1997 Jeep Wrangler P0300, p0301, p0302, p0303, p0304, p0305, p0306 - Jeep Wrangler Forum
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Old 02-14-2011, 05:18 PM   #1
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1997 Jeep Wrangler P0300, p0301, p0302, p0303, p0304, p0305, p0306

I just took my 97 wrangler through inspection and they told me that I failed emissions. I looked up the codes, p0300 -p0306 and they say that I have firing issues on all six of my cylinders. I am experiencing no symptoms at all. The Jeep runs like a champ, and I have almost 300k miles on it. What would cause all of these error codes?

Thank you
-Joe-

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Old 02-14-2011, 06:04 PM   #2
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spark plugs, wires, distributor cap and rotor, ignition coil.

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Old 02-14-2011, 06:51 PM   #3
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I hope mine makes it to 300k, that would be sweet

On second thought, I would be spending about $45,000 in gas to get there. I'll try not to think about that.
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Old 02-14-2011, 07:26 PM   #4
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so i need a tune up
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Old 02-15-2011, 10:27 AM   #5
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You may need a tune up, also is the engine heatng properly, not attaining proper temp will cause fireing issues same with O2 sensors.
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Old 02-15-2011, 11:55 AM   #6
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Yes, the engine seems to be heating fine.

If all six cylinders were misfiring I should not be able to drive it.
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Old 02-15-2011, 06:46 PM   #7
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Do your tune up first. If it does not fix the issue, it is likely the valve springs. I have a 1999 4.0 and like the 97, 98, and 2000 models, they have a weak valve spring issue which prevents the exhaust valves from opening and closing properly causing the multiple cylinder misfire error codes and failed emissions.... I am replacing my valve springs soon. I found this out after replacing good wires, plugs, rotor and cap as well as new injectors......... By the way, my Jeep ran fine with these issues, I just clear the codes when it happens.
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Old 02-15-2011, 10:39 PM   #8
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I have a 2002 Jeep Wrangler X, I have been having the same kind of problem. I did the tune up, replaced the power pack and all 6 spack plugs and still continue having the same problem. Not only that but I seem to find some kind of oil residue on the ECU and the connectors, which I really don't know what that is. I have tried cleaning it out several times, it helps at first but will continue to do it. Does any one know what this problem can be?
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Old 02-16-2011, 12:56 AM   #9
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do the tune up first, spark plugs, distributor cap, spark plug wires, and see what happens,,, though if you have misfire in all 6 cylinders,,,, the car wouldnt start at all,,,, or am i wrong

i am also failing emissions for three times now,, though my problem is with some evap and catalyst monitors,,,,
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Old 02-16-2011, 05:39 AM   #10
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I hope mine makes it to 300k, that would be sweet

On second thought, I would be spending about $45,000 in gas to get there. I'll try not to think about that.
I hear that, on both counts!!
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Old 02-16-2011, 07:01 AM   #11
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What oil and how many miles between changes?
300K means you are doing something right.
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Old 02-16-2011, 09:34 AM   #12
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Quote:
Originally Posted by joehernandez View Post
do the tune up first, spark plugs, distributor cap, spark plug wires, and see what happens,,, though if you have misfire in all 6 cylinders,,,, the car wouldnt start at all,,,, or am i wrong

i am also failing emissions for three times now,, though my problem is with some evap and catalyst monitors,,,,
No, you are wrong A misfire is usually intermittent. If there was no spark, it would not run enough to throw a misfire code. Generally if you have a misfire on all cylinders, the AFR mixture is off. It could be the timing, but not if its computer controlled with COPs. I would look into the upstream o2 sensors and maybe the map sensor. Its possible the tps could throw these codes, but less likely.

The evap and catalyst monitors are unrelated. Depending on what evap code you have you could have a cracked charcoal canister, or lines to and from the canister to the gas tank and purge valve. The catalyst codes could be caused by a bad downstream o2 sensor (and maybe an upstream, but less likely) or bad cats. I have a catalyst efficiency code that I have narrowed down to a bad o2 sensor. Its still in there because I don't have smog for another 1.5 yrs and the sensor is only there for emissions bs.
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Old 02-17-2011, 05:29 AM   #13
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I change the oil every 5000 miles or so. It has worked for 13 years so why change. Even with the misfire codes, I am still getting about 20mpg on the highway, Drove it to DC fro NJ yesterday, and it ran great.
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Old 03-28-2011, 04:57 PM   #14
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@jlipski- did you ever figure this out. I am new to this site and just bought a 97' TJ. I some of the same codes: po300, po302, po306. I clear them and they come back within a couple weeks. I can't pinpoint an event that trips the codes. I have replaced plugs, cap, rotor, and camshaft position sensor so far. I noticed last week that my fuel vapor return line is basically rusted through- so I'm going to replace that this week. There is no sign of a noticeable misfire. Could this really be wires or a coil?
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Old 03-28-2011, 05:03 PM   #15
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That many misfire codes is normally a quirk of '97-'98 TJ 4.0L engines due to a weak batch of valve springs that hit the 4.0L engine those two years. Jeep has a TSB to address that problem which is nothing more than replacing the valve springs and cleaning the carbon that typically builds up from this problem out the combustion chambers.

If replacing the spark plugs, distributor cap, rotor, and ignition wires doesn't fix this problem, my next suspicion would be the valve springs. Replacing my valve springs in my previous '97 pretty well took care of the same issue though mine was only on two of the cylinders.
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Old 03-29-2011, 08:42 AM   #16
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Does anyone have recommendations on what brand of valve springs? Have they changed the OEM springs since the bulletin? Is there anything else that should be done while doing the springs (sorry for hijacking the thread).
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Old 03-29-2011, 12:45 PM   #17
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Just go with the OE springs with the original p/n. There was just a bad batch of them that are long gone. I'd get them from the dealer which is what I did when I replaced mine.

Incidentally, if you have many miles on your TJ and especially if there were a lot of miles on it after those misfire codes began, odds are very good that it's going to take a complete valve job plus the springs to completely fix the misfire. This is because the weak valve springs can cause the valves and valve seats to burn.

Depending on the cost you can find for a complete valve job, which can be priced either reasonably or absurd depending on your local pricing, you might be able to find a rebult ready-to-install head for less than the cost of a valve job. My local machine shop wants $600-800 for a complete valve job but I've seen entire rebuilt heads for $600.
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Old 03-31-2011, 08:47 AM   #18
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Well... there is only 1 valve spring from OEM Jeep in entire Milwaukee area and total of 4 springs in all of southern Wisconsin and the parts counter couldn't even tell me where/when they could get more. Do any larger auto parts stores carry them- tried NAPA so far. Now you have me scared- if I put in new springs and nothing else I may be wasting my time, but it seems that just that has helped a lot of people. I have 93k miles and the check engine just came on less than 1000 miles ago.
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Old 03-31-2011, 09:23 AM   #19
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Old 04-04-2011, 10:38 AM   #20
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I voted. YOu have to join jeepforum to be able to vote, just going to the link won't work.jj
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Old 04-04-2011, 04:03 PM   #21
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Jerry, i've never seen a part on there listed as "Chrysler, Mopar, OEM, etc...". Do you have a couple trusted manufacturers you'll order from? I was looking for an OEM TPS on RockAuto recently, but the options looked kind of shady... I've read that nearly all of the 3rd party TPS modules would throw CEL codes after install.
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Old 04-04-2011, 05:07 PM   #22
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While there might some instances of a cheap TPS throwing a code, I doubt very much that "nearly all" would.

I just checked on the TPS for a '97 at Rock Auto and they have one for $23 and another for $47 with comments that the $47 unit is similar to or is the OE TPS. I'd trust the $47 unit will work fine for a long time, the $23 TPS probably would too but for perhaps not as long.
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Old 05-01-2011, 02:37 PM   #23
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I am having the same problems with my 01 TJ 4.0 P0301,302, 303. In addition, I am now getting P0443. One xpert told me to replace the coil rail, and the gas cap, and the codes will go away after resetting. Have you tried that? I am going for a gas cap tomorrow. Any body out there dispute these recommendations??
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Old 05-01-2011, 03:40 PM   #24
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ddarrough - see the other misfire thread.

I'm not disagreeing with the weak valve springs idea, just trying to understand it. Even TSB's have been issued about it - according to Jerry. It's "fixed" several vehicles, so it must have merit.

But --

Weak springs will not close the valve fast enough - at idle and low speeds there is plenty of time to close. At higher speeds weak springs will cause "valve float" - the valve doesn't close fast enough. Push it faster results in bent push rods or worse.

The complaints are at idle, not high speeds.

But at idle there's plenty of time for it to close.
Could it be that they are not closing the valve hard enough? Like the springs are too short? Anybody made a comparison?
Will a compression test show low compression? Leak down test?

There must be a way of identifying/diagnosing the weak spring problem other than just the symptom, year, and throwing parts at it.
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Old 05-01-2011, 06:10 PM   #25
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Unhappy

I'm showing P0123 throttle posion sensor ,P0118 coolant temp sensor and ,P0113 air temp sensor,and I'm still having issues of no starts every 4 dayslike clock work. Did a tune up with no change.
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Old 05-01-2011, 07:15 PM   #26
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If you got 300K miles on it and it runs like a champ. Then ignore the codes. and Hammer down!
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Old 05-02-2011, 07:43 PM   #27
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I don't , but I would like to.That is if I can get it to run for more than 4 days in a row. It just turns over and not start, if I remove a wire any wire it will start. I did a tune up thinking it was not firing right,and it helped for 2 weeks now I'm back to square 1. any ideas???
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Old 06-14-2011, 07:04 AM   #28
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Question firing issues

I just got a 97 TJ 4.0L sport and i am having the same issues that are being discussed here on the forums. I did a tune up and then started to replace parts.everything, the distrub, the coil, plugs, plug wires and i had auto zone clear out the codes and every 2 or 3 days the the check engine light comes back on and the codes tell me that the is a firing issue. Sometimes it says number 6 cylinder is not firing and then it shows me that there is multi miss fires. What can i do to fix this problem? It is weird because i can start it up and drive it all day and it will studder only a few times but at the end of the day i check it again and it tells me the same again. I am puzzled.
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Old 07-03-2011, 05:07 PM   #29
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im getting the same codes but also bogging down when i get up to running temp. checked all the usual suspects and nothing, still happening, Valve springs cause it to bog down???? cpdes p0300, p0301, p0302 p0303
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Old 07-04-2011, 09:24 AM   #30
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D.A. Darrough

I wound up running a compression check, and discovered some bad valves. Wound up pulling the head and doing a valve job. Runs good now.

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