P0301 & p0304

[stev0]

I have been having a weird error code for the last 3000miles after I had the piggyback ecu and cat foolers fitted.

The tuner tells me its the coil packs, but Im finding it hard to believe that this error occurred right after they did the service (changed the plugs too)

In the beginning I would have the error codes run from 301 to 306, but lately its only 301 and 304. The Kj has only gone into limp mode once. (complete limp)

Drive it around normally and you would not know anything is wrong. Engine light is off and no real issues so to speak. If I pop it in OD off and have the RPMS up to about 4-5000, the engine light will start to flicker and eventually stay on. I can drive it around like that and occasionally, the light would go off completely and sometimes, it would just flicker and then trigger full limp.

I had it back at the tuner recently and they assured me that its not the Uni chip. They also changed coil packs from different cylinders and its still the same 2 cylinders that is giving me troubles.

My question to them was, why not change the plugs out... and I got the response, because they are new.

Is it just me or has some of you had plugs fail or "break down" under load, on you?


If its not the plugs, is there anything else I can look at?

 

[Porkchop]

What plugs did they use and how was the gap set? I don't like the foolers and piggy backs on a Libby, always issues and never needed IMO.

 

[dude1116]

Ten bucks said they used some platinum plugs or something. Trying throwing copper plugs in there and see what happens.

 

[stev0]

I think they used some ngk non platinum plugs.

The piggyback gained me some decent power and some awesome mpg

 

[CactusJacked]

Since spark plugs aren't monitored, a bad one isn't going to throw a cylinder specific misfire code. A bad plug can cause a misfire, but you would get a PO300 random misfire code, read by that bank's O2 sensor picking up a rich fuel condition. Plug wires that are shorting to ground on the other hand, will throw a cylinder specific misfire code. The first thing I would have done too is swap the coils and see if the code follows the coil, which you found that wasn't it. In addition to a plug wire, you could have an electrical issue with those fuel injectors.

 

[stev0]

I did see a random misfire code too, before I cleared it.

If I clear it and drive decently, the light stays off. As soon as I hit the OD off, the light will flash.

 

[tjkj2002]

Since spark plugs aren't monitored, a bad one isn't going to throw a cylinder specific misfire code. A bad plug can cause a misfire, but you would get a PO300 random misfire code, read by that bank's O2 sensor picking up a rich fuel condition. Plug wires that are shorting to ground on the other hand, will throw a cylinder specific misfire code. The first thing I would have done too is swap the coils and see if the code follows the coil, which you found that wasn't it. In addition to a plug wire, you could have an electrical issue with those fuel injectors.

1st no plug wires in a KJ with the 3.7(only 2.4 gasser).While the spark plugs are not specifically monitored the PCM still will throw a specific cylinder code for a bad spark plug since a bad plug can cause a misfire.Both the coils and injectors are monitored because they are electrical and directly controlled by the PCM.The PCM uses the crank sensor to detect specific cylinder misfires.



To the OP put the electrics back to stock to determine if it's the cause of the problem,which in most cases mods like you have done are the issue.

 

[CactusJacked]

1st no plug wires in a KJ with the 3.7(only 2.4 gasser).While the spark plugs are not specifically monitored the PCM still will throw a specific cylinder code for a bad spark plug since a bad plug can cause a misfire.Both the coils and injectors are monitored because they are electrical and directly controlled by the PCM.The PCM uses the crank sensor to detect specific cylinder misfires.

To the OP put the electrics back to stock to determine if it's the cause of the problem,which in most cases mods like you have done are the issue.

I didn't see which engine he had, it was a cya statement. Ok looking back he did mention once getting a 306 code, so that lets the cat outta the bag there.
A bad spark plug will cause a misfire, as I mentioned earlier, but what that will cause more often than not is a rich fuel condition due to an incomplete burn. The O2 sensor in that same bank of cylinders will pick up a rich condition and throw a PO300 random misfire, since the O2 sensor doesn't have a clue as to which cylinder is causing it. A bad plug will not throw a cylinder specific error code. Unless that is, if the PCM in our Jeeps had the ability to read spark plug resistance. But that can't be so, since you said the PCM doesn't monitor the plugs.

 

[tjkj2002]

I didn't see which engine he had, it was a cya statement. Ok looking back he did mention once getting a 306 code, so that lets the cat outta the bag there.
A bad spark plug will cause a misfire, as I mentioned earlier, but what that will cause more often than not is a rich fuel condition due to an incomplete burn. The O2 sensor in that same bank of cylinders will pick up a rich condition and throw a PO300 random misfire, since the O2 sensor doesn't have a clue as to which cylinder is causing it. A bad plug will not throw a cylinder specific error code. Unless that is, if the PCM in our Jeeps had the ability to read spark plug resistance. But that can't be so, since you said the PCM doesn't monitor the plugs.

The PCM monitors the crank sensor to throw a cylinder specific misfire code,it does it by the square wave pattern since the rpm's will increase a bit when the cylinder fires so if the PCM does not detect the increase in rpm's it starts counting misfires.The PCM does now which cylinder is firing from the crank signal as cylinder 1 has a longer square wave pattern and it just uses simple math to know which cylinder should be firing.It does not use the O2 sensors to monitor misfires at all,they just tell the computer what is coming out of the cylinder so the PCM can adjust the injector pulse width(short tern and long term fuel trims).When the PCM detects a specific cylinder misfire and it's bad enough it will actually kill the injector on that cylinder so no fuel is being pumped in dumping raw fuel into the cats.OBDII can be very nice in most cases and rather simple once you actually learn what it does and how.

 

[streetglideok]

Should also add, an ignition misfire will more often than not show up as a lean condition thru the O2 sensor, due to a charge failing to ignite.

 

[CactusJacked]

The PCM monitors the crank sensor to throw a cylinder specific misfire code,it does it by the square wave pattern since the rpm's will increase a bit when the cylinder fires so if the PCM does not detect the increase in rpm's it starts counting misfires.The PCM does now which cylinder is firing from the crank signal as cylinder 1 has a longer square wave pattern and it just uses simple math to know which cylinder should be firing.It does not use the O2 sensors to monitor misfires at all,they just tell the computer what is coming out of the cylinder so the PCM can adjust the injector pulse width(short tern and long term fuel trims).When the PCM detects a specific cylinder misfire and it's bad enough it will actually kill the injector on that cylinder so no fuel is being pumped in dumping raw fuel into the cats.OBDII can be very nice in most cases and rather simple once you actually learn what it does and how.

As an example, if you had one cylinder on bank 1 running rich, the O2 sensor is going to adjust the injector pulse on all 3 cylinders since it can't know that there is only one running rich. That would then unnecessarily lean out the other two cylinders. It would seem to me that the O2 sensor would have the injectors chasing their tails. So what you're saying then, the PCM doesn't compare bank 1 and bank 2 through the O2 sensors to know something is wrong, and trip a code?

 

[tjkj2002]

As an example, if you had one cylinder on bank 1 running rich, the O2 sensor is going to adjust the injector pulse on all 3 cylinders since it can't know that there is only one running rich. That would then unnecessarily lean out the other two cylinders. It would seem to me that the O2 sensor would have the injectors chasing their tails. So what you're saying then, the PCM doesn't compare bank 1 and bank 2 through the O2 sensors to know something is wrong, and trip a code?

That is where the codes P017* codes come into play,there the bank 1 or 2 rich or lean if the PCM can not lean/richen out that bank enough to get back to 0 long fuel trims(+/- a few).This will not set a misfire code unless the PCM detects a misfire via the crank sensor along with this condition.There can be many things that can lead to a overly lean/rich condition besides a misfire.

 

[stev0]

I've been thinking of disconnecting the piggyback. I do have cat foolers on the Kj because im completely cat free. Would I still trip a code?

I just want to make sure its not the Piggyback doing all of this.

If I reset the code, drive it normally It will stay off for ages. As soon as I start throwing the RPM's up to the 5-6k mark (especially on overtaking) It will sometimes flash. Sometimes, it will flash and go out and sometimes it will just stay on.

 

[tjkj2002]

I've been thinking of disconnecting the piggyback. I do have cat foolers on the Kj because im completely cat free. Would I still trip a code?

I just want to make sure its not the Piggyback doing all of this.

If I reset the code, drive it normally It will stay off for ages. As soon as I start throwing the RPM's up to the 5-6k mark (especially on overtaking) It will sometimes flash. Sometimes, it will flash and go out and sometimes it will just stay on.

Yes you will get some O2 codes along with possible cat codes.