I've been lurking here for about 6 months since I bought my truck, and this forum has been an awesome resource.

I've searched quite extensively, but I seem to be having a problem that I can't pinpoint the cause of, and I was hoping for some advice on what to try next.

Problem:

My '04 Disco II, 140k miles, with SAI, is throwing a P0304 (Cylinder #4 misfire) only on warm startup and idle. I have not been able to produce a misfire under load or at high RPM, even when trying to do so, and the truck runs smoothly after about 10-15 seconds of rough idle after starting, if it does it at all (which is only 1 out of 5 times or so, and only on hot start -- for example if I let the truck sit for about 1-1.5 hours or so while out at a restaurant).

I don't know if this is a coincidence, but this problem only started after I put some Techron fuel system cleaner through the tank and performed a Seafoam induction treatment, which produced lots of smoke, as usual.


I've cleared the P0304 code with my Scangauge about 5-6x now, and it has kept coming back intermittently. The SES light generally has flashed for 2-3 seconds accompanied by rough idle right after startup, then stays lit after the engine smooths out as described above. I am running a Motorad 180 degree Tstat, and the truck runs about 195-200 on the highway and 200-204 in town, in 90-95 degree Texas weather. I am running Rotella T6 5w-40.


I've done the following:

1. Checked Plugs and wires. I am running Bosch Platinum (replaced 1k miles ago, ran just fine prior to the fuel system and Seafoam induction treatment mentioned above) with STI 8mm wires in good shape. I've let the engine idle in the dark to watch for sparks, there is no visible arcing, and all plugs seem to be getting a spark.

2. Pulled the #4 plug and replaced it with a different one. The plug I pulled out was not fouled, and was gapped at .042 (which I think is correct for these trucks).

3. Checked for coolant in the cylinder head after letting the truck sit overnight. The truck has no history of eating or leaking coolant since I've had it. I did notice that the coolant reserve was a little low after replacing the thermostat, so I topped it off and it hasn't moved in about 150-200 miles.

4. Just to be sure, and on the advice of the forum, I pressure tested the cooling system with the kit from Advance Auto. The kit they rented me was brand new, and the system held pressure (15 psi) for a full hour.

5. I checked for vacuum leaks (smoke test, and by spraying TB cleaner to try to induce a stumble) but have not been able to locate any.



Conclusions I've drawn so far:

After doing some reading on here, I feel that the coil pack is probably in good shape, due to the fact that I have never gotten a Cylinder #7 misfire, and the engine doesn't misfire under load. The spark plugs are new and in good condition, so I don't think those are the problem either.

The cooling system pressure test pass, lack of coolant in the cylinder after letting it cool down, and the fact that the coolant level is stable lead me to believe that the head gaskets are still intact and the block isn't cracked.

There is no tell tale "diesel" sound to make me think that there is a slipped liner.

Being a Disco, my truck is slow as molasses, but the power delivery is linear through the range. I can floor it and it doesn't hesitate, and it revs smoothly.


Possible Conclusions:

Sticky Intake/Exhaust valve? I am not sure if there is a good way to test for this, but I have read that this can cause issues like this. However, a sticky valve would cause a misfire at higher RPMs if I am not mistaken, not just at idle. I am worried the Seafoam treatment might have broken some deposits loose and caused the valves to stick, but the code started showing up a few days and about 100-150 miles after the Seafoam treatment, so it seems unlikely.


Clogged injector? Again, I am wondering if there was some gunk in the fuel system that was freed by the Techron additive that is causing #4 to run lean on start up. I did, only once, while the low fuel light was on, get a second code P1319 (Misfire with Low/Empty Fuel) stored.


Today:

I put a full tank of gas in it today (premium, as usual) and it ran fine on the way to the gas station (cold start, SAI pump came on, then cycled off like normal, etc), when I drove it back from the gas station, when I started it roughly 30 minutes later to drive to dinner (still hot, no SAI kick on), but threw a P0304 code on startup after I started it on the way home from dinner about an hour and a half later (also still warm/hot, no SAI kick on). The truck drove fine on the way home, no hesitation, rough idle, or other weird issues.


I apologize for the novel, but I wanted to include all the facts. I'm stumped. Thank you in advance for your help and expertise!

 

Thank you for the quick reply -- it makes sense. I'll see if I can pressure test the fuel rail this weekend sometime. I took the rover to the gym this morning after reading your reply to see what would happen, and this time I got the same P0304 code on cold start, but not on hot start about an hour later....sigh. I'll post back with my fuel pressure findings. Thanks!

 

Figured I'd report back. I tested the fuel pressure on the rail, and it holds pressure. I borrowed my friend's inspection camera to have a look at the cylinder head through the spark plug hole, then swapped out the spark plugs again while I was at it.

The cylinder head was a little gunked up wtih carbon/black residue that was a little sticky/oily almost (from what was stuck on the tip of the inspection camera). The spark plug didn't seem abnormal.

The misfiring is intermittent, and the truck seems to work fine (most of the time) on a cold start. Warm starts after a heat soak seem to be where the problem is, and again, it goes away after 30 seconds at most (or with a little throttle), and runs fine until you shut it off again.

Could a gunked up valve cause this issue on startup? The reason I ask is that this issue seemed to come about after I ran some seafoam and fuel system cleaner through it, and I am wondering if it broke up some deposit that is now wedged in one of the valves. Perhaps the answer is more seafoam.....

Thanks again for any input you can provide!

 

I have been monitoring closely, and I figured out that I am, very slowly, losing coolant out of the reservoir, but I am not sure if this is related to the misfire or not. Temps on my ultragauge seem to be stable, and I don't seem to be having overheating issues.

I'll probably put a bit of dye in the cooling system and see if I can locate a leak, but I don't see anything obvious leaks or any coolant on the engine or underneath the vehicle.

I did the spray bottle test and watched the engine in the dark (again) to make sure it's getting a spark, and it is.


Another question: How much gas leakage (say from a leaky injector) would it take to cause a misfire? I did a string test after letting the vehicle sit overnight, but it didn't come out soaked with gas, and the plug wasn't wet either.

 

Had this issue a while back. It is an interesting situation.
Check my posts " Rough idling when cold. Smooth running when warm: My experience"
I only noticed rough starts that promptly disappeared after the truck warmed up.
And yes, it as enough to trigger a CEL which disappeared. I also wasn't getting a super
Pressurized cooling system that you can with a slipped liner or cracked block...BUT..if the crack is in the head AND it the intake valve area, you WILL NOT get a over pressurized cooling system because the intake valve is preventing high pressure.

Probably a coolant leak into your cylinder 4 ( P0304 ) via your intake head to that cylinder.

Anyway, to date, my problem hasn't returned.
Good luck.

 

A flexible borescope check into that cylinder will PROBABLY not show any moisture or obvious leak since it is minute. My hunch is that your coolant level is only noticeably low after a couple of weeks...maybe more.

 

Evn,

Thanks for the perspective, I'll check out your thread. If I am losing coolant, it's incredibly slow. I've been monitoring it and driven 100 or so miles with no noticeable drop, but I have been driving it only on short trips (5-10 miles). of late. The coolant seems to like to settle about an inch below the cold full line, but doesn't move much ( if at all) after that.

One question though -- if there is a crack in the head and I am leaking coolant into #4, shouldn't I be able to see a steam cleaned or "washed" cylinder head with the boroscope, even if the leak is slow?

 

Not sure....probably not in the very early stage since it's very slow.
Your suggestion about a dye/tracer in the cooling system sounds like a good idea like the ones that lite up with UV. That should show up all over your # 4 plug. Just will be hard to illuminate your cylinder and intake valve area.

 

Good suggestion, ill do that. Will report back once I run it a bit. Thanks!

 

Did you ever pinpoint the problem, Zeb? I have the same thing happening. I think I'll try to swap out the 4 and 6 injectors to see if my misfire moves.