Single misfire: valve train inspection

[Jkid]

2001 Disco with 160k miles. Recurring p0306 with a p1319 thrown once (coincidence maybe). Runs rough at low rpm under load ( low speed in overdrive). Starting to misfire bad on acceleration now too. I had a pretty good exhaust leak at the manifold/pipe. Leak is fixed. My spark plugs appear to have a good amount of black carbon build up. I tried switching the plugs around and installed new wires, it did not help. I have not noticed any coolant loss or overheating.

I pulled the intake off so I could switch the injectors and coils around. Since I had all that off I pulled the rocker arm off so I could get a good leak down test reading with all the valves completely closed. (I’m waiting for my new tester to arrive since my HF tester was giving me inconsistent readings). I also pulled the lower intake off because a lifter fell out when I pulled the rocker arm. Is there anything else I should look at while that’s all opened up? I’m thinking of taking the valve spring off and seeing if the valve is sticking at all. I’m wondering if there is anything else I should look for while that’s all opened up. Any other ideas on the misfire that seems to be getting worse?

 

[Jkid]

Also.... the heads were rebuilt (at least planed, cleaned and valves checked) 30k miles ago when I did my headgaskets. I’m wondering if I should just replace the lifters on that cylinder since I’m there? Or maybe the springs, seals, guide....? Obviously I don’t want to get into throwing parts at it but if they aren’t too expensive and Im already there...

More info.... no vacuum leaks, replaced crankshaft sensor, maf has maybe 50k miles on it. Original O2 sensors and catalytic converters

 

[discostew]

Do a compression test and cylinder leak down if you have a tester

 

[Jkid]

Yeah my leak down readings were all over the place so figured I’d pull the valve cover off and try it with the rocker arms off and all valves closed. My first reading was 80%, but then all the cylinders on that bank we’re reading 80. That made no sense. Then they all started reading about 20% so the hf tester seems pretty inaccurate . So definitely somewhere between about 20 and 80% leakage haha. I’m waiting for my new tester to arrive now. I didn’t have a compression tester before I took the intake and everything off unfortunately. So I’m assuming a weak spring or sticking valve would show up on a compression tester but probably not a leak down? That’s why I was thinking about just pulling the springs off checking those and also manually checking the valve for sticking since I’m right there. Seems like I could tell if it’s sticking or not seating right. Of course I don’t know how to check for a weak spring. Not sure how to check a lifter though and I guess the push rods look straight...

 

[Jkid]

I got my new Leakdown tester today.... wow what a difference. The harbor freight one is pretty much useless, you might as well just blow compressed air in there with no gauge and just listen. The hf gauge seems to be good at telling if you might have a massive leak but don’t trust the percentage for anything. All cylinders under 10% but 3 of the intake valves were leaking as noted by the air bubbling out of the valve from the coolant that got in the head when I took the intake off. Cylinder number 8 had the only clean intake port and the only valve not leaking

 

[4Runner]

You could check your cam lift while your in there and look for a collapsed lifter. But the later is usually noisy. Finding a weak spring requires a different tester. Never tried testing springs on a head that had shaft mounted rocker arms.

 

[discostew]

Check that the exhaust valves aren't sticking in the guides. Put air in the cylinder once you have the rockers out. Then get the spring off and open n close the valve while you rotate the valve by rolling it between your thump and finger. If it's hanging up you will make it stick.
If you want to see if your cam is ok get the intake off it and look at the bottom of your lifters