Tach reading vs Torque App

[jvarnadoe]

I was going to reset the adaptive values recently, but then noticed that my tachometer and Torque app readings were off by a wide margin.

The tach wire on the alternator isn't corroded and is well seated. The Torque app reads 14.1 volts when coasting (no throttle), but just on throttle it dips to 13.7 and then recovers to 14.1. Is this a sign that my alternator is on the way out? Or, is this just normal 28 year old Disco behavior? The alternator was last replaced 9 years and 96k miles ago.

	Tach	Torque App
Idle Neutral	900​	694​
Idle in gear	900​	614​
	1250​	1170​
	1500​	1500​
	1750​	2000​
	2000​	2478​

 

[kris812]

I had issues with my NEW alternator with pulsing headlights. Ordered a new rectifier/module to change it..

Got it off the vehicle only to find the Nuts that hold the wires down were loose..

So order a good module to be safe 45$ on ebay, cheapo are 20$ probably best to avoid.. Good part to carry!

Check the module nuts after pulling rear cover off.. If they're loose you can tighten without removing Alt.

 

[kris812]

Also logically, your tach guage is probably off.. it's getting fed the same info as the OBD2 port.. However again I think the module is in play here..

 

[jvarnadoe]

I'll check that module to see if it has loose connections. The tach signal comes from a connection on the alternator, so I'm pretty sure the tach and OBD2 readings are calculated separately. If I remove the tach lead from the alternator, the tach goes dead but the Torque App still shows engine speed.

 

[kris812]

I stand corrected then! OBD2 tach is clearly fed from CPS. Dash tach fed from Module. So Module is the cheapest part to do some binary deduction on the issue.

 

[Newlandy]

I had issues with my NEW alternator with pulsing headlights. Ordered a new rectifier/module to change it..

Got it off the vehicle only to find the Nuts that hold the wires down were loose..

So order a good module to be safe 45$ on ebay, cheapo are 20$ probably best to avoid.. Good part to carry!

Check the module nuts after pulling rear cover off.. If they're loose you can tighten without removing Alt.

Hi, can you provide the ebay details of where to buy that module, please, like you said, a good part to carry!

 

[jvarnadoe]

Here's a link to a rebuild kit. It doesn't include the rectifier, but they do sell one separately.

Alternator Rebuild Kit for 1996-1998 Land Rover Discovery 4.0L Regulator Brushes Bearings Slip Ring - 13727RK

<h5>Alternator Rebuild Kit: Regulator, Bearings, Brushes </h5> <ul> <li>Voltage Regulator with Brushes 14.1 Voltage Set Point; ref# Marelli 83617181, 85561921, RTM153B Other IX123 </li> <li>NTN Bearing 53507 17x35x10mm 6003-2RS Replacing F00M990405, F00M990405370, F00M990432 - 6-103-4N </li>...

www.maniacelectricmotors.com

 

[kris812]

39$ shipped on ebay from Maniac EM.

1996-1998 Land Rover Discovery Alternator Kit | eBay

Land Rover Discovery V8 4.0L 1996-1998. Application Land Rover Defender 90 V8 4.0L 1997. Unit #s Land Rover AMR3021, AMR3107, AMR4247 Marelli 063341353010, 54022543, 63321353, 63341353 Other 13727. h5>Alternator Rebuild Kit: Regulator, Bearings, Brushes.

www.ebay.com

 

[WaltNYC]

I have rebuilt a few alternators using Maniac Motors kits. Always good fit and function.

 

[kris812]

I have rebuilt a few alternators using Maniac Motors kits. Always good fit and function.

Hey Walt, have you ever seen the OP issue of Tach reading different than OBD2? This module seem like the correct route to go? Wanna make sure we sending him in the right direction is all..

 

[p m]

OBD-2 tachometer is fed from the ECU, not the alternator.
It is the tachometer that's dying. I have the same issue in my 95 Classic - the tach over-reads at low RPM and reads about 10-12% low above 3k.

 

[jvarnadoe]

Apparently there's a board in the gauge cluster you can replace to fix this issue. I'll try to snag one the next time a D1 shows up at the local U Pull & Pay.

I appreciate the responses!

Tach erratic / Alternator appears ok - Land Rover Forums - Land Rover Enthusiast Forum

Discovery I - Tach erratic / Alternator appears ok - Hello- I know an erratic Tach may mean a bad Alternator but I've had the issue for 2 months and my battery is ok although I NEED to test the alternator myself. So turning on headlights, honking horn, turn signals will cause the Tach to move up...

landroverforums.com

 

[p m]

Apparently there's a board in the gauge cluster you can replace to fix this issue. I'll try to snag one the next time a D1 shows up at the local U Pull & Pay.

I appreciate the responses!

Tach erratic / Alternator appears ok - Land Rover Forums - Land Rover Enthusiast Forum

Discovery I - Tach erratic / Alternator appears ok - Hello- I know an erratic Tach may mean a bad Alternator but I've had the issue for 2 months and my battery is ok although I NEED to test the alternator myself. So turning on headlights, honking horn, turn signals will cause the Tach to move up...

landroverforums.com

The thread in the link talks about a 95 D1 - which uses a tap from the alternator to run the tachometer.
The tachometer itself appears to be the same between 14CUX and GEMS trucks - the issues may be both electrical (with the little PCB controlling it) and mechanical (dirt in the rotating assembly, weakened return spring).

 

[WaltNYC]

I agree with "p m" ....though I have not experienced this myself.

 

[DiscoClay]

The thread in the link talks about a 95 D1 - which uses a tap from the alternator to run the tachometer.
The tachometer itself appears to be the same between 14CUX and GEMS trucks - the issues may be both electrical (with the little PCB controlling it) and mechanical (dirt in the rotating assembly, weakened return spring).

PM is spot on here. This is why it's handy to be overly detailed when describing your wagon, ex: mine is a 1995 NAS [North America Spec] Lucas 14cux (pre-GEMS) 3.9 with manual (R380) tranny. It is equipped with one of the crappiest stock alternators known to Man: The Magnetti-Marelli (https://www.maniacelectricmotors.co...5-discovery-land-rover-amr3107e-yle10124.html)... But it does have a field winding tap for the tach, unlike the 96-99 GEMS version of the same (https://www.maniacelectricmotors.com/new100ampmaa.html) alternator, which is also a Marelli.

You can make a later (or other) alternator work for your '95 and earlier 14CU/X by getting in there and soldering a wire onto one of the field windings. I recommend proper lead based high temp solder for the job, or a crimp and solder. For those Stateside, who will not find proper high temp solder on the shelf at <insert cardboard autoparts "store" name here>, I can dig up the contact name of the guy who works at the manufacturing facility and sells direct to the public precisely for alternators and motor repair.