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P0300 Random Misfire Code

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  #1  
Old 09-11-2009, 10:26 AM
cdnron
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Default P0300 Random Misfire Code

I periodically am getting 4 codes pop up on my '97 3.9L.

P0300 (Random Misfire)
P0301 (Random Misfire Cylinder 1)
P0303 (Random Misfire Cylinder 3)
P0305 (Random Misfire Cylinder 5)

All codes come up at the same instant, always the same cylinders, 1,3 &5...which I thought was kind of strange all being on the same side of the engine. I always thought that misfire codes were the result of electrical problems.

This occurs after the van has warmed up and I'm cruising at highway speed. No other symptoms (rough running, stumble...anything) other than the CEL coming on.

Van has new coil, new distributor & rotor, new plug wires, new plugs and new (used) computer all within the last 2 weeks. Crank sensor was replaced last year. Code still pops up when I'm on the highway. Doesn't seem to do it around town.

Any thoughts or suggestions? I'm thinking of maybe swapping back to the previous computer (which it turns out was OK but replaced during electrical troubleshooting recently.)

It's not a big problem...I carry my code reader with me and just reset them when the pop up...just a bit of a "pain" and I'm wondering what is going on.
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Old 09-11-2009, 11:11 AM
alloro
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I've been struggling with this same exact issue since I bought my van. I'm to the point where I believe it is a cracked head on that side of the engine. I was going to replace the heads this past summer but time did not allow me the opportunity.

BTW - Drive with the CEL on, don't keep clearing the codes. Doing so also wipes out the learned programming and the readiness test results. The downside to this is the computer controls the engine based a a set of default parameters instead of what it's learned by your driving habits.
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Old 09-11-2009, 01:14 PM
cdnron
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Thanks for the tip on erasing codes.

I've been doing some more searching and found this:

Quote:
A random misfire code can be set on newer vehicles with OBD II
onboard diagnostics when multiple misfires occur randomly in multiple cylinders. The cause is typically a vacuum leak in the intake manifold, throttle body or vacuum plumbing, a defective Exhaust Gas Recirculation (EGR) valve that is leaking exhaust into the intake manifold, or even bad gasoline. Less common causes include bad spark plug wires, worn or fouled spark plugs, a weak ignition coil, dirty fuel injectors, low fuel pressure, or weak valve springs. If a misfire is occurring in only one or two cylinders, you will usually find a misfire code for that specific cylinder rather than a random misfire code.
I found that here: http://www.random-misfire.com/

Interesting thing is I also have a rough idle...even after cleaning out the Idle Air valve. Maybe it is a vacuum issue somewhere?
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Old 09-11-2009, 01:53 PM
alloro
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Well we don't have EGR valves on these engines and I did replace my intake manifold gasket as well as the plenum gasket on the bottom of the intake when it was off. Also, I did a compression test on all cylinders and all of them are up in the 145-155 PSI range, so I'm ruling out rings, valves, and head gaskets. Trust me, I've been aggravated over this for a long time. It's probably the only thing in my life to date that I haven't been able to fix (yet).
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Old 09-28-2009, 11:30 PM
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Usually, when the P0300 or P030X shows up, it's time to change the cap-n-rotor. The cheap-o aluminum types will toss these codes more often.

Also, if you happen to side gap the plugs, these codes will happen more frequently as the plug life tends to go sooner.

My code is always P0304. #4 cylinder. The engine light will blink on-n-off every time it happens. Most of the time, this happens while above 50mph and punching the pedal to the floor to get on the expressway or to pass.

Other things that could cause these codes to happen are fuel injectors, related wiring, sensors, the PCM/ECM, ran out of gas recently, forgot to tighten the gas cap, bad gas, gas that contains aditives and higher than 10% ethanol, incorrect fuel pressure, leaking egr valve, restrictive ports, faulty coil, wires, plugs cap-n-rotor and if need be timing.
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Old 09-29-2009, 12:38 PM
alloro
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Quote:
Originally Posted by stev View Post
Usually, when the P0300 or P030X shows up, it's time to change the cap-n-rotor. The cheap-o aluminum types will toss these codes more often.

Also, if you happen to side gap the plugs, these codes will happen more frequently as the plug life tends to go sooner.

My code is always P0304. #4 cylinder. The engine light will blink on-n-off every time it happens. Most of the time, this happens while above 50mph and punching the pedal to the floor to get on the expressway or to pass.
Only brass contacts for me, and no I don't side gap the plugs.

Change your #4 spark plug and I'd almost guarantee your problem goes away.
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Old 01-01-2017, 10:05 PM
Skeeter 5050
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alloro,
Did you ever find a fix for this? I have a 2001 Dakota 3.9L with the same issue. I get the same codes, but only on the highway. I have given it a tune up, and replaced various components. I'm just about to give up.
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Old 01-02-2017, 09:18 AM
alloro
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Quote:
Originally Posted by Skeeter 5050 View Post
alloro,
Did you ever find a fix for this? I have a 2001 Dakota 3.9L with the same issue. I get the same codes, but only on the highway. I have given it a tune up, and replaced various components. I'm just about to give up.
The problem went away when I changed the crank sensor for the 3rd time. Mind you I had changed it twice before and the problem persisted, so it's a crap shoot as to weather or not you get a good crank sensor. I did go aftermarket, so if you want to avoid the hassle you could get and OEM one from the dealer. Obviously it will be more expensive.
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Old 01-02-2017, 12:27 PM
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Use delphi parts, They actually make sensors/wiring harnesses for the auto industry. Who actually makes the oem ones is unknown but a doubt it's Chrysler. I had issues with the junk the local parts stores sell so i don't buy sensors there any more. Some parts stores carry them but you have to ask because they want to push the store brand or something else they make more profit on. Rockauto always has the best price compared to the local parts stores.
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Old 01-02-2017, 12:45 PM
Skeeter 5050
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alloro,
I'm only getting the codes when on the highway. Was this your experience? Do you remember what brand part you used?

Last edited by Skeeter 5050; 01-02-2017 at 01:06 PM.
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