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Cylinder 6 misfire


fast240z

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2000 ranger 4x4 3.0L with 170k miles. Just bought the truck a month ago and it's been problems from the start. Cylinder 6 started misfiring badly at idle but truck runs fine otherwise. ForScan shows cylinder 6 misfire 5% of the time and 0% misfire for any other cylinders. I've replaced plugs, swapped the coil pack and #6 injector for a junkyard set (tested good), but the problem still persists. Anything else simple this could be?

I haven't swapped the plug wires yet but that's next on my list.
 


adsm08

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The 3.0s around that year seem to have issues with the valve seats, which can cause a misfire at idle. It has popped up here a few times in the last 6 months.
 

fast240z

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I read a few threads about valve seat recession and I'm pretty sure this is the problem I've got. I'm going to buy a compression tester and will check #6. If low, there's a set of heads I'll pick up from eBay.

Stupid used vehicles.
 

heavy breather

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I would check the plug wires sooner than later. They can cause horrible mis fire problems. For now just switch the one on 6 with a different one and see what happens.


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fast240z

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Checked compression and #6 is at 60 psi while the rest are at 115-120 psi. I added oil to the cylinder and the compression only rose a few psi, so my money is that the valve seats have recessed. Time to order new heads.
 
pjtoledo

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you might want to pull the valve cover to check the rocker arm, pushrod, and lifter.
 

fast240z

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Follow up - I determined the head experienced valve seat recession after doing a wet compression test. Cylinder 6 was around 60-80 psi, while the rest of the cylinders were 115-120 psi. I ordered two rebuilt cylinder heads from ebay and replaced both sides and gaskets this week, finishing last night.

The truck fired right up after the head swap and immediately idled smoother and has much more power than when I bought it a month ago.

Let's pray there's no more issues with this dang thing.
 
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