bouncing tachometer

[thejum57]

What would make an aftermarket tach ( assumming it's installed correctly) bounce up and down....sometimes? Most other times it is nice and steady. Also the engine seems to falter a little. I'm guessing ignition, but what part??? Lot's of new parts too.

[SpruceMoose]

anything that would cause an intermittant signal to the plugs. my jacobs ignition system went out a while after the same thing started happened to my waggy. you shoulda heard the backfires when it finally went! sounded like a 30-06 in tha car with me!

sm.

[Rogue]

sounds as though you have a misfire from your description

i once had an acura legend that had a funny tach - turned out to be one of the diodes in the alternator was shot - tach signal needed all three phases to display properly

[Cecil14]

Also check grounds. A loose ground could cause that. Make sure your plugs wires are on tight and aren't arching. Check cap and rotor for wear, etc.

Anthony

[Bambi]

another thing is that it could be a loose timing chain, check your backlash on the rotor.

[Joe Guilbeau]

Cable driven or electronic?

[thejum57]

The tach is electronic. I put in new plugs, rotor, and cap. Wires are really good, and tight. Drove it, was really smooth, once it got good and warm it started to flip out again. Truck ran fine this time though. Today, I re-checked tack wires, and re-did some crappy connections under hood. One wire from the sylenoid was running right beside the engine, one for the electric choke was starting to melt to the valve cover. I moved both! Could heated up wires be doing this? I haven'd driven it yet. Again, it's fine when cold!

[Cecil14]

It could be, the hotter a wire gets the more resistance there is through that wire.

Anthony

[thejum57]

O.K., I re-did some of the wireing connections, replaced plugs, rotor & cap. When it's cold it's fine, once it warms up it starts bouncing. On the highway yesterday, I thought it was going to die, it was jerking. Any more suggestions????

[carrotman]

Does your Jeep have the original Prestolite distributor and ECU? If so, the best thing to do is replace it. Do a search on the tech site for a guy who sells a Chevy HEI, modified to work in your 258. Definitely worth the money and should fix your problems.

[thejum57]

I'm not sure what it has. I know it has been replaced cause the one on my old engine crapped out and was replaced. Then when the new motor was put in, the dist. went with it. It's probly used though! I'll definately look into that, Thanx!!!