way home just as I was turning onto my street I noticed that the tach seemed to be jumping in sequence with the urn signal. Basically, when the turn signal lamps where on, the tach went to normal and when they went of it bounced up, so when I pulled in the garage I put the headlights on and the current draw seemed to allow the tach to resume a normal steady reading.

The voltage gauge was at 14v, but had a very slight, almost undetectable twitch to it. Now I'm starting to think voltage as opposed to the ECU, but as per Big John's advice (post #5) I have installed a Wells VR706 regulator.

 

[Big John]

Aftermarket or factory tach?

 

[Ranger]

Aftermarket
It's the repo, not the original.

http://www.amazon.com/Sunpro-SST802R-Retro-Super-Tachometer/dp/B0030MTCY0

 

[Ranger]

I think I fixed it. In addition to the jumping tack, it was rather hard starting lately. Whoever installed the electronic ignition module, for some odd reason did not use (or buy) the wiring harness with the plug. They used crimp pins like the one in the center pictured below. I pulled and closely inspected them today and they seemed to be oxidized in the center. I cleaned them up and low and behold she started on the first crank AND the tach sat still. I'm a happy camper again.

A new wire harness is on order.

 

[Basketcase]

that just might be it, and soldering the new harness wouldn't hurt while you're under the hood.

 

[Ranger]

Suspicions confirmed. Took her for a ride to a cruise night and she started immediately in the garage. Tach was dead nuts steady and when I stopped for gas and she heated up while shut down, she restarted in an instant. Another gremlin annihilated. :banana:
The new wiring harness is enroute.

 

[Basketcase]

I think I'm gonna pop for a new engine harness this winter. has some tape on it, and be nice to have new.
glad you got to have some fun with it. BTW...where's the pics of the night out?:redx:

 

[Ranger]

Didn't take any, but I do need to take some new pics. Need to find a nice setting. The only ones I have are the PO's from when I bought it and the ones I took in the garage for the wheel poll.

 

[Ranger]

Well, she's back at it again. Tach is jumping all over the place. It seems to be affected by voltage. Turn on the lights and it settles down (for a while). Running at night it started acting up after a bit, but setting at a light (low voltage) it settled down. Start driving (voltage increases) and it starts jumping again. Ammeter setting normal (just a tad right of center). Voltage normal as well (14v lights off/13v lights on). The voltage gauge did have the slightest twinge to it when the tach is bouncing, but it was almost Imperceptible. That said, I don't feel the regulator is the problem. Read on.

Just a quick recap, voltage regulator was replaced with a Wells VR706.
ECU was replaced.
ECU wiring harness was replaced.

After all this it was running fine, starting well and the tach was dead steady (until a couple days ago).
P.S.
Engine runs just fine. No misfiring and not responding to the tach.

Since voltage is correct and the mechanical regulator was replaced with an electronic one, I am kind of ruling that out.

Someone correct me if I'm wrong, but the tach gets it signal from the coil, and the coil gets its signal from the ECU, thus I am suspecting the ECU (again). Not happy since it is only a few months old.

Any chance this could be the problem?
http://www.69roadrunner.net/mopar/showthread.php?12461-ECU-Wiring

 

[Basketcase]

If I read your post right, the car runs fine...it's just the tach that's acting up? If so, I'd replace the tach.

 

[quikbird]

I vote with Dave. Try a new tach.

 

[Ranger]

Hmm, I find that hard to believe, but it is an interesting concept. I hate throwing parts at it hoping one will stick.

 

[Basketcase]

well think about it...with everything you've done, the car is running fine. all is ok except for the tach. If nothing else, unhook the tach, and if the car is still running ok.......

 

[Ranger]

The reason I find it hard to blame the tach is that it is less than a year old. I'm wondering if the tach is indicative of a pending ECU failure. Is it possible for a tach to be that erratic and not be responding to the input it is receiving? I suppose I could check this out if I had a spare tach.