I am posting this because just about everyone who had these symptoms and posted on forums never followed through and posted their results. The following is my own account. It is long in an attempt to be thorough.

I was headed out of town with my boat and "Bruiser", my 99 Disco2, when it started running like crap and the check engine light started flashing and then went solid. I pulled over and ran the codes (amazon sells code readers for $25)- P0300, P0305, P0306. I checked my Fuzzycode app (free) and it tells me 0300 is misfire on multiple cylinder, 0305 is misfire on cylinder 5, 0306 on cylinder 6.

A little background- at 70k new plugs, wires. Mobile1 synthetic every 5-10k with k@n oil filter. Sitting at 90k now. Just finished a long winter here in AK, and it's freezing at night and hitting 50 in the day, which is the perfect recipe for water in the gas. I had just ran the tank dry and filled up with Premium (that's $90 a fill up here.)

I bumped around a bunch of forums looking for a solution. They ranged from water in fuel to bent valves. Blown head gasket but I wasn't losing antifreeze other than the little bit around the intake manifold- that is on my to do list.. Bad plugs/wires but mine are only 20k old. Nowadays maybe. My wife's Hemi likes 16 new ones every 10k. I liked it better when it was every 60k. Clogged injectors was common. Discomike tells people to dump trany fluid in their gearbox to clean it up. The problem is, nobody ever reports back. Did the engine fail 10k later? Yah.

I bought "Bruiser" from the nicer part of Scottsdale, but it dawned on me that people losing their condos don't generally care about putting premium unleaded in their rigs. I decided to go the Seafoam route. I hadn't Seafoamed anything before. I found a funnel and pulled the hose that connects the valve cover to the intake manifold on the passenger side. You are supposed to dump this into the intake. It's a relatively big hose, but finding a funnel that would fit was a chore. I started it up and started dumping... slowly. It was supposed to take a minute. I shut off the engine and dumped another can in the gas tank. That was a quick $20. Half hour later I ran it down our road. The smoke pouring out would bring the fire dept., so I figured i would give them a moving target. I ran high consistent RPMs but wasn't rowdy. Ten minutes later and it all but cleaned itself out. There were 8 trouble codes this time- misfire on every cylinder basically. I reset and went for a test ride. No trouble codes. It ran a little rough once, but didn't trip the check engine light.

P0300 vs Seafoam? Seafoam-1, P0300-0. If I get the same code again I will post any results. I will probably change the plugs on the way out of town tomorrow, just to be safe. It's a long drive.

 

Last time I used seafoam I had to change the plugs out, and mine only had 10,000 miles on them.

 

This is not rocket science, you have misfires and additives won't cure it. Who's plugs and wires did you last install, what octane gas are you using? By the way, doing and induction cleaning with Seafoam will not kill plugs.

 

Seafoam, or just plain luck got me another 200 miles with zero problems. But once the truck sat for a few days the SES light came back on at startup. #6 misfire. I pulled the plug wire off and charcoal fell out of the boot. That might do it.

I then replaced the Bosch Super Plus Plugs with +4s, figured the plug wasn't the culprit, but it couldn't hurt either. Glad I did as none of the plugs had been torqued properly and one was finger tight. After that everything ran great. I have yet to replace the wires, as they are on order.

Mike, the Premium available here has an octane rating of 90. The wires are generic.

 

You lucked out if its just a set of new plugs/wires! I had more/less the same missfire issue on my 99 D2, solved by replacing one coil and getting the injectors cleaned, after replacing plugs/wires to no avail. The bonus for me was that i have regain way more power than I had before the problem showed up, possibly had dirty injectors for a while. Dunno.

 

I think my Disco, "Thor", is your Disco's twin. I just picked it up from a public auto auction and got three codes: P1179, P0300, and P0305.

I'll try the plugs and wires first and report back on the progress. I bought a composition book to log Thor's journey. Hopefully, I can help him avoid Valhalla, lol

 

P1179 is fuel mixture. That's a vacuum leak, air filter type issue? I am not sure the misfire is connected unless it's a bad cat caused by the misfire. Changing plugs/wires is a good place to start, but you may have more than one problem to troubleshhot. Let us know how it goes.

 

Phatduc, I noticed significant power gains as well. Obviously the misfire sucked power, but it may have been the Seafoam that cleaned things up a bit?

 

I'll post up my P1179 journey up on another thread(funny stuff so far).

Friday or Saturday I may change the plugs and wires; I'll let you guys know what that does for the misfires.

Think I should pour in an injector cleaner fuel additive while I'm at it?

 

A lot of guessing going on here, if you still need/want some help, send me your number and I'll call you.