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M90A no spark, no fuel

tpgurgle

New member
This 2002 M90A TDLI is a "new to me" motor, bought as-is. The motor cranks, but the high pressure fuel pump does not operate, and I have no spark.

There is 12v to the ECU,12v to the fuel pump, 12v to the coils, and 12v to the fuel injectors. The ground connections at the ECU plug are good. The fuel pump operates when a ground is jumpered, so it is good. The fuel injectors click when a ground is supplied.

It appears the ECU is not supplying grounds to the fuel pump and other circuits. The kill swith is good. the neutral switch is good. The oil level sensor is good. the alternator coils read the correct ohms. The ECU is new. What else would keep the ECU from completing the circuits?
TIA,
Tom
 
Ooops! My bad. Its a MD90A 3t9. Thanks for replying, Paul!

Part of the difficulty I have is this was a replacement motor on a trailerable houseboat, and the MD90A tach didn't make it to the pilot station in the conversion, so I cannot read trouble codes. Also, I only have a Seloc manual and there isn't a pin-out chart for the ECU plugs. The wiring diagram is also incorrect. I have been unable to find a factory manual, so I am at a disadvantage!
 
I would check the ECU to verify any of the legs that require ground are getting it.
Part of the issue is that the MD90 series has now gone through B and C revisions, so the old manuals may now be out of print. I will check. And thanks to EPA, the TLDI is no longer being sold in North America.
 
As best I could tell from the Seloc manual, the ecu has 3 legs requiring a ground and each has a good ground. I have gone over all the grounds I could find. Thanks for looking into this.
 
The A manual is indeed out of print. I don't have a reprint, either. Sorry.
Do you have the old ECU to test?
 
You can install the old ECU and see if you get grounds where you need them. The seloc manual is worthless.
 
Yeh, Paul, I get no grounds where I need them on either the original or replacement ECU, leading me to believe that I am missing something. I am presently tracing every conductor. Think I will ask the forum for an electrical wiring diagram. I am not a mechanic, but do have electronic/electrical background. I agree - Seloc sucks! Tom
 
Yeh, Paul, I get no grounds where I need them on either the original or replacement ECU, leading me to believe that I am missing something. I am presently tracing every conductor. Think I will ask the forum for an electrical wiring diagram. I am not a mechanic, but do have electronic/electrical background. I agree - Seloc sucks! Tom

Hi TPGurgle I have same issue with 2019 30HP EFI and wondering if you resolved this? I have no fuel and no spark despite there being 15 volts at the high pressure fuel pump. Thanks for any advice.
 
Stand by; I'm working on a reply[
The high pressure fuel pump is energized at all times from the battery. You will always see battery voltage on the blue wire. To complete the circuit, the ground for the pump comes through the ECU. You can check the pump by grounding the yellow wire. I do this by sticking a safety pin through the insulation and jumper it to the engine block. (Seal the pin prick with liquid tape or silicon seal). Does the pump run? If not, replace the pump innards.

If the pump runs, then I would check the safety kill switch, the brown wire at the ECU 12 pin connector. It should check infinity to ground. If not, then the kill switch is the problem.

I would next check the two black wires on the same ECU plug. If you do not have 0 ohms to ground, or very close to it, then I would find the points of connection to the motor block or motor housing the conductors are attached to, and clean, sand the connectors to ensure a good, conductive connection.

If the problem is not resolved at this point, let me know and we will pursue the next step.
 
Thanks for the response TP. The HP fuel pump is an aftermarket copy so may be the problem. Unfortunately I am going away for a few weeks now and won't be able to check until I come back.
I am curious however would a fuel pump problem also result in no spark?
I did check the kill switch by disconnecting it but will check by your method when I get back. Thanks again.
 
Thanks for the response TP. The HP fuel pump is an aftermarket copy so may be the problem. Unfortunately I am going away for a few weeks now and won't be able to check until I come back.
I am curious however would a fuel pump problem also result in no spark?
I did check the kill switch by disconnecting it but will check by your method when I get back. Thanks again.


In the 90 TLDI, the ECU supplies grounds to the fuel pump as well as the ignition coils. No grounds - no fuel, no spark. I had a conductor missing from the switch to the ECU that kept the ECU from “turning on”. It looks like your ECU wiring is significantly different than my 90, so I don’t think I can be much help, but I’ll tell you who can help. I spoke to Tohatsu factory mechanic Vic on a few occasions and he greatly assisted me, although I’ve heard all the factory mechs are great! The Texas factory tech number is 469-771-3740
 
FYI I cut the fuel pump ground coming from the ECU and earthed the fuel pump directly to the block and the motor is starting and running fine now. Haven't run it under load yet so not sure if its a permanent fix. Thanks for your help.
 
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