Glow light too short, tach too low

[jb86]

91 Eco diesel
Didn't have a tach
Bought one from a forum member
Swapped out the speedo for mph
When I rev the engine high enough to turn off battery light the tach begins to work
But seems low throughout the rpm scale
Idle shows 500, rev it considerably it shows about 1,000 when it should be maybe 1,800

I wired the glow plugs as Vince Waldon shows with the tractor solenoid off the glow plug wire that was to go to number 1 glow
I have a slow start relay and plugs - I may change that sometime
The glow light comes on with key as it should
Goes off after about 4 seconds
But
The starter solenoid makes enough noise I can hear it stays on in time with the slow relay
Maybe 13 seconds or so
Any reason why the light goes off when the relay is still sending power to plugs?
Jon

[Vincent Waldon]

The light is a "wait until I go out before trying to start the engine" light as opposed to a "your glowplugs are getting power" light. 

[wdkingery]

The light is a "wait until I go out before trying to start the engine" light as opposed to a "your glowplugs are getting power" light. 

Yes I second that.. My relay is loud and clicks much later than the light goes out

[jb86]

A friend has an 85 turbo diesel
With fast start relax
Turn key on and light stays on for the appropriate time of the relay
8seconds or so

If my tach registers too low
I wouldn't say 1/2 of what it should be but close to that
Is it possible that the "W" terminal isn't outputting correctly?
Any way to test?
Jon

[92EcoDiesel Jetta]

You posted 2 separate problems in the same thread. Are you suggesting they may be related to each other? They are 99% not related.

You can test the W terminal output with a photo tach and and an oscilloscope. Can you verify that the pulley diameters are the same on the tach donor vehicle and your vehicle? If they are not the same that may be your problem.

I modified my glow plug relay so the cluster LED indicates actual glow plug on time as well as a manual on/off switch. No hacking into the harness. I can go back to stock by simply swapping the relay to a unmodified one.

[jb86]

I didn't think they would be related problems
Just figured since both issues were in the cluster I'd only start one thread
I would imagine that the pulley diameter would be the same
But I'll check that
The cluster originally came from someone in Canada
I have no way to test with an oscilloscope
I'll try a different relay to see if the light operates different
Jon

[Baron VonZeppelin]

I have 4 running 1.6 vehicles, and service quite a few others.
Have not seen one yet that the dash indicator stays on the same length of time as when the relay clicks.
They all go out ahead of the relay click.

I wouldn't get too skeptic on that feature.
If i timed each one exactly - they'd probably all measure differently.

On the tach - pulley size is one variable.
The tension on your belt and condition of belt/pulley is another variable.
You "might" have some slippage.

Fatmobile has posted there is an adjustable dashpot within the cluster.
But i'd check all else before tampering.

It was either AutoZone or AdvanceAuto that checked an alternator for me on  the car once - and their device measured my idle speed. It blanked out on reading when engine was revved.

But you could try that route to get an idle reading to compare.
Could be some compromise within your W terminal devices.

I was supposed to get some readings from W terminal for a guy on Vortex from my 85 Faktry Tach car - when i do - i'll post them here too.

Also have a second 85 Faktry Tach car here for service, that i haven't started on yet. Might grab some data from it too.

[jb86]

I have about 5 relays on hand
Slow and fast
I tested all of them
All seem to have very close to the same timing
They all seem to leave the light on 4-5 seconds or so
All of them - I hear the tractor solenoids under the hood click on and click off at something more than 11 seconds
I read the Bentley manual - says it tells you when it turns on but time on isn't necessary timed with power to plugs

The belt was especially loose
The light would stay on or flicker
If the light is on tach shows 0
I put a new one on
I temporarily deleted ac till I complete the car
So I fabricated a tensioning bracket
A SOB to get belt tensioned
I've got the belt very tight IMHO
But still seems to have some whip to it while running
Light goes out once Rpms go up a light rev
And then tach works
Idle shows about 500 or slightly less
While driving it looks quite low
Example:
Sounds around 2,000 but registers maybe 1,200
It looks to work smooth
Comes right to life once the alternator kicks in
Operates consistently
Just too low
I bought an ac delete pulley (16v version) from toywagen.com
I'll compare diameter to original pulley diameter
Can I get a link

[JamesT]

Loose ground for the instruments on the side of the head. Not removed, but making bad contact. It happened on my car, and had a similar problem. When my engine was at idle, it read between a quarter and half what it should have. Between 1200 and 3000 it read half of what it should, and was fine over 3000 rpm, until it dropped down bellow 2700 again. It also caused my temperature gauge to read a quarter all the time until it warmed up. Then it went to where it should have. My car has two sensors for temperature: one for the instrument and one for the glow-plug relay. I never noticed an overly short glow, but I fixed the problem before it got too cold out. All it took was tightening down the nut on the side of the head.

[fatmobile]

 There is an adjustable pot on the tach.
 It has to be removed/pulled apart to adjust.
 
 I drilled a hole through the front of my cluster so I could adjust from the driver's seat while the car is running.

[92EcoDiesel Jetta]

My tach works as soon as the engine starts even before the alternator starts charging (red alt LED on), but then my tach does not run off the W terminal. Try measuring the W terminal with a meter set on AC and see what voltage you get with the alt LED on and off.  Did you try adjusting the pot on the tach?

In your first post you wrote:

"Swapped out the speedo for mph"

I am scratching my head wondering why you posted that and what significance it has relating to the problems you're having.  Am I missing something?

[JamesT]

In your first post you wrote:

"Swapped out the speedo for mph"

I am scratching my head wondering why you posted that and what significance it has relating to the problems you're having.  Am I missing something?

So one could infer that the reason for swapping the cluster was not wiring related.

[jb86]

I wanted to get more info before posting
I measured original pulley - same diameter as current pulley
I swapped speedo to get mph, that's all. I just noted it, nothing electrical there
I'm fine with the glow light, after testing 5 relays I have, I understand that
Drive belt is tight, now.
I find it strange that the tach doesn't operate until alternator light goes out. A friend has an 85 jetta turbo diesel his tach operates immediately as another post says here
The tach is maybe 50-60% of actual
Idle shows less than 500
While running id say 1800 is actually 3,000 or so
I finally got it on the highway
Rotella 15w40, Mann filter, 15miles on oil change
Got it warmed up around town
81f ambient temp
Car was plenty hot
within 20seconds on highway the oil buzzer and light came on
Not sure if tach actually hit 2,000 which would trip dynamic oil system
I have a 2ft stainless steel flex line to fender well (from filter flange), 2 tees- electric sender to non operating electric gauge (works sporaticly, or occasionally), liquid filled 100psi mechanical gauge and oem white sender
I tested the body of the sender for ground, so the ground flows thru the stainless steel flex line
Lifted hood - mechanical gauge shows better than 10psi at idle, revved engine, hit 40psi around 3k or just over, 30psi was around 2k, according to my autometer gauge that world immediately at start up and smoothly as I'd expect
Using a light tester on positive
Engine at idle I verified the blue sender on head to be ok
The white one also checked out ok, at idle no ground at plug, revved engine till psi went somewhere near 30psi light came on
so the sensor works
Next test is to tap onto the yellow wire at the sensor, run into car, when light and buzzer goes off ground that wire to see if the light goes out
Is it possible that the dynamic oil pressure and tach operation are the same issue?
How do I know if "W" output is correct?
Jon