I have a 2001 jeep xj runs great but cel code p0303
11-27-2017, 04:50 PM
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Year: 2000
Model: Cherokee
Engine: 4.0 I6
I have a 2001 jeep xj runs great but cel code p0303
My car is running great she has 165,000 miles on her I just bought her
precious owner said they changed coil pack spark plugs and injectors (who really knows though rite)
i erased the cel to see if it comes back on
a week later the light comes back on
i take her to autozone the p0303 code come up
shes running good if u ask me starts rite up I drive like 70 miles a day up and down i95
never stalls or shakes or nothing
wanted to know if anyone else ever changed all plugs coil injectors but the misfire code p0303 still comes up but car still drives fine
precious owner said they changed coil pack spark plugs and injectors (who really knows though rite)
i erased the cel to see if it comes back on
a week later the light comes back on
i take her to autozone the p0303 code come up
shes running good if u ask me starts rite up I drive like 70 miles a day up and down i95
never stalls or shakes or nothing
wanted to know if anyone else ever changed all plugs coil injectors but the misfire code p0303 still comes up but car still drives fine
11-27-2017, 09:38 PM
#3
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Did it happen after a hot restart? My wife's 01 has the issue of fuel vaporizing when it's shut down hot and restarted before it cools sufficiently. Po303 comes up most frequently.
11-28-2017, 08:00 PM
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No no she’s never given me any problems starting her up in the morning or after a long drive
i guess my quiestion is if I really have a misfire in cylinder 3 will it be noticeable?
she don’t sputter shake or nothing
11-29-2017, 02:22 PM
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Year: 2000
Model: Cherokee(XJ)
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There are several things that can cause a P0303. I have included some specific known issues below, but I would start with the basic tests of spark and fuel. Some of these tests require special testing tools, but you can usually borrow all of them from Autozone through their tool loan program if you don't have them yourself.
The first thing I would do is inspect and check the gap on the plugs, then swap the #3 plug with another plug to see if the misfire moves. If it moves, you know you have a bad plug. You might as well replace them all at that point.
You can do the same thing with the injectors. If you swap the #3 injector to another cylinder and the misfire moves with it, the injector is bad. You might as well replace them all at that point.
You can test whether your injectors are getting a signal using a noid light, which is a little light that plugs into the injector connector and pulses when it gets a signal. If #3 is not flashing steadily, you may have a wiring issue. Note: Using the noid light will cause a new code for injector circuit, so you have to be prepared for that and clear it. People have convinced themselves they had injector circuit issues when they actually caused the code themselves.
You can test your fuel pressure by hooking up a test gauge to the schrader valve on the fuel rail. It should be 49 psi + or - 5 psi at idle. Low fuel pressure usually manifests as a P0300 multiple cylinder misfire, however, so I doubt it's your issue. But it's an easy test to rule out fuel pressure.
You can do a cylinder compression test to make sure you haven't lost compression in the #3 cylinder. That could cause a misfire.
If you have a known good coil rail, you can swap it with the one in the misbehaving Jeep to see if the misfire goes away.
You can try reindexing your camshaft position sensor. That's free and not too difficult, but I seriously doubt it's your problem.
Now, to the known issues:
The heat soak issue mentioned above can cause a P0303. However, you would probably know if that was your problem. The symptoms involve getting the engine hot, shutting it off for ten to twenty minutes and then experiencing a difficult restart and/or stumbling when it is restarted. Cold starts are not an issue.
The next issue is more sinister.
Closely watch the coolant level in your overflow tank. The original casting of the 0331 head used in the 2000 and 2001 XJs had a casting flaw that sometimes caused it to crack between the #3 and #4 cylinders. It often cracks to the top and causes coolant to seep out into the oil. Sometimes it cracks to the bottom, into the #3 combustion chamber, so that coolant seeps into the chamber and causes a misfire.
You can test for it. As the crack gets worse, it can allow hot exhaust gas into your cooling system. You can detect that gas using a combustion leak tester, AKA a "block tester."
You may also be able to detect it with a cylinder leak down test. The simple compression test noted above often misses a crack, because the crack itself can be tight enough that the cylinder still builds pressure. That pressure can leak out during a leak down test, however, and tell you that you have a problem. This test is slightly more complicated than a compression test because you need a source of compressed air, either a compressor or a fully charged air tank.
And as I said above, watch your coolant level. Often one of the earliest signs of a cracked head is often coolant disappearing without an obvious leak, because it's going into the oil or into the combustion chamber and being boiled or burned out. You could still have enough of a leak to cause a misfire without the coolant loss being obvious. Some people take their cars to a shop for oil changes and never realize they're losing coolant because the oil change guys top off the overflow bottle without mentioning it.
Finally, your motor is also subject to the decarbonization and valve rotation TSB found here:
http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
Just anecdotally it seems like that usually affects cylinders 1 and 6 or throws a P0300 whenever anybody mentions it, but it could affect any cylinders. The issue is that the valves don't rotate properly under certain driving conditions, causing carbon to build up on the valves themselves and prevent them from closing properly. A compression and/or leak down test could tell you that you have a valve issue.
There are two procedures in that TSB, one to decarbonize the valves and another to manually rotate them. The decarbonization procedure uses a can of Mopar combustion chamber cleaner, but you can actually do the exact same thing (carefully) with a cup of water. Here's a link to that procedure:
https://www.cherokeeforum.com/f30/st...-4-0-a-226299/
Some people find that decarbonization enough to solve their problem, so it could be worth a shot, and it's free if you use water instead of the Mopar cleaner.
Good luck.
The first thing I would do is inspect and check the gap on the plugs, then swap the #3 plug with another plug to see if the misfire moves. If it moves, you know you have a bad plug. You might as well replace them all at that point.
You can do the same thing with the injectors. If you swap the #3 injector to another cylinder and the misfire moves with it, the injector is bad. You might as well replace them all at that point.
You can test whether your injectors are getting a signal using a noid light, which is a little light that plugs into the injector connector and pulses when it gets a signal. If #3 is not flashing steadily, you may have a wiring issue. Note: Using the noid light will cause a new code for injector circuit, so you have to be prepared for that and clear it. People have convinced themselves they had injector circuit issues when they actually caused the code themselves.
You can test your fuel pressure by hooking up a test gauge to the schrader valve on the fuel rail. It should be 49 psi + or - 5 psi at idle. Low fuel pressure usually manifests as a P0300 multiple cylinder misfire, however, so I doubt it's your issue. But it's an easy test to rule out fuel pressure.
You can do a cylinder compression test to make sure you haven't lost compression in the #3 cylinder. That could cause a misfire.
If you have a known good coil rail, you can swap it with the one in the misbehaving Jeep to see if the misfire goes away.
You can try reindexing your camshaft position sensor. That's free and not too difficult, but I seriously doubt it's your problem.
Now, to the known issues:
The heat soak issue mentioned above can cause a P0303. However, you would probably know if that was your problem. The symptoms involve getting the engine hot, shutting it off for ten to twenty minutes and then experiencing a difficult restart and/or stumbling when it is restarted. Cold starts are not an issue.
The next issue is more sinister.
Closely watch the coolant level in your overflow tank. The original casting of the 0331 head used in the 2000 and 2001 XJs had a casting flaw that sometimes caused it to crack between the #3 and #4 cylinders. It often cracks to the top and causes coolant to seep out into the oil. Sometimes it cracks to the bottom, into the #3 combustion chamber, so that coolant seeps into the chamber and causes a misfire.
You can test for it. As the crack gets worse, it can allow hot exhaust gas into your cooling system. You can detect that gas using a combustion leak tester, AKA a "block tester."
You may also be able to detect it with a cylinder leak down test. The simple compression test noted above often misses a crack, because the crack itself can be tight enough that the cylinder still builds pressure. That pressure can leak out during a leak down test, however, and tell you that you have a problem. This test is slightly more complicated than a compression test because you need a source of compressed air, either a compressor or a fully charged air tank.
And as I said above, watch your coolant level. Often one of the earliest signs of a cracked head is often coolant disappearing without an obvious leak, because it's going into the oil or into the combustion chamber and being boiled or burned out. You could still have enough of a leak to cause a misfire without the coolant loss being obvious. Some people take their cars to a shop for oil changes and never realize they're losing coolant because the oil change guys top off the overflow bottle without mentioning it.
Finally, your motor is also subject to the decarbonization and valve rotation TSB found here:
http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
Just anecdotally it seems like that usually affects cylinders 1 and 6 or throws a P0300 whenever anybody mentions it, but it could affect any cylinders. The issue is that the valves don't rotate properly under certain driving conditions, causing carbon to build up on the valves themselves and prevent them from closing properly. A compression and/or leak down test could tell you that you have a valve issue.
There are two procedures in that TSB, one to decarbonize the valves and another to manually rotate them. The decarbonization procedure uses a can of Mopar combustion chamber cleaner, but you can actually do the exact same thing (carefully) with a cup of water. Here's a link to that procedure:
https://www.cherokeeforum.com/f30/st...-4-0-a-226299/
Some people find that decarbonization enough to solve their problem, so it could be worth a shot, and it's free if you use water instead of the Mopar cleaner.
Good luck.
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11-29-2017, 06:34 PM
#8
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Thanks your awesome
There are several things that can cause a P0303. I have included some specific known issues below, but I would start with the basic tests of spark and fuel. Some of these tests require special testing tools, but you can usually borrow all of them from Autozone through their tool loan program if you don't have them yourself.
The first thing I would do is inspect and check the gap on the plugs, then swap the #3 plug with another plug to see if the misfire moves. If it moves, you know you have a bad plug. You might as well replace them all at that point.
You can do the same thing with the injectors. If you swap the #3 injector to another cylinder and the misfire moves with it, the injector is bad. You might as well replace them all at that point.
You can test whether your injectors are getting a signal using a noid light, which is a little light that plugs into the injector connector and pulses when it gets a signal. If #3 is not flashing steadily, you may have a wiring issue. Note: Using the noid light will cause a new code for injector circuit, so you have to be prepared for that and clear it. People have convinced themselves they had injector circuit issues when they actually caused the code themselves.
You can test your fuel pressure by hooking up a test gauge to the schrader valve on the fuel rail. It should be 49 psi + or - 5 psi at idle. Low fuel pressure usually manifests as a P0300 multiple cylinder misfire, however, so I doubt it's your issue. But it's an easy test to rule out fuel pressure.
You can do a cylinder compression test to make sure you haven't lost compression in the #3 cylinder. That could cause a misfire.
If you have a known good coil rail, you can swap it with the one in the misbehaving Jeep to see if the misfire goes away.
You can try reindexing your camshaft position sensor. That's free and not too difficult, but I seriously doubt it's your problem.
Now, to the known issues:
The heat soak issue mentioned above can cause a P0303. However, you would probably know if that was your problem. The symptoms involve getting the engine hot, shutting it off for ten to twenty minutes and then experiencing a difficult restart and/or stumbling when it is restarted. Cold starts are not an issue.
The next issue is more sinister.
Closely watch the coolant level in your overflow tank. The original casting of the 0331 head used in the 2000 and 2001 XJs had a casting flaw that sometimes caused it to crack between the #3 and #4 cylinders. It often cracks to the top and causes coolant to seep out into the oil. Sometimes it cracks to the bottom, into the #3 combustion chamber, so that coolant seeps into the chamber and causes a misfire.
You can test for it. As the crack gets worse, it can allow hot exhaust gas into your cooling system. You can detect that gas using a combustion leak tester, AKA a "block tester."
You may also be able to detect it with a cylinder leak down test. The simple compression test noted above often misses a crack, because the crack itself can be tight enough that the cylinder still builds pressure. That pressure can leak out during a leak down test, however, and tell you that you have a problem. This test is slightly more complicated than a compression test because you need a source of compressed air, either a compressor or a fully charged air tank.
And as I said above, watch your coolant level. Often one of the earliest signs of a cracked head is often coolant disappearing without an obvious leak, because it's going into the oil or into the combustion chamber and being boiled or burned out. You could still have enough of a leak to cause a misfire without the coolant loss being obvious. Some people take their cars to a shop for oil changes and never realize they're losing coolant because the oil change guys top off the overflow bottle without mentioning it.
Finally, your motor is also subject to the decarbonization and valve rotation TSB found here:
http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
Just anecdotally it seems like that usually affects cylinders 1 and 6 or throws a P0300 whenever anybody mentions it, but it could affect any cylinders. The issue is that the valves don't rotate properly under certain driving conditions, causing carbon to build up on the valves themselves and prevent them from closing properly. A compression and/or leak down test could tell you that you have a valve issue.
There are two procedures in that TSB, one to decarbonize the valves and another to manually rotate them. The decarbonization procedure uses a can of Mopar combustion chamber cleaner, but you can actually do the exact same thing (carefully) with a cup of water. Here's a link to that procedure:
https://www.cherokeeforum.com/f30/st...-4-0-a-226299/
Some people find that decarbonization enough to solve their problem, so it could be worth a shot, and it's free if you use water instead of the Mopar cleaner.
Good luck.
The first thing I would do is inspect and check the gap on the plugs, then swap the #3 plug with another plug to see if the misfire moves. If it moves, you know you have a bad plug. You might as well replace them all at that point.
You can do the same thing with the injectors. If you swap the #3 injector to another cylinder and the misfire moves with it, the injector is bad. You might as well replace them all at that point.
You can test whether your injectors are getting a signal using a noid light, which is a little light that plugs into the injector connector and pulses when it gets a signal. If #3 is not flashing steadily, you may have a wiring issue. Note: Using the noid light will cause a new code for injector circuit, so you have to be prepared for that and clear it. People have convinced themselves they had injector circuit issues when they actually caused the code themselves.
You can test your fuel pressure by hooking up a test gauge to the schrader valve on the fuel rail. It should be 49 psi + or - 5 psi at idle. Low fuel pressure usually manifests as a P0300 multiple cylinder misfire, however, so I doubt it's your issue. But it's an easy test to rule out fuel pressure.
You can do a cylinder compression test to make sure you haven't lost compression in the #3 cylinder. That could cause a misfire.
If you have a known good coil rail, you can swap it with the one in the misbehaving Jeep to see if the misfire goes away.
You can try reindexing your camshaft position sensor. That's free and not too difficult, but I seriously doubt it's your problem.
Now, to the known issues:
The heat soak issue mentioned above can cause a P0303. However, you would probably know if that was your problem. The symptoms involve getting the engine hot, shutting it off for ten to twenty minutes and then experiencing a difficult restart and/or stumbling when it is restarted. Cold starts are not an issue.
The next issue is more sinister.
Closely watch the coolant level in your overflow tank. The original casting of the 0331 head used in the 2000 and 2001 XJs had a casting flaw that sometimes caused it to crack between the #3 and #4 cylinders. It often cracks to the top and causes coolant to seep out into the oil. Sometimes it cracks to the bottom, into the #3 combustion chamber, so that coolant seeps into the chamber and causes a misfire.
You can test for it. As the crack gets worse, it can allow hot exhaust gas into your cooling system. You can detect that gas using a combustion leak tester, AKA a "block tester."
You may also be able to detect it with a cylinder leak down test. The simple compression test noted above often misses a crack, because the crack itself can be tight enough that the cylinder still builds pressure. That pressure can leak out during a leak down test, however, and tell you that you have a problem. This test is slightly more complicated than a compression test because you need a source of compressed air, either a compressor or a fully charged air tank.
And as I said above, watch your coolant level. Often one of the earliest signs of a cracked head is often coolant disappearing without an obvious leak, because it's going into the oil or into the combustion chamber and being boiled or burned out. You could still have enough of a leak to cause a misfire without the coolant loss being obvious. Some people take their cars to a shop for oil changes and never realize they're losing coolant because the oil change guys top off the overflow bottle without mentioning it.
Finally, your motor is also subject to the decarbonization and valve rotation TSB found here:
http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
Just anecdotally it seems like that usually affects cylinders 1 and 6 or throws a P0300 whenever anybody mentions it, but it could affect any cylinders. The issue is that the valves don't rotate properly under certain driving conditions, causing carbon to build up on the valves themselves and prevent them from closing properly. A compression and/or leak down test could tell you that you have a valve issue.
There are two procedures in that TSB, one to decarbonize the valves and another to manually rotate them. The decarbonization procedure uses a can of Mopar combustion chamber cleaner, but you can actually do the exact same thing (carefully) with a cup of water. Here's a link to that procedure:
https://www.cherokeeforum.com/f30/st...-4-0-a-226299/
Some people find that decarbonization enough to solve their problem, so it could be worth a shot, and it's free if you use water instead of the Mopar cleaner.
Good luck.
07-10-2021, 05:49 AM
#9
just remember that there's a TSB ON most cherokees for a P0303 from jeep which they did a recall on most of the cherokees doing the extra vapor in cly#3 causing it to throw a 303 code.