Re: Tach way far out!!!!
 

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.

Re: Tach way far out!!!!
 

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.

Re: Tach way far out!!!!
 

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 :eek:

Re: Tach way far out!!!!
 

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.

Re: Tach way far out!!!!
 

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

Re: Tach way far out!!!!
 

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

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 :neutral:

Re: Tach way far out!!!!
 

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

Re: Tach way far out!!!!
 

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)?

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.

Re: Tach way far out!!!!
 

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

Re: Tach way far out!!!!
 

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 :thumbsup:

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 :p