Hi all,
looking for any advice I can get on a 2004 disco 2. I have a cylinder 4 misfire. The truck will idle and run all day and not throw a miss fire code unless you take it above 2250 rpm or put it under a heavy load like climbing a hill. Sits and idles great. No miss at all.. Really weird.
Here is everything I have checked and done.
Checked injector pulse. No problem there.
changed cylinder 4 injector. Did not fix the issue.
Switched coils. Did not fix issue.
Changed plug wires. Did not fix issue
Swapped cylinder 4 plug with cylinder 2 plug problem stays at cylinder 4.
Continuity tested injector 4 wires back to ECM. Both wires checked out fine.
there are only 2 things i can think of now and thats a funky cam position sensor but i would think this would cause a random misfire and not only on cylinder 4 or my bigger fear which is a problem with the ECM.
anyone have any ideas or have seen this before?

 

Coolant leak or oil leak into the cylinder? How did the plug look when you pulled it?

 

Pull the plug from 4 and check to see if it is wet. another test is to take a look into that cylinder with a boroscop, cheap USB type hooked to phone works fine... Do this when the engine is warm, look for bubbles coming in through the top of the combustion chamber. Sounds like cracked block behind 4. Been there done that.

If you are not missing any coolant and the plugs are clean then I would suspect worn cam shaft. Been there done that too. Could be caused by either low oil pressure or running 5w30 synthetic oil.

 

plug looks perfect! Nice creamy tan color. Appears to be burning beautifully. No smell of burning antifreeze in the exhaust fumes either.

 

when we first bought the truck it had a leaking head gasket. Not leaking into the cylinder but down the back of the driver's side block. Pulled the heads and had them checked for cracks and ground flat. Machine shop said ther were only about 1 thousands out of flat so they ground them flat. The cylinders all looked great. Still had the hash marks in the cylinders from the original machining. Previous owner said the engine was replaced about 30,000 miles before we bought it. So I don't really think it's a cracked cylinder. Truck ran great for about a month after head gasket job and now all of a sudden we got this cylinder 4 misfire issue. I did not change the cam as it still looked good. Cleard all the oil ports in the rocker rail also just to make sure oil flow was good. Any other ideas?