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Old 12-20-2008, 08:41 PM   #1
scostagl
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2004 Discovery Engine Misfire - could it be the head gasket


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Hi everyone,

I've had a P0306 (#6 cyl engine misfire) intermittently now for about 5,000 miles. The check engine light (with this code) usually comes on when I start the rover and drive it before letting it warm up - but this only occurs maybe only 2-3 times/month and the CE light it will eventually turn off after a few driving cycles. It will run rough though a bit when the CE light comes on - but smoothes out after about 30 seconds.

Anyway, I've also noticed some coolant loss that started around the same time the P0306 code started coming on. And I hear gurgling noises from the radiator too. Coolant loss is getting progressively worse, about a pint every 300 miles or so.

Its a 2004 Rover and has 56k miles on it. I've changed all the plugs (with correct gaps) and wires, cleaned the MAF, new air filter, and performed the seafoam procedure - all recently done. No change after all this work, as I still get the intermittent 306 code. No milky oil...looks fine. And I don't see any rad fluid leaks, however I can sometimes smell it after I park it from a drive.

So now I'm thinking that it must be a small head gasket leak. I checked the compression on cyl 6 and cyl 4, but both were at ~150psi (#6 was 146, #4 was 150).

Any ideas? I don't want to start the head gasket job until I'm sure that it is the issue. FYI, I always use premium gas, and all maint. is up to date. Rover has never overheated, however I sometimes use it for heavy towing (6500lbs).

Any ideas would be appreciated. I'm close to bringing it to the stealership to get a diagnosis as I'm running out of ideas.

Last edited by scostagl; 12-20-2008 at 08:51 PM.
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Old 12-20-2008, 09:29 PM   #2
joey
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If you take it to the dealer I hope you have an extended warranty, because they will try to sell you a new engine.

What does the #6 plug look like compared to the other plugs? If real clean then it may be a bad head gasket leaking antifreeze.

http://www.aa1car.com/library/reading_spark_plugs.jpg
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http://www.usarovers.com/ (call for Rover parts ask for Nathan 502-222-5859)

Rover Radio issues or IPOD Adapters http://home.valornet.com/splacket/index.htm

EAS fault http://www.rswsolutions.com

When working with GEMS vehicles. Never try to locate a misfire by pulling plug leads off - pull the injector connector instead. Otherwise you can blow up the ECU.

Secondly never swap ECUs between vehicles to test them, because both vehicles and ECUs may stop working, and you'll have to have them all reset by a franchised LR dealer (ouch!).

To download the RAVE manual, follow this link http://www.landroverresource.com/
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Old 12-20-2008, 10:06 PM   #3
scostagl
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Just pulled the plugs tonight....they all looked the same to me, then again, they were replaced about 3k miles ago when I did the wires.

Yeah, I wouldn't be surprised if they wanted to sell me a new engine. I was hoping to get at least 100-130k miles out of this engine until I needed a new one....and then I plan on a diesel.
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Old 12-21-2008, 07:30 PM   #4
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Could also be a bad Wire... even if you changed them, there could be one bad one. I always keep old wires for at least 3 months to make sure I will not need one.

As far as coolant... keep filling it. and drive unless you want to pull the top end down.
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Cincinnati OH
http://www.customroveraccessories.com Home of the New D2 horn buttons!
02 Disco
13 Jaguar XF
97 Disco - Out to pasture due to rusted frame

http://www.usarovers.com/ (call for Rover parts ask for Nathan 502-222-5859)

Rover Radio issues or IPOD Adapters http://home.valornet.com/splacket/index.htm

EAS fault http://www.rswsolutions.com

When working with GEMS vehicles. Never try to locate a misfire by pulling plug leads off - pull the injector connector instead. Otherwise you can blow up the ECU.

Secondly never swap ECUs between vehicles to test them, because both vehicles and ECUs may stop working, and you'll have to have them all reset by a franchised LR dealer (ouch!).

To download the RAVE manual, follow this link http://www.landroverresource.com/
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Old 12-22-2008, 07:39 PM   #5
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Funny....I had ordered another set of STI wires just to check this. Unfortunately, after changing the wire I'm still getting the #6 misfire. I just ordered my gasket set and head bolts today to do the job after xmas. I'm a little disappointed that I'm having these issues at <60k miles, but the only other thing I can think of would be a bad coil....but the gurgling, loss of coolant and the bit of white smoke at start-up is really pointing me in the direction of a head gasket leak. I wouldn't be surprised if I find a small breach on the gasket adjacent to cyl 6 when I pull the heads.

I'll post with any progress after I finish the job.
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Old 01-21-2009, 09:21 PM   #6
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I performed a compression test, and the numbers don't really indicate a gasket leak....or do they?

Test was performed after truck was fully warmed up, all plugs removed, fully charged battery with throttle wide open.

#2:155
#4:143
#6:144
#8:136

#1:151
#3:150
#5:146
#7:142

What concerns me is that according LR, I thought that all my readings should be close to 180psi as this is a high compression engine. The bigger issue is that cyl #8 is over 10% difference in psi from the others. When I put a bit of oil in #8, the psi rose from 136 to 160....which could indicate a worn ring. :(

The bottom line is that I'm consistently getting the P0306 (misfire in #6) now almost every morning during startup, but the compression in that cylinder is actually decent (144psi).

Other things to note: I frequently smell burning coolant (but I can't see any leaks)....I constantly hear the coolant "sloshing" sound...and the engine runs rough for about 20 seconds after I start it, and it is usually worse in the cold. It smooths out after warming up, but it still doesn't sound like it used to.

Sorry for the long post, but I'm really close to just bringing it to the stealership to get a diagnostic before doing anything else (I've already replaced plugs, wires, cleaned MAF). thanks for any insight you can offer!
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Old 01-21-2009, 09:30 PM   #7
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Could be several things unfortunately. A slipped liner, head gasket, carbon build up on the exhaust valves.... hmmm try doing the seafoam treatment via the drivers side vacuum line going into the intake... cheap test. If it blows a bunch of black smoke, it could just be carbon build up causing the issue.
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Cincinnati OH
http://www.customroveraccessories.com Home of the New D2 horn buttons!
02 Disco
13 Jaguar XF
97 Disco - Out to pasture due to rusted frame

http://www.usarovers.com/ (call for Rover parts ask for Nathan 502-222-5859)

Rover Radio issues or IPOD Adapters http://home.valornet.com/splacket/index.htm

EAS fault http://www.rswsolutions.com

When working with GEMS vehicles. Never try to locate a misfire by pulling plug leads off - pull the injector connector instead. Otherwise you can blow up the ECU.

Secondly never swap ECUs between vehicles to test them, because both vehicles and ECUs may stop working, and you'll have to have them all reset by a franchised LR dealer (ouch!).

To download the RAVE manual, follow this link http://www.landroverresource.com/
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Old 01-21-2009, 09:36 PM   #8
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Thanks for the quick response. Yeah, I forgot to mention that seafoam was the first thing I tried....with no change. Ran a few bottles through the gas too. Think I should just bite the bullet and pull the heads? I'd hate to do the job and still have the same issues...
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Old 01-21-2009, 10:10 PM   #9
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anti freeze smell is probably the back of the intake manifold, or near the water pump.

gurgle sound is because you have gotten it low on anti freeze and the heater core has an air pocket.

The other issue could be a head gasket, but if you do tear it down, check the sleeves first, then have the heads reworked while your there or it would be a waste of time.
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Joey
Cincinnati OH
http://www.customroveraccessories.com Home of the New D2 horn buttons!
02 Disco
13 Jaguar XF
97 Disco - Out to pasture due to rusted frame

http://www.usarovers.com/ (call for Rover parts ask for Nathan 502-222-5859)

Rover Radio issues or IPOD Adapters http://home.valornet.com/splacket/index.htm

EAS fault http://www.rswsolutions.com

When working with GEMS vehicles. Never try to locate a misfire by pulling plug leads off - pull the injector connector instead. Otherwise you can blow up the ECU.

Secondly never swap ECUs between vehicles to test them, because both vehicles and ECUs may stop working, and you'll have to have them all reset by a franchised LR dealer (ouch!).

To download the RAVE manual, follow this link http://www.landroverresource.com/
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Old 03-26-2009, 01:07 PM   #10
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So, just to follow up on this. I ended up replacing both head gaskets. What a PITA job....about a 20hr job in total. Anyway, what was interesting was that the old gaskets looked ok to me...no noticeable tears or holes that would allow blow-by. The heads / valves were also in decent shape, although it was very clear that something was going on in cyl #6 (where I had the recurring mis-fire). It was much cleaner than any of the other cylinders, likely indicating entry of coolant. All the other cylinders had an even amount of carbon build-up but #6 was clean. Anyway, I checked that all the clyinder sleeves were also in place (all good) and I didn't notice any cracks or warping on the head nor cyliner walls. After a thorough cleaning of the heads and block, I polished everything and it looked new. After new gaskets and bolts (torqued to spec, of course) it is definitely running smoother and I haven't had a CE light in a week....until this morning! #6 misfire again. I'm pissed! The only thing I can think of now is that I must have a small crack in my block on that cylinder, or perhaps the head is slightly warped in that area. Anyway, the truck is running much smoother, and the CE only came on this morning when I quickly put the car in gear after starting it (I usually let the idle come down - about 7-10 seconds or so after initial start - this time, I didn't).

Anyone have any other ideas? At this point, I don't think I'm going to tear in to it again. I'll just live with any issues and drive this thing until the engine dies. At that point, hopefully it will be time for a new truck anyway!

Last edited by scostagl; 03-26-2009 at 01:12 PM.
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