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Discussion Starter #1 (Edited)
This issue continues to plague MKIV OBD1 owners so I thought it was time to compile all the information into one thread for the FAQ section.

Summary:
There is a known problem with the OBD1 ECU which causes stock twin and small single cars to run lean between ~4-6k rpms at high boost. The example below is from an FJO wideband datalog captured from my '95 TT while doing some street tuning at ~18psi. Further raising the boost causes the problem to worsen. Attempting to add fuel using an SAFC-II or similar piggyback does not resolve the problem.
253891

After doing a bunch of research I found that installing an OBD2 ECU completely resolves the problem.
Note: Lagtime also discovered that this problem could be resolved by using a Greddy E-Manage with optional injector harness to raise the injector duty cycle.

Another benefit of running the OBD2 ECU is you can connect an OBD2 scantool to read and clear MIL's. It will also allow you to monitor and datalog engine parameters such as timing, short and long term fuel trim, coolant temp, TPS, intake air temp, engine load, vehicle speed, air flow rate, and O2 sensor voltage.

Below is another FJO wideband capture after installing an OBD2 ECU without any SAFC fuel correction. No other changes were made. As you can see the problem is no longer present. OBD2's run pretty rich stock.
253892

Below is after tuning the OBD2 ECU with the SAFC was completed.
253893


How to upgrade an OBD1 car to OBD2:
Installation of the ECU is plug and play. Disconnect the battery. Simply disconnect your OBD1 ECU from the harness and connect an OBD2 ECU. The car should run at this point. The only thing I know of that doesn't work is the TRAC system. In order to get everything working correctly the issues below need to be addressed.

1) Like any OBD2 car you will need to run an O2 simulator if you have a catless downpipe installed. Failure to do so will result in a MIL from the secondary O2 sensor.
How to install an O2 simulator by Stu Hagen

2) On OBD2 cars there an additional ground wire that's not present on OBD1 cars. Not having this ground wire causes the primary O2 sensor heater to not function. This will prevent the car from entering closed loop operation when there is insufficient heat from the exhaust gas to keep the sensor at operating temp. This happens when the car is cold or idles long enough (4-5 minutes) for the sensor to cool off. It can cause the car to run very rich at idle. Adding the groundwire to the ECU harness fixes the problem.

How to get the primary O2 sensor heater functioning:
Since there's an additional pin needed for the new groundwire you will have to find one to use. This will require you to either cut a wire off of the ECU harness or find a donor pin from another harness. I used the pin from TE2 (E10-19) which is not used on OBD2. On OBD1 it's used for the special diagnostic test mode.

On the ECU wiring harness remove the yellow protectors, they pop off with a small screw driver. Remove pin TE2 (E10-19). It's a pink wire with a green stripe. To accomplish this take a small safety pin and carefully push up the plastic tab that holds the pin in the harness and lightly pull on the wire on the other side of the connector. It should pop right out with a slight tug. Cut the wire a couple of inches away from the ECU connector.

Insert this pin into the new ground wire location E03 (E9-78). Lengthen the wire so it's long enough to reach to a suitable ground point. I used the mounting point for the trac ecu. Attach the wire to the ground point.

3) OBD2 uses a different communications protocol and connector. The existing OBD1 diagnostic connector will not work. In order to read and clear MIL's you will need to install an OBD2 diagnostic port.

How to install an OBD2 diagnostic port:
Disconnect the battery. Remove the wiring harness from the ecu. Remove the yellow protectors, they pop off with a small screw driver. Next you have to move a pin on the ECU harness to another location. On obd1 cars pin E9-29 (vf1) is used for serial communications. This pin is not used on obd2 cars. On obd2 cars pin E10-8 (sdl) is used for serial communications. This pin is not used on obd1 cars. So you have to move pin E9-29 to E10-8.
253896

On the ecu wiring harness where it attaches to the ecu move pin E9-29 (vf1) to pin E10-8 (sdl). It's a light green wire. To accomplish this take a small safety pin and carefully push up the plastic tab that holds the pin in the harness and lightly pull on the wire on the other side of the connector. It should pop right out with a slight tug.
253897


Next identify E10-8 and remove the yellow plug that's installed in unused locations. Now carefully insert the pin into the harness. It should pop right in.
253898


Next you need an obd2 j1962 female connector. I got mine from here.
http://www.multiplex-engineering.com/products.htm
They also sell OBD2 connectors and pins so you can make your own.
Here are the connections that need to be made (4 wires).
253899


Pin 16 on the obd2 connector goes to +12v power. Run this to the a power source that is 12v with the ignition on. I used the cigarette lighter circuit. For safety you will want to put a fuse between the power source and obd2 connector.

Pin 4 on the obd2 connector goes to chassis ground. Run this to a suitable ground location. I used an existing ground point located just above the drivers side kick panel.

Pin 2 on the obd2 connector goes to pin E10-8 (SDL) on the ecu, this is the light green wire you moved on the ecu harness. The easiest way to do this is to tap in to pin 7 (light green wire) on the OBD1 diagnostic connector D5.

Pin 5 on the obd2 connector goes to the ECU ground which is E9-69 (E1) brown wire. The easiest way to do this is to tap in to pin 3 (brown wire) on the OBD1 diagnostic connector D5.
253900


That's it, now you should have a working obd2 dlc3 port to plug in in whatever obd2 scan tool you want.
253901

 

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We all owe toyotafan (and others like SupraSol) a debt of gratitude for figuring out this mod...something that would cost a small fortune to figure out if in the hands of a private shop I bet.

I'll have pictures available soon...we just completed this on my car yesterday at toyotafan's garage. Thanks again bud! :)

***THIS WILL BECOME A FAQ SOON***
 

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^^ I totally agree.

Thanks guys for providing this community with a great mod. Your contribution is highly appreciated. :bigthumb:
 

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thank you for your R&D, im sure a lot of supra owners will make use of this knowledge!
 

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Great work, thank you.

Now I need to have this done.
 

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Supra Owner Since 1996
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And this whole time I have been hating my OBD2 ecu. I guess there is a purpose for it after all.
 

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So, what do you mean by nobody has successfully installed an OBD2 in an auto? Is this something that cant be fixed in my car?

Jason
 

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I am using a 94 ecu with a full g-force upgrade in my 98.So are you guys saying that it is better for me to go back to my obd2 ecu?
 

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Discussion Starter #10
HotSoup said:
So, what do you mean by nobody has successfully installed an OBD2 in an auto? Is this something that cant be fixed in my car?

Jason
I was just pointing out that I have not personally tested this on an auto. There were a couple of people that said they were going to try it but I never heard if they were successful.
 

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Toyotafan,This is a bit off topic.Are you using the old version FJO data logging software or the new version,because i can't get the new version to give me the graft type you posted.
 

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Discussion Starter #12 (Edited)
jam98tt said:
Toyotafan,This is a bit off topic.Are you using the old version FJO data logging software or the new version,because i can't get the new version to give me the graft type you posted.
I'm running version 2.26. It displays that graph when you click on "view plots". You can zoom in by clicking on an area and dragging to highlight a specific area.
 

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Erven,
are you keeping your OBD2 ECU? If you consider selling it, let me know. Thanks.
 

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Not that this isn't an awesome post. It is. But just a little late. Slap in the aem ems and you can forget all of your OBD woes and create a whole set of news ones with tons more control and options. Why anyone would want a standard non tinker box is beyond me. With the ems you are able to get your hands dirty on so many other functions it's lightyears ahaed of OBDI and OBDII stuff.
 

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Bill,

Wrong target market here. The guys doing this mod probably have no interest in the AEM. toyotafan and I and SupraSol could all have AEM's if we wanted them...but choose not to for various reasons. I would ask that we please not turn this into an AEM vs. the world thread...there are far too many of those on Supraforums. Let's treat this as an FAQ post only...thanks.

Steve T.
 

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toyotafan has edited the original post to contain the complete set of photos now. Check it out!
 

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Excelent! moving this to the faq!

Thanks for all the hard work guys!
 

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Will this work if I am running an AEM V2 ? If so will the obd scanner be able to pick up ce codes and actually work?
 

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94 with PHR single kit, Tanabe DP, AEM boost, fuel pressure and afr, dual setting MBC, TE37SL, HKS
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This issue continues to plague MKIV OBD1 owners so I thought it was time to compile all the information into one thread for the FAQ section.

Summary:
There is a known problem with the OBD1 ECU which causes stock twin and small single cars to run lean between ~4-6k rpms at high boost. The example below is from an FJO wideband datalog captured from my '95 TT while doing some street tuning at ~18psi. Further raising the boost causes the problem to worsen. Attempting to add fuel using an SAFC-II or similar piggyback does not resolve the problem.



After doing a bunch of research I found that installing an OBD2 ECU completely resolves the problem.
Note: Lagtime also discovered that this problem could be resolved by using a Greddy E-Manage with optional injector harness to raise the injector duty cycle.

Another benefit of running the OBD2 ECU is you can connect an OBD2 scantool to read and clear MIL's. It will also allow you to monitor and datalog engine parameters such as timing, short and long term fuel trim, coolant temp, TPS, intake air temp, engine load, vehicle speed, air flow rate, and O2 sensor voltage.

Below is another FJO wideband capture after installing an OBD2 ECU without any SAFC fuel correction. No other changes were made. As you can see the problem is no longer present. OBD2's run pretty rich stock.



Below is after tuning the OBD2 ECU with the SAFC was completed.



How to upgrade an OBD1 car to OBD2:

Installation of the ECU is plug and play. Disconnect the battery. Simply disconnect your OBD1 ECU from the harness and connect an OBD2 ECU. The car should run at this point. The only thing I know of that doesn't work is the TRAC system. In order to get everything working correctly the issues below need to be addressed.

1) Like any OBD2 car you will need to run an O2 simulator if you have a catless downpipe installed. Failure to do so will result in a MIL from the secondary O2 sensor.
How to install an O2 simulator by Stu Hagen

2) On OBD2 cars there an additional ground wire that's not present on OBD1 cars. Not having this ground wire causes the primary O2 sensor heater to not function. This will prevent the car from entering closed loop operation when there is insufficient heat from the exhaust gas to keep the sensor at operating temp. This happens when the car is cold or idles long enough (4-5 minutes) for the sensor to cool off. It can cause the car to run very rich at idle. Adding the groundwire to the ECU harness fixes the problem.

How to get the primary O2 sensor heater functioning:
Since there's an additional pin needed for the new groundwire you will have to find one to use. This will require you to either cut a wire off of the ECU harness or find a donor pin from another harness. I used the pin from TE2 (E10-19) which is not used on OBD2. On OBD1 it's used for the special diagnostic test mode.

On the ECU wiring harness remove the yellow protectors, they pop off with a small screw driver. Remove pin TE2 (E10-19). It's a pink wire with a green stripe. To accomplish this take a small safety pin and carefully push up the plastic tab that holds the pin in the harness and lightly pull on the wire on the other side of the connector. It should pop right out with a slight tug. Cut the wire a couple of inches away from the ECU connector.

Insert this pin into the new ground wire location E03 (E9-78). Lengthen the wire so it's long enough to reach to a suitable ground point. I used the mounting point for the trac ecu. Attach the wire to the ground point.

3) OBD2 uses a different communications protocol and connector. The existing OBD1 diagnostic connector will not work. In order to read and clear MIL's you will need to install an OBD2 diagnostic port.

How to install an OBD2 diagnostic port:
Disconnect the battery. Remove the wiring harness from the ecu. Remove the yellow protectors, they pop off with a small screw driver. Next you have to move a pin on the ECU harness to another location. On obd1 cars pin E9-29 (vf1) is used for serial communications. This pin is not used on obd2 cars. On obd2 cars pin E10-8 (sdl) is used for serial communications. This pin is not used on obd1 cars. So you have to move pin E9-29 to E10-8.



On the ecu wiring harness where it attaches to the ecu move pin E9-29 (vf1) to pin E10-8 (sdl). It's a light green wire. To accomplish this take a small safety pin and carefully push up the plastic tab that holds the pin in the harness and lightly pull on the wire on the other side of the connector. It should pop right out with a slight tug.



Next identify E10-8 and remove the yellow plug that's installed in unused locations. Now carefully insert the pin into the harness. It should pop right in.



Next you need an obd2 j1962 female connector. They are hard to find. You could go cut one off a car from a junkyard. I got mine from here.

http://www.multiplex-engineering.com/products.htm

They also sell OBD2 connectors and pins so you can make your own.

Here are the connections that need to be made (4 wires).



Pin 16 on the obd2 connector goes to +12v power. Run this to the a power source that is 12v with the ignition on. I used the cigarette lighter circuit. For safety you will want to put a fuse between the power source and obd2 connector.

Pin 4 on the obd2 connector goes to chassis ground. Run this to a suitable ground location. I used an existing ground point located just above the drivers side kick panel.

Pin 2 on the obd2 connector goes to pin E10-8 (SDL) on the ecu, this is the light green wire you moved on the ecu harness. The easiest way to do this is to tap in to pin 7 (light green wire) on the OBD1 diagnostic connector D5.

Pin 5 on the obd2 connector goes to the ECU ground which is E9-69 (E1) brown wire. The easiest way to do this is to tap in to pin 3 (brown wire) on the OBD1 diagnostic connector D5.



That's it, now you should have a working obd2 dlc3 port to plug in in whatever obd2 scan tool you want.


Sorry to bring back from the dead. But when I am cutting the o2 heater wire and adding a ground. What do I do with the wire that runs up through the harness? Just tape it off? Does it connect back to the new ground wire coming from the ecu?
 
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