my tach is reading low....but why???

[53 willys]

So I got a Diesel cluster from "Burn your money"(thanks buddy) I just got it installed/hooked up on my 91 GLI that's been converted to Diesel..
problem is the tach wont show a reading until I "excite" the alternator regulator by goosing the accelerator pedal..then it reads REALLY low...right now it says I am idling at 200 RPM.
why would it do this?? is there an adjustment "pot" like on the gasser tachs??
if there was a "pot" then I could use my phototach to adjust the stock tach to read the proper RPM...but if there is not a "pot" then what do I do??

[79rabbit4dr]

if there is no pot then what do I do??

 :lol:  :lol:

you should just send that cluster to me and not worry about it. I'll even pay for shipping  :wink:  Sure, you can have my clock cluster. Straight up, sounds good!

[jtanguay]

my alt used to do that when the belt was slipping... something is wrong with either the cluster or the alt.

[53 willys]

my alt used to do that when the belt was slipping... something is wrong with either the cluster or the alt.

Hmmm my belt is new and snug..so I guess that leaves the alt or cluster???
is there a way to diagnose it so I don't have to throw parts at it??

[Vincent Waldon]

The "won't show a reading until I rev the engine once" is 100% normal... presumably the alternator light is on until this initial rev as well ??

Does it seem like you are getting random readings, or is it off by about 5X (ie 1000 RPM reads as 200, 2000 RPM reads as 400, 3000 reads as 600) ??

Testing the alternator W terminal is best done using an oscilloscope:



if you have a multimeter you can start by confirming you see an AC signal of appropriately 8 volts at the W terminal:

[53 willys]

Thanks Vince!
its kinda weird...it will read up to 3k...or more?? thats just about as far as I have gone with RPM's since I am unsure of the real reading...we have a phototach I'm gonna try and get some comparing readings.
I have some other issues I'm working out on this build so I have not had lots of time to investigate the tach....I* wish it was just the tach instead or the..
dipstick oil leak
turbo coolant line leak(cant find the metric thread pitch I need)
heater blower motor quit working after heater core install(might just be a ground or something?) normally this would not bug me but winter is almost here and I need defrost.

blah blah blah...my list is to big to post..lol

[fatmobile]

Yeah, there's an adjuster pot on the tach circuit board.
 I like to desolder it and move it to outside the cluster so I can adjust it while the cluster is hooked up.
 On my first CE2 diesel tach (gasser converted to diesel) I drilled a hole in the front of the cluster and just turned the screw with a small screwdriver, through the face.

[53 willys]

Yeah, there's an adjuster pot on the tach circuit board.
 I like to desolder it and move it to outside the cluster so I can adjust it while the cluster is hooked up.
 On my first CE2 diesel tach (gasser converted to diesel) I drilled a hole in the front of the cluster and just turned the screw with a small screwdriver, through the face.

got any pics of the soldering job?? I would love to see where and how it is soldered on....
 

[burn_your_money]

Does the tach appear to be reading correctly once you are up and going? Like once you've started moving does it kind of jump to the "approximate" correct RPM?

[53 willys]

Does the tach appear to be reading correctly once you are up and going? Like once you've started moving does it kind of jump to the "approximate" correct RPM?

yeah it jumps up...but I have a feeling it's still off..by how much?? I'm not sure??....I will phototach it on Tuesday..I wont have time tomorrow..

[fatmobile]

The tach thread has pictures of the pot.
 I've never seen a CE2 TD circuit board so can't help much but when you find the pot desolder it and solder 2 wires to the circuit board and solder the pot back on, hanging out the right side of the cluster.

[zukgod1]

Once he excites it and it wakes up it says he's idling @ like 2-300 rpm.

Listening to his engine I would say closer to 900. I didn't pay attention to it on our little test run he took me on to be able to comment if it sounded like it showed.

Mark try adjusting the belt just a tad tighter just to be sure.
I've had mine slip at idle before and it looked tight. I just gave it a couple turns on the tensioner and from then on it seemed to work fine.

Rambling now better go.

Dan