95 F53 Tachometer needle wiggling

[House Husband]

My MH has 118,000 miles on it and the tach has been flawless until yesterday. While cruising on flat ground the needle is rock solid, but when I throttle up for any reason, the needle starts wiggling, The harder I push the gas peddle, the more the needle wiggles. Now knowing that the tach is driven from the ign. coil and the coil must produce more energy when the engine is under load, I suspect a reduced signal to the tack when under load. So where is the flaw? I hope Subford will weigh in on this with some thoughts.

Richard
95 Bounder F53 32H

[subford]

There are only four possible items in the tachometer circuit.
1. The Tachometer.
2. The Ignition coil.
3. The ICM.
4. Wiring.

I would look at the wiring first for loose connections or a bad wire (mice or whatever).
I do not see how a load change would do it with any of the items above.

The ICM just takes the circuit to ground about the way the old points did.
If you replace the ICM make sure it is Black in color.
Could also be a bad ground and I think I would look there second.

Most of the time a bouncing tachometer winds up to be a bad Tachometer.

[House Husband]

Thanks Bill,

I had the same thoughts as you but didn't want to sway any responses by posting them. I just needed confirmation from a Ford Guru.. I'll make sure there are no high resistance connection and then throw some parts at the ol beast. The wife and I have been bumming around Canada and Alaska for the last 6 weeks and don't want to break down in the boonies. I'll pick up a ICM (TFI?) and coil as soon as I see some signs of civilization again. Can't have too many spare parts in the ol tool box.

Richard

[subford]

Originally Posted by RLS7201

I'll pick up a ICM (TFI?)

The ICM or Ignition Control Module is of the type TFI or Thick Film Integrated.

[House Husband]

A few days after the Tach started wiggling, I experienced a slight mis-fire, under heavy acceleration. First I check and cleaned all connections that could be involved with the Tach wiggling. Give the flat pins, in the connectors, a little twist and check the coil wire for proper resistance (6K ohms). No improvement. I purchased an ICM and ign. coil and replaced the ICM first because it was easy, after I remembered to buy the special nut driver, it was easy! DUH....No improvement. So I dug in after the coil. According to Murphy's Law, the last item checked or replaced will be the problem. And it was. The coil cured the problem with the Tach wiggling and the mis-fire went away.
Again thanks to Subford for his input.

Richard

[jamesrxx951]

Originally Posted by subford

There are only four possible items in the tachometer circuit.
1. The Tachometer.
2. The Ignition coil.
3. The ICM.
4. Wiring.

I would look at the wiring first for loose connections or a bad wire (mice or whatever).
I do not see how a load change would do it with any of the items above.

The ICM just takes the circuit to ground about the way the old points did.
If you replace the ICM make sure it is Black in color.
Could also be a bad ground and I think I would look there second.

Most of the time a bouncing tachometer winds up to be a bad Tachometer.

The coil was likely sending RFI back into tach. This is not uncommon for RFI from ignition sources or the alternator to cause similar issues. It can also cause and engine to shut down under certain loads. The coil ground circuit is wired directly to the tach and ignition module, in this case so the coil makes a lot of sense based on his symptoms.