M30B35 Swap FAQ

[rondwyer]

Hi,

I am doing the M30B35 swap to an e12, the wiring is nowhere near as easy to follow with these current flow diagrams. Does anyone have a diagram of the engine harness? I am particularly confused by a plug that seems to go to the variable Throttle position sensor instead of to the ECU. Sorting out the harness will help me determine what wires are important and which ones could be removed without any ill effects. Last I did one of these it was an E28 engine to my E3 coupe.

Any assistance that the group could provide would be greatly appreciated.

I don't check messages often, please e-mail me.

[rondwyer]

Many thanks to Mike for contacting me with the link to the Rosetta stone. My conundrum was a connector that seemed to be attached to some portion of the throttle position sensor which being an engine component, was not readily apparent as to what it connected to. Ends up the automatic transmission was looking for the variable resistance outputs other than the simple TPS outputs and are now redundant. For anyone attempting to map the harness off the BMW current flow diagram, give up. It is a worthless POS. I spent way too many hours attempting to make sense of a publication that only vaguely hinted at portions of the bigger picture. I am not yet certain of the origin of the diagram I now have but it is either a Mitchell, Chilton or Haynes creation. As a first choice, it is invaluable. The BMW current flow diagrams come in to help figure out if you have identified the appropriate connectors, etc. Today I confirmed there is indeed a significant amount of wiring in the 735i harness that can hit the trashcan. The wiring diagram tells exactly what the color codes are that can be deemed redundant.

Good news, if anyone wants one of these harnesses ready to install, it can be had for a reasonable cost. The man I met today has 7 coupes in various stages of upgrade in his shop and since I am a coupe restoration veteran, we had a lot to chat about. Essentially a harness takes him 16 hours to do correctly. They are priced accordingly as he has a business to run...(rent to pay). After I finish this E12 project, I realized I need another E28 and am on the hunt!

Glad I posted, thanks Mike!

[BuzzBomb]

Ron, the level of difficulty and frustration felt was compounded by the fact that not only did you use a harness from a car that is physically laid out differently, you have additional wiring meant for a car with an automatic trans. Regardless, the 1.3 harness is straightforward and not that hard to understand. It just takes once doing it. Now that you know what is involved, you're in a good position to help others that want to do similar builds. Consider posting a diagram for the connection at the fusebox for 1.3 into e12 conversion. I know I'd like it for reference...

[BuzzBomb]

For reasons unknown, information for a 1.3 install while retaining an automatic transmission hasn't been posted in this FAQ.
Thanks to Mark at Bahn Motorworks for his help over the phone with a few last mystery wires.
If anyone needs assistance with wiring questions, PM me.

[bkbimmer]

I am in the middle of modifying a e34 harness for a 1.3 conversion on a b34 engine....

I am pretty confused at the moment on where the charge light wire comes from with the b35 harness. The b34 had a alternator harness built in, the b35 doesn't seem to? What am I missing?

I feel really stupid right now!

[demetk]

I am in the middle of modifying a e34 harness for a 1.3 conversion on a b34 engine....

I am pretty confused at the moment on where the charge light wire comes from with the b35 harness. The b34 had a alternator harness built in, the b35 doesn't seem to? What am I missing?

There is a secondary harness inside a steel tube that the alternator charge wire, alternator charge light, oil level sensor, o2 sensor connect to. It's shown here on page 1 of the faq,



On the right side of the engine are the two connectors, I've labelled them for you,

[bkbimmer]

I am in the middle of modifying a e34 harness for a 1.3 conversion on a b34 engine....

I am pretty confused at the moment on where the charge light wire comes from with the b35 harness. The b34 had a alternator harness built in, the b35 doesn't seem to? What am I missing?

There is a secondary harness inside a steel tube that the alternator charge wire, alternator charge light, oil level sensor, o2 sensor connect to. It's shown here on page 1 of the faq,



On the right side of the engine are the two connectors, I've labelled them for you,

What does the red/white and brown wires go to on the left foreground of the bottom picture? I am installing this harness on a b34 and it doesn't seem to go anywhere.

[demetk]

What does the red/white and brown wires go to on the left foreground of the bottom picture? I am installing this harness on a b34 and it doesn't seem to go anywhere.

They would be for the purge valve solenoid.

[bkbimmer]

What does the red/white and brown wires go to on the left foreground of the bottom picture? I am installing this harness on a b34 and it doesn't seem to go anywhere.

They would be for the purge valve solenoid.

I don't need that correct?

[demetk]

I don't need that correct?

If you're using the b34 purge setup, you don't need the connection.

[bkbimmer]

Thank you.

[tig]

It's the 24lb injectors.

Ok. Thanks. Now what?

24 lb injectors use a shorter pulse width to deliver cruise fueling than stock. The dash econometer and OBC functions are both based off injector pulse width, so they think you're using less fuel. Search the archives, I remember somebody mentioning an adjustable pot on (I think) the OBC that could be used to adjust the calculation for larger injectors. Bit of a guess and check process so it's a PITA, but if it's important to you that it works correctly you could try it. The econometer on the dash is a lost cause though I think.

Found this: http://www.seattlecircuit.com/fuel_signal.htm

Onboard Computer fuel signal correction
Restores complete accuracy after you install larger injectors


The fuel signal converter is designed to correct for larger than stock fuel injectors on most Bosch and Siemens equipped vehicles. The usual symptoms of installing larger fuel injectors is that your On Board Computer (OBC) will display inflated mileage and range information. This is due to the fact that the larger injectors require a shorter signal than the stock injectors to flow the same amount of fuel. Your OBC interprets the shorter fuel pulse as increased fuel economy.

The fuel signal converter digitally conditions the fuel signal to match the signal for your stock injectors. Your OBC will once again display accurate mileage and range information.

The circuit is simple to connect and requires only power, ground and a fuel signal as input. It is available in two versions: the original version that will work with factory ECU’s and the standalone version. The standalone version will bypass your ECU completely and read the fuel signal directly from a single injector. This is useful for Megasquirt, Autronic, MOTEC and other standalone ECU’s. It is extremely small, rugged and can be mounted almost anywhere.

It is fully adjustable for any injector upgrade and in most instances will reach accuracy exceeding +/- .2 mpg!

I might get one and see if it works.

My injectors are Bosch model 280-155-715 “light blue”. According to this website: http://users.erols.com/srweiss/tableifc.htm this model # flows 22.45 lbs/hr.

This site (https://www.injectorrx.com/bosch-fuel-injectors/) says: 24lbs/hr.

I had mine flow-tested. The results of the flow test showed "20 second static flow (average across all 6) of 98mL" which is 240mL/minute. This tool converts between flow rates:

http://www.deatschwerks.com/resources/f ... conversion

Using it I get 28lbs/hr.

[tig]

[
Found this: http://www.seattlecircuit.com/fuel_signal.htm

Onboard Computer fuel signal correction
Restores complete accuracy after you install larger injectors


The fuel signal converter is designed to correct for larger than stock fuel injectors on most Bosch and Siemens equipped vehicles. The usual symptoms of installing larger fuel injectors is that your On Board Computer (OBC) will display inflated mileage and range information. This is due to the fact that the larger injectors require a shorter signal than the stock injectors to flow the same amount of fuel. Your OBC interprets the shorter fuel pulse as increased fuel economy.

The fuel signal converter digitally conditions the fuel signal to match the signal for your stock injectors. Your OBC will once again display accurate mileage and range information.

The circuit is simple to connect and requires only power, ground and a fuel signal as input. It is available in two versions: the original version that will work with factory ECU’s and the standalone version. The standalone version will bypass your ECU completely and read the fuel signal directly from a single injector. This is useful for Megasquirt, Autronic, MOTEC and other standalone ECU’s. It is extremely small, rugged and can be mounted almost anywhere.

It is fully adjustable for any injector upgrade and in most instances will reach accuracy exceeding +/- .2 mpg!

I might get one and see if it works.

Purveyor of these just replied to my inquiry:

Charlie,

Sorry for the tardy reply.

It will work just fine with the m30, as long your're getting some kind of OBC reading on mileage (probably like 55mpg?)

It has an internal software range that works for most cars, the fine-tuning is done via a potentiometer on the board.

I'm def getting one.

[D Unit]

I would appreciate some help trying to figure out how to swap a b35 into my US spec e23 (1986 735i) because right now the engine is not sitting straight.

I already bought the Left and Right Koala engine mount adapters, but when mounted the engine still looks crooked. The passenger side adapter worked perfectly, but once you try to mount the drivers side, things get weird. Since this is an e23, do I need to order the driver side engine support bracket too?

Here's the 2 Koala adapters I bought so far... (I borrowed the picture below for the Interwebz... I do not have the other engine support bracket in the picture)



Here's how crooked it sits...


Here's a pic of the driver side Koala adapter....


Here's a pic trying to use the existing e23 b34 mount...



e28 535i driver side engine support bracket #3. Is this what I need (11811175591) to make it fit into an e23?

[fresco505]

So glad i found this thread, appreciate all the info everyone has posted. Still have a few questions regarding swapping a m30b35 into 528e e28.

I have a complete and running 1990 e34 535i that i am going to use as the donor car for my '88 e28 528e. The e28 has the m20b27 with i believe the g260/5 transmission. I plan to use as much as i possibly can from the e34 535i donor car. What i can't seem to get a straight answer on is can I use the transmission from the e34, which i believe is a g260/6? What about the driveshaft from the e34? Im guessing whatever that is not compatible from the e34 I'll need to source b34 parts?

Thanks for any help!!

[demetk]

What i can't seem to get a straight answer on is can I use the transmission from the e34, which i believe is a g260/6? What about the driveshaft from the e34? Im guessing whatever that is not compatible from the e34 I'll need to source b34 parts?

Tranny I'd say yes if you convert the motronic to 1.3.
Driveshaft is a no because of the fact the e34 driveshaft has the cv joint on the back.

[fresco505]

What i can't seem to get a straight answer on is can I use the transmission from the e34, which i believe is a g260/6? What about the driveshaft from the e34? Im guessing whatever that is not compatible from the e34 I'll need to source b34 parts?

Tranny I'd say yes if you convert the motronic to 1.3.
Driveshaft is a no because of the fact the e34 driveshaft has the cv joint on the back.

Cool thanks for the reply!! I guess ill have to now search the junkyards for b34 driveshaft...

[Neel]

Just picked up a b35 e34 motor... now to read, re-read and read some more. The purpose of my post is really to just say thank you for this write up and contributions to this post. Hopefully I have the patience to do a write-up that is up to the caliber of this one. Oh and it will take quite some time but there will be a post.

Thank you everyone.

[Cube]

Hi cek,

Looking through your posts of the B35 wiring loom and the C103 connector problem with pin2 (the green wire).
What was the solution to this? Have you just left that pin unconnected?
I am going through the same issue at the moment and that wire is the only one I cannot find a solution for.

Thanks

[tig]

Hi cek,

Looking through your posts of the B35 wiring loom and the C103 connector problem with pin2 (the green wire).
What was the solution to this? Have you just left that pin unconnected?
I am going through the same issue at the moment and that wire is the only one I cannot find a solution for.

Thanks

Here's where I asked the same question above:

Buttoning up the harness and a few things have me stumped.

First is the green wire that comes off #86 on the main relay. It's not going anywhere now.

I think it's supposed to go to the C103:


Here's what it looks like inside the car:


The C103 pins
1 - Black - Goes to Tach. Comes from Pin 6 on ECU (B35).
2 - Green - Goes to OBC Relay Box (pin 4). Comes from ???.
3 - White - Goes to economy meter. Comes from pin 32 on ECU (B35).
4 - Green/Yellow - Goes to AC Switch (sort of). Not connected on B34. Comes from Pin 40/41 on ECU on B35.

On my B34 pulled out of Vlad it does.

However, in all the instructions above regarding C103 people say "Just hook up pins 1 & 3".

This doesn't seem right. Can someone confirm that this is supposed to be hooked up for a B35.

I never got an answer from anyone, but I obviously figured it out. I'll look at my car this morning and see if it just goes to #86 on the main relay as the ETM indicates it should.

[Cube]

Thanks for your effort cek

[tig]

I just confirmed that Pin 2 of my C103 is a geen wire that goes under the dash. I assume to the OBC.

I the wire that goes into the other side of the connector is also green.

The wire that goes to pin 86 of the main relay is green.

I did not put an ohmmeter on it to test, but it seems we have our answer.

[BuzzBomb]

The only necessary wires when converting to 1.3 in an e28 are pins 1 and 3. 2 and 4 are redundant and unused.

[Cube]

Mhh... but how does the ECU know to adjust the idle when there is no signal from the A/C switch???

[demetk]

Mhh... but how does the ECU know to adjust the idle when there is no signal from the A/C switch???

Judging by the schematics, I'm going to say that m1.3 ecu does use the a/c compressor signal as input at pin 40. So you can try connecting pin 4 of c103 to pin 40 of the ecu.

For a m1.3 ecu map go to the 1992 e34 ETM, section 1210.2 Digital Engine Electronics (DME M1.3, 6- Cylinder M30)