Can't seem to narrow down misfire

[degride]

Guys-

Synopsis:

03 DII (meticulously maintained and set up for overlanding), 170k, HG done at 68k (due for another), used like a Rover should be used (trips with varying degrees of difficulty to BC, WA, OR, CA UT, AZ, NM, CO), oil changed every 3500mi, parts replaced as needed at first sign of failure, added CDL and other goodies. Plugs/wires (NGK/STi) changed approximately 40k ago.

Symptoms:

P0300, P0306 started appearing on our way home from Utah last week. Luckily we were close to home, <50 miles.

Attempted remedies:

Cleaned MAF (original MAF)
Verified wires are not the culprit (swapped 4 and 6 leads as well as used an inline tester)
#6 plug looks fine when pulled (could swap plug from #4 with #6)

Again, MAF is original as well as coil-packs. Pretty much everything else has been replaced including all ancillaries as well as new water pump, low-temp thermostat, new radiator and all new hoses. This truck has been taken care of. CKS has not been replaced nor has TPS.

My take might be coil pack or CKS. I could see how CKS could cause a misfire reading. Just not sure.

So what is the collective thought on what the likely top two culprits are?

 

[KyleT]

Swap coil packs and see if it follows.

 

[degride]

Did not even think about that (trying to over analyze the situation). Will do and report back.

 

[crown14]

Swap plugs 6 & 8 and try again

 

[SGaynor]

Your plugs and wires are 40Kmi old. I'd replace them.

They are the cheapest and easiest to replace, and you are due anyway.

FYI - go with Kingsborne wires (kingsborne.com).

 

[p-dawger]

You have 170k on your original MAF? I would start there...


I find every 20k I need a new MAF to take care of misfires...


Misfires come, replaced MAF and they have gone away...I think I am on my 5th and I have 250k.

 

[discostew]

If the misfire didnt move with the plugs or the wires then you might want to think about the exhaust valve sticking in the guide on that hole . Since it happens when its hot on a long trip , thats kinda when that stuff happens . You can check it by removing the valve spring and moving the valve open and closed while turning it . It will hang up if thats the problem .

 

[roverover]

Get it to someplace that can read your ECU live and see where the misfires actually are I've seen more than one with an 06 code and it was #5 that was bad usually wires but do coils at the same time

 

[Plain2000DII]

Having a similar problem right now as well, misfire always on cyl 1, heavy stumbling at highway speeds, could be a lot of things but I'm going the maf route first. if it turns out to be a head gasket, its going to be up for sale to the highest bidder. bidding starts $1 over scrap yard quote....

 

[discostew]

How could a mass air flow sensor cause a misfire only on cyl. 1 ? I want the old mass air flow sensors if you guys actually spend the money to buy them .

 

[degride]

Sorry for the delay in posting back. Travel schedule has kept me away.

It ended up being the coils. Replaced them and it started running like a 12 y/o Disco should run. The plug wires (STI Blue) look fine upon inspecting all of them.

However, now with a few hundred miles on the new coils, the dreaded codes have returned; p0306 and p0300. I'm glad, as it was running a little sluggish below 2k RPM with no codes and me scratching my head. So the next steps are:

swap 6 and 8 plugs to see if it at least does away with the p0306 code. If it does, then new plugs. If not, then perhaps MAF. Yes, 170k on original MAF is a long life on these trucks especially considering all the places mine has seen.

Will report back on this specific topic. On another note, four, yes four, P/S pumps in 1 1/2 years; three alone since March of 2014. Luckily the dealer has been replacing them under warranty even past the 12 month mark. The first time it went out, I was on my way down to the Arizona LR Rally and it puked on me at a gas station. My only option at that point was a dealer a few miles down the road. Gotta have thick skin with these things. Still wouldn't trade, burn, give it away.

 

[KyleT]

Your steering box is going out.

And maf failures are not that common.

 

[degride]

You know, I was wondering if it was the steering box. Need to add that to the list.

As far as the plugs, I went out to swap them and the connector on the plug on #8 snapped off in the socket. Went and procured eight new ones so we'll see shortly.

 

[degride]

Update:

After replacing all the plugs, she is back running like she should and I just turned over 171k on the clock. Still going strong.

So, in the end, it ended up being a combination of the coil packs and plugs.

 

[crown14]

I thought as much

 

[Plain2000DII]

finally got around to changing out the spark plug wires, misfire gone, runs as good as ever .... er...well you know. It was a four hour-ish job, didn't remove intake manifold, so maybe a hour was just for dicking around with the secondary air pipes. found a good write up with pics over the LRO site.