Interesting P0300 Code on 2001 Passport

[chevyrulez1]

I got a MIL showed up on my 2001 Passport, and upon checking it the code scanner showed a P0300 (Random / Multiple Cylinder misfire)
I cleared the code and kept driving because I really didn't notice anything out of the way.
To make a long story short, it kept coming back. Since I have been working so much lately, and since I figured it could be caused by so many different things (I was thinking Fuel pressure, EGR, etc.) I thought I would just take it to the dealer to check it out.
Well, they checked it and said it was the spark plugs (doh!!) and that they had changed them and cleared the code. My wife goes to pick the truck up and they charged $181.40!!
They charged $68 labor and $17.50 per plug!! Dispite my checkbook and pride being hurt, at least it was fixed or so I thought.
Two days later the check engine light came on again but started blinking on and off but not showing a trouble code. After searching long and hard on the Internet, I could not find any information about this.
I called the dealer back and talked to the service manager, and he told me that when the MIL blinks, that means that the computer has picked up on a problem and is monitoring it. He said that if it continued for 3 start / stop cycles then it would lock the code in, so he told me to keep driving it untill the light came on and stayed on.
Well, a day later it came back on and guess what, P0300 again! Cleared the code and it came right back.

I figured it was time to investigate further, and broke out the Haynes manual and computer to research the problem. Heard about the Ion sensing module that actually detected the misfires, etc. but still could not find out any details on how the system worked or how to troubleshoot it. In my search, thinking it might be a bad coil, I went to a couple of auto parts websites to see how much they were, then I realized that there were actually two different ignition coils for this vehicle. There is one part number for Cylinders 1 through 5, and a different number for cylinder 6. So I pulled my coils and checked them with a multimeter, etc. and found out that indeed one coil did have a different number on it than the others and was slightly shorter than the others, but it was on cylinder #1 instead of #6. To make an already long story a little shorter, I swapped the coils and cranked it up and she purrs like a kitten. Drove it all day today and no more check engine light. Apparantly the mechanic at the dealership put the wrong coil on the wrong cylinder, or someone had done that before I got the vehicle and they didn't catch it. Anyway, since the coil connector boot is shorter it must have not been making good contact with the plug.

Since I had such a heard time figuring this one out, and also had trouble finding any detailed information on the net after two days of searching, I thought I would post this to perhaps save someone else a little trouble and money. And for future problems like this one, I have a Factory service manual on the way since I am planning on keeping this vehicle for a long time.

[amigo-2k]

how many miles do you have on the truck?

My guess is that the intake manifold gasket is broken (super common which causes mis-fire codes).

[trooperbc]

Originally Posted by amigo-2k

how many miles do you have on the truck?

My guess is that the intake manifold gasket is broken (super common which causes mis-fire codes).

ryan... come on...everytime you hear misfire you jump immediately to that intake manifold gasket response.

in this case, he's telling you he found the problem and fixed it:
the #6 & #1 coils were swapped; he installed them correctly and solved his problem:::

So I pulled my coils and checked them with a multimeter, etc. and found out that indeed one coil did have a different number on it than the others and was slightly shorter than the others, but it was on cylinder #1 instead of #6. To make an already long story a little shorter, I swapped the coils and cranked it up and she purrs like a kitten. Drove it all day today and no more check engine light. Apparantly the mechanic at the dealership put the wrong coil on the wrong cylinder, or someone had done that before I got the vehicle and they didn't catch it. Anyway, since the coil connector boot is shorter it must have not been making good contact with the plug.

now. if he posts back in a week and says that didn't *really* solve his problem, then let's all jump on the img bandwagon.....

chevyrulez1... thanks for the writeup


//bc

[amigo-2k]

I think I read mis-fire and then just started typing my canned answer. oops!

[trooperbc]

LOL



//bc