Come and go misfire
11-27-2011, 10:01 PM
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Come and go misfire
Well over the summer I had this same issue come and go on me without touching it and now it's back again to haunt me. Once again throwing random/multiple and bank 3 and 5 misfire codes and having a rough idle. Hoping it's not the good old cracked head or stuck valves like I've been reading that are usually the cause of this. Gonna be testing compression, injectors, spark and changing plugs tomorrow, hope to find something smaller to be the problem. Basically just wondering if anyone has any advice on this or other suggestions as to what could be causing this. I've been reading a lot about champion plugs being good in these things but I've never been a fan personally. Went with the delcos since it's probably a similar design and I've had better experiences. Are these good plugs to use and does it matter copper/platinum? Thanks guys.
11-30-2011, 09:02 AM
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So update time. Changed plugs which were very white. Changed pcv valves and checked TPS, IAC, and MAP. Checked coil pack and injectors with no bad readings. Fuel pressure is good. Did a compression test on all 6 cylinders turning up slightly lower on cylinder 3 at about 110. Leakdown test proved well on all cylinders with it taking barely any psi to turn the crank. I'm baffled as to what it causing this because I still have a MIL and feel a miss at idle and lack in power.
11-30-2011, 10:05 AM
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Year: 1990
Model: Cherokee
Engine: The venerable 4.0
White plugs are likely indicative of a lean condition. Are the plugs the same heat range as stock? If so you should test your O2 sensors.
11-30-2011, 10:21 AM
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Year: 2000.1999,1996
Model: Cherokee
Engine: 4.0
Might help get an answer if we had the year and info on your friggin jeep ! I can figure out it's a 2000 -01 but maybe someone else can't, I'm also quite sure I know what your problem is to.
Last edited by 413maxwedge; 11-30-2011 at 10:23 AM.
11-30-2011, 07:53 PM
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Sorry thought I put the info, 2001 sport 80k miles. Plugs were gapped a little less then .35 when I checked them. They were autolite platinums. I put in standard delcos at .35 and it's running smoother while driving but you can still feel it missing bad at idle. I read something about O2's somewhere but I don't want to throw parts at it. Is there anyway to test them? Also I cleared the code and it came back in under 5 minutes of driving.
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11-30-2011, 08:12 PM
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Year: 2000.1999,1996
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Engine: 4.0
Go with champion plugs ,2000-01 just run better with them, when you gap plugs use feeler gauges 100 times better than those stupid round gappers,Did you replace the boots and springs on the coil pack this should be done if they are old, did you test coil packs?next try a run of seafoam to clean any carbon off of valves. Swap injectors around when you have the miss fire, see about testing injectors.The filter in the tank can be changed sepratily for just the cost of the sock (filter)this is just a maybe.O2's should throw a code have you checked for stored codes?Check all plug ins on injectors coil pack etc make sure they are clean. Also check grounds and battery cables for corrosion inside jacket also. (Now it doesn't only start the misfire when you have driven it and shut it off then restart it does it?)Try these cheap to free things and let us know what happens.
Last edited by 413maxwedge; 11-30-2011 at 08:16 PM.
11-30-2011, 08:44 PM
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Year: 1990
Model: Cherokee
Engine: The venerable 4.0
When you test an o2 the best way is to warm it up then get underneath and backprobe the ground an output. The voltage will jump every second or so if its working. If it doesn't jump or jumps slowly or intermittently is replacing it
12-02-2011, 02:56 PM
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I tested the coil pack with a pretty consistant reading across the board. I didn't replace anything but I'm pretty sure it's fine though I could be wrong. I would run seafoam but I've never trusted that crap and don't plan to use it now. I'm trying other less harsh engine cleaners like Marvel. I tested the injectors and fuel pressure with no problems but I will try switching them around and see if anything happens. The fuel filter is in the tank? That sounds like loads of fun to get to lol. O2's seem fine though I haven't tested them. There is no wear on anything or rust/corrosion I've been all over this thing this past week and I haven't found anything suspicious yet. It's not the whole heat soak misfire deal. Whether it be a cold start or heat soak start or any start for that matter it constantly misfires. You can feel it missing bad at idle and it's lacking on power a bit. Also lately I've been running it harder to clean out any potential carbon and I've noticed above 3k at heavier throttle the thing really shutters bad.
Last edited by JerseyTrueBlue; 12-02-2011 at 02:59 PM.
12-02-2011, 03:47 PM
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I assume you have a coil rail type. That's a DIS ignition.
Look at the underhood label - IT TELLS YOU WHAT PLUGS TO USE.
Ditch those Autolite junk ones.
I think you'll find Champions or NGK were the right ones. Plain old regular plugs not plats or any other junk stuff.
The design engineers know more about what they designed it to use rather than a parts idiot.
Listen very closely while it runs, if you hear snapping from the coil rail it's dead.
Testing it with an Ohmmeter won't tell it's bad.
But you can test it - infra-red thermometer - run at 2000 rpm for 2 minutes, go under, measure the temps at the exhaust outlets - they should all be the same temps. A cooler one indicates a bad coil rail.
The only way to know for sure is replace it.
Be sure to get real one, lots of Chinese junk around. OEM was made by Standard Ignition - NAPA or dealer.
The junk ones don't last. Quality only costs slightly more initially, but junk costs more by the time you replace it several times.
White plugs with a DIS means good nowdays.
Look at the underhood label - IT TELLS YOU WHAT PLUGS TO USE.
Ditch those Autolite junk ones.
I think you'll find Champions or NGK were the right ones. Plain old regular plugs not plats or any other junk stuff.
The design engineers know more about what they designed it to use rather than a parts idiot.
Listen very closely while it runs, if you hear snapping from the coil rail it's dead.
Testing it with an Ohmmeter won't tell it's bad.
But you can test it - infra-red thermometer - run at 2000 rpm for 2 minutes, go under, measure the temps at the exhaust outlets - they should all be the same temps. A cooler one indicates a bad coil rail.
The only way to know for sure is replace it.
Be sure to get real one, lots of Chinese junk around. OEM was made by Standard Ignition - NAPA or dealer.
The junk ones don't last. Quality only costs slightly more initially, but junk costs more by the time you replace it several times.
White plugs with a DIS means good nowdays.
12-02-2011, 09:06 PM
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I assume you have a coil rail type. That's a DIS ignition.
Look at the underhood label - IT TELLS YOU WHAT PLUGS TO USE.
Ditch those Autolite junk ones.
I think you'll find Champions or NGK were the right ones. Plain old regular plugs not plats or any other junk stuff.
The design engineers know more about what they designed it to use rather than a parts idiot.
Listen very closely while it runs, if you hear snapping from the coil rail it's dead.
Testing it with an Ohmmeter won't tell it's bad.
But you can test it - infra-red thermometer - run at 2000 rpm for 2 minutes, go under, measure the temps at the exhaust outlets - they should all be the same temps. A cooler one indicates a bad coil rail.
The only way to know for sure is replace it.
Be sure to get real one, lots of Chinese junk around. OEM was made by Standard Ignition - NAPA or dealer.
The junk ones don't last. Quality only costs slightly more initially, but junk costs more by the time you replace it several times.
White plugs with a DIS means good nowdays.
Look at the underhood label - IT TELLS YOU WHAT PLUGS TO USE.
Ditch those Autolite junk ones.
I think you'll find Champions or NGK were the right ones. Plain old regular plugs not plats or any other junk stuff.
The design engineers know more about what they designed it to use rather than a parts idiot.
Listen very closely while it runs, if you hear snapping from the coil rail it's dead.
Testing it with an Ohmmeter won't tell it's bad.
But you can test it - infra-red thermometer - run at 2000 rpm for 2 minutes, go under, measure the temps at the exhaust outlets - they should all be the same temps. A cooler one indicates a bad coil rail.
The only way to know for sure is replace it.
Be sure to get real one, lots of Chinese junk around. OEM was made by Standard Ignition - NAPA or dealer.
The junk ones don't last. Quality only costs slightly more initially, but junk costs more by the time you replace it several times.
White plugs with a DIS means good nowdays.
12-02-2011, 09:16 PM
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Year: Several
Model: Cherokee
Engine: 4.0
White no longer means lean - not with a DIS.
The DIS fires the plug twice. It runs much cleaner now. Once on the compression stroke, the 2nd time on the "backside called the waste spark.
A DIS has to have either regular copper plugs, or if plats are used they have to be DOUBLE PLATS - both electrodes have to be plat. Otherwise they'll misfire.
The factory knows what they designed it to use and puts it on the underhood label. Gap is .035
But it does sound like a coil rail - but before replacing it - do the temperature test.
When they fail they usually kill 2 cylinders - opposing or companion cylinders - it'll still run fairly smooth, just no power.
Often you can hear it snapping - if you have good ears.
It rarely sets a code - since the engine still runs smooth.
I keep a spare coil rail handy - I use it to test - you'd be surprised at how many are going bad after the years. The cheapies are good for less than a year, get a quality one.
The DIS fires the plug twice. It runs much cleaner now. Once on the compression stroke, the 2nd time on the "backside called the waste spark.
A DIS has to have either regular copper plugs, or if plats are used they have to be DOUBLE PLATS - both electrodes have to be plat. Otherwise they'll misfire.
The factory knows what they designed it to use and puts it on the underhood label. Gap is .035
But it does sound like a coil rail - but before replacing it - do the temperature test.
When they fail they usually kill 2 cylinders - opposing or companion cylinders - it'll still run fairly smooth, just no power.
Often you can hear it snapping - if you have good ears.
It rarely sets a code - since the engine still runs smooth.
I keep a spare coil rail handy - I use it to test - you'd be surprised at how many are going bad after the years. The cheapies are good for less than a year, get a quality one.
Last edited by rrich; 12-02-2011 at 09:19 PM.
12-04-2011, 02:00 PM
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White no longer means lean - not with a DIS.
The DIS fires the plug twice. It runs much cleaner now. Once on the compression stroke, the 2nd time on the "backside called the waste spark.
A DIS has to have either regular copper plugs, or if plats are used they have to be DOUBLE PLATS - both electrodes have to be plat. Otherwise they'll misfire.
The factory knows what they designed it to use and puts it on the underhood label. Gap is .035
But it does sound like a coil rail - but before replacing it - do the temperature test.
When they fail they usually kill 2 cylinders - opposing or companion cylinders - it'll still run fairly smooth, just no power.
Often you can hear it snapping - if you have good ears.
It rarely sets a code - since the engine still runs smooth.
I keep a spare coil rail handy - I use it to test - you'd be surprised at how many are going bad after the years. The cheapies are good for less than a year, get a quality one.
The DIS fires the plug twice. It runs much cleaner now. Once on the compression stroke, the 2nd time on the "backside called the waste spark.
A DIS has to have either regular copper plugs, or if plats are used they have to be DOUBLE PLATS - both electrodes have to be plat. Otherwise they'll misfire.
The factory knows what they designed it to use and puts it on the underhood label. Gap is .035
But it does sound like a coil rail - but before replacing it - do the temperature test.
When they fail they usually kill 2 cylinders - opposing or companion cylinders - it'll still run fairly smooth, just no power.
Often you can hear it snapping - if you have good ears.
It rarely sets a code - since the engine still runs smooth.
I keep a spare coil rail handy - I use it to test - you'd be surprised at how many are going bad after the years. The cheapies are good for less than a year, get a quality one.
I've been having this problem since the summer I said this in the first post and you aren't supposed to run high octane in these I thought? Believe the manual says to only run regular, and no it's not heat soak I stated that.