Hey everyone first post here, I’ve got a PO 306 misfire in my 04 V6 ranger with the 3.0 engine. I think it’s gotta be the valve recession or the heads as it happens only at idle and wobbles for a minute before returning to normal just like the other people described, and it doesn’t do it if I hold the gas down and keep it above 1500 rpms or so. I’ve had spark plugs and wires and coil pack replaced by my mechanic and it didn’t help . I doubt it’s injectors or anything like that. I don’t really have the tools or time to tear this thing apart, how likely is it that it’s valve recession?

I’ve been driving it for a few months and it happened after a month and in the month or two since it started misfiring it only got a little worse in that it happens a little quicker. If I ignore it what happens? How long do I have before I drop a valve? Will I still continue to wear out the heads and risk dropping a valve if I keep the rpms high and stop it from misfiring? What’s the best course of action here, it’s really not a bad truck besides this misfire issue. Someone said they replaced cam synchronizer and replaced the heads with some heavy duty ones and that seemed to fix the issue, but that was quite a few years back. Is there a consensus now on what to do with this misfire? Getting rid of the truck would be a real pain with the misfire so I’d either wanna drive it as is or get it fixed, or eventually just do an engine rebuild or put a new engine in it, or one from a ranger year without this problem. Any help would be much appreciated,

Thanks,
Peter

 

Welcome to the forum

Valve won't drop if its a failing seat

Only way to confirm if a valve is the issue is with compression test, dry and then wet, and could be a burnt valve, if it only effects the one cylinder, doesn't matter really, the fix is the same, replace BOTH heads, or have BOTH rebuilt, new seats, guides and valves

If the heads were replaced already then its for sure NOT the recessed valve seat issue, that was from a batch of bad seats installed at the Ford 3.0l engine assembly plant in 2003-2005, these were installed in 2004-2006 Rangers
They were never used as spare parts, so replacement heads could never have this issue

A dirty injector can cause issues at idle
But do compression test FIRST take that off the table before spending money on non-fixes, if its a compression issue

 

Thanks for the reply. What will the compression test show that will prove it’s valve recession? I doubt heads have already been replaced, but I’m not 100% sure. If it’s a dirt injector is the solution to replace bad injector or all injectors, or can it be fixed in other ways. Either way, what will happen if I drive the truck for the foreseeable future with this misfire? I’ve read it can damage your cat converter, but if I stop it from misfiring most of the time then should I be fine?

 

Any time you have a misfire the first thing you should do is a compression test on all cylinders, because if it IS a compression issue you can waste alot of time and money on parts that don't help
Changing the spark plugs is fine because they do wear out, so not really a waste of money or time

The compression test tells you if compression is or is not an issue
If it is then heads will have to come off, but if the wet test doesn't show a big increase in compression then just the heads have to come off, you don't need a full rebuild because piston rings are bad

If valves are at fault for the lower compression then doesn't matter if its seats or burnt valve, fix is the same for either, new heads or full valve job


Injectors rarely fail, but if they do then its best to swap all 6(V6 engine) since they will be from the same Factory batch which can raise the probability of another failure


Compression test is not hard to do
Pull out all 6 spark plugs
Screw compression gauge into #1 cylinder
Push gas pedal to the floor and crank engine
You will hear it "hit" compression stoke, it needs to "hit" 5 times at least
Look at pressure on the gauge, it holds highest pressure seen
WRITE IT DOWN, #1 = XXX

Let pressure out of the gauge, there will be a button/pin to do that

Repeat for each cylinder

Expected pressure on 3.0l is 160+ PSI

All 6 should be within 10% of each other
The exact numbers are not as important as the AVERAGE number, because the exact numbers vary because gauges are not calibrated for exact pressure, but as long as all cylinders are tested with the same gauge the results can be averaged

 

I own a 2001 ranger with the 3.0 flex fuel engine that I purchased with 10,000 miles on it in 2004 When I reached 65000 the miss started ,bad comp, the valves had recessed into the heads. This engine had never been replaced.

 

Very unusual for 2001 model

 

After I replaced the heads the truck ran fine for a year then I had to replace the cats. I'm 72 and in all my life I have never seen valves recess into the heads like this. I now have 97000 on it and going strong.

 

I have a 02 ranger 3.0 and I’m having similar issues leaning towards the valves 🤦🏻‍♂️ Did the paper test at the exhaust pipe and it was flapping in and out but I haven’t got compression test yet , random misfire code I reset it and gonna check again when it pops back up , I swapped coil pack from a friend still no fix . I pulled the wires off the coil and plug 5 made no difference in the engine idle so I’m thinking cylinder 5 is the one damged I really don’t know 😔 anyone in in NC want to make some money 🤣

 

I don't know about the 03 to 05. I have a 2001 ranger that I bought and 3 years ago I had a miss and tried everything did a compression test and found two cyl low. Pulled heads and the valves had recessed into the heads. Bought two cyl heads rebuilt on ebay and has been running like a clock since. Now have 97000 only 66000 when it happened.