M20b25 swap into my 1986 325e wiring question?

[savagesaint21]

Hey guys I’m really confused about the gas tank part of my swap. I know I have the smaller gas tank on my car so would I need to upgrade to the bigger gas tank so my harness from the I engine work? I bought a m20b25 engine from a 1990 325i thinking it would be a direct swap but the fuel tank is confusing the shit out of me.... I know I have to splice square plug from the fuse box to the i harness but the fuel tank thing is confusing me..Please help me I’ve been stuck with this thought for weeks and I’ve been looking around this forum but there is no solid answer. I’ve never done anything like this so any feedback would be appreciated greatly. I just want to know how to make the i harness work with before I start taking shit apart. Please help man.... I just want to enjoy my car but my engine is shit rn. Sorry I’m newb


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[THE DUDE ABIDES]

Ok. I might be able to help with this one. I just recently finished a M20B25 swap into my eta car. But that's the first thing to figure out. You probably don't need to worry about swapping fuel tanks. Here's the list of questions you need to answer and things you need to do first:
-does your fuel tank have one or two level senders? They are located on opposite sides of the tank underneath the rear seat.
-the square plug that you need to splice in order to get tachometer and econometer working is not in the fuse box, it's above the glove box. Called the C104. I can walk you through wiring for that as well.
-Do you have a 7K tach instrument cluster from an i engine to swap in as well? If so, the best choice for you may be to remove only the tach assembly from the cluster and swap it into your eta cluster. That way you keep the gas gauge that is calibrated to the car. That's what I had to end up doing with my cluster. VDO or Motometer. It shouldn't matter. I swapped VDO tach into a Motometer cluster and it works fine.
Answer those questions and get back to me.

[savagesaint21]

Hey thanks for the help. I just checked the backseat it looks like it has one fuel sender and I do have the 7k odometer only I already swapped out the gas gauge


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[Andre3127]

Could you post how to wire the c104 in the thread? Looking at the diagrams I'm pretty sure I got it covered, but vericarion would be nice.

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[ForcedFirebird]

You don't need to swap anything on the fuel system, except using the injectors and pressure regulator from the "i" car. The 87 325i had the small tank and dual pump system. If you swap the tank and senders, then you will need to change the coding plug if equipped (or cluster if not) since the early cars had a single sender signal, the later cars have dual senders.

Are you sure the car has the square c101? I know in 5/85, the round plug near the fuse box was there, but you will have to wire the small white plug in the glove box since the tach, eco-gauge and OBC drive-away protection are wired in there (88+ used the c101 for the tach).

Also, be aware that the c101 pin #20 was either a ground, empty, or power depending year and options. If you just plug the c101 without checking you run the risk of frying your body harness. Otherwise the c101 from the later eta and 325i are plug and play.