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Motec M8 - attempting to run twin Jaguar Fuel Pump PWM units - advice please

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Hello All,

I am attempting to run two of the Jaguar Fuel pump PWM units (part number C2C35672)

current settings in Motec M8:

1. Aux Output table 2 - Set to user defined PWM table

2. frequency - 100HZ

3. Min Duty Cycle is 2%

4. Max Duty Cycle is 50% (the Jaguar unit puts out 100% duty cycle output with 50% input ask)

6. X Axis - set to RPM

7. Y Axis - set to Throttle Position

8. PWM/switched is set to 0 (Zero) for PWM on

Fuel pump relay is currently set for Load/RPM 1 and is on all the time the key is on, as I was trying to test it when I set it to be on all the time, and still getting no output from Jaguar (siemens) PWM controllers; otherwise, I had it set for fuel pump 101, with a 10 second delay to off.

In the user defined table, I have it set for 99 on every cell for 0 to 500 RPM.

On the Jaguar units, I have the following wired to the corresponding pins:

1. Ground

2. not used

3. Ground to fuel pump

4. +12V Input to PWM

5. INput of Motec PWM wire from Aux 2

6. Output +12V to fuel pump

I do get full power from the relays to the PWM harnesses as soon as the ECU is switched on, as well, I tested the output Hz from the Motec Output and it is 100hz, showing correct.

No matter what I seem to change, I can't get any voltage output from the Jaguar PWM units.

Any help is greatly appreciated.

Bit of a wild guess, but you don't have it set as a pull down/ground, do you?

Where are you checking the voltage signal - at the pump or ECU?

Greetings Gord,

Thanks for the quick help.

Currently, I am not sure at which reference point you are asking about me testing to see if it is a pull down/ Ground.

I am checking the voltage signal at the harness that connects into the Jaguar PWM units from my relays, as well, when I test for a PWM frequency on the wire coming out of the Motec, it shows it correctly on the #5 wire of the Jaguar PWM harness.

There is virtually no voltage going to the pumps (shows .1 V), and no frequency on the output to the pumps either.

Im pretty sure the M8 PWM will work backwards compared to what that that controller wants. 100% DC on a low side drive means "100% low" - ie zero volts.

The controller wants the opposite - 100% "high" for max flow and 50% high for minimum flow. If the M8 doesnt have a setting to invert the PWM logic then you will have to invert the numbers in your PWM table. 0% in the PWM table will be max flow and 50% will be min flow.

Adam, thank you for the kind and thoughtful response.

This made sense to me if the Jaguar PWM controller wanted a backwards signal than what the Motec M8 can provide normally and it can't be switched to a 100% high output.

I modified the table to be 0 in all cells that are in the range from 0 rpm to 2500 rpm and 0% to 100% throttle position.


X Axis set to 1- RPM

Y Axis set to 1- Throttle position

PWM/Switched set to 0 - PWM

Frequency set to 100

Minimum duty cycle set to 50

Maximum duty cycle set to 0

After making these changes:

Relays are still coming on, and there is definitely voltage into the input side on the PWM, but, still no Voltage to the pumps from the PWM outputs.

I swapped the Minimum and maximums around but it did not change.

I noticed that when set to 0, and the minimum at 50 and maximum at 0, the PWM output was showing 50% duty cycle, which should correspond to make the Jaguar PWM controllers go to 100% output duty cycle to the pumps.

As a side note, would it matter if I have more than one pump connected to each each Jag. PWM?

I have a facet lift pump and a Bosch 044 pump wired to the output of each Jaguar PWM (these seem to be capable of more than 20amps draw), and two of these setups for redundancy and enough fuel capacity for max effort with our combination.

Read this bit again: "0% in the PWM table will be max flow and 50% will be min flow."

If the Motec is outputting 50% duty cycle the controller will be outputting nothing - the pumps wont run.

If the Motec is outputting 0% duty the pump controller will be outputting maximum.

Set the aux table parameters minimum to 0 and max to 40. Your aux table will have zeros in it in regions where you want the pump to run at full speed and probably around 40% in areas where you want the pump to run at low speed - there will be a limit to how slow the pump will actually run but it will probably be somewhere around 40% (this would be a 20% output from controller to pump)

When I was messing with it earlier tonight, I had done this and swapped the numbers around on the max and minimum parameters also where it was showing 0% duty cycle then flipped the numbers back to make it show 50%..... and still no output.

Apparently, I am lost here...

I do understand what you are saying about the minimum 20% PWM because the pumps can only run so slow without stopping, this is how I had it set up originally.

So with a constant 12V going in to the FP controller pin 5 do you have no voltage coming out of the pump side of the controller?

I will test tomorrow and make sure what voltage is being sent to pin 5 (the PWM signal wire from the Motec)... I never tested it for voltage output, just frequency.... should have tested it for voltage....

If I remove the Motec wire after testing it, and jumper over a constant 12V+ signal to the pin 5 input to the Jag PWM, I should get 100% voltage output with no PWM from the Jag PWM, correct?

Thanks Again for all your help Adam, I sincerely appreciate your kindness. I am so close here.....

Unfortunately, the day held too many challenges at work to get out to where the car is garaged..... I plan to make it there tomorrow.

Updates to come soon.

Greetings Adam,

I was able to make it to the garage where we keep the car, and I loaded the program with it like I had the other night, with it set up like you describe :

Set the aux table parameters minimum to 0 and max to 40. Your aux table will have zeros in it in regions where you want the pump to run at full speed and probably around 40% in areas where you want the pump to run at low speed - there will be a limit to how slow the pump will actually run but it will probably be somewhere around 40% (this would be a 20% output from controller to pump).

With the relay switched on, it is putting 12.28 volts to the input power side of the PWM units, as tested at pin 1 (Ground) and pin 4 (+12V).

at the 0 RPM and 0 Throttle position on the table, I have the PWM set to 0

When the Pulsewidth on the output shows to be 0%, Testing the pin 5 wire for PWM output from the MOTEC Auxillary output shows +10.98 V (it is a 20 foot long 20 Ga. wire from the ECU to the trunk where I have the PWM units mounted, so I would think this would be about right.

Here is the odd part, as I increase the number in the table value towards 100, the voltage drops to +5.45V, or exactly half. I am stumped because I didn't think the voltage was supposed to go down on a PWM signal, I thought it was supposed to just change the pulsewidth.

There is still no response from the Jag Fuel pump controllers and no voltage on the output side of the PWM units at any time.

Thanks again for bearing with me....

Might be time for a full review of the wiring you have? The voltage drop is around what would be expected with ~15A current and the variation is possibly due to averaging out the PWM values? If so, it's no wonder the pumps don't work.

I don't quite follow exactly what your wiring setup is, but I suspect it's going to come down to using way too light a gauge wiring for the currents that will be drawn by the pumps - especially as some have a higher initial draw and may not have enough voltage to initiate?

I would suggest sizing ALL the pump wiring for a minimum current of 30A, each.

There are some places I would recommend going a few sizes higher than what might be the nominal value, as these are often specified for a 10% voltage drop. These include headlights, starter motors and fuel pumps, as the power is proportional to the square of the voltage and, for the latter two, there will be a minimum voltage before they even operate. Oh, and not forgetting the ground/return path!

This may help - https://www.wirebarn.com/Wire-Calculator-_ep_41.html

Greetings Gord,

I appreciate your thoughts on this, but because only the PWM signal (auxillary output trigger) wire from the Motec is the small 20 gauge ETFE (TEFZEL) wire from here: https://prowireusa.com/c-32-m22759-16.aspx , I hope I have it wired sufficiently.

I have 12 gauge ETFE (from ProwireUSA also) wire ran to all the fuel pumps, using proper crimp connectors and gold plated solid copper wiring lugs.

Loking at a test that was performed on the Bosch 044 pump and other specs, it won't be pulling more than 15 amps max at 100psi of fuel pressure. At 3 bar, the 044 tested by RC Engineering draws 12.4 amps. The Facet lift pump draws about 1-2 amps.

The PWM controller is supposed to be able to handle 20 amps or more per unit. I have two PWM fuel pump controller units that will control two Bosch 044’s and two Facet Lift pumps; one pair of pressure and lift pumps per controller.

I have a 30 amp relay feeding power to each PWM controller. All Ground wires are ran directly with the same size 12 gauge ETFE wire and are also well connected and correct.

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