97 XJ P0301, misfire, knock

So my XJ started throwing a code recently (P0301) cylinder one misfire. Looks like it's a common one on these but I see so many fixes. I just want to start a thread to keep track of suggestions and what I have tried so far.

History of the vehicle.

I bought it with a knock coming from the block, didn't mind it much, I was just excited to get it. it's a 97 4.0 aw4 np24?. 232k miles. I have noticed it running rougher since the code and more fuel consumption.

I recently changed all wires and the single plug for cyl 1. Monday night I swapped injector 1&2, cleared the codes, and removed the battery for about ten minutes. It has run even rougher since. Today I ohmed the injectors out, they 1,2,3,and 4 read 12.9-13.1 ohms.

I ran a compression test, or at least thought I was. These are with just that one plug removed and vehicle running.

cyl 1 - 70
cyl 2 - 95
cyl 3 - 90
cyl 4 - 85

these are WAY too low if I am supposed to get 150-180

The code has not come back up, still waiting on that...

I recently had a rough idle and a miss while driving and I had the same code pop up. I swapped in new plugs and wires and replaced the distributor cap and rotor and it solved all the issues. Mines a 98.

Maybe look into the cap and rotor... They're cheap and easy to do.

Not sure what to say about your compression though.

Same thing I just posted in another thread on this forum. You have worn valves in your head allowing gas to escape (low compression). You need to have your head rebuilt.

I am NOT a mechanic. But it seems to me that people in the forums will offer every explanation possible...fuel pumps, injectors, heat soak, coils/distributors, etc....to avoid stating the obvious: Low compression. Need a head.

I just went through this on my 00 XJ. Misfires on 5, then 3 and 5, then 2, 3 and 5. Ran fine at speed. Threw CELs at hot idle sitting at red lights.

If you have low idle oil pressure, like 5-10 psi, when hot AND low compression....you need to have the engine pulled and rebuilt at your local machine shop. Don't buy a reman engine. Junk. Don't buy a recast head. Junk. Find a reputable, recommended machine shop and have the work done locally.

Good luck.


JG

That's a running compression test, the other cylinders are sharing the load which is why your pressures are considerably lower.The values still tell you something though.

With the traditional cranking compression test you have all the plugs pulled and one cylinder is doing all the work as you manually crank the engine over, if you did it that way you'd be a lot closer to the values you're expecting.

In any case you now have a starting point to start investigating further. Figure out why cylinder 1 is lower than the others.

I am able to run tests right now. Still no code, but man does it feel bad.I will look into cap and rotor

I must since I swapped the injectors it has gotten worse

Just finished changing the cap and rotor. No change.

I tried putting compressed air through cylinder one and noticed that the plug was very closed up. I fixed the gap and is feeling better but still has a shake to it.

Swapped the plugs last Night. Didnt check the codes but is running better.

Check compression the correct way. Warm engine, all spark plugs out, one cylinder at a time. If below 100 psi, repeat with a teaspoon of oil in each cylinder. Let us know results. If too low, you are wasting money changing other stuff.

finally back to it. I will be doing as winterbeater suggested.

Just to confirm I will be doing it right.

take all plugs out. check compression while cranking.