!993 XJS 6CYL.

Where is the tachometer sending unit located in the engine compartment?
Can it be opened to repair?
Assume tach can be attached directly to sending unit. One ground and one sensor lead.

Installed two tach's and they advance about a quarter inch when the ignition is turned on. No further readings

Is there a simple method to determine trouble in the tach?

Connectors on printed circuit cleaned and plugs cleaned.

THANK YOU WILL PROVIDE INFO WHEN FIXED

 

Tachometer sending units went away in the 60s....but I guess there's always an exception. I'm not familiar with XJS 6 cylinder specifics.

Typically...and I'm betting on your car as well....the tachometer has power, ground, and a trigger or pulse signal from the ignition system, usually the ignition module or "-" side of the coil. On the Jags I'm familiar with the trigger wire is white with a blue spiral tracer, or white with blue and slate spiral tracers.

Others will chime in

Cheers
DD

 

It's hard to find something that doesn't exist! The '93 Electrical manual shows a sender and there was mention of it on another posting. I spent about three hours looking for it on the internet before I sent this post, but found nothing. I'm with you on the "-" side of the coil. I think you can also form a coil around plug one and use that for the trigger, but why if you can get the same from the coil.
Do you have any info on the other part of the question posted?
Thanks
Afterburner

 

Afterburner:


You are confusing me. Not that hard to do, though.


A coil of wire around plug one as a trigger? Where would the end not connected to the tach be connected?


And, if indeed that did create a triggering pulse, it would be 1/6th of the required. Odd tach reading, if at all.


Might just google up "how to wire a tachometer" for generic information. CAVEAT, all materal may not be correct.


Carl

 

Carl
Saw it on You Tube, but did a fast scan and passed it by. Never figured on using it. It's on YouTube if you want to pursue it.
Other than that can you help me with my post?

Did find out three active contacts: One at 11 o'clock and it is earth, one at 2 o'clock and it is positive for 12vts, and one at 5 o'clock the trigger lead. The 5 o'clock lead goes to pin 8 on the "A" plug. Started the car and got doodley-squat!!!! This was with the tach outside the dash and connected with alligator leads. Also did it with a second tach and got the same result. Need one of you people to spread your brilliance across this page and solve the problem. I suspect the trigger wire some how broke lose from the distributer??? OR two defective tachs

 

Just checking.....we've definitely concluded that there is no sending unit? Just for curiosity I'd like to see the page from your diagram that shows it. Very odd, IMHO.

The "1993 Model Year Update" (from the sticky thread) does not show a sending unit. I does show a wire from the coil "-" post for the tachometer. The wires starts off as white/black, then turns blue, then turn red/yellow . The blue section contains a 6.8 ohm resistor. From the diagram I can't tell if this is within inches or feet of the coil itself. I'd simply start at the coil, find the white/black wire, and trace away as far as you can....looking for any problems.

I wonder if the resistor is on the blink?

Do you have a multi-meter to check the continuity and resistance of the wire from the cluster to the coil? That would be a big help.

Cheers
DD

 

I must have mistaken the distributer amp for the tach amp. But I did see one post that talked about a tach amp. Yes I have a multi-meter just about worn it out chasing circuits. Did find a diode that conducted both ways. Will change that out and see if that affects the tach performance. Pin 8 on Plug A carries the distributer signal through the 6.8 ohm resister. I suspect the resister is attached to the distributers negative pole. I plan to run a wire from pin 8 to the multi-meter and then to the negative pole on the distributer. I'll either get an open or 6.8 ohms. Either way I'll know where to look.
By the way, the tach has a very simple internal circuit. All components are readable except for one integrated circuit chip. There may be a number on the flip side but with 14 solder points I am not that interested in looking. Will keep you informed...Thanks for your help.
Afterburner

 

Well back again! Tested contact 8 to "-" on distributer. Continuity with 6.8 resistance. Unfortunately have two defective tachs. I hooked them up directly via alligator clips to contact 8 and 12 vts and ground. Needle didn't flicker when I started the car! Would like to attempt a rebuild but lack the schematic for tracing the circuits. Isn't that the fun of having a Jaguar?

Thanks to all that responded to my quest for help: always appreciated!

ANYBODY: NEED TACH SCHEMATIC

 

After:


1. Just for fun, I did check the You Tube piece. It was how to read rpom's on a one banger engine!!!


2. Check with David Boger at everydayxj for a known good tach.


3. Mark those with a "?" but, don't toss them just yet. Might be a further way to diagnose them and even fix them.


At least you have a good idea of where you stand.


Carl

 

Thanks Carl/Doug
Did not know about Boger. Good resource! No Tach or Schematic. Did order new Tach from eBayUK. Twenty five +Ten for shipping. NOS Jaguar. I considered that a real bargain. I should be able to troubleshoot the old tach's using the new tach as a model.
I had another idea and that was to remove the jag electrics and substitute electrics from a cheap electric tach. Not a difficult job basically exchanging the face plates and needles and then fitting the instrument to the printed circuit. If you are dealing with a hundred dollar instrument that's the way to go, but for thirty five dollars...why bother!
I have been down the road with a couple of E-type and two XJ6/12 . Electrics have never been Jaguar's strong point until they decided to drop Lucas. I did a lot of electrical rebuilding on those cars. Why did I buy an XJS? Minimum Lucas and the most ethically pleasing car on the road!

 

Can't edit the above post so on the last line change "ethically" to "esthically" or better still the most beautiful car on the road! (In my opinion.)

 

Pull 1 leg of the diode and re-check it. If it's in parallel with another component it could appear as if it conducts both ways.

When you check continuity on the wire with the 6.8R resistor make sure BOTH ends of the cable are disconnected or you could get false readings.

 

Thanks for your info. Warren,
Removed Diode and it conducted both ways. From Pin 8 on the printed circuit across to the connection on the "-" negative post gave me a clear reading of 68K. Circuit was open on the pin side. As a result I was not reading through the distributer.

 

Are there any other components on the board, they could be in parallel with the diode. 68k is a strange resistance for a bad diode, I would expect the revers resistance to be lower than this.

Does your meter have a diode test function?

 

I released the diode on one end and tested it. It was short. Then reversed the meter leads and again short. After removal got the same results. Sixty eight k shows on the schematic. Meter does not have a diode check. Reversing leads appears to be a good test.
Replaced diode. Tack worked fine. Problem solved.

 

Good you got it fixed, I misunderstood what you meant with 68k

 

Perfect! Knowledge added.


Toss the bum diode, so as to never mislead you or anyone else.


Carl

 

Tale:


Way back when, I added an after market tach to my Tbird 312 powered 57 FDord Pickup. Kinda tiny for practical purpose. But, as the truck had a granny low transmission, t was fun. Then old dependable, quit running!!!! After much travail, I found no spark. Then more travail, the tach was the culprit. Unhooked and the big V8 roared happily....




Carl