Hey guys, tried searching for the answer but this problem is a little strange, wondering if anyone else has had it.

background: 305 TPI engine with an LT1 T56 trans

in 1st gear only.. if i am more than 50% throttle, the tach bounces all over the place... in any other gear its normal.. i can floor it, give it just a tad bit, or mash the gas in any other gear and its fine...

now in 1st if im just babying it, its fine, but as soon as i lay it down, bouncing.

the car is a B4C 1LE so it has the 145mph cluster.. all ther gauges work normal with no issues..

any ideas?

 

If it were not for the fact that it works in other gears, I would say have your ignition module tested.
That old idea, from back when vehicles just started going electronic, that if the module is bad the vehicle wont run is not true. A number of times and with different vehicles I have seen a tach jump around while the engine was running smooth and a module has always been the fix. Some of these vehicles also had intrmitent poor running conditions but all the time with smooth running the tack would bounce around.
Places like autozone can test the module for free. You just have to pull it out of the car.

 

Check for a misfire.

 

im getting no codes.. no loss of power... it just bounces all around until i lift then go half throttle... shift gears to 2nd and i can hammer it, no bouncing,.. 3rd.. hammer it.. no bouncing, 4th 5th and 6th... no bouncing..

no clue.. going to change the igition module anyway because its still the original one and has 150k miles on it.. going to change the cap and rotor and do plug wires while im in there because im putting in hedman headers this week

changed plugs a few weeks ago thinking that might help, but it didnt..

thanks for the suggestions, anything else?

 

Nothing more unless you have some funky wiring and it really has nothing to do with what gear you're in.
But if you do change the module and that takes care of it let us know. It may help others in the future. (at least those others that use the search feature)

 

update:

looks like now its doing it in all gears.... ? odd.. bought a new ignition module from O'Reily's, going to put it in tomorrow and report back.

 

Mine is doing the same thing (85 IROC 305 TPI).

Let us know how it works out!

 

I thought it was odd just doing it in one gear. Now that it is in all gears it seems like a more normal problem

 

problem solved:

Ignition module.. replaced with a new one, car runs perfect. Thanks for the help guys

 

No problem,
Right on..... or is it Rock On!

 

I was having the same issue, changed out my Ingnition Control Module today. No change. My Tach is still running higher than the actual RPM's... What else can I check or look at??

Any suggestions are appreciated.