P0301, P0304, P0300

[Austin O.]

P0301, P0304, and P0300 are all codes my TJ just started throwing.

Its a 98 4.0l

CEL came on at some point when I was in 4low with high RPMs.

I’m not entirely sure what typical symptoms are, but here are mine.

When accelerating at lower rpm’s (under 1500) the car is shuddering pretty badly. As an example, if I’m in 3rd gear, rpm’s at 1200 and try to accelerate, it shudders until I I hit about 1500 rpm’s. Then it’s fine until I shift to 4th and it happens again. If I stay at 1200, but don’t accelerate, just keeping gas pedal in the same position, there is no issue.

Where do I start? How do I diagnose this? Thanks!

 

[GregBelleville]

I had a friend with these codes recently and it ended up being resolved after replacing injectors.

I believe 301 and 304 are misfire codes for cylinders 1 and 4. If so, you could try swapping injector from one of the other cylinders that don't have a code to see if the code then fires for the cylinder you swapped with. If so, this would narrow it down to that injector.

 

[macleanflood]

My 97 had that issue... although it would randomly misfire on different cylinders.

I changed the cap , rotor and coil with Accel. New spark plugs. Checked for wiring harness issues.

Ended up being the crank position sensor. Replaced with a Napa Echlin since Mopar is no longer available.

-Mac

 

[Austin O.]

Was going to take the spark plugs out to look at them, found this - on the wires for 1 and 4

Both were super corroded. Picked up a whole new set of wires and put them in, seems to have fixed the issue. Looks like I got pretty lucky…

 

[macleanflood]

I'd look at the cap and rotor...

-Mac

 

[Austin O.]

I'd look at the cap and rotor...

-Mac

May I ask why?

 

[macleanflood]

May I ask why?

Well if one end of the spark plug wire looks that way...then what's the other end look like? And it's connected to the cap and rotor...so it would seem easy enough to check.

I did my cap, rotor, spark plugs and wires all at the same time. Peace of mind and easy notation of date and mileage for my future reference.

-Mac

 

[Jerry Bransford]

May I ask why?

Because their contacts eventually wear out and you should check their condition. Pull the distributor cap off and look inside it and at the rotor which sits under the cap.

 

[Austin O.]

Well if one end of the spark plug wire looks that way...then what's the other end look like? And it's connected to the cap and rotor...so it would seem easy enough to check.

I did my cap, rotor, spark plugs and wires all at the same time. Peace of mind and easy notation of date and mileage for my future reference.

-Mac

So I did the plugs themselves not too long ago.

When I took the wires off today to put the new ones on, the opposite end of the wires looked fine. Is that not what you mean?

Because their contacts eventually wear out and you should check their condition. Pull the distributor cap off and look inside it and at the rotor which sits under the cap.

I’m confused, I don’t know how this stuff works, so is what yall saying is that there is something underneath what the distributer end of the wire plugs on to? That come apart somehow?

 

[macleanflood]

 

[tr21triton]

So I did the plugs themselves not too long ago.

When I took the wires off today to put the new ones on, the opposite end of the wires looked fine. Is that not what you mean?



I’m confused, I don’t know how this stuff works, so is what yall saying is that there is something underneath what the distributer end of the wire plugs on to? That come apart somehow?

did you replace all 6 plugs or just 3 or 4 ? the same spark that jumps the gap on the spark plug jumps from the rotor to the cap and they wear out the same as the gap will open up on the plugs. spend a couple dollars and do it right or don't and when your sitting on the side of the road remember "we told ya so" !

 

[Austin O.]

I’ll check that out in a bit. Thanks

 

[Austin O.]

did you replace all 6 plugs or just 3 or 4 ? the same spark that jumps the gap on the spark plug jumps from the rotor to the cap and they wear out the same as the gap will open up on the plugs. spend a couple dollars and do it right or don't and when your sitting on the side of the road remember "we told ya so" !

I did do all of them at the same time

 

[tr21triton]

I did do all of them at the same time

I was being a smart ass ! it's best to replace the cap and rotor button at the same time as the spark plugs. we normally replace the plugs because after the spark jumps that gap millions of times it wears away the electrode and opens the gap until it becomes inefficient, that same thing happens on the other end on engines with a distributor cap and rotor button. the cap and rotor wear out just like the plugs. I hope I explained it in understandable terms

 

[Austin O.]

I was being a smart ass ! it's best to replace the cap and rotor button at the same time as the spark plugs. we normally replace the plugs because after the spark jumps that gap millions of times it wears away the electrode and opens the gap until it becomes inefficient, that same thing happens on the other end on engines with a distributor cap and rotor button. the cap and rotor wear out just like the plugs. I hope I explained it in understandable terms

That makes sense. Thank you. So I checked and I actually replaced the spark plugs a little longer ago than I thought… about 8k miles ago. Do you suggest that I get all new spark plugs as well as a new distributer and rotor, or just the distributer and rotor to replace now? Once again, thanks for the help.

 

[macleanflood]

That makes sense. Thank you. So I checked and I actually replaced the spark plugs a little longer ago than I thought… about 8k miles ago. Do you suggest that I get all new spark plugs as well as a new distributer and rotor, or just the distributer and rotor to replace now? Once again, thanks for the help.

What plugs did you use?

-Mac

 

[Weasellee]

Pull the plugs. Look at em. Replace the Distributor Cap and Rotor regardless since you just replaced the wires.

 

[tr21triton]

That makes sense. Thank you. So I checked and I actually replaced the spark plugs a little longer ago than I thought… about 8k miles ago. Do you suggest that I get all new spark plugs as well as a new distributer and rotor, or just the distributer and rotor to replace now? Once again, thanks for the help.

8k miles on plugs is nothing, just replace the rotor button and cap since you just did the wires and you'll be good to go .

 

[Austin O.]

What plugs did you use?

-Mac

Autolite app985 double platinum - I believe those are the forum recommended ones?

 

[Austin O.]

8k miles on plugs is nothing, just replace the rotor button and cap since you just did the wires and you'll be good to go .

Will do. Thanks! Does brand of these parts matter? I assume so… I know for plugs it does, for the wires it said that people generally thought no, so I just got whatever was available at autozone.