Intermittent misfires and lack of power

[TheSeanLeonard]

Hey all! I'm new around here, so I apologize if this isn't the place to post this but...

My 4L 2001 Jeep TJ is struggling with misfires. It runs fine normally after starting it up cold. I can drive it down the road without problems, has power and everything. but when I drive for a little while using constant throttle, the CEL light starts blinking (only code is P0301) and it has almost no power and everything shakes. If I sit and idle after the CEL blinked it's noticeably shaky, until I restart the engine and it goes back to normal for a couple minutes. But it seems like when I drive a little more aggressively (higher throttle bursts/faster) it runs perfectly fine.

I've taken it to the mechanic and they said it's the coils, I replaced the coils and the problem still persists.

I tested the ohms of the injectors, they seemed to be within spec of what I can find.

Any insite as to what is happening would be awesome! The whole jeep does have 289,000 miles on it so it's probably due for an engine rebuild. But for now I would love to pinpoint the problem.

 

[macleanflood]

I'd swap injectors 1 and 2 and see if the code changes.

I'd also pull apart the wiring harness especially where it turns at the back of the valve cover and look for broken wires.

Check the coils with an ohm meter.

Do you have a TUPY head?

-Mac

 

[TheSeanLeonard]

I just swapped Injectors 1 and 2. The issue persists. The code says cylinder 1 still. I tested all Injectors with a 12v power supply.

From best I can tell, I don't have a TUPY head. I looked down the oil filler place and it didn't say TUPY.

As for the coils, I didn't test them. But I got new blue streak coils after the problem started happening.

And the wiring harness, I haven't got there yet. Hoping to look into it tomorrow.

 

[TheSeanLeonard]

Well, I dug into the wiring harness up there behind the engine. It looks OK to me, no visible broken or loose connections. I even replaced the crankshaft position sensor off another jeep engine. Still having the same problem.

At this point I'm wondering if it's mechanical? I'm not really sure.

 

[macleanflood]

Compression and leak down test time.

Might want to run the engine without the valve cover and visually confirm the valves are traveling the same distances and the rockers are similar to each other. Make sure the pushrods rotate.

-Mac

 

[JKP]

Assuming you didn't see any coolant on the head when looking for TUPY on the head.

Just turned 289K mi on my YJ, still runs fine. Only things replaced inside the engine were the timing set, distributor, and rear main seal.

Have 285K on the TJ. Only thing replaced in the engine was the OPDA.

So, if maintained, it shouldn't be worn out.

In addition to the compression test Mac suggested, check out the carbon TSB attached. When I was idling for extensive periods every morning in line to get on base, my TJ would eventually develop a cyl 1 misfire every so often. A can of Techron and some high RPM driving would cure it every time.

 

[TheSeanLeonard]

I did a compression test on all the cylinders. If it seemed low, I added some oil in the cylinder and did it again. let it do 3 compressions on each.

Here are what the plugs looked like. 1 and 4 maybe look a little orange? they are in order 1-6.

Compression test results were as follows in psi: (snap-on compression tester)

Cylinder 1	Cylinder 2	Cylinder 3	Cylinder 4	Cylinder 5	Cylinder 6
115 (125 after adding oil)	130	130	113 (120 after adding oil)	125	135