Misfire Mystery
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4wd High
Joined: Nov 2014
Posts: 9
Likes: 0
Misfire Mystery
I have a 2004 Disco II with 120k miles, and it is encountering misfires. The plugs and wires have been replaced, the O2 sensors and catalytic converter were recently replaced. The head gasket and items relating to cooling have been replaced within the last 20k miles. The misfire happens after about 30 minutes of driving and is primarily on cylinder 4, every now and then cylinder 6. My mechanic has done extensive compression, leak, and cylinder testing, and is stumped. The truck does not overheat, when all of this is occurring the temp stays at 194. The mechanic does not want to just throw parts at it, so we are looking for ideas. Thank you in advance for your help.
Recovery Vehicle
Joined: Jun 2017
Posts: 1,238
Likes: 240
From: Alabama + Vegas + Texas
Swap the locations of your misfiring fuel injector with a non-misfiring fuel injector to see if your misfire location/code moves.
Swap the locations of your coil packs to see if the misfire location/code moves.
Check your fuel pressure if the above doesn't identify a problem. Low fuel pressure might be a fuel check valve, fuel pressure regulator, or fuel pump problem (or clogged fuel rails).
You can do all of the above diagnostics without buying any new parts.
I'm a big fan of free diagnostics locating the precise problem before throwing parts at the issue...though I get that there are moments where it makes sense to simply try a cheap part.
Swap the locations of your coil packs to see if the misfire location/code moves.
Check your fuel pressure if the above doesn't identify a problem. Low fuel pressure might be a fuel check valve, fuel pressure regulator, or fuel pump problem (or clogged fuel rails).
You can do all of the above diagnostics without buying any new parts.
I'm a big fan of free diagnostics locating the precise problem before throwing parts at the issue...though I get that there are moments where it makes sense to simply try a cheap part.
Last edited by No Doubt; Jul 18, 2017 at 11:18 AM.
Recovery Vehicle
Joined: Mar 2016
Posts: 856
Likes: 154
Might try this
Blow the cobs out of it. Take it out on a lonely stretch of road and give it hell for about 10 miles. I had a persistant no. 7 misfire. I tried everything. Then one day i was pi**ed and took it out. It worked.
Rock Crawling
Joined: Jun 2016
Posts: 374
Likes: 66
From: Virginia
Exactly. I run a can of seafoam in a half tank of gas in every one of our vehicles every 3000-5000 miles. Works great.
Baja
Joined: Aug 2013
Posts: 5,845
Likes: 368
From: Near Bordeaux, France
............... coil packs are 'wicked' for most mechs eh.
