Conversion from Jetronic LH 3.2 to Motronic 4.3/4.4 Is it Possible?

callahanoffroad · Post by **callahanoffroad** » 25 Jul 2019, 18:35

Like the title says is it possible to go from Jetronic to Motronic?

This theoretical discussion is going to use my 1995 Volvo 850 with a 2.4L 20V Engine, engine code B5254F(S?) with a manual transmission.

I've been reading up on this idea for a few days but I haven't found anything that shows if anyone actually did it. The documentation on ECU's is so heavily focused on Turbos it can be overwhelming to sort through.

To me, it looks like the the NA motors are all roughly the same until the introduction of coil packs. All the electronic parts seem the same, sensors are the same, etc. Aside from the VVIS of course (which of course I have), and the changing of the timing belt system.

So far I've figured out that you of course need a Motronic ECU, and engine wiring harness. Possibly the wiring harness from the ignition key back. If I upgraded to 4.3/4 I'd lose VVIS, but I might be able to get it back by tracking down an old Yitsbox, or fabricating my own electronic actuator.

I'm looking for links, and opinions that anyone has. Then I'll be trying to track down the parts to make this work.

I know you're going to ask why. Here's the why, my old '96 wagon got better gas mileage and had an OBD2 port that I could run diagnostics off of. It'd be nice to have that back and the 6 extra MPG wouldn't hurt either.

Thanks in advance Brain Trust.

Post by **Ozark Lee** » 25 Jul 2019, 20:30

With enough time and money anything is possible. The question becomes is it practical?

IMHO, not really. In the end it will wind up costing you more than the price of buying a Motronic car and there are little things that interface with the ECU other than the engine like the climate unit for sure and they are different between the two ECUs. There may be others things as well.

...Lee

callahanoffroad · Post by **callahanoffroad** » 26 Jul 2019, 05:50

Ozark Lee wrote: ↑25 Jul 2019, 20:30 With enough time and money anything is possible. The question becomes is it practical?

IMHO, not really. In the end it will wind up costing you more than the price of buying a Motronic car and there are little things that interface with the ECU other than the engine like the climate unit for sure and they are different between the two ECUs. There may be others things as well.

...Lee

Okay, just purely from an academic stand point what are the differences?

I know the climate control is different between a 4.3 and 4.4 (mostly how the AC compressor works iirc).

Let's throw 4.4 out the window. What are the differences between 3.2 and 4.3 setups?

Also I have Manual Climate Control. Not sure if that'd make a difference.

Maybe the solution is to wire the motronic unit like a piggyback/standalone ecu and have it only run the engine systems.

Again purely academic.

Post by **misha** » 26 Jul 2019, 15:27

M 4.3 & M 4.4 are pretty much the same system management with minor differencies...Jetronic 3.2 is TOTALLY different management and NOT compatible with Motronic.
Sensors are totally different...from Maf to o2...wiring harness,ecu box and slots...etc.

callahanoffroad · Post by **callahanoffroad** » 26 Jul 2019, 18:57

misha wrote: ↑26 Jul 2019, 15:27 M 4.3 & M 4.4 are pretty much the same system management with minor differencies...Jetronic 3.2 is TOTALLY different management and NOT compatible with Motronic.
Sensors are totally different...from Maf to o2...wiring harness,ecu box and slots...etc.

Well if that's true then it would be too much effort.

Post by **Ozark Lee** » 27 Jul 2019, 10:17

It is true.

...Lee

callahanoffroad · Post by **callahanoffroad** » 28 Jul 2019, 05:27

Ozark Lee wrote: ↑27 Jul 2019, 10:17 It is true.

...Lee

I wasn't saying I didn't believe you guys, it was a figure of speech.

Also I double checked the part #'s are you guys are totally correct. Crazy.