Hey,

I am at my wits end and I am tempted to blow it up, sink it, or trade it for a burro. I recently retired my Disco 1 that had over 260k miles and picked up a replacement disco.I now have a 2000 Disco and besides the random 3 amigos I am getting a po305 code, cylinder 5 misfire. It is not constant and it will appear when I accelerate up a long highway hill and then as the throttle eases out I will get my favorite check engine light. I will list the things that I have checked.....

1. the head gaskets were replaced about 7k miles ago. There was a faint coolant smell from the engine bay but the thermostat was coming apart and I replaced it with the chevy thermostat and I am running about 183 degrees all the time and no more coolant smell. I am loosing zero coolant since I repaired the problem.

2. I figured it might be the plugs so I pulled all the plugs (ac delco) and replaced them with bosch 2. The old plugs looked fine with no abnormalities including #5

3. Since I was still getting the check engine light every now and then decided to replace the plug wires today with STI wires. I have the air crap on my heads but I was able to swap them out without removing the IM and it took about an hour.

4. So I thought I might get lucky and it would be a bad wire so I went to the usual entrance ramp on the highway and when I reached the top of the hill I got my little buddy light as usual.

5. I had put some sea foam in the tank when I got her about a month ago and cleaned the intake with seafoam at the same time. I thought what the hell and did it again today and after fogging out all the joggers around my house I tried the old entrance ramp again and same code popped up.

6. At this point I decided to pull out the old compression tester out and give it a shot. I hate pulling the tester out because everytime I do it never turns out well. So I checked all the cylinders and I got lucky for once. They all were within 2% of each other and each cylinder is almost pulling 180.

So I am not loosing coolant, compression is fantastic, new plugs, new wires, seafoam,ect. So I am stumped at this point. What next should I look at? Should I go ahead and replace the coil for #5? The only thing that I noticed was the coil bracket was not bolted down nor was the silver air pipe. I replaced the missing bolts and tightened everything back to the way it should be. I talked to the previous owner today and he said that he would get p0305 every once in awhile. Maybe every month or so but I am getting it more frequently. He said that he thinks that it would only do it when it would get below half a tank but he can't remember. Please help

Here are some pics. My compression number on #5, all the other cylinders read just about the same. The second pic is the plug from #5


All th other plugs look the same

 

Sounds like a misfire under load. Since the coil was not grounded properly I would think the coil pack. Have someone check the misfire counter on scan tool, at idle. Also pressure test the cooling system over night with that spark plug removed, see if coolant comes out in the morning. Switch that fuel injector between cylinders, see if the misfire moves.

 

Yeah it seems to do it only under load. I forgot to say that I have pressure tested the system a couple of weeks ago and let it sit for a day and no pressure drop. Do I have to pull the manifold to swap injectors?

 

I have 109k miles

 

Here is a video of when it does it. Slight long highway incline and then I get the misfire around 50 mph when it levels out and the load is lessened. http://s205.photobucket.com/user/ach...018ac.mp4.html
This time it threw three codes[URL=http://i205.photobucket.com/albums/bb188/achtungschnell/AC847B78-EB59-4788-8869-34A4C47319DA-5129-000003B4A21F2774_zpsdac018ac.mp4][IMG]http://i205.photobucket.com/albums/bb188/achtungschnell/th_AC847B78-EB59-4788-8869-34A4C47319DA-5129 P0305 the usual, p0303, and p1300. That is the first time I saw p0303 but I am guessing that it was from the seafoaming yesterday. Should I pull the manifold, replace the coil and swap injectors around next?

 

here are the codes

 

That plug looks rich.
Replace the O2 sensor on the #5 side.
That is sensor 1 on the driver's side.
Way too much rich carbon on that plug.

Put high detergent oil into the engine.
You may have a valve sticking which is causing misfires.

 

the upstream sensor, Is that the one you mean by 1? I am running rotella and the previous owners did too.

 

I think I might have come to a guess tonight. I think I will change the coil tomorrow. I constantly can throw #5 misfire and I threw a #3 and #8 randomly the other day and the #8 was while it was raining hard. I am guessing that coil may have a crack or just weak. Also when I got home tonight at looked under the hood in the dark. I can see the spark plugs firing through the porcelain and #5 had a random rhythm and was not as bright. Since the coil bracket was not bolted down I am guessing that it may have been cracked or something between the firewall.

 

Did you replace the coil? How did it help?