Wandering tachometer

Geophilist · 08-16-2006, 11:36 AM

I am having a problem with the Tach on my 82 Excella gasser. At idle the reading is completly steady. However, at speed it wanders about 500 to 1k rpm. I have noticed that if I push in the cigar lighter, it will jump even more.

I have cleaned the HEI connections and have crimped in the connector a tad to make it fit a bit tighter, but to no avail.

Any thoughts?

Steve

Robfike · 08-16-2006, 11:54 AM

You may want to check your grounds behind the dash. I have fixed a number of odd readings of different instruments just by making the grounds better.
My latest one was when I opperated my switch for the door dead bolt, I noticed the light in the vacuum guage would come on slightly. I found that the switch uses the ground for the vacuum guage illumination, and it was loose.
Good luck, Rob

Geophilist · 08-17-2006, 03:20 PM

Rob,

Thanks for the tip. You indicate that there are a number of grounds behind the dash. Any idea how many? I have cranked down on one, but don't remember more than one. Than again, I don't remember what I had for lunch either.

I will go look for more.

Thanks again,

Steve

silver buffalo · 10-11-2006, 08:48 PM

Steve,
Have you cured your wandering tach problem? My 310 does exactly the same thing. The tach is very steady and smooth all the way up to 3200 - 3300 RPM for the first 4 or 5 minutes the engine runs, after it is good and warmed up, anything over 2400 RPM and I get about a 500 RPM bounce, always down. I have had the gauge panel out and tried to check all the grounds but it is pretty intimidating back there (a mess of wires that all seem to end up running to each other at some point). This bounce just developed at the end of last season.

Geophilist · 10-12-2006, 11:58 AM

Rick,

I am yet to solve the mystery, but if I do, I will share.
I have gone over the grounds and everything looks good there. The problem with finding this is that I have to be going highway speeds to find it. Not recommended if you work alone.

I know whatyou mean about the spaghetti behind the instrument panel. A number of folks have changed out their gauges and have had to deal with the mess. It seems like the only thing that the wiring diagram and the real wiring have in common is coincedense!!

Good luck in finding your problem. Let me know if you do, please.

Thanks,

Steve

Dog Trainer · 10-17-2006, 09:10 PM

Try running a ground from the ground lug on the tach directly to the battery ground. If this solves your problen then you know to look deeper into the dash wiring. If not then you have eliminated that potential problem

Fyrzowt · 10-17-2006, 11:12 PM

This may be from left field and have nothing to do with your vehicle. But....
When I worked for GM way back when, I seem to recall that they used a tach filter to smooth it out. Have you checked with the manufacturer or dealer? Just a thought.

Geophilist · 10-20-2006, 10:36 AM

Good advice, Dog Trainer. Next time I get on the road I will give it a shot.

As to the tach filter, I have no clue. I have looked at the wiring diagram, and do not see that one was installed. What do they look like and where might one be? I guess if there is one it could have failed. How would I be able to replace one?

Thanks,

Steve

Fyrzowt · 10-20-2006, 10:54 AM

Quote:

Originally Posted by Geophilist

Good advice, Dog Trainer. Next time I get on the road I will give it a shot.

As to the tach filter, I have no clue. I have looked at the wiring diagram, and do not see that one was installed. What do they look like and where might one be? I guess if there is one it could have failed. How would I be able to replace one?

Thanks,

Steve

Steve, I'm sorry, it's been too long and the cobwebs of the mind are too thick. A call to the dealer should let you know if that's even a possibility. I worked on Cadillac and Oldsmobile, the tach input came off the distributor as I recall. There were two wires with push-in plastic connectors to the distributor cap where the coil is. One was the 12v power lead, the other the tach lead.
I do know the filters were used, but I don't recall if it was original or a problem fix part. FWIW.
Dave

silver buffalo · 10-23-2006, 06:55 PM

Steve,
We just returned from the rally in Ga.. Before we left I replaced the coil, cap, rotor and ?? (the flat thing in the bottom of the distributor with 4 male spade terminals on it), no more wondering. She was rock steady.

ralley · 10-23-2006, 07:53 PM

Quote:

Originally Posted by silver buffalo

Steve,
We just returned from the rally in Ga.. Before we left I replaced the coil, cap, rotor and ?? (the flat thing in the bottom of the distributor with 4 male spade terminals on it), no more wondering. She was rock steady.

ignition module. Buy another and put it it your tool box.

Geophilist · 10-24-2006, 11:00 AM

Rick, Rally,

Had not thought of the "flat thing in the distributor", I will buy a pair and try it out. You know where the second one goes; along with an alternator and starter motor. Thanks.

Dave, I really know about the cobwebs. I hear that forgetfulness is the second sign of getting old. I forgot the first. I will call around about the filter. Thanks for the help and good thoughts.

Steve

Geophilist · 10-24-2006, 11:29 AM

Geophilist · 10-24-2006, 11:38 AM

Dave,

Ok, I have called around to half of the Chevy dealers, RV dealers, and an electronics store in Tidewater, and they tell me that the filter is no longer available. One said, "oh, yeah, back when they made cars with points and carbs they used to have those filters." Now I am really feeling old. One counterman described it as looking like a condenser only with two wires and was mounted somewhere on the maifold. Guess I will go on a snipe hunt.

Thanks again

Steve