1, 2, 3 Cylinder Misfire

[Saucer_Face]

Hey y'all looking for some advice. I have 2006 ranger 4.0L that is consistently misfiring all on one side of the engine. The CEL is on for the misfires and a lean condition on that side.

Truck still starts and drives, but engine performs poorly, no power on acceleration.

I've confirmed the spark plug wires are in the correct order, and there is good spark getting to these cylinders. Plugs are new, so hard to tell, but look a bit blacker on the misfiring cylinders.

Compression tester shows cylinder 1 @ 75psi, cylinder 2 @ 80psi, cylinder 3 @ 100psi. Cylinders on the opposite bank are around 150psi (on average).

Leakdown test shows cylinder 1 & 2 to have about 45% leakage. Cylinder 3 @ 20%. Nothing significant found on the other cylinders. I could only hear air escaping on cylinder 1, and it was from the exhaust pipe. So I'm thinking that cylinder has a bum exhaust valve.

I'm wondering though, low compression on two adjacent cylinders makes me think head gasket. But I didn't get any bubbling in the coolant reservoir or rad with the leakdown test. I also haven't seen any other tell tale signs of hg failure: no coolant loss, oil looks normal, no smokey exhaust. Is it still possible to have a hg issue?

What about a timing issue? Like if the camshaft chain on this side of the engine was slack would it cause issues like this?

Thanks for any ideas you guys have on this.

 

[RonD]

Cam is out of time on passenger side, but leak down test should have been OK, 10%
(how did you test for both valves closed on leak down?)
So more than likely 3 burnt exhaust valves on passenger side, not head gasket as that doesn't lower compression that much, and as you said no cooling system symptoms of that

The question would be why burnt valves on one side but not the other
Lean code on that side is from the low compression misfires so not diagnostic, its a symptom

How many miles on the engine/head?

Exhaust valves burn from heat of course so constant lean condition can do that, but would have had the Lean code way before(months) any damage would have occurred

Bad seats, factory defect on that one head
Bad rockers, valves not rotating on each cycle, factory defect
Bad valves
But any of these should have occurred well before 100k miles

 

[Saucer_Face]

Hey Ron thanks for the quick reply. This is my first time trying the leakdown test. I assumed both valves are closed at TDC? I placed the cylinder being tested at TDC by rotating the crankshaft by hand, watching a carefully placed screwdriver rise. Definitely wasn't foolproof, sometimes I found I was a bit off with positioning. So I repeated the test a few times to check my results.

As far as I know the engine is still original with 146k miles.

I did ground the vehicle immediately after the CEL thrown, but could it have been running lean for a long time without having thrown any codes?

 

[RonD]

No, it would throw a code as soon as it was lean but still being compensated for by the computer, so cylinder wouldn't be running lean, just a fuel trim issue at that point


If the cam was out of time on that bank then the crank TDC would be off

While doing the leak down you could have moved the crank one way and then the other to see if it sealed better as the cam moved a bit one way and then the other, that would confirm Cam timing being off on that bank

 

[Saucer_Face]

Oh! I didn't think about that at all. I'll have to run another test and try that! Thanks, Ron.

 

[funguy26]

there's some wrong with the engine under 100psi means the engine is worn out and due for a replacement.