Comanche runs only with the key held on run.

[Krisbodean85]

Ok so I’ve been working on the Comanche 4.0 that I recently acquired and installed a cps sensor it has a new tps and a new fuel injector control valve the PO said that’s all it needed of course . It turns over and cranks for a second then dies. The fuel pump is working. Now hear me out so as I was sitting in the Comanche thinking of what else to check I decided to try it again but this time I held the key on the run position and and it ran and idled up when I gave it gas I did this for only a couple of seconds so I wouldn’t burn the starter up. I did it a couple of times every time it ran perfect. Before when it would crank for those few seconds I would give it gas and nothing would happen. It’s almost like if you just turned the key off while it was trying to crank. What do you guys think it could be. I’ve been working on it religiously for the past week and I’m at a lost. Thanks in advance 

[Ωhm]

When key is turned to the run position, can you hear the fuel pump run for 2-3 seconds and then shut off?

EDIT:  Run position is Key On, not cranking.

[Krisbodean85]

i Tried to listen for it but can’t tell if it’s the pump or the bussing in the cab . But when I crank it the fuel pressure is upper 30’s Something and holding pressure 

[AZJeff]

The 4.0 engine has a fuel pump ballast resistor that is mounted on the firewall just below the cowl.  This resistor is designed to drop the voltage to the fuel pump, but ONLY does it when the key is in the "RUN" position.

 

When the key is in the "START" position, power to the fuel pump is sent via a different path.

 

It sounds like your fuel pump is only running when the key is in the "START" position, and that is a sign of a failed ballast resistor.

[Krisbodean85]

I jumped the wires in that ballast and no change occurred 

[Krisbodean85]

Your talking about that porcelain looking thing on the driver side next to the air filter right? 

[Ωhm]

11 hours ago, Krisbodean85 said:

Your talking about that porcelain looking thing on the driver side next to the air filter right? 

That is the location for the fuel pump ballast.

 

12 hours ago, Krisbodean85 said:

i Tried to listen for it but can’t tell if it’s the pump or the bussing in the cab . But when I crank it the fuel pressure is upper 30’s Something and holding pressure 

Good to see you have a fuel pressure gauge. If that buzzing sound you heard in the cab/wherever was for 2-3 seconds, good chance that was the fuel pump on, when key was cycled from OFF to ON (no cranking). With fuel pressure gauge hooked up, hopefully a trusted pressure gauge, cycle key from OFF to ON. Fuel pressure should read around 39 psi and hold that pressure.

[Krisbodean85]

15 minutes ago, Ωhm said:

That is the location for the fuel pump ballast.

 

Good to see you have a fuel pressure gauge. If that buzzing sound you heard in the cab/wherever was for 2-3 seconds, good chance that was the fuel pump on, when key was cycled from OFF to ON (no cranking). With fuel pressure gauge hooked up, hopefully a trusted pressure gauge, cycle key from OFF to ON. Fuel pressure should read around 39 psi and hold that pressure.

It’s holding pressure. I think I found the problem. On the slots does it go just in the middle or all the way to one side? 

[Ωhm]

7 minutes ago, Krisbodean85 said:

On the slots does it go just in the middle or all the way to one side? 

I don't understand the question. Also look at the harness side connector. Something heated up.

[HOrnbrod]

^^ This. These threads will help with the ignition switch / connector:

 

https://comancheclub.com/topic/49293-complete-shutdown-at-65mph/?tab=comments#comment-501275

 

http://www.jeepforum.com/forum/f12/basic-maintenance-ignition-switch-1226376/

[Krisbodean85]

22 minutes ago, Ωhm said:

I don't understand the question. Also look at the harness side connector. Something heated up.

Hornbrod sent a link that will help a lot. Thanks for the help. I’ll report back when I get it installed and I’ll check to see what burned the connector up. 

[Krisbodean85]

1 hour ago, Ωhm said:

 

[Krisbodean85]

Ok so I went and installed the new switch. No change still does the same thing. As long as the key tumbler is held on the run/start position it will run. You let go and it dies. I’m at a total lost 

[Jeep Driver]

Drop your column again. 

With a test light, run the switch through each position. 

Back probe each connector and see what is happening at the switch. 

 

Red- power in. 

Brown- accessory.

Orange- run. 

Yellow- ignition. 

Green- starter. 

Other two wires are to ground, bulb check, ignore. 

 

I may have the orange and yellow backwards, don't remember, however, both must be hot during start and run positions. 

 

 

[Krisbodean85]

Ok I’ll get a meter and check it. If they aren’t then what could it be? 

[Jeep Driver]

Is it in the switch? in the column?

Or somewhere else, that's what you need to find out. 

[Krisbodean85]

25 minutes ago, Jeep Driver said:

Is it in the switch? in the column?

Or somewhere else, that's what you need to find out. 

Ok thanks I’ll check it and report back 

[Ωhm]

Could be things:

1. Bad gas
2. New TPS, was it adjusted properly?
3. Crack vacuum line going too the MAP.
4. What is battery voltage while cranking the engine (without battery charger)?

[Eagle]

On 6/1/2018 at 9:16 PM, Krisbodean85 said:

Ok so I’ve been working on the Comanche 4.0 that I recently acquired and installed a cps sensor it has a new tps and a new fuel injector control valve the PO said that’s all it needed of course . It turns over and cranks for a second then dies. The fuel pump is working. Now hear me out so as I was sitting in the Comanche thinking of what else to check I decided to try it again but this time I held the key on the run position and and it ran and idled up when I gave it gas I did this for only a couple of seconds so I wouldn’t burn the starter up. I did it a couple of times every time it ran perfect. Before when it would crank for those few seconds I would give it gas and nothing would happen. It’s almost like if you just turned the key off while it was trying to crank. What do you guys think it could be. I’ve been working on it religiously for the past week and I’m at a lost. Thanks in advance 

 

I'm going to be "that guy," and ask you to please restate the problem more accurately. There are several confusing statements in your opening post.

1. "Turning over" = "cranking" ... both refer to when the starter is turning the engine but the engine is not running.
2. The RUN position of the key is where it sits when the engine is running. The starter is not engaged when the key is in the RUN position.

Are you saying the engine will start, but it won't stay running after you release they key to the RUN position?

[Krisbodean85]

1 hour ago, Eagle said:

 

I'm going to be "that guy," and ask you to please restate the problem more accurately. There are several confusing statements in your opening post.

1. "Turning over" = "cranking" ... both refer to when the starter is turning the engine but the engine is not running.
2. The RUN position of the key is where it sits when the engine is running. The starter is not engaged when the key is in the RUN position.

Are you saying the engine will start, but it won't stay running after you release they key to the RUN position?

Yes the Comanche will start but won’t stay running after I release the key. Unfortunately I leave out of town for work and won’t be back for a couple of weeks. But I did some wire checking and came down to two things it’s either going to be the latch relay or the ecm

[HOrnbrod]

Did you do / check the ignition switch alignment procedure after you replaced the ignition switch? If the switch isn't aligned, that's a symptom (start but won’t stay running after I release the key). Also did you replace the ignition switch connector?

[Strokermjcomanche]

I had the same thing happen to me on my 89 MJ , in my case it was a blown fusible link that comes off of the starter relay . With your test light make sure both sides of the links have power , it may have blown when whatever caused that ignition switch  to melt . 

[Krisbodean85]

9 hours ago, HOrnbrod said:

Did you do / check the ignition switch alignment procedure after you replaced the ignition switch? If the switch isn't aligned, that's a symptom (start but won’t stay running after I release the key). Also did you replace the ignition switch connector?

Yes I did 

[Eagle]

11 hours ago, Krisbodean85 said:

Yes the Comanche will start but won’t stay running after I release the key. Unfortunately I leave out of town for work and won’t be back for a couple of weeks. But I did some wire checking and came down to two things it’s either going to be the latch relay or the ecm

 

What this usually means is that the ballast resistor in the fuel pump circuit has failed. The START circuit bypasses that, so the engine will start. Once the key is released to the RUN position, power to the fuel pump passes through the ballast resistor. If the ballast resistor is bad, the fuel pump stops running so the engine sputters along for a few seconds until the fuel in the rail has been used up, then it dies.

 

To test, you can jump the two contacts on the ballast resistor. You have tried that, so I'm out of suggestions. Sorry.

[Krisbodean85]

Yeah I put a jumper wire in the obd red and orange I believe were the fuel pump runs constant and turned the key to start and the Comanche cranked and stayed running. Fuel pump relay is doing its job. That’s why I think it’s going to be either the latch relay or the ecm (which is around 100$ For the ecm at Oreilly’s). But I’ll know more about it when I get home and do more wire checking.