Any Jeepers in here?

[Caleb]

p0301 is a cylinder 1 misfire. Check the plugs and wires for wear, shorting out, etc. Id make sure to pay close attention to cyl 1 if it had that code. Also check all the wiring and connectors for the CKP and CMP sensors. Be sure theres no frayed/broken wires, or oil in the connectors. Also, fwiw, Chrysler products love Champion spark plugs. Use whats specified as the factory plug. Used to fix ALOT of misfires when I worked for a Chrysler/Jeep dealer here in Ft Wayne by just putting the right plugs back in. I never would have thought a brand of plug would have made such a difference had I not seen it so many times myself

Where specifically should I be inspecting the wiring harness for faults? I still have p1391 after replacing both sensors with no dice...this is getting depressing

 

[Dick]

Where specifically should I be inspecting the wiring harness for faults? I still have p1391 after replacing both sensors with no dice...this is getting depressing

Anywhere and everywhere. Just trace any of it you can see and watch for any frayed or broken wires, damage to the loom that may indicate issues inside, etc. May also need to consider taking it to a shop. A scan tool can go a long way in diag. It will be able to determine which sensor actually is having issues, and possible bring a few more things to light as to where the problem could be

 

[Caleb]

Anywhere and everywhere. Just trace any of it you can see and watch for any frayed or broken wires, damage to the loom that may indicate issues inside, etc. May also need to consider taking it to a shop. A scan tool can go a long way in diag. It will be able to determine which sensor actually is having issues, and possible bring a few more things to light as to where the problem could be

I have a scan tool that keeps showing a p1391...how much would a shop charge to trace it if I can't find it? Would it be economical to replace the whole harness, or at least pull the entire harness out of the jeep to inspect the whole thing?

 

[Dick]

I mean an actual scan tool, not just a code reader. The scan tools can get in and look at a lot more, including live data. I wouldnt pull the harness, just inspect it in the vehicle. That may not even be your problem though. Just another thing to check. It could be so many things. The tone ring on the flex plate that the CKP reads off of could be damaged, ECM could be bad, distributor could be bad, etc. Someone with a scan tool could watch the live data from the sensors and hopefully see which one is dropping out or reading erratically. Then go from there

 

[Caleb]

I mean an actual scan tool, not just a code reader. The scan tools can get in and look at a lot more, including live data. I wouldnt pull the harness, just inspect it in the vehicle. That may not even be your problem though. Just another thing to check. It could be so many things. The tone ring on the flex plate that the CKP reads off of could be damaged, ECM could be bad, distributor could be bad, etc. Someone with a scan tool could watch the live data from the sensors and hopefully see which one is dropping out or reading erratically. Then go from there

How much would a shop charge to perform such a scan on my jeep?

 

[Roll Tide]

How much would a shop charge to perform such a scan on my jeep?

I have a ultra gauge that I picked up for $50. Totally worth it. Scans all codes and will erase them. Also shows all kinds of parameters.

 

[Hookeye]

FWIW I had a horrible time for a spell with my Grand. Notorious for bad ECM's. I had intermittent drop out (total Jeep die).

I unplugged EVERY connector, cleaned and re-seated. PITA.

Problem has been gone for 4 yrs (knock on wood).

 

[Dick]

How much would a shop charge to perform such a scan on my jeep?

Its going to vary shop to shop, just call around and ask. Or see if anyone can recommend someone local to ya.

 

[tat2clod]

My avatar was my last project the one under construction has Rockwells getting ready to go in and working on a V tread set up this time

 

[Caleb]

Its going to vary shop to shop, just call around and ask. Or see if anyone can recommend someone local to ya.

I thought about eating $70 bucks and buying a real jeep crank sensor....a lot of people say to buy only jeep sensors. Thoughts?

An unrelated question, what should oil pressure be on a 1998 cherokee 4.0L before warm up and after warm up? Before warm up, I'm getting 20-30psi according to the instrument cluster however it's down to 10psi after warm up...wasn't sure if this was normal or not.

 

[terrehautian]

Before warm up right now, a tick above half, after, around half.

 

[Caleb]

Before warm up right now, a tick above half, after, around half.

Should I be concerned if I get 10psi while cruising down the highway?

 

[terrehautian]

Possibly, checked your oil level? If it is normal, is the oil old? If so, change it. If not and everything is fine, your oil sending unit (or however that is monitored) might be bad.

 

[Jerry]

An unrelated question, what should oil pressure be on a 1998 cherokee 4.0L before warm up and after warm up? Before warm up, I'm getting 20-30psi according to the instrument cluster however it's down to 10psi after warm up...wasn't sure if this was normal or not.

This sounds about like a bad oil pressure sending unit. I was working on a 99 TJ that had an oil sensor displayed similar results except it would just drop to 0 occasionally. After a sending unit (easy swap) it was back to normal. Possibly see if you can get a hold of a mechanical gauge and see what it reads for your engine.

 

[eldirector]

Get a real gauge if you want to know the actual pressure. The factory gauge is an "indicator" at best. The sender in my TJ has failed twice in 55K miles, and isn't accurate at all. Luckily, it is fairly easy and cheap to replace.

If the needle is in the middle 1/2 of the gauge (above 1/4 - whatever the number actually is), I'd call it good.

 

[Caleb]

Get a real gauge if you want to know the actual pressure. The factory gauge is an "indicator" at best. The sender in my TJ has failed twice in 55K miles, and isn't accurate at all. Luckily, it is fairly easy and cheap to replace.

If the needle is in the middle 1/2 of the gauge (above 1/4 - whatever the number actually is), I'd call it good.

"20" is 1/4 of the gauge, "40" is half

 

[REWSTER]

I wouldn't worry about the oil pressure unless its 0 at all times. jeep says something like 2-3psi is as low as you should go.

my wifes WJ with the 4.0 drops to 0 every time i stop. then rises to 15-20 when i gas it. if it ant knocking or ticking don't stress it too much. or run thicker oil...

 

[Caleb]

I wouldn't worry about the oil pressure unless its 0 at all times. jeep says something like 2-3psi is as low as you should go.

my wifes WJ with the 4.0 drops to 0 every time i stop. then rises to 15-20 when i gas it. if it ant knocking or ticking don't stress it too much. or run thicker oil...

How hard would it be to permanently install an oil gauge?

 

[eldirector]

So, it is reading at 1/8th of the gauge at 10PSI while cruising?

Wish I had a "real" oil pressure gauge handy. Be interesting to know what the actual pressure is. I suspect the sender is just reading low. The 4.0 isn't known for really high oil pressure anyway. Pretty sure anything above about 15 PSi (at idle) is considered good.

 

[Caleb]

So, it is reading at 1/8th of the gauge at 10PSI while cruising?

Wish I had a "real" oil pressure gauge handy. Be interesting to know what the actual pressure is. I suspect the sender is just reading low. The 4.0 isn't known for really high oil pressure anyway. Pretty sure anything above about 15 PSi (at idle) is considered good.

it's above that till the engine gets to it's normal temp