random missfire

[mark D]

random missfire and coil refit

I keep getting a random miss fire code and miss fire on cylinder 1, on my 02 discovery.
Ive changed the O2 sensors, new plugs, wires are good, checked vacuum running 18.5 pounds, the scanner is showing 19.5 to 20.5 which is telling me the computer is running lean on the LFT bank.

I"m thinking coil pack, of bad injector

any input????

 

[Disco Mike]

What are the exact fault code numbers and how do you know your wires are good, what brand and size are they.

 

[mark D]

Not sure of the wire size. they were replaced by the previous owner from what he said just before he sold it to me a month ago. I get P0300 once in a while and P0301 every time.
I replaced the before O2 sensor and got that code to clear.

I pushed a black split wire smurf tube (wire harness tube) to isolate tube back to the coil on the #1 plug wire in case it was grounding out, seeing as the coil pack is so fun to get to.

 

[mark D]

Thanks Mike. I have a more comprehensive in put for you that may give you more insight into the working of my Discovery 2.
I lost the last post I made??? so I have attached a word doc with the scanner results on it. You asked about the plug wires they are 7mm high heat resistance.
vacuum pressure is 17.5 and compression is 125 PSI give or take 1 or 2 pounds.

 

[Disco Mike]

What about the compression on the other cylinders, need to have something to compare with.

 

[mark D]

#3 is 124 #5 is 126 #7 is 125
#2 is 1241/2 #4 is 125 #8 is 125

They are pretty darn close.
has 145,000 on it
I want to do a head job later after I get the smog and it cools off in the fall.

 

[Disco Mike]

Low numbers but most likely due to a slightly inaccurate gauge, but consistant.
So, if it were mine I would look closely at the wires especially if they are inexpensive 7 mm wires that normally don't hold up well with our engines heat.
If you want some help, PM me your number and I'll call you.

 

[mark D]

Mike, thanks for your help last week. After the process of elimination I have cleared the codes on my 2002 Discovery.

After changing the #1 spark plug wire and #1 plug, I still had the same codes. P0300 and P0301. After talking to you, I ordered 2 new coil packs and went to work shoving my hands and socket wrenches back behind the intake and fire wall.
After removing the coil pack I decided to change the spark plug wires. As a cost savings I used less expensive 7mm wires in case the code issue was not resolved. I saved about 3/4s of the cost of 8mm wires and for now is was a another guess seeing as I was still in diagnostic guessing mode.

You were right it was the coil pack. I cleared the codes and along the way I repaired some of the wire harness that was fatiguing.

I am running -3.1 on my O2 sensors so it appears I am within standards.

Next issue change my U joints on the drive line so I don't pole vault on the FWY.

 

[mark D]

Oh and start saving for 8mm wires

 

[Disco Mike]

Consider the 8 mm silicone STI wires sold at British Parts of Utah at $70 a set.