Alternator not charging; known good alternator and battery. Any Ideas?
- Thread starter DiscoClay
- Start date
So, the duel alt is working like a champ. One problem though: the stock alt is now from a 97 GEMS 4.0. This means the tach signal is different.
In the non-NAS D1/14cux, the tach signal is a DC ~squarewave that comes from the coil [as is proper]... but be annoying to us Yanks they changed this up for the NAS: The tach signal comes off a stator winding I the alternator! WTF[?]. The 14cux ECU still gets it's engine speed signal from the coil though.
Because of this, the later alts are not set up to work oob in a =<'95. Even if they do have a W [wave] terminal, the pulley diameter is different [reads fast], and because the frequency of the alternator revolution is 3.75×[ish] higher [and because it's AC vs. DC/square wave], i cannot simply connect the tach to the coil.
Has anyone else ran into this problem? Do you know if the tach pc board has a NAS/Global circuit that i can modify?
Here is what grok spit out, it looks pretty good but I prefer humans intheknow confirm/correct:
In the non-NAS D1/14cux, the tach signal is a DC ~squarewave that comes from the coil [as is proper]... but be annoying to us Yanks they changed this up for the NAS: The tach signal comes off a stator winding I the alternator! WTF[?]. The 14cux ECU still gets it's engine speed signal from the coil though.
Because of this, the later alts are not set up to work oob in a =<'95. Even if they do have a W [wave] terminal, the pulley diameter is different [reads fast], and because the frequency of the alternator revolution is 3.75×[ish] higher [and because it's AC vs. DC/square wave], i cannot simply connect the tach to the coil.
Has anyone else ran into this problem? Do you know if the tach pc board has a NAS/Global circuit that i can modify?
Here is what grok spit out, it looks pretty good but I prefer humans intheknow confirm/correct:
How to Convert the 1994-1995 NAS Land Rover Discovery 1 Tachometer to Use the Ignition Coil Signal
Overview: Why Convert and Technical Background
The 1994-1995 North American Specification (NAS) Land Rover Discovery 1 (D1) with the Lucas 14CUX ECU uses the alternator’s W terminal to provide an AC pulse signal for the dashboard tachometer, generating approximately 15 pulses per engine revolution (6 pulses per alternator revolution × 2.5:1 pulley ratio, e.g., 750 Hz at 3000 RPM). In contrast, the ignition coil’s negative terminal, used by the ECU for engine speed (via Pin 1 with a 6.8k ohm resistor), produces a DC-based square wave with 4 pulses per engine revolution (8 firings over 2 revolutions for the V8, e.g., 200 Hz at 3000 RPM). The alternator signal’s higher frequency and AC nature mean the stock tachometer is calibrated specifically for it, not the coil’s lower-frequency DC signal.
Converting to the coil signal may be desired to simplify wiring, align with other Rover V8 setups (e.g., non-NAS models using coil-based tachometers), or troubleshoot alternator-related tach issues. However, the conversion requires:
- Rewiring: Redirecting the tachometer input from the alternator to the coil.
- Signal Conditioning: Adding components (resistor, diode) to protect the tachometer from the coil’s noisy, high-voltage pulses.
- Calibration: Adjusting for the frequency difference (4 vs. 15 pulses per revolution), as the stock tachometer will read ~3.75 times too low (4/15 = 0.267) without correction.
The coil signal is reliable (used by the ECU) but noisier than the alternator’s, requiring careful conditioning. A tach adapter is typically needed for accurate readings, as the stock tachometer’s internal circuitry is AC-optimized and may not handle the coil’s DC signal well without modification.
Sources:
- Land Rover Discovery 1 RAVE manual: https://www.landroverweb.com/Pdf-files/Manuals/1995-Discovery-RAVE-Manual.pdf
- Dakota Digital SGI-100BT manual: https://www.dakotadigital.com/pdf/SGI-100BT.pdf
- AutoMeter tachometer installation guide: https://www.autometer.com/media/manual/2650-1564.pdf
How to Convert the Tachometer to Use the Ignition Coil Signal
Step 1: Gather Tools and Materials
- Tools:
- Multimeter (for testing voltage/frequency).
- Wire strippers, crimpers, and soldering iron (for wiring).
- Screwdrivers and socket set (to access the instrument cluster and coil).
- Materials:
- Insulated automotive wire (18-16 AWG, ~2-3 meters).
- 1k ohm, 1-watt resistor (to limit current): https://www.digikey.com/en/products/detail/1k-ohm-1w-resistor
- 1N4007 diode (to block reverse voltage spikes): https://www.digikey.com/en/products/detail/1N4007
- Optional: 12V zener diode (1N4742, to clip voltage): https://www.digikey.com/en/products/detail/1N4742
- Optional: 0.1 µF ceramic capacitor (to filter noise): https://www.digikey.com/en/products/detail/0.1uF-ceramic-capacitor
- Tach adapter (e.g., Dakota Digital SGI-100BT): https://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=1269/
- Electrical tape, heat shrink tubing, and connectors (spade or butt connectors).
Step 2: Disconnect the Battery
- Disconnect the negative battery terminal to prevent electrical shorts or damage while working on the wiring.
- Why: The ignition coil and tachometer circuits operate at 12V, and accidental shorts could damage components or cause injury.
Step 3: Locate and Disconnect the Stock Tachometer Wire
- Find the Alternator W Terminal:
- Locate the alternator (front of the engine, passenger side in LHD vehicles).
- Identify the W terminal (a spade connector or part of a multi-pin plug, often labeled “W” or “TACH”).
- Trace the wire (likely white/slate or black/yellow) from the W terminal to the instrument cluster, referencing the RAVE manual wiring diagram: https://www.landroverweb.com/Pdf-files/Manuals/1995-Discovery-RAVE-Manual.pdf
- Access the Instrument Cluster:
- Remove the dashboard trim and instrument cluster (see RAVE manual, Section 86, Electrical, for steps).
- Find the tachometer input wire on the cluster’s multi-pin connector (typically Pin 5, confirm with wiring diagram).
- Disconnect the Wire:
- Disconnect the tachometer wire from the alternator’s W terminal and the instrument cluster connector.
- Why: The stock wire carries the alternator’s AC signal (15 pulses per engine revolution, 750 Hz at 3000 RPM), which must be replaced with the coil’s DC signal (4 pulses per revolution, 200 Hz at 3000 RPM).
Step 4: Connect the Tachometer to the Ignition Coil
- Locate the Ignition Coil:
- Find the coil (near the distributor, driver’s side in LHD vehicles).
- Identify the negative terminal (marked “-” or terminal 1, typically connected to a white/black or black wire).
- Run a New Wire:
- Run a new 18-16 AWG wire from the coil’s negative terminal to the tachometer input pin on the instrument cluster’s connector.
- Secure the wire through the engine bay and firewall, avoiding heat sources and moving parts.
- Use spade or butt connectors for a secure connection, and insulate with heat shrink or electrical tape.
- Why: The coil’s negative terminal provides a 12V pulsed signal (4 pulses per engine revolution) already used by the ECU, making it a viable tachometer source. Rewiring bypasses the alternator’s W terminal.
Step 5: Add Signal Conditioning
- Build the Conditioning Circuit:
- Connect a 1N4007 diode in series (anode to coil, cathode to resistor) to block reverse voltage spikes.
- Connect a 1k ohm, 1-watt resistor in series after the diode to limit current and reduce noise.
- Optional: Add a 12V zener diode (cathode to tachometer input, anode to ground) to clip voltage spikes to 12V.
- Optional: Add a 0.1 µF ceramic capacitor across the tachometer input to ground to filter high-frequency noise.
- Example Circuit:
- Coil negative → 1N4007 diode (banded end toward resistor) → 1k ohm resistor → tachometer input.
- Optional: Zener diode and capacitor from tachometer input to ground.
- Install the Circuit:
- Solder or crimp the components into the wire near the tachometer input (e.g., behind the instrument cluster).
- Insulate all connections with heat shrink or electrical tape.
- Why: The coil’s signal is a noisy 12V square wave with potential high-voltage transients (unlike the alternator’s cleaner AC signal). The diode, resistor, and optional components protect the tachometer and ensure a stable signal. The 1k ohm resistor is a standard value for coil-based tachometer circuits (e.g., AutoMeter setups: https://www.autometer.com/media/manual/2650-1564.pdf).
Step 6: Calibrate the Tachometer
- Problem: The stock tachometer is calibrated for the alternator’s 15 pulses per engine revolution, but the coil provides 4 pulses. Without adjustment, the tachometer will read ~3.75 times too low (4/15 = 0.267, e.g., 800 RPM at 3000 RPM).
- Options:
- Check for Internal Calibration:
- Inspect the tachometer for a calibration potentiometer or jumper (rare in stock D1 gauges).
- Adjust to scale the 4-pulse signal to match RPM (requires specialized knowledge and may not be possible).
- Use a Tach Adapter:
- Install a tach adapter (e.g., Dakota Digital SGI-100BT, ~$100) between the coil and tachometer: https://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=1269/
- Program the adapter to multiply the coil’s 4 pulses by 3.75 to output 15 pulses per revolution, mimicking the alternator’s signal.
- Follow the adapter’s manual for wiring and calibration: https://www.dakotadigital.com/pdf/SGI-100BT.pdf
- Check for Internal Calibration:
- Why: The frequency difference (coil: 200 Hz at 3000 RPM; alternator: 750 Hz at 3000 RPM) causes the stock tachometer to misread the coil signal. A tach adapter adjusts for the lower pulse count, ensuring accurate RPM display.
Step 7: Test and Verify
- Reconnect the Battery:
- Reconnect the negative battery terminal.
- Start the Engine:
- Start the vehicle and observe the tachometer at idle (~700-800 RPM), 2000 RPM, and 3000 RPM.
- Verify Accuracy:
- Compare the tachometer reading to a diagnostic tool (e.g., OBD scanner or ECU data via a Land Rover test tool) or a handheld tachometer.
- If using a tach adapter, adjust its settings if the reading is off (e.g., fine-tune the pulse multiplier).
- If the tachometer is erratic, check the conditioning circuit (diode orientation, resistor value, connections) for issues.
- Troubleshoot:
- No Reading: Verify the coil connection, diode polarity, and tachometer wiring. Test the coil signal with a multimeter (expect ~200 Hz at 3000 RPM).
- Erratic Reading: Inspect for loose connections, noise (add the capacitor), or voltage spikes (add the zener diode).
- Why: Testing ensures the coil signal is correctly processed and the tachometer displays accurate RPM. The coil signal is reliable (used by the ECU) but may require fine-tuning due to its noisier nature.
Step 8: Secure and Finalize
- Secure Wiring:
- Route and secure the new wire with zip ties, avoiding heat sources and moving parts.
- Ensure all connections are insulated and protected from vibration.
- Reassemble the Dashboard:
- Reinstall the instrument cluster and dashboard trim (see RAVE manual, Section 86).
- Final Test:
- Drive the vehicle and confirm the tachometer operates correctly across the RPM range.
- Why: Proper installation prevents electrical faults, ensures durability, and restores the vehicle’s appearance.
Additional Notes
- ECU Compatibility: The coil signal is already used by the 14CUX ECU (Pin 1, with a 6.8k ohm resistor). Tapping into the coil for the tachometer won’t affect the ECU, but avoid introducing noise (e.g., ensure tight connections).
- Frequency Recap:
- Coil: 4 pulses per engine revolution (8 firings over 2 revolutions for the V8), e.g., 200 Hz at 3000 RPM.
- Alternator: 15 pulses per engine revolution (6 pulses per alternator revolution × 2.5:1 pulley ratio), e.g., 750 Hz at 3000 RPM.
- The coil’s lower frequency (3.75 times less) necessitates a tach adapter for accurate readings.
- Parts Sourcing:
- Resistor, diode, capacitor: DigiKey: https://www.digikey.com/
- Tach adapter: Dakota Digital: https://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=1269/
Troubleshooting Tips
- Tachometer Reads Low: Adjust the tach adapter’s pulse multiplier to correct the reading.
- No Signal: Check the coil’s negative terminal with a multimeter (expect 12V pulses). Verify diode orientation and resistor continuity.
- Erratic Behavior: Add the zener diode/capacitor, or use a tach adapter to clean the signal.
This. Recently replaced mine on the '94. Swapped the pulley and drilled out the terminal to fit onto the new alt stud.
Does the GEMS engine use the W terminal? I thought it uses the GEMS ECU. 100% the pulley is a different size.
Also, you are saying it's hallucinating.. fair enough, but which part is wrong? ...Just the GEMS info? Because the wiring appears correct.
--I ask because I need to update that or delete it so that it does not lead anyone down the wrong path.
I am going to run off the coil and use a converter. Then, when the Low RPM Torque Engine is finally built...I'll just pull from the ECU (FOME based).
Hey Robert, just to be clear: you mean all NAS 14cux (3.9/4.2) and GEMS (4.0/4.6) 1994 through ~2003 D1/D2? Do you know if this includes RRC & P38?
In a Disco 1, GEMS = 1996 through 1999, noting that 99 was the changeover year when both the D1 and D2 were on the market. 94 and 95 were 14CUX.
In a P38, GEMS = 1996-1998. 99-02 are Bosch.
All 1990s RRCs are 14CUX although the 1995 model has a bunch of properties unique to that model year, making it an oddity and trickier to source parts for.
The P38 GEMS alternator is higher output than the D1 GEMS alternator (130 vs 100? Something like that?). I have the P38 alternator in my 1998 Disco for the rare occasions when all 10 forward facing lights are switched on for an extended period of time. One of those "nice to have but not necessary" touches. Kind of like the analog dash clock I put in my Disco from a 1995 Range Rover.
I just replaced the alternator in 1998 d1 gems. It uses the w terminal for the tacho. Brand new china thru ebay. See my thread on alternator specification.
So on the pulse / frequency converter.
I have modified several tachs from different brands and engines. All of them had a specific chip to manipulate the pulses to a DC voltage for the movement.. I have to add these are tacho before canbus control engines.
The principle to DC conversion goes thru a monoflop electric conversion. The value of the output ( tacho reading) is depending on a resistor/ capacitor rc time . Often the circuit board has a small potentiometer to adjust for part tolerances. By changing the capacitor you easily can make a 8 cul tach into a 4 or 1 cylinder engine or as I have done with a inductive sensor measure rotation at the camshaft for a diesel conversion.
I haven't had the dash apart of my d1 so I do not know what it looks like but it should be easy to change the capacitor without buying an ,I assume pricy converter box.
Let me know if you need help
Johan
So on the pulse / frequency converter.
I have modified several tachs from different brands and engines. All of them had a specific chip to manipulate the pulses to a DC voltage for the movement.. I have to add these are tacho before canbus control engines.
The principle to DC conversion goes thru a monoflop electric conversion. The value of the output ( tacho reading) is depending on a resistor/ capacitor rc time . Often the circuit board has a small potentiometer to adjust for part tolerances. By changing the capacitor you easily can make a 8 cul tach into a 4 or 1 cylinder engine or as I have done with a inductive sensor measure rotation at the camshaft for a diesel conversion.
I haven't had the dash apart of my d1 so I do not know what it looks like but it should be easy to change the capacitor without buying an ,I assume pricy converter box.
Let me know if you need help
Johan
Interesting thread. Please do not pull cables off batteries while the engine is running. This something you could do on a very old car with a generator and no electronics. With an alternator, and modern electronics, it could cause a damaging voltage spike and, not coincidently I fear, pop diodes. A few simple tests with a voltmeter and inductive ammeter will quickly tell you if the charging system is working.
Yeah. I was looking at a converter. I will be using a FOME based ECU at some point (see: https://discoweb.org/index.php?threads/alfreds-holy-grail-low-rpm-high-torque-rv8.102126/). until then, I just want to remove it from the alternator.. and use the coil signal that is feeding the 14CUX it's engine speed signal.