M20B25 in 323i, Starting Problems

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chapelja
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Posts: 8
Joined: Tue Dec 10, 2013 8:07 am
My E21(s): 1978 e21 323i manual

M20B25 in 323i, Starting Problems

Post by chapelja »

Hello there,
Its been two weeks since i installed a M20b25 into my 1978 323i and im having problems to get the engine to crank and fuel pump to work.
Everything went smoothly until i got to the wiring,
Ive used a full wiring harness out of a 89 325i with everything hooked up as it should be and all the earths are good.
The Ecu gets power on pins 18, 27
I did the wiring as per Todors write up and used the fuse box side of the C101 plug
E30 pin to E21 Pin
1 5 (altenator)
4 13 (coolant temp)
5 1 (oil pressure light)
6 6 (ignition power fused)
7 8 (ignition power unfused)
9 15 (Tachometer)
13 3 (fuel pump power)
18 10 (ignition starting switch)
Im using the original fuel pump set up out of the 323i and 5speed transmission out of the 323i aslo the M20b25 is completly standard and have heard it run before it was removed from a 1989 e34 525i.

It seems the main issue is that i am not getting ignition power to the starter motor or fuel pump when I turn the key, im getting 12 volts to starter motor but only via the battery, solenoid gets zero. And the fuel pup is not engaging. Alternator is getting power also. Coil gets power too.
I tried bypassing the (fuel pump) wire and the (ignition start) wires straight to the 12 volts battery and it worked and i did hear the engine crank and the fuel pump working but i did not have spark or fuel getting to the injectors.

Is the problem perhaps with the three main relays?
When i turn the key the dash lights up and im getting the ICV buzzing noise but nothing else.
I should also mention that the wiring out of my e21 rectangular fuse box plug didnt just go down the e21 harness, some of the wires went into two black relays, i bypassed those two relays as i needed the wires to meet up with the corresponding E30 pins.

Any input or suggestion would be much appreciated, electrical is not my strong point and i heed help starting my E21 :launch

Thanks a lot in advance :D


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Jeroen
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Posts: 29199
Joined: Tue Sep 14, 2004 12:23 pm
My E21(s): '81 323i Baur
Location: The Netherlands
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Re: M20B25 in 323i, Starting Problems

Post by Jeroen »

Moved to Tech section for better exposure.

Sounds to me like relays not engaging but I'm no expert on these conversions. Good thing is that the engine type used is the one that just used a combined speed/position sensor at the vibration damper at the front. Early ones with the bell housing sensors are more known to cause issues.
Regards/groeten, Jeroen
chapelja
Newbee
Posts: 8
Joined: Tue Dec 10, 2013 8:07 am
My E21(s): 1978 e21 323i manual

Re: M20B25 in 323i, Starting Problems

Post by chapelja »

Thank you Jeroen,
today I found out that the two big relays I bypassed while connecting the rectangular e21 to m20b25 c101 plug were: fuel pump relay and diode relay.

Some of the e21 wiring went into these two relays and the rest went down the harness, now the relays also had their own wiring which went down the harness so I'm not sure exactly how to hook them up now, will they even function.
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