[AlexE]

Hello,

After succesfull design of Speeduino PnP board for MX5/Miata NBfl 01-05 i designed board for 99-01 cars (64 pin connector). During testing on friends car I encountered issue - fuel pump is not working. Bypassing fuel pump relay in diagnostic box makes pump running, car starting and running properly.

Now trying to understand the problem and find right solution. According to schematics I have (attached) FP control is connected to pin 3N, LG wire. Grounding this wire should make pump running

well, maybe should but its not. Mosfet used for FP control is properly energized. But measured voltage on 3N (LG wire) and its 0V so grounding cannot change anything. I expected to be be around 12V as according to schematic there should be wire connected to relay coil and also F/P pin on diagnostic connector (second is true and helped us make car running as I wrote).

it seems there can be something in between on a wire to ECU pin 3N. Maybe another relay controlled by immo circuit? I cant find it on schematic anyway. Maybe schematic I have is wrong (US, instead of EU equipmmed with immo)

could you please help me?

[JHolland]

Have you checked the silk screen markings on the circuit board? I have seen other Denso ECUs where they use jumpers to swap a couple of the pin designations so a non-immo ECU won't work in an immo car.

[AlexE]

I dont suspect there will be anthing on original ECU. If you mean Speeduino board - I designed it

[EdMcGuirk]

Are you sure that your schematic matches your car? My schematic for a US 2001 with immobilizer is quite different. Different color wires at the FP relay (R/W not LG) and ECU pin 2M for fuel pump with 3N not used.

I assume immobilizer and variable cam are major differences to the wiring harness during 1999-2001 time span. I believe the immobilizer only interfaces with the ECU (and dashboard light). It does not affect the starter motor or the fuel pump in 2001.

Otherwise, I agree, a ground at the correct ECU pin should be all you need to send power to the fuel pump if the bypass at the diagnostic box works. In any case the wire color code should match at the FP relay, ECU, and the Diag box. There are no fuses or junctions that should affect continuity between those 3 pins.

[AlexE]

FP on 2M pin is in 01-05 NBfl, completely different connector and pinout


anyway solved!

FP control in EU versions 99-00 is on pin 3P, not 3N, also wire color is different RED/WHT not LIGHT_GREEN. Wire LIGHT_GREEN is also present on ECU connector but probably going only to X16 connector then left unconnected there. Maybe because of harness standarization or so

so my boards are ready If someone needs one PM me

1693645708439.jpg (2.29 MiB) Viewed 3955 times

[Hesara]

Hey Alex, ive run into the same issue on my 1999 NB as well and glad to hear you've found a solution but due to my newbness when it comes to all this I don't really understand the solution. I've got the PNP speeduino for a 99-00, what would the process be to mimic what you've done. Pictures if possible would be greatly appreciated.

[AlexE]

just connect pin 3N with 3P on the board