OBD I to OBD II Conversion Issues

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All of the sensors are the same for the most part. As was mentioned, injector plugs are different depending on year and application.
As of now, there is no spark, injector pulse, and fuel pressure primes at key on to 45 psi and drops while cranking. I'll hook my old Snap On scanner up and see what's going on.
 
My theory is that something is going on with ASD and fuel pump control. The Dakota's ASD relay is triggered by the ECM, and the ASD completes the circuit of the fuel pump relay. I checked for power with ignition switch on and off, and had power at the right pins of both relays for both tests.
The OBD II ECM completes the circuits of both relays separately. I might rig up a test harness directly from the ECM as test. I just find it hard to understand how a working circuit is not working with the new ECM, especially since the ASD relay is triggered and the fuel pump primes at key on.
I also have a 1999 Dakota 3.9 automatic transmission ECM that came with the harness I bought. It does exactly what the V8 ECM does when plugged in. I figured it would at least start the engine, but it did not. So I don't think it's a computer related problem.
 
tcanin00 said:
There is no communication with my scanner from the diagnostic port at the moment.
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If you somehow had it before and not now, there's your answer.

Frankly though, this seems like a nearly impossible task as the CAN architecture is completely different. I'm surprised you were able to get the fuel pump to prime but they may not have changed that circuitry much between the systems. OBD1 is fairly crude compared to OBD2. The connectors are all different which means the termination resistances are different as well.

I'm not being snide but I'll be surprised if you somehow get this to work. Perhaps there's a way I'm not aware of (I didn't read the GJ thread) but I'm not sure why you'd waste your time when you can just get the appropriate harness out of an OBD 2 vehicle. Modern electrical systems are really not meant to be Frankenstein'd together.

Good luck.
 
rmchrgr said:
If you somehow had it before and not now, there's your answer.

Frankly though, this seems like a nearly impossible task as the CAN architecture is completely different. I'm surprised you were able to get the fuel pump to prime but they may not have changed that circuitry much between the systems. OBD1 is fairly crude compared to OBD2. The connectors are all different which means the termination resistances are different as well.

I'm not being snide but I'll be surprised if you somehow get this to work. Perhaps there's a way I'm not aware of (I didn't read the GJ thread) but I'm not sure why you'd waste your time when you can just get the appropriate harness out of an OBD 2 vehicle. Modern electrical systems are really not meant to be Frankenstein'd together.

Good luck.
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Yes, the OBD I SBEC would communicate with the scanner.

The communication networks are different, since JTEC uses a CAN/BUS network for sensor output to the instrument panel and whatever modules are in the system.

The fuel pump priming is has me confused. It's like the JTEC is powering on for a few seconds and then turning off. The two harnesses and connections are similar in layout and operation. The main difference being the control of the fuel pump relay.

GJ spliced in at C130 60 pin connector and it worked for him. His approach seemed like the best way to convert, since he had the existing harness that was known to be good. That's what I started with, a known, working harness. I'll mess around with some more and see if I can figure what I did wrong, or what isn't working. If I can't figure it out, I still have the 1999 Dakota harness and PDC.
 
tcanin00 said:
The communication networks are different, since JTEC uses a CAN/BUS network for sensor output to the instrument panel and whatever modules are in the system.
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That's really it in a nutshell. It's not just a simple matter of wiring, the systems are totally different. IMO, it's really not worth the exercise.
 
I feel like there is enough data in your responses to rule this idea out, but just asking to make sure.

Are you still using the original key switch? If so, have you verified that the PCM sees power both in start and run position? You probably already know they are separate. But maybe something got dropped during the swap?

Just spitballing. My apologies if you have covered this.
 
tcanin00 said:
All of the sensors are the same for the most part. As was mentioned, injector plugs are different depending on year and application.
As of now, there is no spark, injector pulse, and fuel pressure primes at key on to 45 psi and drops while cranking. I'll hook my old Snap On scanner up and see what's going on.
Click to expand...
tcanin00 said:
There is no communication with my scanner from the diagnostic port at the moment.
Click to expand...
Is there another vehicle available with a JTEC PCM to try your scan tool on, to verify it is capable of reading this one?

I will suggest basically starting over with diagnostics. Start checking power and ground to the PCM itself. If the scan tool would communicate with the PCM, I want to know if there is RPM showing while cranking.

When wired and working properly, the PCM will turn on ASD relay a couple seconds when key is turned on to prime the fuel system, then PCM turns ASD relay off. When cranking, if no crankshaft sensor signal is detected by the PCM it has no reason to turn the ASD relay back on; PCM thinks the engine is not being cranked. When crankshaft sensor signal is not present during cranking, there will be no spark, no injector pulse, and ASD relay will not be turned on.
 
DionR said:
I feel like there is enough data in your responses to rule this idea out, but just asking to make sure.

Are you still using the original key switch? If so, have you verified that the PCM sees power both in start and run position? You probably already know they are separate. But maybe something got dropped during the swap?

Just spitballing. My apologies if you have covered this.
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I am using my Dart's original ignition switch. I have not checked for power in both positions at PCM. I would assume so, since it works with SBEC. I will find out for sure.
 
Bobzilla said:
Is there another vehicle available with a JTEC PCM to try your scan tool on, to verify it is capable of reading this one?

I will suggest basically starting over with diagnostics. Start checking power and ground to the PCM itself. If the scan tool would communicate with the PCM, I want to know if there is RPM showing while cranking.

When wired and working properly, the PCM will turn on ASD relay a couple seconds when key is turned on to prime the fuel system, then PCM turns ASD relay off. When cranking, if no crankshaft sensor signal is detected by the PCM it has no reason to turn the ASD relay back on; PCM thinks the engine is not being cranked. When crankshaft sensor signal is not present during cranking, there will be no spark, no injector pulse, and ASD relay will not be turned on.
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No, there isn't another vehicle available for testing. My Dart is the only Chrysler product I own now, and it's easier on my marriage and wellbeing.
I will go through power and ground connections to see if I find the problem.
I considered an input sensor issue as the cause for not turning on or operating anything else. I did not find a problem going through the connections I made at C130, and the car runs when the SBEC is plugged in.
 
Sensors are probably all working since it runs with the SBEC.

With JTEC wired in, unplug crankshaft sensor, turn ignition to on, then use a volt meter to check voltage on each pin in the harness where that crankshaft sensor plugs in. Testing harness side, not sensor side. Black lead of meter on battery negative post.

Next, unplug all three JTEC connectors and check each power feed to the PCXm for voltage. List the connector, the pin, and what voltage you see with ignition off, ignition, and ignition in crank position.
 
Bobzilla said:
Sensors are probably all working since it runs with the SBEC.

With JTEC wired in, unplug crankshaft sensor, turn ignition to on, then use a volt meter to check voltage on each pin in the harness where that crankshaft sensor plugs in. Testing harness side, not sensor side. Black lead of meter on battery negative post.

Next, unplug all three JTEC connectors and check each power feed to the PCXm for voltage. List the connector, the pin, and what voltage you see with ignition off, ignition, and ignition in crank position.
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Thank you for the advice, I will go through this procedure tomorrow.
 
Bobzilla said:
Sensors are probably all working since it runs with the SBEC.

With JTEC wired in, unplug crankshaft sensor, turn ignition to on, then use a volt meter to check voltage on each pin in the harness where that crankshaft sensor plugs in. Testing harness side, not sensor side. Black lead of meter on battery negative post.

Next, unplug all three JTEC connectors and check each power feed to the PCXm for voltage. List the connector, the pin, and what voltage you see with ignition off, ignition, and ignition in crank position.
Click to expand...
Ok, had a chance to test everything.
Crankshaft Position Sensor
Pin #1 VT/WT 0 V
Pin #2 BK/LB 0 V
Pin #3 GY/BK 5.2 V
This seems backwards, I would think pin #1 would be powered.

PCM C-1
Pin #2 LG/BK
Switch off 0 V
Switch on 12.68 V
Switch on, cranking 9.8 V
Pin #22 RD/WT
Switch off 12.68 V
Switch on 12.68 V
Switch on, cranking 10.2 V
 
tcanin00 said:
Ok, had a chance to test everything.
Crankshaft Position Sensor
Pin #1 VT/WT 0 V
Pin #2 BK/LB 0 V
Pin #3 GY/BK 5.2 V
This seems backwards, I would think pin #1 would be powered.

PCM C-1
Pin #2 LG/BK
Switch off 0 V
Switch on 12.68 V
Switch on, cranking 9.8 V
Pin #22 RD/WT
Switch off 12.68 V
Switch on 12.68 V
Switch on, cranking 10.2 V
Click to expand...
Pin 3 of crankshaft position sensor is supposed to be 5 volt reference, so that is correct.

Like DionR said, cranking voltage is low and concerning. Check voltage at the battery terminals while cranking, with black lead of meter on battery negative post and red lead on battery positive post. If the battery is staying much higher than 10 volts you are losing too much voltage through the wiring and that needs to be addressed before continuing. If the battery is also showing around ten volts or less while cranking, charge the battery a while then check battery and PCM c1 voltages again.

Edit to add: I will also go through the wiring diagrams when I get a chance and try to determine if there is anything else that may be different.
 
Thank you @DionR and @Bobzilla for your responses. I agree that the voltage drop during cranking is significant. The battery is a cheap, old one. I'll check voltage at the battery during cranking and see what it does.
 
Welp, I decided to modify the 1999 harness by changing the connectors out to ones that match my engine. I had a spare OBD I harness from a 1992 B250 van, so it became the donor. I will leave the majority of the '99 harness intact for testing, instead of rigging something up to test the ASD and fuel pump relays. I should have this done in a few days and ready to test.
20250416_201848.jpg
 
Didn't get as far as I hoped on the harness. I was originally just going to solder the C1-3 connectors back on, find the start/run wires from C200, and go for it. But I decided that while it's out of the car, it would be easier to work on.
My car has a 1994 Dakota harness, and it fit the car okay, but some things are positioned differently between a Dart and a Dakota. So I lengthened and shortened the Dakota's harness to make it fit better. I also moved the SBEC to under the passenger seat and extended the wiring for it. I know the PCM's are designed to operate under the hood, but it doesn't look right to me.
So that's what I'm doing now with 1999 harness. I completed the C1 connector and started on C2. I want to make the engine harness separate from the body harness, so it can be disconnected whenever I have to pull the engine. Late 90's and early 2000's Japanese and European cars are made that way, so that harness comes out with the engine. Seems easier than disconnecting everything before pulling the engine.
Anyway, this will not be a quick process. I work on it a few hours in the evening after work.
Happy Easter, and thank you to everyone who has helped and offered advice.
20250418_193904.jpg
 
tcanin00 said:
Didn't get as far as I hoped on the harness. I was originally just going to solder the C1-3 connectors back on, find the start/run wires from C200, and go for it. But I decided that while it's out of the car, it would be easier to work on.
My car has a 1994 Dakota harness, and it fit the car okay, but some things are positioned differently between a Dart and a Dakota. So I lengthened and shortened the Dakota's harness to make it fit better. I also moved the SBEC to under the passenger seat and extended the wiring for it. I know the PCM's are designed to operate under the hood, but it doesn't look right to me.
So that's what I'm doing now with 1999 harness. I completed the C1 connector and started on C2. I want to make the engine harness separate from the body harness, so it can be disconnected whenever I have to pull the engine. Late 90's and early 2000's Japanese and European cars are made that way, so that harness comes out with the engine. Seems easier than disconnecting everything before pulling the engine.
Anyway, this will not be a quick process. I work on it a few hours in the evening after work.
Happy Easter, and thank you to everyone who has helped and offered advice.View attachment 1716394798
Click to expand...
Take your time and check each connection carefully.
Happy Easter.
 
Bobzilla said:
Take your time and check each connection carefully.
Happy Easter.
Click to expand...
That's what I'm doing, extending each wire one at a time with schematics and pin outs. I didn't label anything when I cut the C1-3 connectors off, so I had to trace the ground path to figure out where an "extra" BK/BR ground wire went. The '99 harness treats the oil pressure sending unit as a sensor, so it is tied into the sensor ground circuit. I think that the way the '99 harness is grounded is part of the reason I couldn't splice in at the C130 60 pin connector.
 
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