Fuel pump doesn't come on with stock ecu only megasquirt

[kickingklutch]

as the title states my fuel pump wont come on with my stock ecu the car is a m20b25 89 525i i've been having major issues with the car not running and have just been going through everything trying to get it to run again and figured i'd use the stock ecu to test it to rule out bad tuning which i dont think it is. i haven't checked if the engine gets spark on stock ecu just tried it and didn't hear the fuel pump come on and felt pretty defeated lol

[Dj Buttchug]

Alright so the first thing you want to rule out is any changes made to the car when the standalone was installed. If pin outs were changed for the fuel pump output signal that could cause only the standalone to cycle the pump. Also confirm the stock ECU is known working?

[kickingklutch]

thanks for the reply. gonna look at pin outs when i get back to the nightmare lol and another good point ecu could be fried bought the car with it on the standalone

[illmaticD]

If I'm not mistaken, M20 cars do not prime in the ignition on position with the stock DME / ECU. Megasquirt does prime in the ignition on position and it allows you to adjust the duration of the prime as well.

As stated above, first see if there were any changes made to the wiring when the Megasquirt was installed. A stock DME is designed to run on an AFM and not an IAT sensor.

If it is a MS2PNP, the usual changes are:

• Adapting the M20 AFM wiring to run a GM IAT sensor (GM IAT only uses 2 out of the 4 wires in the stock M20 AFM harness. The stock DME cannot run off of an IAT sensor)
• Converting the M20 TPS wiring to use a E36 TPS (Requires flipping the order of two out of the three wires in the stock M20 TPS harness. Because of this, using a stock DME + E36 TPS will cause the car to immediately shut off once the pedal is pressed)
• Wiring a wideband o2 sensor into the factory harness instead of directly to the Megasquirt. (Shouldn't really be an issue. If anything, the stock DME will start the car in open loop)
• Using the green ignition coil wire to power a wasted spark ignition setup. (Stock DME can only run on a distributor-style ignition)

Since the fuel pump prime works with Megasquirt, it sounds like your fusible link, fuel pump, and fuel pump fuse are all fine. I recommend checking out the following:

• The C191 connector: The small round fuel injector harness connector located under the throttle body. Coolant from the throttle body heater hoses tends to leak onto this connector causing it to fail. Sometimes loosening it a little allows it to work again.
• Crankshaft Position Sensor: By design, the DME needs a crank signal to power the fuel pump/provide spark
• Blue coolant temperature sensor: Located on thermostat housing. The wiring is a part of the C191 injector wire harness. M20s use coolant temp to regulate fuel/air mixture on startup