Tach Issues

Ron R. · 6th July 2012, 09:31 PM

My tach falls to zero whenever I "get on it", or really anytime I get above about 3K RPM.

I'm running an MSD 6AL, and I'm aware that there can be tach issues with these. Should I be running their adaptor? In the user's manual, MSD mentions similar malfunctioning on GM vehicles using an in-line filter, and suggests bypassing it. I don't have the schematic in front of me, but I don't recall seeing one mentioned.

Anyone seen this before? What did you do?

Oh, and I'll check the grounds again.

Thanks.

Alan Watkins · 6th July 2012, 09:47 PM

Quote:

Originally Posted by Igofaster

My tach falls to zero whenever I "get on it", or really anytime I get above about 3K RPM..

A friend of mine not on the forum had exactly the same problem a year ago (well, he said above 3.8K

), I've e-mailed him and will report back.

Dimi Terleckyj · 6th July 2012, 11:58 PM

Hi All

In a lot of instances if you have a multi spark ignition system the tacho gets confused by the multiple sparks and shuts down as the revs pick up.

When I first connected my tacho it read fine at idle but as soon as the revs got up above 1500 it would stop reading.

I had to use an adaptor which piggy backed off the crank sensor on my 5.4 modular motor to get a stable pulse the tacho could read.

Dimi.

Alan Watkins · 7th July 2012, 12:56 AM

Quote:

Originally Posted by awatkins

A friend of mine not on the forum had exactly the same problem a year ago (well, he said above 3.8K

), I've e-mailed him and will report back.

Sorry to say he's getting to work on that problem this week....

But I'll pass on whatever I learn ASAP.

Ron R. · 9th July 2012, 11:53 AM

Alan, Demi,

Thanks.

Alan, I'll be interested to hear what your friend finds out. I've got other issues to tackle that are more pressing, but I'd rather not have to re-invent the wheel if I can avoid it.

Ron

Alan Watkins · 9th July 2012, 01:25 PM

Quote:

Originally Posted by Igofaster

Alan, Demi,

Thanks.

Alan, I'll be interested to hear what your friend finds out. I've got other issues to tackle that are more pressing, but I'd rather not have to re-invent the wheel if I can avoid it.

Ron

Ron --

While we're waiting, is your MSD white wire connected to the SPF black-green wire? (That being the "obvious" way to hook it all up).

If Demi's explanation turns out to be the problem I'm really going to wonder about MSD, because I would expect a signal designed to drive a tachometer (the white wire) would be a nice clean square wave.

Ron R. · 9th July 2012, 01:45 PM

Alan,

I can't say from memory, but I'll check tonight.

Ron

Ron R. · 9th July 2012, 01:50 PM

Regarding Demi's idea,

It would seem strange that the problem would be at the upper RPM range, as the MSD only sends multiple sparks in the lower-mid range. As the RPMs speed up, there is not enough time to send multiple sparks...

So, you'd think that any problem induced by multiple sparks would be more likely to occur at the lower range, and correct in the upper range.

Hmm.

Ron R. · 10th July 2012, 11:54 AM

Alan,

I checked, Yes, black-green to white.

David · 10th July 2012, 12:24 PM

Quote:

Originally Posted by Igofaster

Regarding Demi's idea,

It would seem strange that the problem would be at the upper RPM range, as the MSD only sends multiple sparks in the lower-mid range. As the RPMs speed up, there is not enough time to send multiple sparks...

So, you'd think that any problem induced by multiple sparks would be more likely to occur at the lower range, and correct in the upper range.

Hmm.

Actually that would make sense, if the tacho is setup to expect 8 spark events per revolution but then that drops to 4 over a certain rpm it will drop the rpm reading in half.

That's not it appears to be what you are suffering from however as I'd expect the reading to drop to half rpm if that was the case rather than totally die.

Alan Watkins · 29th July 2012, 09:06 PM

Quote:

Originally Posted by Igofaster

Alan,

I checked, Yes, black-green to white.

I heard back from my friend with the same symptom. He has not been able to test his car yet (has other issues like jammed brakes) but he said he pulled the tach and it was miswired at the factory. Someone else told me that Olthoff said this is common. I asked him for details, haven't heard back yet, but in the meantime there is a tach wiring table in the manual that says:

Harness to Tach:
Black to Green
Brown to Black
Grey/Black to Red/white
Black/Green to White/Black.

I found the following text in an otherwise authoritative article on Smiths tachs:

"Smiths tachometers typically use a color code of:

Black = Ground,
Green = +12v,
White/Black = Signal (coil (-))
Red/White = Lamp"

This and the manual table are completely consistent. So, you could pull the tach and take a look; you might get lucky.

I did post a pretty thorough description of how to pull the tach a while ago here: How to Remove Tach?

It's unpleaseant but perfectly doable. And in my case worth doing simply because the f------g builder jammed it in there in such a way that there would have been an electrical failure from a pinched wire eventually, so I was glad I found that. (Typical SPF; just like the speedo cable jammed against the frame.)

Ron R. · 30th July 2012, 12:25 AM

Alan,

Thanks for the write up. I'll probably tackle that problem when i finally get my voltmeter.

Speaking of brakes, Dennis told me that they get rid of the threaded rod ends (the part that is pinned), and just use regular rod ends retained by a couple of nuts. I just checked...the second pin was sheared off too. In drilling out the remnants, the pins appear to be brass, and are very soft. I'll replace them with steel pins tonight.

Steve C · 30th July 2012, 10:16 AM

Ron,

I must be dense

Can't figure out what partyou are talking about Re

" Dennis told me that they get rid of the threaded rod ends (the part that is pinned), and just use regular rod ends retained by a couple of nuts. "

Are they the rods connecting the masters to the bias bar assy? If so mine are threaded rod with stop nuts against the rod end so isn't the rod ennd locked against the threaded rod by the nut.

Can't figure where the "pin" you speak of is located.

Look forward to your reply

Steve P2125

Alan Watkins · 30th July 2012, 11:40 AM

Quote:

Originally Posted by steve c

Can't figure out what partyou are talking about Re

" Dennis told me that they get rid of the threaded rod ends (the part that is pinned), and just use regular rod ends retained by a couple of nuts. "

Take a look at the second picture here: brake bias bar

and see if that rings any bells.

BTW the entire thread makes good reading.... it contains a moment in history: probably the last time a quality- or safety-related statement directly from SPF or Hitech was made in public, although they studiously avoided addressing the problem at hand (the factory's omission of parts from the pedal cluster).

Steve C · 30th July 2012, 04:13 PM

Alan,

As you know I'm pretty savvy but, I don't get it.

Where is "the part that is pinned"?

For the brakes there are 2 threaded rods, associated lock nuts and rod ends and this assembly at this end of the threaded rod looks to be pretty robust.

Now I see the bias bar guides with the two shoulder pins that keep the rod end aligned....is the "pin" being discussed the two shoulders on the guide?

Steve P2125