Budget build 99 M3 with M52 OBD1 conversion questions

[Richkid79]

Please understand this is a budget build using mostly parts that I already have to build a car that wont be anything more than an extra BMW to beat on (My RX-8 is too expensive to rebuild/replace engines every 20k, and my work truck and CLK are the daily drivers). So...
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I was in process of swapping my 94 325iC auto with an M52/5sp from a 98 328iC. This meant that I do an auto/manual conversion and to swap the M52 with all the required parts from M50, making it an OBD1 M52.
Halfway through the auto to manual AND the M50 to M52OBD1 conversion, I got a 99 M3/5sp with minor rear damage of trunk, bumper, and lights. The M3 was missing its drivetrain-it was put into an E30. So I decided to strip the Black 94 for the Silver 99M3.
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Next was pulling the half completed drivetrain out of the 94 and installing it into the 99M and this is what I end up with
99 Body with M52 5/sp. OBD1, with automatic wiring harness, and red label DME.. So far I have swapped the intake mani w/M50 ignition coils, valve cover, alternator, crank sensor, and spliced the 4 wire temp sensor(s). Now Im not too sure how to approach this next.


1)Could/should I use the injectors from the M52 manifold, or are the M50 ones ok to use for now?
2)Fuel System-is the OBD2 fuel delivery different from the OBD1 setup thats now being used?
How is it different from the gas tank to the engine bay?
3)Does the harness just plug and play into the round connectors, or does it need to be re-pinned somehow? It looks like there are extra wires coming from the car, but Im not completely sure as of yet.
4)Who can burn a chip for this application once I get it running (again, im on a budget)

I might try to locate the OBD1 5-sp harness from the salvage yard in order to eliminate the extra computer, but as I said, I want to do this using most of the parts I already have. I do not have the OBD2 alternator, engine harness, or DME so I dont want to go that route. There are no emissions or inspection tests in Florida so Im not worried about that
Thanks for your help.

Richie

[jc43089]

If you have an OBD2 shell, and an OBD2 engine why are you trying to convert to OBD1? It will cost more and be worse performing. Stick with the OBD2 fuel routing, use the M52 injectors, and use the ECU for an M52 and the only thing you will have to deal with is setting up the EWS which shouldn't be hard at all. The OBD2 setup on the M52 should plug right into the M3 harness because it was the same thing before just larger displacement.

[ed323i]

1)Could/should I use the injectors from the M52 manifold, or are the M50 ones ok to use for now?
2)Fuel System-is the OBD2 fuel delivery different from the OBD1 setup thats now being used?
How is it different from the gas tank to the engine bay?
3)Does the harness just plug and play into the round connectors, or does it need to be re-pinned somehow? It looks like there are extra wires coming from the car, but Im not completely sure as of yet.
4)Who can burn a chip for this application once I get it running (again, im on a budget)

I might try to locate the OBD1 5-sp harness from the salvage yard in order to eliminate the extra computer, but as I said, I want to do this using most of the parts I already have. I do not have the OBD2 alternator, engine harness, or DME so I dont want to go that route. There are no emissions or inspection tests in Florida so Im not worried about that
Thanks for your help.

1) The M52B28 injectors flow more than the M52B25 and M50B25 injectors (which are identical). If you don't upgrade the engine/hp then the M50 injectors will just do.. If you decide to install M50 manifold etc then you might get in trouble..
2) In Europe I don't think there is any difference. In the US OBD2, the fuel pressure regulator is below the floor of the car, instead of on the fuel rail with M50 and European M52. As the chassis and engine are OBD2, I don't think you need to do anything, but I'm not 100% sure about all the wiring differences in the engine bay OBD1 vs OBD2.
3) Not sure.. You'd have to look up all the pin-outs and compare those. ETK is your friend.
4) Not sure..

I concur with JC (+1), that it would definitely be easier to go OBD2. You can get a complete EWS-deleted, chip-tuned DME for $170 (see link in signature, but there are more options). You can ask the DME seller to disable the post-CAT O2 sensors and make some other adjustments you'd like.. Then you'd only need an M52 wiring harness and the alternator (and you can sell your OBD1 one, so shouldn't cost you much in the end, just the hassle of buying and selling).

Getting a chip for the M50 DME to run the M52 engine, and the hassle of converting the engine sensors and stuff to OBD1, and the fuel delivery conversion, and perhaps also some other wiring changes needed, will eventually cost you more and be more work than just going the OBD2 route. And way more complex.

Advantage of OBD2 is that you can tune (Romraider) and log the car yourself, for free. Also using INPA is a lot easier on OBD2 compared to OBD1 as you need a more expensive interface with OBD1 (ADS).

[XnWarden]

As the other person said. Your M3 chassis is obd2 and it sounds like your engine is obd2. Just stick with obd2.

The fuel system has an additional vent valve in the rear on obd2. Obd1 just vents at the front. A few other things are different also.

Just sync the ews and run obd2

Sent from my VS987 using Tapatalk

[Eric93se]

He wants to tune.....

[ed323i]

He wants to tune.....

He needs a tune if he decides to go OBD1. Then he would use an M50 DME and would need a tune for the M52B28 (buying an EPROM), optionally also adjusted for the M50 injectors (best to just use the M52 ones, higher flow)..

If he goes OBD2, he won't need a tune, as the engine and car are already OBD2 and stock. He only needs to sync the EWS, and that can be done with any Windows laptop, about $25 of adapter cables and a very simple computer program.. Or he can get a pre-tuned, EWS-deleted DME for $170 and enjoy +/- 205-210 HP and more torque across the rpm-range as a bonus. If he wants to manually retune the DME he can do it himself using RomRaider, which only supports the MS41 (M52) DMEs. All that's needed is the free Romraider program, the laptop and the adapter cables. The OBD1 DME only accepts EPROM chips, and you would need a lot more equipment to tune it yourself, and less logging possibilities.

[jc43089]

If he wants to tune then OBD1 is also a terrible idea. I see no mention of cams or other upgrades that would need a tune, it looks like a budget project to me.

He wants to tune.....

[Richkid79]

Thanks for everyones reply. I figured most of the replys would be "just go obd2" but that really wasnt what i was asking. I did find the answer on another thread so ill go that route.
In case anyone else ever runs into this, heres the link (with pics!)

https://www.bimmerforums.com/forum/s...bd1+conversion

Cheers

Richie

[E36328Coupe]

Just use the M50 Manifold on the M52 with it's M52 OBDII

Why make life more complicated than it needs to be.

[ed323i]

Thanks for everyones reply. I figured most of the replys would be "just go obd2" but that really wasnt what i was asking. I did find the answer on another thread so ill go that route.
In case anyone else ever runs into this, heres the link (with pics!)

https://www.bimmerforums.com/forum/s...bd1+conversion

Thanks for the link.. It's a great, very detailed write-up..
It's even more complex than I thought..

I think most of us don't see the benefit of converting an OBD2 chassis and an OBD2 M52 to OBD1, but if you really prefer to only use the stuff/parts you already have, and have enough time to do it, I understand your choice. You'll learn a lot along the way. If, on the other hand you think of time as "time=money", even if you only value it at a few dollars per hour, then it becomes a tricky proposition and you might end up "paying" more for the OBD1 setup.. Cost-wise it will also be important to find a guy who can tune the OBD1 M52 for a low price, otherwise you might end up paying more for the OBD1 setup (especially if you end up needing another fine-tune afterwards). Please note you can also downgrade an OBD2 DME such that lots of its "features" won't bother you, like disabling the air injection, disabling the post-CAT oxygen sensors, disabling EWS, and just use the OBD1 M50 intake manifold.

Good luck, and let us know the results!

[Richkid79]

Thanks ed323! I have a small warehouse where I keep my toys and I have more time than money so slowly working on this car is no problem for me. Being single with no kids helps.
My M52 engine is pretty much done as far as the obd1 sensors, intake, maf, throttle body, etc. I was able to pull a 5sp harness from junkyard for $35 and Active Autowerke's chip is only $250 (and they're just a couple hours away from me) I sent an email to AA to see what injectors to use with the m50 manifold.
I am still using the stock m50 exhaust manifold but I'm thinking of using the M52 exhaust manifold (junkyard) or going with shiny eBay headers if there's a performance gain. I can either go stock M52 exhaust manifold with a cat delete midpipe and stock M3 rear section, or eBay headers with stock m50 cats and stock M3 rear section. Any suggestions?