New Engine Install - Rough start then Stalls

[roaniecowpony]

I have just got my 3.6 engine from a 2024 Gladiator installed and to the point of trying to start it. It cranks long and then when it starts it's very rough and stalls after a few seconds.

The company I bought the engine from said it was removed from a Gladiator with 160 miles on it, for a Hemi conversion. It appears as new. Even the oil was new. They told me the only thing I needed to do for installation in my 2018 JL was to change the Oil pressure sending unit under the intake manifold and put my engine harness on it. I installed my 2018 sender and the 2018 harness.

I haven't done a crank position sensor relearn nor a throttle position sensor relearn, since both require you to start the engine, which seems to be a problem for me.

So, thinking the old engine's throttle body might be recognized by the PCM, I quickly installed it. No difference at all.

Any ideas on what it may be? I'm leaning toward some sensor not being connected. But I haven't found one.

Can a crank relearn be done without running the engine?

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[jeepingib]

Double check any timing sensors. You may want to check them and make sure that they still use the same part number.

 

[roaniecowpony]

My old engine is still at my friend's warehouse. I want to pull the sensors. Not sure if anyone is there over the weekend. If so, maybe swap cam and crank sensors.

 

[Stetson]

Can you tell if it is getting fuel? Rough idle and then stall sounds like not enough fuel. I haven’t tinkered with a 3.6 much, can you pull a injector and see if it is sending fuel at start?

 

[cosmokenney]

At this point I'd also be taking a close look at all the connectors to make sure no pins are bent. Especially the ECU (or whatever its called in the JL).

 

[roaniecowpony]

Double check any timing sensors. You may want to check them and make sure that they still use the same part number.

Just did a comparison of all the sensors online. All the same part numbers, a few have letter suffix revisions. But that shouldn't be a deal breaker.

 

[roaniecowpony]

At this point I'd also be taking a close look at all the connectors to make sure no pins are bent. Especially the ECU (or whatever its called in the JL).

Yeah that crossed my mind. More so, a pushed back pin. I'll check it this morning.

 

[roaniecowpony]

Can you tell if it is getting fuel? Rough idle and then stall sounds like not enough fuel. I haven’t tinkered with a 3.6 much, can you pull a injector and see if it is sending fuel at start?

It's getting some fuel. At least enough to smell it. But fuel supply has crossed my mind. I have the old engine's intake manifolds here, which have the injectors still in them. Maybe pull an injector from the old and hook a connector to it on the new and see if I get fuel spray. It is getting something. My thoughts are it could be low pressure by the way it's acting. Maybe i can find fuel pressure in JSCAN and see.

 

[Stetson]

It's getting some fuel. At least enough to smell it. But fuel supply has crossed my mind. I have the old engine's intake manifolds here, which have the injectors still in them. Maybe pull an injector from the old and hook a connector to it on the new and see if I get fuel spray. It is getting something. My thoughts are it could be low pressure by the way it's acting. Maybe i can find fuel pressure in JSCAN and see.

That is my initial thought based on what it is doing. Doesn’t seem to be getting enough fuel. Other thing to also look at is the security system / alarm is a fuel shut off. If for some reason that is triggering you might get the same symptoms

 

[roaniecowpony]

That is my initial thought based on what it is doing. Doesn’t seem to be getting enough fuel. Other thing to also look at is the security system / alarm is a fuel shut off. If for some reason that is triggering you might get the same symptoms

I noted it now, won't crank and the Unconnect display asks for a security code. Not sure where to go next.

 

[Stetson]

I noted it now, won't crank and the Unconnect display asks for a security code. Not sure where to go next.

Yep. That’s the issue. Do you have your old ecu? Might try that. Have to get around this security issue to get it to start .

 

[roaniecowpony]

Yep. That’s the issue. Do you have your old ecu? Might try that. Have to get around this security issue to get it to start .

Im using the old ecu and engineharness. The 2024 ecu's aren't compatible with the old vehicles. All the sensors are the same part number.

I recall some people having trouble with the green canbus block.

 

[jeepingib]

I'm not sure why you are getting a security problem when using your old ecu and engine harness. I can't think of anything else on the engine that would communicate an individual id or anything.

 

[mwilk012]

Can you pull codes from all modules? Sounds like theft prevent but might not be.

The Uconnect asking for a code generally only happens with stupid battery problems. You kill the aux battery?

 

[alphawolff]

I noted it now, won't crank and the Unconnect display asks for a security code. Not sure where to go next.

If the uconnect display is asking for a security code then your PCM is either offline or you installed the PCM from the donor JT for some reason.

Make sure you're using your stock PCM and it's properly plugged in. I strongly suspect you either damaged the pins or didn't plug the engine harness in properly.

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