OBD I to OBD II Conversion Issues

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tcanin00

tcanin00

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As implied, I'm having problems going from OBD I to OBD II. My car is a 1970 Dart Swinger and it has a 5.2 and complete harness from a 1994 Dakota. I have an engine harness, PDC, and ECM from a 1999 Dakota that had a 5.2 and a manual transmission. I cut the C1-3 connectors off the harness and spliced them at the 60 pin OBD I connector. I made sure to go through the schematics, take notes, and check off each wire as I soldered them.
When I was done with that, I tried to start car and nothing. The fuel pump primes, it cranks, but doesn't start. I double checked the connections and made sure the computer was grounded.
I have read that higher trim levels of trucks had a central time module that operates the security system. If the ECM was ever connected over the CAN/BUS network to the CTM module, it will continue to look it. I read that if that is the case, the network wires can be shorted together and trick the ECM into thinking there is a problem with the network and ignore it. I tried that, and it made no difference.
20250411_154743.jpg

Picture of engine in question. I recently moved the battery to the trunk, and plan on moving the washer reservoir and PDC to where the battery was.
 
I wish I knew. I have never seen that you short something. I have read and heard that there are people who can program the security thing out of the ECM, but it likely is not cheap.
 
Sounds like the PCM is looking for a start signal from the network or something. I don’t think it is security, pretty sure that issue is that it starts and won’t stay running.

I would look at the start signal. Are you letting the PCM engage the starter? Maybe that’s what is sticking in my head?
 
Did the you see the engine run before the swap?

How about the key requiring a RFID signal to tell the sec system that the correct key is being used?

There are so many minor things that can prevent a modern electronics car from starting.

Aren't there aftermarket PCM kits that can run things much simpler and easier?
 
I could be mixing things up between G3 swaps and Magnum EFI. I don't have time to dig into it, so my thought about the starter signal going to the PCM and letting it control the relay might be off.

I am fairly confident that it is an issue with the G3 swaps though. The PCM wants to control the starter and won't fire the injectors and/or spark without it.

Might also need a clutch wire to the PCM too? That does seem accurate. Do you have that in the mix?
 
67Dart273 said:
I wish I knew. I have never seen that you short something. I have read and heard that there are people who can program the security thing out of the ECM, but it likely is not cheap.
Click to expand...
It is a possibility that the security would need to be turned off. I plan on getting an OBD II connector and learning the tuning software, but neither of those are very cheap either.
 
DionR said:
Sounds like the PCM is looking for a start signal from the network or something. I don’t think it is security, pretty sure that issue is that it starts and won’t stay running.

I would look at the start signal. Are you letting the PCM engage the starter? Maybe that’s what is sticking in my head?
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That is a possibility. Both OBD I and II have a start/run input pin and fused 12 volt constant power. Neither have anything going to or coming from the starter relay.
Since the entire harness is from a '94 Dakota, I believe the starter is being engaged by the ECM. I will go through the schematics and my notes to confirm.
 
DionR said:
I could be mixing things up between G3 swaps and Magnum EFI. I don't have time to dig into it, so my thought about the starter signal going to the PCM and letting it control the relay might be off.

I am fairly confident that it is an issue with the G3 swaps though. The PCM wants to control the starter and won't fire the injectors and/or spark without it.

Might also need a clutch wire to the PCM too? That does seem accurate. Do you have that in the mix?
Click to expand...
The Dakota was manual transmission and has a clutch switch. It is hooked up and hanging out under the dash since my car has an automatic right now. I did not see any wiring going to the ECM from that switch, just the brake switch input signal. The clutch switch may interrupt the starter circuit. Again, I would have to look at the schematics to know for sure.
 
Dana67Dart said:
Did the you see the engine run before the swap?

How about the key requiring a RFID signal to tell the sec system that the correct key is being used?

There are so many minor things that can prevent a modern electronics car from starting.

Aren't there aftermarket PCM kits that can run things much simpler and easier?
Click to expand...
The engine ran in my car before I started the swap, and runs with the OBD I ECM.
I don't know if the OBD II ECM had an RFID key or not. I bought the engine harness, PDC, and ECM already removed from the the truck.
It has to be something simple that I've missed. Something I just thought of is the the OBD II ECM has an input for oil pressure, and the OBD I ECM does not. I could run a wire from the oil pressure signal wire and see if that makes a difference.
There are aftermarket computers that would work, and can be tuned with open sourcesoftware. I have a DIY Autotune MS3X that I built for this project several years ago. For now, I would like to use a factory ECM for the base tune and the fact it operates the cruise control and air conditioning.
 
Go back to basics. What’s not working? Fuel or spark? The obd2 system is all triggered by the ASD relay.
 
I had a Ford taurus that had an issue with the lockup converter.

I attempted to disable the lockup. By disconnecting the wire that activates the lockup.

Well the computers could tell the wire was disconnected and made error codes.
 
TT5.9mag said:
Go back to basics. What’s not working? Fuel or spark? The obd2 system is all triggered by the ASD relay.
Click to expand...
To be honest, I have not trouble shot deeper into this. I hear the fuel pump prime with the key on, so I know the ASD is being triggered. The OBD II ECM has an output for the fuel pump relay. I read that it might have to be spliced to ASD output on an OBD I harness, since the fuel pump relay is operated by the ASD.
 
Dana67Dart said:
I had a Ford taurus that had an issue with the lockup converter.

I attempted to disable the lockup. By disconnecting the wire that activates the lockup.

Well the computers could tell the wire was disconnected and made error codes.
Click to expand...
Yeah, it's looking for all of the signal wires and outputs. With something missing or disconnected it will cause problems for the ECM.
 
Sounds like you need to do some diagnostic work.

tcanin00 said:
Yeah, it's looking for all of the signal wires and outputs. With something missing or disconnected it will cause problems for the ECM.
Click to expand...
No it won’t. They run just fine without any of that crap.
 
TT5.9mag said:
Sounds like you need to do some diagnostic work.


No it won’t. They run just fine without any of that crap.
Click to expand...
I agree. I was on here to get some guidance as to what to look for.
Yes, it will run without any additional modules or controllers. It will give an error code if something is missing or disconnected.
 
tcanin00 said:
As implied, I'm having problems going from OBD I to OBD II. My car is a 1970 Dart Swinger and it has a 5.2 and complete harness from a 1994 Dakota. I have an engine harness, PDC, and ECM from a 1999 Dakota that had a 5.2 and a manual transmission. I cut the C1-3 connectors off the harness and spliced them at the 60 pin OBD I connector. I made sure to go through the schematics, take notes, and check off each wire as I soldered them.
When I was done with that, I tried to start car and nothing. The fuel pump primes, it cranks, but doesn't start. I double checked the connections and made sure the computer was grounded.
I have read that higher trim levels of trucks had a central time module that operates the security system. If the ECM was ever connected over the CAN/BUS network to the CTM module, it will continue to look it. I read that if that is the case, the network wires can be shorted together and trick the ECM into thinking there is a problem with the network and ignore it. I tried that, and it made no difference. View attachment 1716391572
Picture of engine in question. I recently moved the battery to the trunk, and plan on moving the washer reservoir and PDC to where the battery was.
Click to expand...
Do you have an OBD2 diagnostic connector wired in? If so, read the data and see if the PCM shows rpm while cranking.

Does it have spark?
Does it have fuel pressure?
Does it have injector pulse?
 
I was in the process of wiring in the diagnostic port earlier, but it start raining so I didn't finish.
I will test for all of those later.
 
Aren't the injectors different between OBD1 and OBD2? Seems like I read that somewhere. If the OBD2 harness plugged right onto the old injectors, that may not have anything to do with......but just wanted to throw that out there. Good luck with it. Thanks for posting it, because we'll all learn when you solve it.

:thumbsup:
 
JDMopar said:
Aren't the injectors different between OBD1 and OBD2? Seems like I read that somewhere. If the OBD2 harness plugged right onto the old injectors, that may not have anything to do with......but just wanted to throw that out there. Good luck with it. Thanks for posting it, because we'll all learn when you solve it.

:thumbsup:
Click to expand...
The injectors might have different connectors for different years. I left the existing harness in place and spliced in at the OBD I 60 pin connector.
I hope to get this figured out because it seemed pretty straightforward. Solder up wires, plug in OBD II ECM, start engine, and possibly deal with a security system if the donor truck had one.
 
Also, I connected the oil pressure signal wire and spliced in the fuel pump output to the ASD output. Both, done separately, made no difference. I'll finish wiring up the diagnostic port and hook up a scanner to see what's going, and I'll check fuel pressure, ignition, and injection pulse. Stay tuned...
 
tcanin00 said:
and injection pulse
Click to expand...
is it posable that one of the crank / cam / ignition timing pulse wheels have different patterns I seem to recall that about some modern engine and what would seem like a simple part swap creating a no start issue
 
Dana67Dart said:
is it posable that one of the crank / cam / ignition timing pulse wheels have different patterns I seem to recall that about some modern engine and what would seem like a simple part swap creating a no start issue
Click to expand...
Obd1 and obd2 magnums are the same.
 
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