M20B25 return line

[SAILE30]

Hi guys how are you. I am having an issue here, I did a conversion, jetronic to motronic, first the car was rebuild, new ipistons, new rings and bearings I managed to get the E34 M20 engine harness.
The car starts but it doesn't rev, when I try to rev it, it dies and misfire, today I started it, it was running smooth but my fuel return hose is not returning the fuel there is nothing coming out but the car idle properly not reving once I try reving it dies.
On the Injectors I am still running the white ones I think they are for M20B20 and my air flow is the 5pin, the spark plugs are new, the distributor is a good second hand and the HTC cables looks good.
So my question can I run the M20B25 using white Injectors instead of the blue ones?
The air flow meter of jetronic, is it the same as the one for motronic.

Thank you so much your help will be appreciated
SAILE30.

[flybynite]

Have a look here
https://www.e30zone.net/e30wiki/index.p ... tronic_1.3

[Brianmoooore]

It's never going to run properly with the wrong AFM and injectors, but the immediate problem is why there is no return fuel flow. Either the pressure regulator has failed shut, and the rail pressure is through the roof, or the fuel pump is incapable of providing the required 3 bar, so the rail pressure is low.
You need to get fuel pressure gauge connected up, and see which. Adequate ones are about £12 on ebay.

[SAILE30]

Thank you so much much Brian, I think testing my fuel pressure is the first step then attend the other issues.
Thank you so much

[SAILE30]

Have a look here
https://www.e30zone.net/e30wiki/index.p ... tronic_1.3

Thank you Flybynite will sit down read and attend to it then will give you an update
Thank so much

[SAILE30]

Hie guys how are you doing wherever you are. Remember my car was not reving up and the return line was dry.I managed to fix it using the the E30 zone.
I used the jetronic Afm on motronic. I connected it like so;
On the jetronic Afm
pin 1 is connected to pin 5 ecu
Pin 2 is connected to pin 9 ecu
Pin 3 is not connected
Pin 4 is connected to pin 7 ecu
Pin 5 is connected to pin 8 ecu
Then I connected them like so(motronic)
Pin 1 I connected it to pin 26 ecu
Pin2 I connected it to pin 44 ecu
Pin 3 not connected
Pin 4 I connected it to pin 7 ecu
Pin 5 I connected it to pin 8 ecu.
So I managed to run her smooth without any misfiring. Then the problem with the return line, I changed the Fuel Pressure Regulator and the petrol was now running properly.
Thank you so much guys my car is now running properly. I am waiting for the proper Injectors to come as you know I was running the 320i ones instead of the 325i ones.

[Brianmoooore]

It's very unlikely that the Jetronic AFM is ideal for Motronic. The potentiometer inside is far from linear, or even logarithmic in the normal sense. It'll probably run on it, just as it will on a M20B20 AFM, but the performance and fuel consumption will be down on what it should be, so I'd extend your parts hunt to include the correct AFM.

[SAILE30]

It's very unlikely that the Jetronic AFM is ideal for Motronic. The potentiometer inside is far from linear, or even logarithmic in the normal sense. It'll probably run on it, just as it will on a M20B20 AFM, but the performance and fuel consumption will be down on what it should be, so I'd extend your parts hunt to include the correct AFM.

Thank you Brian, I will definitely change it as time goes on, I haven't checked my fuel consumption yet. The lockdown is making it difficult to get the spares and driving around.

[boiliebasher]

Glad you've managed to get your new m20b25 running