Cylinder One Misfire - 2000 XJ

K5Matt

NAXJA Member
NAXJA Member
Hello all!:wave:

Recently, I have acquired a 2000 XJ Limited with a 4.0, aw4, np242, 156k miles.

When I got the Jeep, it didn't start. Crank, but no start. Turns out, the fuel pump was bad, so I swapped in a good one....fired right up. Didn't idle well. Not very smooth, and the exhaust rattles. But it runs, and that's all I cared about. Drove it around some, ran and drove well on the street.

When I took it out last week, the CEL light flashed 5 times, then went off. A code was stored, P0301 Cylinder 1 Misfire Detected code came up. During this drive, there were three seperate occasions of flashing CEL.

Fast forward to tonight. I changed the plugs(NGKs to NGKs) and air filter(nasty!), took it for a drive, and got the flashing CEL at pretty much the exact places it came on the first time. When it comes on, I am at WOT.

Here are the facts that I have gathered.

- Added a new battery.
- Oil pressure is very good, 40 at idle, 60 or so when at WOT. Have NOT confirmed via mechanical gauge.
- Oil is dark and dirty, but it is at the full level.
- The oil fill cap smells like oil and has the same color.
- Coolant overflow bottle is in the exact same level. I have not added any since I installed a new radiator.
- Using a screwdriver, I can feel the 'tick' of all the fuel injectors, including #1. But when I unplugged the cylinder 1 injector, the motor sounded no worse at idle than when plugged in. I did the other cylinders too, and noticed a slight loss of rpms when unplugged.
- I cranked the motor in clear flood mode, and it sounds normal. No weird noises or anything like that.
- Probably unrelated, but when idling, there is a noticeable vibration when I'm inside the Jeep, but undetectable inside the engine bay and under the Jeep. It goes away when acceleration. Probably exhaust related, but thought I would mention it.
- Probably unnecessary to include, but volts are at 14 when idling, 13.5 when accessories are running.
- Overall, the engine just doesn't sound right at idle. When you rev the engine, it sounds good. There doesn't seem to be any alarming noises either(no knocking, pinging, even no typical lifter tick).

Here are the spark plugs.



Cylinder one looks lighter in color than 3-6. It also has no smell, and all the others smell like burned fuel.

My next step is to spray some water around the cylinder 1 wiring and intake manifold to see if there is any change in RPMs.

After that, what's the next step? Compression/leak down test? Throw an injector at it? Test something else?
 
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MrShaft696

New member
i would compression test before i spent any money at all..... good compression, then follow routine,,, tune up, wires, plugs, cap, rotor, then start to branch out to all the unusual stuff....made this mistake before....
 

md21722

NAXJA Member
NAXJA Member
Yep. Do a compression check.

I suspect you'll need to pull the head and send it to a machine shop.

None of those plugs look good to me. Valve seals and valve seats maybe.
 

K5Matt

NAXJA Member
NAXJA Member
Thank you for your comments. I figured that's what the conscientious would be.

I will pick up one up tomorrow and post up results.
 

four_shot

How 'bout it Gonzo
NAXJA Member
If compression comes up ok, get a hold of a mechanics stethoscope and listen to the injectors.

A sharp mechanical tick is good, a duller thud or thump indicates a partial or total restriction.

If this is the case, using something like a 6" 3/8 drive extension or the like, try tapping with a light to moderate froce on the injector to free it up. (I have a brass drift that I use)

And again IF that works, have the injectors cleaned to prevent recurrance.

(lotta if's in this one...lol)

hth
 

Talyn

New member
All those plugs look pretty bad except #1. They also look heavily worn with a very large gap. #4, 5, 6 looks like they may have been running rich.. or just a crappy burn. Does it have federal or cali emissions? The Cali package will have 4 o2 sensors and 2 pre cats.
- Using a screwdriver, I can feel the 'tick' of all the fuel injectors, including #1. But when I unplugged the cylinder 1 injector, the motor sounded no worse at idle than when plugged in. I did the other cylinders too, and noticed a slight loss of rpms when unplugged.
Are you saying that the engine's running changed when disconnecting the injectors except for #1?

Compression test would be a good check as others have said.
 

JeepNoob

New member
Sounds like it. You can do the same thing with the ignition system by running a bit of vacuum hose from the distributor cap to the spark plug boot and then touching a grounded test light to the hose. Whichever cylinder changes the least is producing the least power.
 

Talyn

New member
Sounds like it. You can do the same thing with the ignition system by running a bit of vacuum hose from the distributor cap to the spark plug boot and then touching a grounded test light to the hose. Whichever cylinder changes the least is producing the least power.
You don't say...

I was actually asking him to clarify his statement, not for details on what happens when you remove fuel from a cylinder.
 

K5Matt

NAXJA Member
NAXJA Member
If compression comes up ok, get a hold of a mechanics stethoscope and listen to the injectors.

A sharp mechanical tick is good, a duller thud or thump indicates a partial or total restriction.

If this is the case, using something like a 6" 3/8 drive extension or the like, try tapping with a light to moderate froce on the injector to free it up. (I have a brass drift that I use)


And again IF that works, have the injectors cleaned to prevent recurrance.

(lotta if's in this one...lol)

hth
The bold above seems to have fixed the problem. You rock!:cheers:
I jumped the gun a bit and bought a mechanics stethoscope along with compression tester kit, and I figured for $10, the stethoscope was worth a shot.

I went to the first injector, and it was a dull knock. I increased the RPMs, and it was a faster dull knock. Cylinders 2-6 all had that nice, sharp tick, even louder at increased RPMs. Then I tried hitting the first injector with the 3/8" extension. I hit it twice(gigidy), and almost instantly, the idle smoothed out, and the vibrations were gone. Before, you could see the motor laboring, but afterward, smooth as silk.

Took it out for a drive, and damn, this thing is quick! I tried like hell to get that misfire code to come back but to no avail. Even did the same route as yesterday, no dice. :D

TBH, I thought it was the #1 injector all along. The motor felt like it had decent power, and something, either spark or fuel, was holding it back, not a lack of compression. Initially I had no evidence to back that assertion up, and I wasn't about to throw parts at it without hard evidence. After pulling the plugs, and discovering the #1 spark plug did not smell like burnt fuel, while the others did, was a big clue. That cylinder was not getting enough fuel, or none at all.

With all that said, I was ready to do a compression test if messing with injector #1 didn't yield any changes. Knowing those compression figures would have been great information to have. I considered doing the test anyway, almost as a check.

Am I out of the woods and ready to DD it this winter? Not so fast. Still need to monitor the idle and see if it happens again. I plan on adding some in-tank fuel system cleaner, and that should help some more. If some time goes by and I can't duplicate the misfire again, then it should be in good shape.

Thanks to all who helped, especially four_shot.

Oh, and add a mechanics stethoscope to your toolbox if you don't have one.
 
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Talyn

New member
Then I tried hitting the first injector with the 3/8" extension. I hit it twice(gigidy), and almost instantly, the idle smoothed out, and the vibrations were gone. Before, you could see the motor laboring, but afterward, smooth as silk.
Nice!

Personally I would replace that injector just to be on the safe side. Get a few miles on it and pull the plugs to see what they look like. Just to rule out any other issues because those old ones did look pretty bad. However, that could have just been from running them way to long. I would also reset the PCM to clear out any bad habits it picked up from the old plugs and stuck injector.

Oh, and add a mechanics stethoscope to your toolbox if you don't have one.
Definitely. Its a good tool to have.
 

Rockhound-NC

New member
Congrats dude. I had the same issue with my 2001 about 3 yrs ago. I would replace all 6 injectors if you can. I think this ran me like $180ish. If one went, others will follow. I did that and my flashing CEL has disappeared for good!

Now, to find some wood to knock on....good luck!
 

four_shot

How 'bout it Gonzo
NAXJA Member
My advice would be to find a reputable shop and have the injectors cleaned with a pressurized through the rail cleaning system.

If not feasable, Berrymans chemtool B12 in the next 3 tanks of fuel should do it. Just make sure to use a funnel cause the lable says it eats paint.:thumbup:
 

md21722

NAXJA Member
NAXJA Member
Glad you were able to identify the issue. I missed the part about the discoloration being fuel looking. As others have suggested, probably needs some more cleaning/work to resolve long term.
 
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