Computer Code PO300
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Computer Code PO300
I'm getting a code PO300, "random multiple misfire occurring" on our 1999 Ford Explorer with the 4.0 EFI engine. About 85,000 miles on it.
My son thinks we got a tank of bad gas, and water in the gas led to the computer code. AutoZone guy read the code, but he had no real idea on what could be causing it.
The plugs and wires are essentially new, with about 5,000 miles on them since they were installed.
Any thoughts will be highly appreciated.
Regards from Tennessee,
Tom Norman
My son thinks we got a tank of bad gas, and water in the gas led to the computer code. AutoZone guy read the code, but he had no real idea on what could be causing it.
The plugs and wires are essentially new, with about 5,000 miles on them since they were installed.
Any thoughts will be highly appreciated.
Regards from Tennessee,
Tom Norman
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From: Homer, Alaska
Randoms are really difficult. I would reset the codes and drive it for a while. Removing the negative battery terminal for about 5 minutes will reset the computer. See what happens. Good luck.
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From: Connecticut
Hi Tom,
What hreed said is true, the random misfires are a bit more difficult to nail down. However, there are a few things you can try. Here is a pretty good writeup on how to go about resolving misfires:
SOLVING ENGINE MISFIRES.
Hope this helps. Good luck!
What hreed said is true, the random misfires are a bit more difficult to nail down. However, there are a few things you can try. Here is a pretty good writeup on how to go about resolving misfires:
SOLVING ENGINE MISFIRES.
Hope this helps. Good luck!
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Thank you for your inputs! I went to the "misfire" link and printed a copy. Looks like I've got my work cut out for me. I never dreamed there could be so many potential causes for my computer code!
Regards from Tennessee,
Tom Norman
Regards from Tennessee,
Tom Norman
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Random misfire
First of all removing the battery connection on a 1999 ranger will not reset the codes a scanner must be used to do this. Random misfires are cause by Ignition problems or fuel problems like bad wires or bad plugs or fuel related like partialy plugged fuel injectors if you have replaced the plugs and wire's a coil could also do the same most of the time if its not a plug or a wire its a injector. Someone with a good scanner can tell you what cylinder is miss firing. Hope this helps!
Sam
Sam
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From: Connecticut
Hi Sam, welcome to FTE!
I believe disconnecting the battery for 20 minutes or so will indeed clear the codes and reset the PCM on Tom's '99 Ranger.
Also, a code P0300 is a specific code that means different cylinders are misfiring at different times. So I don't think it really matters what kind of scanner is used to pull that code, because it is meant to tell us that there is a random misfire, as opposed to a misfire in a single, isiolated cylinder.
I believe disconnecting the battery for 20 minutes or so will indeed clear the codes and reset the PCM on Tom's '99 Ranger.
Also, a code P0300 is a specific code that means different cylinders are misfiring at different times. So I don't think it really matters what kind of scanner is used to pull that code, because it is meant to tell us that there is a random misfire, as opposed to a misfire in a single, isiolated cylinder.
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P0300
Tom
By definition a multi cylinder misfires will be a weak electrical, or more probably a lean mixture. Look for something else to limit the possibilities. Can you tell if the misfire occurs at higher engine speeds, idle when warm, or idle when cold. I have seen p0300 codes traced to weak valve springs (high speed), MAF (idles ok cold but misfires when warms up), all the time (bad ign. pack). So look for a clue and maybe we can solve it.
Dave
By definition a multi cylinder misfires will be a weak electrical, or more probably a lean mixture. Look for something else to limit the possibilities. Can you tell if the misfire occurs at higher engine speeds, idle when warm, or idle when cold. I have seen p0300 codes traced to weak valve springs (high speed), MAF (idles ok cold but misfires when warms up), all the time (bad ign. pack). So look for a clue and maybe we can solve it.
Dave
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Dave,
We experience a slight engine vibration/rough idle at initial start-up. After initial start-up, the engine runs smooth as silk and we experience no other symptoms at all.
Regards from Tennessee,
Tom Norman
We experience a slight engine vibration/rough idle at initial start-up. After initial start-up, the engine runs smooth as silk and we experience no other symptoms at all.
Regards from Tennessee,
Tom Norman
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I hate P0300 codes..
Tom, I am going to ramble for a bit. Something you can try is start it cold and put you hand by the tail pipe. You should feel a rhythmic flow of gases out of the tail pipe. If you are having multiple misfires you will feel “puffs” out of the pipe. (you’ll notice it) After it warms up and is running better try it again and see if you feel a difference. That will tell when its misfiring. As mentioned above reset the computer and see if that fixes it. If it doesn’t and it is still misfiring when cold. I would rule out ignition problems, valves, injectors, crank and cam sensors, gas, and water because it runs good at speed. and when it warms up. That would leave fuel mixture at idle. Then you can try cleaning the MAF and the IAC valve (80+k miles). I haven’t had much luck doing that ,but some have. (there are some instructions on the board for doing that). If that dosen’t do it My gut tells me it’s the MAF, but it is hard to tell at a distance.
Good luck from Alabama.
Dave
Good luck from Alabama.
Dave
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Dave,
We really appreciate all your help on this. I'll check the exhaust for "puffs" this coming weekend. I have already reset the computer and ran two bottles of drygas through the engine. So far no "check engine" light, but my wife says that the engine still shakes a bit for a couple seconds after initial start-up.
The IAC valve is new because that component died about 5,000 miles ago. I should have mentioned that the engine has about 85,000 miles on it.
I'll try and clean the MAF sensor and let you know what happens.
Thanks again,
Tom Norman
We really appreciate all your help on this. I'll check the exhaust for "puffs" this coming weekend. I have already reset the computer and ran two bottles of drygas through the engine. So far no "check engine" light, but my wife says that the engine still shakes a bit for a couple seconds after initial start-up.
The IAC valve is new because that component died about 5,000 miles ago. I should have mentioned that the engine has about 85,000 miles on it.
I'll try and clean the MAF sensor and let you know what happens.
Thanks again,
Tom Norman
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From: Connecticut
Another thought.
Leaky fuel injectors and/or leaky head or intake gaskets can cause engines to stumble (misfire) a bit when first started, and the stumble usually remains until these extra fluids are burnt off in the combustion chamber(s).
Leaky fuel injectors and/or leaky head or intake gaskets can cause engines to stumble (misfire) a bit when first started, and the stumble usually remains until these extra fluids are burnt off in the combustion chamber(s).
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I think in your case Dave is on the right track, you say that it runs fine when cold but bad when hot (to temp). Remeber when all cars had a choke, and if that choke stuck you didn't notice (except for high idle)until the car started to warm-up. Your computer uses a engine coolant temp.sensor - incomeing air temp.sensor ect. to do the samething by changing injector pulse width. I work on a crownvic once with a simular problem, and a simple temp. sensor change fixed it.
p.s. there is more that one sensor that reports coolant temp. one is for the guage or light in your dash.
also have you pulled your plugs to see what info they can give you about a rich/lean mixture.
p.s. there is more that one sensor that reports coolant temp. one is for the guage or light in your dash.
also have you pulled your plugs to see what info they can give you about a rich/lean mixture.
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I didn't have a chance to try the removing the negative battery terminal routine (yet).
While I was at AutoZone, we cleared the codes using their scan-tool.
So far, though, the "check engine" light has not come back on. If it does, I'll try removing the negative battery terminal and see if it resets the computer.
BTW---my wife's vehicle is a 1999 Ford Explorer, not a Ranger.
Tom Norman
While I was at AutoZone, we cleared the codes using their scan-tool.
So far, though, the "check engine" light has not come back on. If it does, I'll try removing the negative battery terminal and see if it resets the computer.
BTW---my wife's vehicle is a 1999 Ford Explorer, not a Ranger.
Tom Norman