Hi everyone I’m currently having a p0303 Cylinder 3 misfire code . It’s a 2015 jku with 89,000 miles . I changed all 6 fuel injectors all spark plugs . Ignition coil #3 replaced . Leak down test and compression check done and no issues were found . I’m still having the CEL come on for this code . Idk what else to check for . The local mechanics can’t seem to figure out the issue . Has anyone encountered this problem and fixed it? Thank you .
P0303 cylinder 3 misfire
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Robert12
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Hi everyone I’m currently having a p0303 Cylinder 3 misfire code . It’s a 2015 jku with 89,000 miles . I changed all 6 fuel injectors all spark plugs . Ignition coil #3 replaced . Leak down test and compression check done and no issues were found . I’m still having the CEL come on for this code . Idk what else to check for . The local mechanics can’t seem to figure out the issue . Has anyone encountered this problem and fixed it? Thank you .
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Welcome to the Forum, from Cave Creek AZ.
Unfortunately, most of the time, it winds up being a defective cylinder head. I suggest that you at least take it into your Jeep Dealer, and have them diagnose it. Then you will know what you are dealing with. Just throwing parts at it, can get expensive.
Unfortunately, most of the time, it winds up being a defective cylinder head. I suggest that you at least take it into your Jeep Dealer, and have them diagnose it. Then you will know what you are dealing with. Just throwing parts at it, can get expensive.
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Check the injector and coil wiring, iirc most with head problems didnt pass compression tests. How often is the code coming back on?
okay I will thank you . While I plan not driving it until it gets fixed I do need to take 100 mile trip that requires my 4x4 in a few weeks . Will I damage anything on that trip alone ?
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So I’ve been in & out of the dealership for months with this code popping up. They’ve thrown a ton of parts at it and then finally replaced engine with a completely new one. Got about 4,000 miles in on new engine and now it’s back. What are we missing? Any ideas?
Should start your own thread, and to answer your question, welcome to the wide wide world of Fiat...
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I have a 2007 jeep 3.8L manual transmission. I have replaced the engine with a 2009 3.8L with 190,000km 1 year ago. 3 weeks ago I got a po303 misfire code going 110kmh (65~ mph). This code is the only code that is shown. The problem ONLY occurs above 100kmh at highway speeds. I can rev the engine to any rpm and it is fine on city roads, however if I try and accelerate past 110kmh CEL flashes and cuts power, does not stall just drops the speed. I have replaced spark plugs, wires, coil pack, fuel injectors, fuel pump, catalytic converters, battery, fresh oil change, crankshaft sensors and more. I got it professionally inspected by multiple mechanics and they have no idea what the problem is. Compression is good, fuel pressure is good. The jeep idles and runs perfect up to 110kmh. After that the CEL flashes and the jeep loses power. There is a fast rattle when this happens but the noise goes away at any speed below 110kmh. Please leave some suggestions on what the problem could be
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I had the same codes twice, but on cylinders 1 and 6. It's all well documented elsewhere.
Bottom line....rocker bearings froze up both times. It's a bad design on those rocker bearings and a well known thing. That's why there is a new design with a new part number.
If you catch it early enough, it's just the rocker and you're lucky. Let it go too long and it'll eat your cam. Them you'll have some decisions to make.
Bottom line....rocker bearings froze up both times. It's a bad design on those rocker bearings and a well known thing. That's why there is a new design with a new part number.
If you catch it early enough, it's just the rocker and you're lucky. Let it go too long and it'll eat your cam. Them you'll have some decisions to make.
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Jeep Code P0303 Causes
Cylinder 3 misfires can be caused by many reasons from a faulty ignition system, fuel system, or internal engine failure. The most common reason for this to happen is faulty or worn-out spark plug coil packs, especially if it’s been a while since you had a tune-up.
Cylinder 3 misfires can be caused by many reasons from a faulty ignition system, fuel system, or internal engine failure. The most common reason for this to happen is faulty or worn-out spark plug coil packs, especially if it’s been a while since you had a tune-up.
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
- Faulty fuel injector
- Vacuum leak
- Low fuel pressure
- Camshaft sensor defective
- Crankshaft sensor defective
- Engine timing off
- Leaking head gasket
- Low engine compression
- Poor quality fuel
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How is a bad pcm drive diagnosed? Im guessing you had to replace the computer? Just curious.
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I have had the exact same issue only with a different car. city driving was fine. any type of highway speed, or heavy acceleration and i would get a flashing cel. let up off the gas and all was fine. after months of diagnosing, i went to change out plug wires. come to find out, i have a cracked spark plug. replaced the plug and all was fine after that
Yes, I had to replace the PCM. The place I used, Auto Computer Performance in FL offers a test service. If it fails and it can be repaired, they will, somewhere in the $150-$200 range. If it can't be fixed (like mine, the PC board was charred and traces damaged. They did offer to repair with no warranty, I said no thanks), they will sell you one. Mine was about $600 18 months ago.
2016 JKU 75th AE Sarge Green, Auto, 2" lift, Bestop/Mastertop/NX, ARS LowPro Roof Rack
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My 2016 JKU, with 77k miles, two days ago had an engine light and was runnung very sluggish. This incident happened just after I put gas and it was in the evening. I pulled into a well lit business parking lot, turned off the engine, and hooked up my OBD reader and boom, it was the infamous P0303 error code. Anyways, the following morning I was able to drive the Jeep to the nearest dealer (Milton Ruben/Augusta Ga). Within four hours they told me the Jeep was ready for PU. It turned out, the coil wire in cylinder#3 was bad, replaced it with a new wire, and now it runs smooth like before.
The good one good thing, for me, is that the repair was covered with the Jeeps' Lifetime MaxCare Warranty; I only paid the $100 deductible (total).👍I know that I could have performed the repair myself, order the part, etc.... and saved $$$. But, I am more than 2000 miles from home (SoCal) with limited tools at the back of the Jeep. I am just thankful that I am back on the road.😎
The good one good thing, for me, is that the repair was covered with the Jeeps' Lifetime MaxCare Warranty; I only paid the $100 deductible (total).👍I know that I could have performed the repair myself, order the part, etc.... and saved $$$. But, I am more than 2000 miles from home (SoCal) with limited tools at the back of the Jeep. I am just thankful that I am back on the road.😎
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[emoji106][emoji41]
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I have a 2016 JK with 40k on it and have been getting the same code but for cylinder 2. Funny thing is it comes and goes. The speed doesn't seem to matter at all. I've had coil pack #2 replaced along with all plugs. It runs very smooth but occasionally the code comes on. Then goes off. I'm leery of taking it to the local dealer since I don't do my own engine work.
I just don't want to as I don't really trust them.
I just don't want to as I don't really trust them.
Look for worn wires in the harness. The wire loom usually gets brittle and cracks, exposing the wires. This in turn can cause the insulation to rub thru and short. Also check the big connector on the passengers side valve cover. Make sure all the pins are fully extended in the connector.
Been there, done that, have the T-Shirt.
Been there, done that, have the T-Shirt.
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I drive a 2016 with about 42k miles on it. Do you suppose that's enough time/miles for this sort of cracking to occur? Also, could you post photos of the areas you're referencing? Thanks.
My issue was to the left of the master cylinder near the intake manifold (looking at it from the front of the Jeep).
The main harness starts at the ECU/PCM (it has 2 large connectors on it) and follows the exhaust manifold to the rear of the engine. It's a minimum of 1" in diameter. That harness eventually goes behind the engine and comes up to the passengers valve cover where a large connector sits.
The #2 cylinder (injector and coil pack trigger) runs all the way from the PCM, along the engine in that large bundle, thru the big connector and back to the drivers side.
To answer your first question, it's possible. It's also possible that you have rodent damage to your wires as you don't put a lot of miles on your Jeep.
The main harness starts at the ECU/PCM (it has 2 large connectors on it) and follows the exhaust manifold to the rear of the engine. It's a minimum of 1" in diameter. That harness eventually goes behind the engine and comes up to the passengers valve cover where a large connector sits.
The #2 cylinder (injector and coil pack trigger) runs all the way from the PCM, along the engine in that large bundle, thru the big connector and back to the drivers side.
To answer your first question, it's possible. It's also possible that you have rodent damage to your wires as you don't put a lot of miles on your Jeep.
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