My tach needle fluctuates?????

[juiced_94gt]

What would cause this??? it fluctuates when i hit the gas, i just fired up the 331 yesterday and now this. Everything is hooked up and the plugs are gapped at .54 it has a MSD Dizzy could that be it?? it ran fine with it for 4 years but i noticed that the groumet where the plug is on the dizzy is kinda torn, would this cause this?? or could it be the coil??

 

[HISSIN50]

A half-inch gap on your plugs can cause quite the miss.

Kidding aside, I like your ignition suspicions. A leaky plug wire can cause this too (especially if you detect a miss - it might not be apparent till the car is actually on the road and under load).

If it does it pretty frequently (every few seconds or so), I'd have a friend watch the gauge while you carefully move the dizzy's wires around - this will check that idea for you.
Then move each plug wire a little bit (or do they spray bottle test).

A coil would not be my first guess, but who knows.

Good luck.

 

[juiced_94gt]

it does seem to have a slight miss, the plug wires are brand new frpp we wiggled the dist. and the tach needle did nothing

 

[maximos]

Does it seem to just get stuck sometimes?

 

[juiced_94gt]

number 2 and number 8 injectors aren't firing, i switched the harness plugs around and still the same injectors didn't fire so i guess i need new ones...so much for buying used stuff.

 

[HISSIN50]

Put a noid light on the problem injector connectors to ensure you have 12 volts and ground reaching each.

If you don't know how to do it, I can help ya make a test rig to see if your injectors will spray (on the bench) if you want.

Good luck.

 

[juiced_94gt]

Put a noid light on the problem injector connectors to ensure you have 12 volts and ground reaching each.

If you don't know how to do it, I can help ya make a test rig to see if your injectors will spray (on the bench) if you want.

Good luck.

how do you do it??

 

[HISSIN50]

how do you do it??

You can get a noid light at most decent parts stores for a couple bucks. Place it on a good injector connector (one that you know was firing - bench test it so you know it works) and crank the engine over or let it start. The light should flash real quick.

Now put it on one of the injector connectors of the problem cylinders and do the same thing. If the noid light flashes, you're good. If it doesn't, no injector will function because either power or ground pulsing is missing.

The theory is that the injectors receive constant accessory 12 volts. There are drivers in the computer for each injector. The computer fires the injectors by sending a ground-pulse to each.

Good luck.

 

[maximos]

I don't know if I have the same issue or what, but my tach needle seems to just get stuck sometimes. Even at idle it will jump around and get stuck. It's especially annoying when I'm at WOT and it just stops in the middle of it. I was told it's just a malfunction of the tach unit and that it's somewhat common. Same thing?

 

[gcomfx.com]

Are we talking stock tach or aftermarket?

Stock tachs are known for taking a dump with the age of our cars. Mine quite working correctly several years ago. It will jump around, hang, and even spin all the way around and get stuck under the resting peg.

For some reason people riding will get freaked out when they see it doing this. Even though I have a 5" monster tach right next to it behaving correctly.

 

[juiced_94gt]

Are we talking stock tach or aftermarket?

Stock tachs are known for taking a dump with the age of our cars. Mine quite working correctly several years ago. It will jump around, hang, and even spin all the way around and get stuck under the resting peg.

For some reason people riding will get freaked out when they see it doing this. Even though I have a 5" monster tach right next to it behaving correctly.

It is a stock tach...Problem solved, i had 2 dead injectors causing #2 and *8 to not fire thus causing a miss.

 

[Trick95]

I don't know if I have the same issue or what, but my tach needle seems to just get stuck sometimes. Even at idle it will jump around and get stuck. It's especially annoying when I'm at WOT and it just stops in the middle of it. I was told it's just a malfunction of the tach unit and that it's somewhat common. Same thing?

My tach took a dump just like you described. I didn't want to replace the whole cluster since I wanted to keep the original and I had nice a nice white face on it, so I got the motor from inside a V6 cluster and replaced it. It was awhile ago so I don't remember exactly how to do it but I remember it being very easy. Just gotta be careful removing the needle and marking the spot so the tach stays close to accurate.