replaced tach, still doing same thing

[fleming442]

Hell, at this point, you should probably just drop $40 on one of those eBay remans like TURNA swears by. It'll be all new, matched stuff.

 

[azmusclecar]

I didn't see a post by Turna on my thread............but I'll check out Ebay and see what I can find.

 

[Max Headroom]

I don't know squat the doodle about electronics but I did stay at a Holiday Inn Express last night!! I once had a 68 camero with a 350 i built and dropped in the car. I had a similar problem with my tach. It read 750 rpm over what it should have at idle. I scratched my head and when that didn't work, I scratched the other end. No help either way, so I called a friend who told me that sometimes a tach will read twice as much rpm as what the engine idles at. I checked and that was exactly what was happening. Turns out there was a thingamajig or a scrutinizer or some-such in the tach that had flown south for the winter. I gave him the tach and he took a look at it. He couldn't fix it, so the fool threw it away. After an appropriate period of bitching and sulking, I bought another tach and when I installed it, it worked fine. Problem solved. The moral of the story is that the problem may be in the tach, not under the hood. Just a thought.

 

[azmusclecar]

I don't know squat the doodle about electronics but I did stay at a Holiday Inn Express last night!! I once had a 68 camero with a 350 i built and dropped in the car. I had a similar problem with my tach. It read 750 rpm over what it should have at idle. I scratched my head and when that didn't work, I scratched the other end. No help either way, so I called a friend who told me that sometimes a tach will read twice as much rpm as what the engine idles at. I checked and that was exactly what was happening. Turns out there was a thingamajig or a scrutinizer or some-such in the tach that had flown south for the winter. I gave him the tach and he took a look at it. He couldn't fix it, so the fool threw it away. After an appropriate period of bitching and sulking, I bought another tach and when I installed it, it worked fine. Problem solved. The moral of the story is that the problem may be in the tach, not under the hood. Just a thought.

Well now that you got me scratching things I can't scratch in public...........MY OEM Tach and the one I purchased and installed BOTH
do the same thing..........and the seller of the 2nd tach said it worked fine for him.

So other contributors have helped with diagnosing the tach filter and now we are on to the coil itself.

Can't say it's the tach now.......but I think I'm headed to a resolution soon...............and I'll keep posting the good the bad and the itchy.

 

[Max Headroom]

Well now that you got me scratching things I can't scratch in public...........MY OEM Tach and the one I purchased and installed BOTH
do the same thing..........and the seller of the 2nd tach said it worked fine for him.

So other contributors have helped with diagnosing the tach filter and now we are on to the coil itself.

Can't say it's the tach now.......but I think I'm headed to a resolution soon...............and I'll keep posting the good the bad and the itchy.

What about that little barrel-bomb looking thing on the firewall. I know I've replaced that to solve a tach issue. I remember because I went to Morrosso's first speed shop (in Conn) to get it.

 

[azmusclecar]

That little barrel bomb is the tach filter and I ran a test on it and it is functioning as it should.

 

[5spdCab]

Well.......i plugged the tach wire directly from the distributor outlet to the tach wire going through the firewall bypassing the
filter and the tach STILL reads about 500 high at idle and gradually increases the error as the speed increases.

I pulled the tach filter off the firewall cleaned up all contacts and nothing changes. I'm at a loss..........

Thanks to all that posted ideas and directions.

As I was reading this, the thought occurred to me, is the tachometer itself calibrated for the same number of cylinders in the engine? What I mean here is do you have a 6 cylinder tach hooked to an 8 cylinder engine, or vice versa. That would definitely give you goofy readings. Make sure you have the right calibration for the number of cylinders.

 

[fleming442]

If you can get an aftermarket coil and just temporarily wire it in directly to the distributor that would tell you if the problem is in the distributor. If the distributor is ok thn I would wire the tach in to bypass the cluster cucuit board to see if the aftermarket tach works ok. I would not be buying parts without knowing what is wrong.

Although, I'd gamble the 40 on a Ding How distributor.

 

[azmusclecar]

As I was reading this, the thought occurred to me, is the tachometer itself calibrated for the same number of cylinders in the engine? What I mean here is do you have a 6 cylinder tach hooked to an 8 cylinder engine, or vice versa. That would definitely give you goofy readings. Make sure you have the right calibration for the number of cylinders.

I am sure the tach is set for 8 cylinder..............the OEM and the newly installed one are both set for 8 cylinders........but you do have a good point.

 

[azmusclecar]

Although, I'd gamble the 40 on a Ding How distributor.

Okay what is a Ding How distributor..........I hope it's not like windshield washer bearings and headlight oil.............I am hoping my foolish days
are more behind me now at age 70.........