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Thread: S52 OBD1 Conversion Complete...here's what I learned.

  1. #1
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    S52 OBD1 Conversion Complete...here's what I learned.

    My OBD1 conversion is finally done. Whew...it was quite an involved process and don't let anyone fool you by saying it's "just an electronics swap."

    I spent a lot of time researching bimmerforums.com and consulting with a few people that had done it in the past along with many hours staring at wiring schematics in the Bentley manual.

    Here's what my OBD2 S52 looked like before I began the conversion:


    My car is a 99 M3 with OBD2 management and EWS (BMW anti-theft). I sourced an OBD1 engine harness from a 94 325i along with red-label 413 ECU. The chip I'm using is from Active Autowerkes.

    The general stuff you need:

    1. OBD1 harness
    2. OBD1 ECU (413 "red label" preferred b/c they come from non-EWS cars).
    3. OBD1 chip
    4. OBD1 intake manifold
    5. OBD1 fuel rail
    6. OBD1 crank position sensor
    7. OBD1 cam position sensor
    8. OBD1 ping/knock sensor x2
    9. OBD1 oxygen sensor
    10. OBD1 HFM
    11. OBD1 main engine coolant hose (big hose that connects to the coolant pipe fitting on the timing cover, heater core, and radiator expansion tank)
    12. OBD1 throttle boot
    13. OBD1 throttle body (optional)
    14. OBD1 valve cover and coil packs (optional)


    The conversion sounds conceptually simple but there are a lot of little things that need to be addressed.

    1. Valve Cover - The OBD2 valve cover does not have provisions for routing the coil pack connectors because the OBD2 cables enter from the passenger side and the OBD1 cables enter from the driver side. This is where you need to decide which route to go. You can keep your OBD2 valve cover, which allows you to keep your OBD2 coil packs or you can use an OBD1 valve cover which will require OBD1 coil packs. Either way is fine since both coil versions plug into the OBD1 harness. I choose to keep my OBD2 valve cover and will modify it slightly with a Dremel to route the wiring.

    Here's a pic of the OBD2 setup:

    Here's a pic of the OBD1 setup:


    2. Vanos Solenoid - The OBD2 Vanos solenoid wire connector is shorter than the OBD1 solenoid so you will either need to use an OBD1 solenoid, or keep your OBD2 solenoid and extend the cabling with BMW part # 12-52-2-274-971 to the engine harness. The BMW part is a transmission harness used to connect the engine harness to the back up light switch but it's perfect for the Vanos solenoid since the connectors are the same.

    Here's a picture of the harness:


    3. Coolant Pipe - The main coolant pipe from the timing cover (back side of the t-stat housing) is different between OBD1 and OBD2. OBD2 cars use a metal pipe that is fixed in the timing case cover with plumbers sealant. OBD1 cars use a rubber hose that connects to an aluminum neck that protrudes from the timing case cover. You can either use an OBD1 timing cover ($100) or get a coolant pipe adapter ($20) from Bimmerworld, AA, or Turner Motorsport. The coolant adapter fits into the OBD2 timing case cover and is secured with JB Weld. This allows you to pipe clamp the OBD1 coolant hose.

    Here's a picture of the coolant pipe adapter: (it's the aluminum pipe right below the oil filter housing)


    4. Intake Manifold – This is where the “performance gain” from an OBD1 conversion comes from. The M50 intake manifold flows better than the OBD2 (M52/S52) intake manifold. You must use this manifold for the conversion. The OBD1 manifold will have a air temp sensor and vacuum port for the fuel pressure regulator on the underside closest to the firewall. The M50 intake manifold will bolt right up to an M52/S52 cylinder head without modification.

    5. Throttle Body – You can use your OBD2 throttle body but you will need an adapter for the gasket seal. The OBD1 throttle body has a flat mating surface that clamps to a gasket on the OBD1 intake manifold. The OBD2 throttle body is the opposite and has a gasket in the throttle body that clamps to a flat mating surface on the OBD2 intake manifold. You can solve this problem two ways. You can get an adapter plate ($20) that sits between the OBD2 throttle body and OBD1 manifold, which provides a mating surface for both gaskets. The other option is a get an extended gasket ($15) that allows you to clamp the OBD2 throttle body directly to the OBD1 intake manifold. Of course, you can always use an OBD1 throttle body and not use any adapters.

    6. Coolant Temp Sender – OBD2 management uses a single coolant temp sender on the cylinder head under the intake runner for cylinder #1. The OBD1 setup uses two temp senders on the cylinder head under intake runners #1 and #2. You can splice the main engine harness wiring together and use the OBD2 plug connector from your old wiring harness to connect to your single OBD2 temp sender. Another option, which is much cleaner, is to use the coolant temp sender wiring adapter ($50) from Turner Motorsport that is completely plug and play.

    7. Crank Position Sensor – The OBD2 crank position sensor is located on the engine block in front of the starter motor. The OBD1 crank position sensor is located on the timing cover and mounts on a circular tab with a 6mm allen bolt. You must use an OBD1 crank position sensor. Just leave the OBD2 sensor in place to plug the hole.

    8. Fuel Lines – The fuel delivery setup is significantly different between OBD2 and OBD1. The OBD2 fuel rail has both fuel lines attaching in the rear near the firewall and the fuel pressure regulator is located forward of the fuel filter under the driver side of the car. The OBD1 fuel rail has the supply line on the front of the rail and the return line on the back of the rail near the fire wall. In addition, the OBD1 fuel pressure regulator is on the fuel rail itself next to the return line. You must use the OBD1 fuel rail for the conversion, which will require modification to the fuel lines. You will need to remove the OBD2 fuel pressure regulator from the undercarriage of the car and route new 8mm fuel lines to the OBD1 fuel rail. There is a pair of hard lines mounted to the chassis between the OBD2 fuel filter and engine bay. Simply bridge the gap left by the removal of the OBD2 fuel pressure regulator with new fuel line and connect the feed from the fuel filter to the front of the OBD1 fuel rail and the return line from the back of the fuel rail to the return line under the car. You will also need to connect the OBD1 fuel pressure regulator vacuum line to the one-way valve on the bottom of the OBD1 intake manifold. The connection is on the back corner of the manifold closest to the firewall.

    9. PCV – The OBD2 crank case vent is setup up differently than the OBD1 vent. There are several options to address this issue. If you are using the OBD2 valve cover, you can keep your OBD2 PCV setup and figure out a way to mount the breather valve (cone shaped plastic valve with round breather on top) under the intake manifold. If you are using the OBD1 valve cover, you should use the OBD1 breather valve that clips on to the crankcase vent port. The OBD1 valve has a vacuum line that connects to the plug that joins the ICV to the intake manifold and a large oil drain line that runs to the dipstick. The last option is a hook up a hose to the crankcase vent and run a breather catch can. I picked up a small length of 1” rubber hose and connected it to my OBD2 valve cover and hooked up the other end to the OBD1 breather valve and use a barbed connector to join the oil drain line to my dipstick.

    Here's how I hooked it up:


    10. Idle Control Valve – the OBD1 and OBD2 ICVs are the same. You can reuse your OBD2 ICV. You will need to get the connector and hose for the ICV to intake manifold connection and the hose that connects the ICV to the throttle boot vacuum port.

    11. Fuel Tank Breather – You can reuse your OBD2 fuel tank breather valve. You will need to get a couple fittings to connect the vacuum hose to the vacuum port on the throttle boot. I went to the hardware store and picked up 3/8” and 5/8” barb fittings and rigged something up to connect to the throttle body vacuum port.

    12. Oxygen Sensors and Secondary Air Pump – Only OBD2 systems have secondary air pumps. This emission control system is completely removed during the conversion. In addition, you get rid of your two precat OBD2 O2 sensors in the OBD2 exhaust headers and the two postcat OBD2 O2 sensors in the catalytic convertor so do not forget to get plugs for the ports. You’ll need an M18 bolt for the plugs. Any auto parts store should have them. FYI, the Toyota LandCruiser oil pan drain bolt is M18. OBD1 management only uses one precat OBD1 oxygen sensor.

    13. Oil Pan & Dipstick – I kept hearing you needed an OBD1 oil pan and dipstick for the conversion. This is entirely false. You can use your OBD2 oil pan and dipstick without any issues or modification.

    14. EWS – there is a lot of variability in which E36s have it and which ones do not. I used an ECU from a non-EWS vehicle but I still had some ignition issues after the conversion. There is an easy modification to the main engine harness to avoid any issues with EWS. You have to take the protective rubber boot off the connector to the ECU and cut wire #66. It should be solid green but it can also be black/violet according to the Bentley wiring diagrams. Just cut the wire and dress both ends with some electrical tape.

    15. Power Distribution & Grounding – Make sure you take pictures or label where the power and ground connections terminate. *ALL OF THIS SHOULD BE DONE WITH THE NEGATIVE BATTERY POST DISCONNECTED*. The OBD2 main battery positive post is located on the passenger side near the ECU compartment. The OBD2 distribution box is mounted parallel to the fender with two M10 bolts. You will need to move this distribution box slightly to reach the power connections on the OBD1 harness. The removal of the secondary air pump will review two screw holes that will allow you to reuse the M10 bolts and relocate the distribution box more towards the motor and parallel to the firewall. It is a very tight fit but it will reach. You will need to do this to reach the main power feed to the OBD1 harness. There will be on ground connection under the OBD diagnostics port. Make sure you check which wires you are connecting to the power distribution and which ones you are grounding. Power feeds are RED and grounds are BROWN or BLACK. Make sure you peel back the wiring sheath and double-check if you are not sure. There will also be one large power feed going to the starter and one small power feed going to the fuse box. The only other ground I can recall is the small wire (with round terminal connector) coming off the sparkplug rail, which needs to be grounded to the bolt securing the engine hoist loop on the Vanos unit.

    Here's my relocated power terminal: (The bracket on the left side is where the box used to be)


    16. General Wiring – I cannot stress this enough…LABEL THE CONNECTORS prior to attempting to install the harness in your car. Use the Bentley wiring schematics and make sure you check each plug off the harness and label it with painters tape and a marker so it’s easy to see what it should plug into. It’s a jumbled mess and all the connectors start to look the same when you toss the harness into the engine bay. The good thing is the wire lengths are fairly practical and the connectors are in the general vicinities of where they should plug into. I would also suggest taking pictures of any power and ground connections as you are disassembling your OBD2 wiring. Also, make sure you take a picture of the starter wiring connections to avoid problems later…it’s amazing how much confusion 4 wires can cause.

    Here's my harness after I went through all the wiring and labelled the connectors:


    Well, there you have it. That’s what I learned from my conversion. I hope this information helps someone else since I got a lot of help from people gracious with their time.

    Let me know if you have any questions. I will post some pics when I get time to sort through everything.

    Here's my final configuration:

    1999 M3
    OBD1 S52
    AA Cam Chip
    Sunbelt Cams
    Euro 3.5" HFM
    Conforti 3.5" Intake
    24lb Injectors
    Sunbelt Valve Springs
    ARP Headstuds
    AA Race Headers
    AA Race Exhaust
    Zionsville Competition Radiator
    Euro Oil Cooler

    Here's what my OBD1 S52 looks like after the conversion:



    I have dyno time scheduled this Saturday (9/23/06) so I'll post the results when they are in.



    9-24-06 Dyno Update:

    I had the car dyno'd yesterday. 253RWHP, 228TQ. The numbers are about where I was expecting them. I'm running pretty rich so I will send the results to AA and have them lean it out a little which should yield a little bit more. I'll get it dyno'd again with revised software and see what the final setup puts out.

    10-19-06 Dyno Update:

    I just got back from the dyno with the revised chip from AA. 262RWHP, 230TQ. AFR looked good and I'm happy with the results. Woohoo!
    Last edited by vinnymac; 10-19-2006 at 09:46 PM.

  2. #2
    Estrl M3 Guest
    does this mean only sniff tested? whats the advantage of this?

  3. #3
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    Wow, sounds like you took care of lots of details! It sounds like it was much more complicated than the cam install.

    Forget the dyno sheets, when are the test drives?! J/K.

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    Great writeup, Vince. I look forward to reading your results on Saturday. How do you like the new exhaust setup?
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  5. #5
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    Quote Originally Posted by 98M3Sedan View Post
    does this mean only sniff tested? whats the advantage of this?


    My car is being built for BMWCCA Club Racing so I don't care about emissions. It's not a street car anymore. Otherwise, there is no advantage to an OBD1 conversion and it's illegal in most states. There are plenty of OBD2 tuning options now.

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  7. #7
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    NICE write up! What are the average gains for switchin back to OBD-I? 10HP?

  8. #8
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    Quote Originally Posted by Theodore View Post
    NICE write up! What are the average gains for switchin back to OBD-I? 10HP?

    The only "gain" comes from the M50 intake manifold. I bet it's averages 15-20HP at the crank at most.

    As for the overall OBD1 conversion; there really is no reason to do it on a street car unless you are going to add a turbo or something that doesn't have available OBD2 software.

    The only reason I went through the hassle was for compliance for I-Prepared class. I don't have access to someone that can get the Euro 3.5" HFM to work in OBD2 so I had to convert to OBD1 to run my cams.
    Last edited by vinnymac; 09-19-2006 at 05:10 PM.

  9. #9
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    Quote Originally Posted by 99Estoril View Post
    Great writeup, Vince. I look forward to reading your results on Saturday. How do you like the new exhaust setup?


    My too. I can't wait to see the dyno results. AA burned the chip for me but we may need to tweak depending how things look.

    I haven't gotten the car off the jackstands yet because I need to install some new control arm bushings and bleed the radiator.

    The new exhaust is pretty nice. The install is easy and fitment is very good. The V-band clamps are pretty cool. The only thing I do not like is the oval exhaust tip but I think it will grow on me.

  10. #10
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    Quote Originally Posted by vinnymac View Post
    The only "gain" comes from the M50 intake manifold. I bet it's averages 15-20HP at the crank at most. There really is no reason to do it on a street car unless you are going to add a turbo or something that doesn't have available OBD2 software.

    The only reason I went through the hassle was for compliance for I-Prepared class. I don't have access to someone that can get the Euro 3.5" HFM to work in OBD2 so I had to convert to OBD1 to run my cams.
    http://forums.bimmerforums.com/forum...d.php?t=602178

    m50 intake swap averages 15 rwhp from 5.5k rpm till 7k. definetly worth it.

  11. #11
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    Quote Originally Posted by beebo100 View Post
    http://forums.bimmerforums.com/forum...d.php?t=602178

    m50 intake swap averages 15 rwhp from 5.5k rpm till 7k. definetly worth it.

    I didn't mean to say the M50 intake manifold wasn't worth it....it definitely is. I ran that setup with the Eurosport adapter for awhile and loved it.

    I meant the OBD1 conversion wasn't worth it for a street car unless there was some compelling reason to go through the hassle and expense.

  12. #12
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    ic, but just wanted to clarify the m50 intake gain.

  13. #13
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    glad you got it going.
    Sean

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    Quote Originally Posted by SG_M3 View Post
    glad you got it going.
    Yeah, me too. Thanks again for all your assistance during the conversion. Your insight was very helpful and I couldn't have gotten it done without your responses to all my questions.


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    Quote Originally Posted by 99Estoril View Post
    Great writeup, Vince. I look forward to reading your results on Saturday. How do you like the new exhaust setup?


    I had a chance to drive the car a bit tonight but not a whole lot since my temps are running a tad high as I suspect I still have a bit of air in the system.

    The exhaust isn't nearly as loud as I thought it would be. The exhaust has an optional straight pipe that you can install in place of the mid-resonator so I'm tempted to put that on Sunday with I do my rear subframe bushings and new diff install. Overall, I'm very pleased with the setup. I'm anxiously awaiting the dyno runs schedule for this weekend.

  16. #16
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    Quote Originally Posted by vinnymac View Post
    I had a chance to drive the car a bit tonight but not a whole lot since my temps are running a tad high as I suspect I still have a bit of air in the system.

    The exhaust isn't nearly as loud as I thought it would be. The exhaust has an optional straight pipe that you can install in place of the mid-resonator so I'm tempted to put that on Sunday with I do my rear subframe bushings and new diff install. Overall, I'm very pleased with the setup. I'm anxiously awaiting the dyno runs schedule for this weekend.
    Thanks for the feedback. How does it compare to the RSC36? BTW, I'm loving the exhaust! Interested to hear your impressions after installing the optional straight pipe. Can I please request a video and pics of the dyno session?
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  17. #17
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    Quote Originally Posted by 99Estoril View Post
    Thanks for the feedback. How does it compare to the RSC36? BTW, I'm loving the exhaust! Interested to hear your impressions after installing the optional straight pipe. Can I please request a video and pics of the dyno session?
    I haven't driven it enough to have a fair comparison. I'll do what I can during the dyno session. I'm only planning to be there long enough to get 3-4 good pulls so I can send the results off to AA to see if I need a revised chip for my setup.

  18. #18
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    Great write-up. I'm making a copy for future reference.

    On item 2, you said ".....or keep your OBD1 solenoid...". Did you mean to say keep your OBD2 solenoid?

    On item 12, you mention getting rid of your pre-cat sensors. Is that correct or is it the post-cat sensors that are eliminated?

    There's a thread parked at the top of the Track forum that has links to several valuable tech threads. I'm going to add a link to this thread so others in the future will be able to access it. So if there are ever any updates or corrections, be sure to edit your original post.

    Thanks again - Jay

    From wannabe to has been in a few short years..... the older I get, the faster I was

  19. #19
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    Quote Originally Posted by jayhudson View Post
    Great write-up. I'm making a copy for future reference.

    On item 2, you said ".....or keep your OBD1 solenoid...". Did you mean to say keep your OBD2 solenoid?

    On item 12, you mention getting rid of your pre-cat sensors. Is that correct or is it the post-cat sensors that are eliminated?

    There's a thread parked at the top of the Track forum that has links to several valuable tech threads. I'm going to add a link to this thread so others in the future will be able to access it. So if there are ever any updates or corrections, be sure to edit your original post.

    Thanks again - Jay
    Jay - great catch on items #2 and #12. I edited and added some clarifications and corrections.

    I'm going to keep working on updated this thread. I plan to add pics later and more information as I get it sorted out. I hope this helps other people since and OBD1 conversion was a little more complicated than I was anticipating and I never would have gotten it done without input from numerous people.

    Thanks.

  20. #20
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    Now I'm even more confused on item 12. I thought OBD1 used 2 oxy sensors while OBD2 used 4. Is it not true that the upgrade eliminates 2 of the 4? Looks like you're saying all 4 are eliminated. Is this true?

    Jay

    Quote Originally Posted by vinnymac View Post
    Jay - great catch on items #2 and #12. I edited and added some clarifications and corrections.

    I'm going to keep working on updated this thread. I plan to add pics later and more information as I get it sorted out. I hope this helps other people since and OBD1 conversion was a little more complicated than I was anticipating and I never would have gotten it done without input from numerous people.

    Thanks.

    From wannabe to has been in a few short years..... the older I get, the faster I was

  21. #21
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    Quote Originally Posted by jayhudson View Post
    Now I'm even more confused on item 12. I thought OBD1 used 2 oxy sensors while OBD2 used 4. Is it not true that the upgrade eliminates 2 of the 4? Looks like you're saying all 4 are eliminated. Is this true?

    Jay

    The OBD2 setup uses 4 oxygen sensors...2 precat (exhaust headers) and 2 postcat (in the midpipe). You get rid of ALL 4 OBD2 oxygen sensors for the conversion and replace it with a single OBD1 precat O2 sensor.

    The OBD2 oxygen sensor has a small round clip-in connector and the OBD1 oxygen sensor has a large screw-type connector.

  22. #22
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    OBDI uses 1 o2 sensor.
    Sean

  23. #23
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    So you have only one pre-cat sensor, but it's a different type. I suppose it doesn't matter which of the two header locations you use. Correct?

    Jay

    Quote Originally Posted by vinnymac View Post
    The OBD2 setup uses 4 oxygen sensors...2 precat (exhaust headers) and 2 postcat (in the midpipe). You get rid of ALL 4 OBD2 oxygen sensors for the conversion and replace it with a single OBD1 precat O2 sensor.

    The OBD2 oxygen sensor has a small round clip-in connector and the OBD1 oxygen sensor has a large screw-type connector.

    From wannabe to has been in a few short years..... the older I get, the faster I was

  24. #24
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    Quote Originally Posted by jayhudson View Post
    So you have only one pre-cat sensor, but it's a different type. I suppose it doesn't matter which of the two header locations you use. Correct?

    Jay
    well, ideally you want it further down after the header. Where it can read all 6 cylinders.
    Sean

  25. #25
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    Quote Originally Posted by SG_M3 View Post
    well, ideally you want it further down after the header. Where it can read all 6 cylinders.


    Yeah, it's best to install the OBD1 O2 sensor in a bung that gets fed by both cylinder banks. An AA track pipe would be a good addition if you do an OBD1 conversion.

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