Tach reads too slow

Anthony,

Since my Sears dwell/tach reads correctly on my engine, I doubt there is anything odd that your engine is doing compared to other 4-cyl engines. Unless your points are opening half as often as they should (heh -- not likely). I suspect something wrong with the tach. Try setting it to

Ok, here's the latest news. Took the car for a drive last night, and the tach seems to read accurately when ever I stomp the gas. If I'm coasting it drifts down to about 1500RPM...even if I'm doing 60MPH. The other thing is that the needle bounces around like crazy...allthough I've read in the archives this can be fixed by installing a diode in the sender line.

I'm just confused about the reading's I'm getting. They seem accurate when I'm on the gas, much too low when I'm coasting or just applying enough power to go on a level road at a steady speed. If I accelerate, up it jumps...and wildly jumps around what might be an accurate reading, but perhaps 200 rpm too slow.

I have an SVDA distribitor...it seems like the tach is somehow getting a signal from the vacuum advance! I know this is impossible, but that is how it behaves. Do I need a new condenser and points? New coil? (coil hasn't been replaced in....well as long as I've had the car and that's a year-and-a-half).

I have tried 6 and 8 cylinder settings on the tach, that only makes it MUCH worse, the needle barely moves at all. Thanks for any more suggestions.

~Anthony

The signal from the points is a real mish-mash, consisting of multiple pulses, both pos and neg. The tach has the job of trying to make one clean pulse out of all that each time the points open:-(

I don't know if the diode trick applies to the brand you bought, but might work. Also possible that the points need to be changed or the gap set; that can have a big effect. The condensor as well.

Does the Mfr have an 800 help line or web site?

Speedy Jim

That's the way all 4-stroke gasoline engine distrbutors work :)

Jan

Jim,

It's a VDO tach, and I got a part number for the exact diode I would need to fix the bouncing. The instructions FAIL to mention this bit of information, but the VDO gauge FAQ online does mention it.

Should I also replace the points? I mean, the car is due for my 2000 mile tune-up in 150 miles anyway.......this may fix the innacurate readings and the tendancy to jump when I punch the throttle.

~Anth> >

Really? Becuase on the Festiva (Ford) I used to drive, the distributor was attached to the end of the camshaft, and it was an SOHC engine. I don't think the camshafts on SOHC engines turn at half the engine speed....do they?!

~Anthony

Yes, replace points (genuine Bosch) and maybe condensor too. Let us know if that solves it. Jim

Yes they do.

------------------- Chris Perdue

"Sometimes you're the windshield, sometimes you're the bug!"

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As others have stated.. yes they do. Always. On every 4-stroke engine.

Jan

Geez, I only had one beer last night....what the hell was I thinking!

~Anthony

'round hea' we call dat a brain fart...

------------------- Chris Perdue

"Sometimes you're the windshield, sometimes you're the bug!"

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