Is my ECM bad?

[colorator]

Hello, I've got a YJ with a 5.3L from a 2005 suburban. I had a few intermittent non-starts, which acted like bad fuel from sitting, and now it doesn't start. I've done some standard trouble shooting and it comes down to the fuel pump relay not actuating. The relay is good, fuel pump is good. I can jumper the relay and it will start and stay running.

I put a voltage meter on the Green/White wire coming from the ECM and I get 12 volts when I turn the key on. I seem to get a constant 12V, but it will not actuate the relay. I've cleaned the harness terminal, double checked connections and it just won't actuate the relay.

My questions are: Is this an ECM issue? Is there a way to test if it is? If so, what is my best option for replacing it? I didn't do the swap so am not familiar with ECM Flashing/tuning/replacement, but I'm willing to learn and am fairly handy, so would consider investing in an HP tuner or something of the sort if that is the best way. Ideally I could just order a plug n play replacement, but I'm not sure it works that way... or does it.

Thank you for your help in advance.
Noob

 

[85CUCVKRAWLER]

Ok, well, if you can jump out the relay and it clicks and youre getting 12v out of the ECM, then its not the ECM. How is your fuel pump relay situated? Can you take a picture of it? Is it the factory setup? Have you tried a new fuel pump relay? Or try switching with a good relay?

Ive had more than once the factory wiring from the fuel pump relay to the fuel pump go bad from three decades of rubbing. Also, the housing the relay is plugged into might have failed. Or the Relay is bad and is giving you intermittent engaging.

So, the ECM is giving out 12v to the fuel pump relay, so the ECM isnt bad. The fuel pump runs when jumped, so its not the fuel pump. You know the rig will run when the pump is on. So its something between the ECM and the fuel pump.

To add, for relay engagement, you only need 12v with minimal amperage. So if you see 12v coming from the ECM with the key on, then youre good to go as far as the ECM is concerned.

Also, to add, in both my LS swaps ive put the fuel pump on an aux switch on the dash. Its a quick theft deterrent system and rules out all these other issues your kindof seeing here. Every swap ive done ive battled fuel delivery issues.

 

[boogie_4wheel]

Measure the voltage on the Green/White while it is connected to the relay (relay coil). I'm thinking you have the symptom of a bad connection (voltage potential when they're isn't a load, but no voltage when a load is present).
If the voltage falls to 0, then you've got a loose connection or broken wire between the ECM and the pump relay.

 

[Agility Customs]

Hello, I've got a YJ with a 5.3L from a 2005 suburban. I had a few intermittent non-starts, which acted like bad fuel from sitting, and now it doesn't start. I've done some standard trouble shooting and it comes down to the fuel pump relay not actuating. The relay is good, fuel pump is good. I can jumper the relay and it will start and stay running.

I put a voltage meter on the Green/White wire coming from the ECM and I get 12 volts when I turn the key on. I seem to get a constant 12V, but it will not actuate the relay. I've cleaned the harness terminal, double checked connections and it just won't actuate the relay.

My questions are: Is this an ECM issue? Is there a way to test if it is? If so, what is my best option for replacing it? I didn't do the swap so am not familiar with ECM Flashing/tuning/replacement, but I'm willing to learn and am fairly handy, so would consider investing in an HP tuner or something of the sort if that is the best way. Ideally I could just order a plug n play replacement, but I'm not sure it works that way... or does it.

Thank you for your help in advance.
Noob

Who tuned the ECM? I have dealt with many ECMs that were pretuned and in all actuality the tuning was jacked. Shutting of the VATS is the most obvious thing that needs done on a swap and I have had 2 show up with out that being done.

I personally feel that HP tuners is worth every single penny even moving forward after the swap is complete.

I dont think your ECM is bad

 

[colorator]

Thank you all in advance for the assistance:

@85CUCVKRAWLER - Let me clarify, I can supply the relay with 12v direct (to pin 86) and it will click and I can start. Wire pin 86 to the ECM and the relay doesn't actuate. Definitely not a factory installed relay, it is self tapped to fender well. I did swap the relay just to be certain, but no dice. I was hoping to avoid the manual fuel pump switch route, but that is certainly an option.

@boogie_4wheel - You might be on to something, the voltage goes away if connected to the relay. I replaced the splice from the Green/white wire and the relay terminal. However, I did not check the connection at the ECM itself (pin 9 I think). My ECM is somewhat exposed mounted to the firewall, so quite possible I've got something going on there.

I was leaning towards the ECM because I get 12V on the Green/white constant. My understanding is that it should cut off after 5 seconds or so if the engine doesn't crank. Nonetheless I've got a few more things to check...

@Agility Customs - I'm not sure who did the tune, however, I've owned it for 3 years with no issues concerning the tuning, which is why I really hope I don't have to replace the ECM. I would agree that a pre-tune is not likely to work out well for me. Might be time for me to step up my game and learn properly... if nothing else, to be able to save the current tune if I do have to replace the ECM.

 

[Agility Customs]

Thank you all in advance for the assistance:

@85CUCVKRAWLER - Let me clarify, I can supply the relay with 12v direct (to pin 86) and it will click and I can start. Wire pin 86 to the ECM and the relay doesn't actuate. Definitely not a factory installed relay, it is self tapped to fender well. I did swap the relay just to be certain, but no dice. I was hoping to avoid the manual fuel pump switch route, but that is certainly an option.

@boogie_4wheel - You might be on to something, the voltage goes away if connected to the relay. I replaced the splice from the Green/white wire and the relay terminal. However, I did not check the connection at the ECM itself (pin 9 I think). My ECM is somewhat exposed mounted to the firewall, so quite possible I've got something going on there.

I was leaning towards the ECM because I get 12V on the Green/white constant. My understanding is that it should cut off after 5 seconds or so if the engine doesn't crank. Nonetheless I've got a few more things to check...

@Agility Customs - I'm not sure who did the tune, however, I've owned it for 3 years with no issues concerning the tuning, which is why I really hope I don't have to replace the ECM. I would agree that a pre-tune is not likely to work out well for me. Might be time for me to step up my game and learn properly... if nothing else, to be able to save the current tune if I do have to replace the ECM.



View attachment 171841

Thats my bad I thought this was a new swap.

 

[85CUCVKRAWLER]

Thank you all in advance for the assistance:

@85CUCVKRAWLER - Let me clarify, I can supply the relay with 12v direct (to pin 86) and it will click and I can start. Wire pin 86 to the ECM and the relay doesn't actuate. Definitely not a factory installed relay, it is self tapped to fender well. I did swap the relay just to be certain, but no dice. I was hoping to avoid the manual fuel pump switch route, but that is certainly an option.

@boogie_4wheel - You might be on to something, the voltage goes away if connected to the relay. I replaced the splice from the Green/white wire and the relay terminal. However, I did not check the connection at the ECM itself (pin 9 I think). My ECM is somewhat exposed mounted to the firewall, so quite possible I've got something going on there.

I was leaning towards the ECM because I get 12V on the Green/white constant. My understanding is that it should cut off after 5 seconds or so if the engine doesn't crank. Nonetheless I've got a few more things to check...

@Agility Customs - I'm not sure who did the tune, however, I've owned it for 3 years with no issues concerning the tuning, which is why I really hope I don't have to replace the ECM. I would agree that a pre-tune is not likely to work out well for me. Might be time for me to step up my game and learn properly... if nothing else, to be able to save the current tune if I do have to replace the ECM.



View attachment 171841

Ok, well, youre overlooking something then.

If you measure 12v from the ECM fuel pump wire when key is on, then its not the ECM.
If youve swapped relays and and still doesnt work then its not the relay.
If you can jump the relay and it fires the fuel pump, then its not the relay or the pump.

have you tried testing the ECM wire while it is plugged into the relay? Youll have to press the probe needle into the wire casing pretty good, but if you dont get 12v, then you have a bad ground or loose ground.