TJ runs poorly until up to operating temperature

[Keith J. Mundil]

Bought this Tj last summer and dover just fine no problem for months, 3 months back it starting just dying while driving, read up on this forum that it was probably the CKP so I replaced that. That solved that problem but created a new one that I can’t solve.

Ever since I replaced it the jeep would run like crap until warmed up after sitting more than 6 hours. After it’s warmed up it runs basically with no problem. The p1391 code, which is intermittent loss of CMP or CKP, popped up so I ran thru the CKP wires and connections for any problems, as well as, reinstalling it to make sure it was correctly spaced. Looked good, did a PCM reset, didn’t change my problem so I replaced the CMP, still same problem and same code. S

o I then took it to a certified mechanic after I and the guys at autozone where at a loss. The mechanic told me it was something with my distributor, so I replaced that. No luck but now I have a new code as well as the first one. P0320 with my understanding it’s a very generic code just saying there is something wrong with my system. I can’t find any forum whose had a similar issue but any ideas would be helpful. Thank you!

 

[Rubicon88]

Bought this Tj last summer and dover just fine no problem for months, 3 months back it starting just dying while driving, read up on this forum that it was probably the CKP so I replaced that. That solved that problem but created a new one that I can’t solve.

Ever since I replaced it the jeep would run like crap until warmed up after sitting more than 6 hours. After it’s warmed up it runs basically with no problem. The p1391 code, which is intermittent loss of CMP or CKP, popped up so I ran thru the CKP wires and connections for any problems, as well as, reinstalling it to make sure it was correctly spaced. Looked good, did a PCM reset, didn’t change my problem so I replaced the CMP, still same problem and same code. S

o I then took it to a certified mechanic after I and the guys at autozone where at a loss. The mechanic told me it was something with my distributor, so I replaced that. No luck but now I have a new code as well as the first one. P0320 with my understanding it’s a very generic code just saying there is something wrong with my system. I can’t find any forum whose had a similar issue but any ideas would be helpful. Thank you!

Battery condition...age...terminal conditions...?????

 

[Keith J. Mundil]

Battery condition...age...terminal conditions...?????

Sorry, I replaced the battery before the CKP, so brand new.

 

[Jerry Bransford]

Sounds like the PCM is being tricked into thinking the engine or air is warm when it's not. When it does that it tells the PCM to set the air/fuel ratio by the output of the O2 sensors. When it's cold, the PCM doesn't refer to the O2 sensors for its fuel mixture, it uses pre-programmed settings to set the air fuel mixture.

Is your temperature gauge working properly? Does it indicate when the engine is cold properly? That is the ECT (engine coolant temperature) sender that checks that, it's located adjacent to the thermostat housing on the head.

Or the Intake IAT (Intake Air Temperature) sender (located on the intake manifold) could be causing that type of problem too. It changes the engine timing and the pulse width for the fuel injectors.

Either one of those two sensors can cause problems by making the PCM think the air or the coolant is warm when it's actually cold.

 

[Rubicon John]

Any whistling noises or high idle issues when it’s still cold? I think I have a slight intake manifold leak that tends to mask itself when the engine is heat soaked. I plan on replacing the gasket in the near future.

 

[Rubicon88]

Sorry, I replaced the battery before the CKP, so brand new.

So did you replace this then problems start?

 

[Keith J. Mundil]

Sounds like the PCM is being tricked into thinking the engine or air is warm when it's not. When it does that it tells the PCM to set the air/fuel ratio by the output of the O2 sensors. When it's cold, the PCM doesn't refer to the O2 sensors for its fuel mixture, it uses pre-programmed settings to set the air fuel mixture.

Is your temperature gauge working properly? Does it indicate when the engine is cold properly? That is the ECT (engine coolant temperature) sender that checks that, it's located adjacent to the thermostat housing on the head.

Or the Intake IAT (Intake Air Temperature) sender (located on the intake manifold) could be causing that type of problem too. It changes the engine timing and the pulse width for the fuel injectors.

Either one of those two sensors can cause problems by making the PCM think the air or the coolant is warm when it's actually cold.

Tested both these sensors, seemed to work correctly, but I replaced them anyways. No change in my issue.

 

[RMETeeJay]

Have you tested the coil?

 

[Rubicon88]

What year is this?

 

[williambmac]

What year is this?

2021

 

[Keith J. Mundil]

Have you tested the coil?

No, after it warmed up the first start of the day it fires up no problem even when completely cooled down. It seems to happen only if it sits over night or for longer than 6-8 hours

 

[williambmac]

No, after it warmed up the first start of the day it fires up no problem even when completely cooled down. It seems to happen only if it sits over night or for longer than 6-8 hours

Still not answering the most basic question... what year is your jeep.

 

[Keith J. Mundil]

Still not answering the most basic question... what year is your jeep.

All the basic info was in the title of this thread but someone must have edited it out. It’s 97 4.0 auto with 104k

 

[williambmac]

If P0320 is a current code and comes back after clearing it, you need to correct the problem
P0320 is a crank sensor code. You stated that you recently replaced it, what brand sensor did you use? Please don't say autozone brand.
Did you have the paper spacer attached before installing it.
From what I remember, you don't need the spacer when installing with a manual trans, but it is required with an auto trans.

this condition only happens when cold, in open loop?

 

[fizzlebottom]

No, after it warmed up the first start of the day it fires up no problem even when completely cooled down. It seems to happen only if it sits over night or for longer than 6-8 hours

Wonder if that could be fuel injector related. Maybe one of the injectors is leaky (or something) and warming up or building pressure helps to alleviate that until it completely cools again or pressure lowers back to a certain point. I've had a similar issue with my Mini Cooper that was caused by a faulty high pressure fuel pump that I've had to replace 3 times because BMW can't engineer one that doesn't crack if you breath on it wrong. Though a completely different system, your symptom reminds me of that.

 

[Keith J. Mundil]

Have you tested the coil?

No, after it warmed up the first start of the day it fires up no problem even when completely cooled down. It seems to happen only if it sits over night or for longer than 6-8 hours

Have you tested the coil?

If P0320 is a current code and comes back after clearing it, you need to correct the problem
P0320 is a crank sensor code. You stated that you recently replaced it, what brand sensor did you use? Please don't say autozone brand.
Did you have the paper spacer attached before installing it.
From what I remember, you don't need the spacer when installing with a manual trans, but it is required with an auto trans.

this condition only happens when cold, in open loop?

I did use autzones sensor.......and yeah I believe it just for auto. It came with a spacer on it but I have since pulled it out and put a different space on it. Also yeah just when cold, in open loop.

 

[Jerry Bransford]

Stop using Autozone Duralast junk especially sensors, water pumps, radiators, and alternators. For critical components use OEM or at least first quality. I would use Duralast floor mats seat covers or air fresheners but that's it.

 

[williambmac]

I would go to your local Napa store and pick up their brand of crank sensor. Make sure it has the spacer attached.

do you have any other codes?

Do you have access to a scan tool, not a code reader?

 

[Keith J. Mundil]

I would go to your local Napa store and pick up their brand of crank sensor. Make sure it has the spacer attached.

do you have any other codes?

Do you have access to a scan tool, not a code reader?

Copy that. I have the two pcm codes one for the intermittent loss of ckp/cmp, the general code for a problem with the system, as well as, the vapor code because someone stole the stock gas cap.