Injectors not firing?!

[spiDmang]

Hey dudes,

I have an 91' Rebuilt M20b25 going into a 87' 325e chassis. I have re-pinned the C101 and have ran wires to accommodate the C104 needs...I believe I wired this up right but i am getting the following issues...


Upon first start up, the engine would crank for days but not fire up. I proceeded to check if i had spark at the plugs... That checked out FINE!

Next, i checked for fuel..I removed the return line from the FPR, and bridged the fuel pump relay (pins 30 and 86 if im not mistaken), and Fuel gushed out no problem, so i have fuel at the rail.

I didnt know if the pump was kicking on during cranking, so I had someone sit in the car and crank while i bridged the fuel pump relay...Still no start.

I disconnected the injector harness, and proceeded to see if I had 12v power to the harness....there is nothing.

The question is, should i be seeing 12v constantly at the injector wiring harness? Or Is it switched, so that when I crank, the injectors get power? What tells the injectors to fire? From my understanding, I thought the CPS sent a signal to the DME which controls spark and fuel distribution? If thats true, how am i only getting spark, but no fuel?

PLEASE HELP!!

[varg]

They see 12V through the main relay when in run or start and are grounded by the ECU to fire. If the fuel pump turns on, they'll see 12V because the fuel pump relay is triggered by the output of the main relay. Make sure C191's terminals aren't loose or corroded.

[spiDmang]

They see 12V through the main relay when in run or start and are grounded by the ECU to fire. If the fuel pump turns on, they'll see 12V because the fuel pump relay is triggered by the output of the main relay. Make sure C191's terminals aren't loose or corroded.

This is awesome! Thank you. C191 is the injector harness connection??

[varg]

Yeah the round one under the manifold.

[spiDmang]

Yeah the round one under the manifold.

Gotcha. Yeah the connection was solid with no corrosion.

So the fuel pump obviously works because bridging the relay turns it on, and I get flow from the return line, BUT i need to verify that the pump is activating via the ignition switch, that way i can see if its the fuel pump relay, main relay or DME?

[tim88325is]

Gotcha. Yeah the connection was solid with no corrosion.

Did you pull back the rubber boots on the C191 connectors? Many times the corrosion is on the back side of the connectors where the wires connect to the pins, not between the two halves.

[varg]

Put the return line in a bottle and crank the engine for a few seconds.