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P0300 Random Misfire Code

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  #1  
Old 09-11-2009, 11:26 AM
cdnron cdnron is offline
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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, 12:11 PM
alloro alloro is offline
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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, 02:14 PM
cdnron cdnron is offline
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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, 02:53 PM
alloro alloro is offline
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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 09-29-2009, 12:30 AM
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stev stev is offline
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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, 01:38 PM
alloro alloro is offline
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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 09-29-2009, 01:38 PM
 
 
 
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car, code, codes, dodge, highway, misfire, p0300, p0301, p0303, p0305, ram, random, readers, speeds, whats

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