Tach way far out!!!!

[ghlkal]

Originally Posted by VetteMed

On my cluster, 300K was not correct. 200K was close, but 220K was about as close as I think I can get. I think 300K may be more correct for base C4s with the 6K tach.

VetteMed, I bet you are correct ... 300K for the 6K tach.

Paul, thanks again for the write up and follow up. After Bloomington, I'm pulling the cluster and fix this.

[Paul Workman]

Let us know how it works out. Yours is the largest error I've heard of, short of additional problems, e.g., a pegged tach...(don't ask!)

P.

[ghlkal]

Originally Posted by ghlkal

My tach is also way off (maybe not 2K at idle, but not close to being accurate)

Just to follow up now that I can read the RPM from the HVAC display. Here's how far off my tach is:

tach reads / actual RPM

1000 / 650
3000 / 1750
4000 / 2325
4500 / 2700
5000 / 2975
6000 / 3500

This is up to a 70% error

[Paul Workman]

Originally Posted by ghlkal

Just to follow up now that I can read the RPM from the HVAC display. Here's how far off my tach is:

tach reads / actual RPM

1000 / 650
3000 / 1750
4000 / 2325
4500 / 2700
5000 / 2975
6000 / 3500

This is up to a 70% error

Well, it sounds like waaaay more than the run of the mill drift of resistor values in the voltage divider: a connection on the board, or (I hope not) the dual op amp chip.

I'd try the cal approach first and see where we are after that.

P.

[XfireZ51]

Hard for me to believe that 3500rpm could be mistaken for 6k. I would double check using a scan tool to confirm rpms.

[ghlkal]

Originally Posted by XfireZ51

I would double check using a scan tool to confirm rpms.

Yup ... I really want to. The first tech 1 I purchased was defective and I'm on the lookout for another.

Originally Posted by Paul Workman

I'd try the cal approach first and see where we are after that.

Yes, hopefully soon, but I would rather have the scan tool to be sure first. And, Paul, I hope it's just the resistor too

[ghlkal]

I just want to bring closure to my tach story …

I did replace the pot with 220K ohm worth of resistors. I used one 220K plus three 1K ohm resistors in series. Because they are +- 5%, the 223K stated value was actually 220K. The tach works great now!


For future reference, you might want to check out CCM diagnostics http://www.zr1.net/forum/showthread.php?t=17846

Using your HVAC as a tach
http://www.zr1.net/forum/showthread.php?t=17799

And, of course, check out -Solutions-
http://www.zr1.net/forum/showthread.php?t=16778

Thanks for everyone’s input!

Gary

[Dynomite]

Great write up Paul....but I do have a question

I think Paul replaced the suspect resistor on the Dash Circuit Board (Resister across Capacitor C4) with a 240K Ohm resistor to get the Tachometer Calibration correct. Some say 220 K Ohm is the standard resistance in that chip (#4 to #10). It appears Paul was correcting a circuitry that did Drift with Time and the Drift in Resistance possibly do to deteriorating original chip resistance (#4 to #10) and capacitor deterioriation.

What was the resistor in the chip (#4 to #10) that came on the board in the first place? Was it 220 K Ohms?

It seems that one might get very close to a correct Tachometer reading just replacing that chip resistor (#4 to #10) with a resister of 220K Ohms in parallel with the Capacitor C4 (soldering on either side of the circuit board)?

Originally Posted by Paul Workman

ZR-1 Tachometer Calibration


Hope this helps!

P.

copyright 2012 All rights reserved

It appears that Paul was correcting a deterioration error in the original Chip Resistor (chip #4 to #10) and Capacitor C4 deterioration and ghikal was correcting a major deterioration in the standard Chip Resistor (#4 to #10) only.

Originally Posted by ghlkal

Just to follow up now that I can read the RPM from the HVAC display. Here's how far off my tach is:

tach reads / actual RPM

1000 / 650
3000 / 1750
4000 / 2325
4500 / 2700
5000 / 2975
6000 / 3500

This is up to a 70% error

[We Gone]

So Dynamite, did you add this to your solutions for quick access. Thanks Paul for the write up.

[Dynomite]

Originally Posted by We Gone

So Dynomite, did you add this to your solutions for quick access. Thanks Paul for the write up.

Absolutely....I added a Link to Paul's post (Post number 4 above) regarding the details for tachometer correction in the third post of -Solutions- shortly after Paul created the post. The Link was added in the third post of -Solutions- under the Heading KEYLESS ENTRY, TACHOMETER, CRUISE

I ran into a major tachometer error recently over the whole range of tachometer read out on the order of ghlkal's error which ghlkal apparently corrected as Paul suggests by clipping OUT the original (#4 to #10) chip Resistor and replacing with 220K Ohms Resistor. The chip Resistance (#4 to #10) does in fact deteriorate over time as in ghlkal's case maybe not having anything to do with the associated C4 Capacitor