2006 Wrangler SE 2.4 P0303 Code CEL

Before you throw any more time/money into parts, check the wiring harness directly on the firewall side of your injector rail.
The harness that houses all the injector wiring.

There's a bolt on the back-side of the Valve Cover that tends to rub its way through the wiring harness.
My 2006 LJ has this harness inside of a Plastic 'guide', and I would assume yours should as well.
BUT there is a chance that it was removed at some point.

I had similar issues as you on my 2000 Sahara, and found that the bolt had rubbed the wires and was grounding them out, causing issues.

jfondren3 said:

I've read all sorts of threads trying to figure this out, but I don't want to keep throwing money and parts if there is a better way to find the problem and fix it.

2006 Jeep Wrangler SE
6 speed manual
2.4L
98110 miles (I bought it with 95000 miles and no CEL)

It drives great, but it has a rough idle and P0303 is the code I am getting, #3 cylinder misfire.

Below is everything that I have done so far and I used this forum and links to make sure that I was ordering things that work well with the TJ.

Spark plugs and wires - 96954 miles (right after the CEL popped for the first time)
2x O2 sensors - 97162 miles
Idle Air Control Valve - 97162 miles
Throttle Position Sensor - 97723 miles
Crankshaft Position Sensor - 97885 miles

I have a MAP Sensor on my workbench, but I have not installed it yet. The Jeep started driving a lot better after installing these new sensors but the CEL would never stay away. At 98100 miles the Jeep wouldn't crank after I had stopped at a convenience store. It had also died on me a couple times when coming to a stop previously that I hadn't remembered initially. I was able to push start it and get back home.

The engine would turn over, but it would not start. I also measured the voltage on the battery and it was good. Since the engine was turning over I assumed the starter was fine as well. So it appeared to be a fuel problem. The fuel pump is running when I turn the key. Today I sprayed some starter fluid in the intake and it fired up immediately. Since then I have tried starting it at random this evening and it fires up. the P0303 code is still there and the rough idle still happens once the Jeep warms up.

Is it time to replace the injector? Not really sure where else to look based on the code. My other thought was to check the fuel pump for any clogs, but that still wouldn't have anything to do with the CEL, just thought it might be causing me to not get fuel down the lines?

Advice appreciated. Let me know if anything else is needed.

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A fellow 2.4 driver! Do you notice any gas smell? Almost seems like that injector, like you said, isn't firing. On my TBI 350 I could take a 9V battery to test the plunger and listen for the clicking of the solenoid. Maybe worth a shot? Might lead you to work back to front and hunt down a short.

Although the 2.4 wiring harness is a bit different, zackpeakee is likely right about some sort of wiring harness problem. Is the cylinder 3 boot sparking? Put a flathead (old fashioned method) or one of your old plugs on it and put the electrode on the fender or block (something to ground it on) and crank the motor. Have you tested for voltage at the #3 injector?

Look into the ignition coil and cam sensor

cooper32 said:

Although the 2.4 wiring harness is a bit different, zackpeakee is likely right about some sort of wiring harness problem.

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I've got to be honest here, I completely skimmed over the fact that it was a 2.4L engine.
Good catch.

In that case, my previous comment is 90% incorrect.
Your harness will not look like that, and there is no bolt that will rub through.

However, I would still take the premise of what I said into factor, and check your harness well for any issues.
It seems more times than not, when dealing with misfire codes related to the TJ's, wiring is a common culprit.

zachpeakee said:

I've got to be honest here, I completely skimmed over the fact that it was a 2.4L engine.
Good catch.

In that case, my previous comment is 90% incorrect.
Your harness will not look like that, and there is no bolt that will rub through.

However, I would still take the premise of what I said into factor, and check your harness well for any issues.
It seems more times than not, when dealing with misfire codes related to the TJ's, wiring is a common culprit.

Click to expand...

Even so, there's a good few areas on the 2.bore that'll burn through or chafe some wires. Under our intake is where the fuel rail is, and a lot of our wires run from the PCM (pass side in the US) across the firewall to the drivers side just like the 4.0. PO or a shop may have pulled some of those wires out of the loom retainers (to do an IAC valve or TPS), and let them get burned up or chafed and are shorting. The throttle body on a 2.4 is very close to the firewall. My TPS job in the fall was a little annoying, and if I recall correctly, there were a shitload of wires in my way too. Little space, lots of wires, hot ass engine. Makes sense for a wiring issue.

Or it could be no spark at that one plug from a bad coil pack or no fuel from an injector solenoid not firing from an internal failure. OP: jiggle some harnesses around while its running like ass, see if cyl 3 comes around or if the idle changes. Also, like I said, try and get a voltmeter on the connector (or back probe, just be gentle or you're doing a pigtail job too) to the fuel injector. I know the fuel rail is under the intake and is a bear to get to, but it's worth a shot. That'd be the easiest way in my opinion to see if the harness is the issue or the injector itself is. You're gonna be looking for a brown/light blue wire, and a pink and gray wire. Start with the first wire, as it is the only one not shared all the way to the fuel rail. The BR/LB wire only goes to cyl 3, not all 4 cylinders. PK/GY is just from the ASD relay, which is likely not the issue as 1,2, and 4 are firing. Still check up until C181 (left rear side of head) and S178 (towards the firewall).

jfondren3 I know I am playing the "could be could be" card, but misfire codes are a pain in the ass, because unlike a sensor, it doesn't point you in a direction. I hope this helps. The 2.4 has very little support and I hope my narrowish insight will get you back up and running. If spark and fuel are in check, I'd be looking at valvetrain. dropped or burnt valves (compression test will tell you all you need to know). Although the blocks for a 2.4 are scarce, you can get a head pretty easily or rebuild it yourself.

If you haven't yet, try swapping the number 3 injector with another and see if the misfire follows it.