2002 Ranger 3.0. 170,000 give or take.

Rough idle with a misfire of cylinder 5, confirmed by removing plug wires and listening for change. Dollar bill trick shows a possible exhaust valve leak. Runs great driving around with plenty of power and ZERO other symptoms. No codes either.

Here’s where it gets weird.

I did a compression test (correctly, with three different gauges) and each cylinder is between 30-50psi. Yes you read everything correct- it runs with those numbers. I am at about 9,000 feet elevation which definitely drops those numbers but I’ve never seen anything that low run at all let alone as good as this thing does.

I’ve scoped the cylinders and no obvious signs there. No exhaust gas in the coolant, no obvious signs of head gasket leak (other than those numbers). Are all of my exhaust valves that toasted? What’s your guess?

 

i'd drive it until it buggs you too much. leak down test? then do the heads?

 

Since you know that a particular cylinder is missing, it is possible that the injector for that cylinder is partially plugged up or dirty. I would try a fuel system cleaner like Techron, and switch to a top tier gas if you are not already using one. I had an idle stumble after using a cheap gas for awhile, and was able to eliminate the stumble by doing this. There are several other things that can be helpful if you have an idle problem. Checking for a vacuum leak around the intake manifold, and cleaning the throttle body, the IAC, and the MAF, can be helpful for general idle problems.

 

I agree what you’re saying. In my case after I did a compression test I knew it wasn’t an injector the misfire I had wasn’t really bad I could live with it, but it did bother me. I did go after it thinking it could be spark or plugs, etc. Like I say compression test ended what I was chasing

 

An occasional misfire or one cylinder at idle sounds like a partially plugged injector, making one cylinder too lean to fire reliably. I would only suspect compression if the missing cylinder had substantially lower compression than the rest. Running a tank of high additive gas like Shell or Exxon or Mobil or other top tier gas might clean the injector at very low cost. Not all name brand gas is high additive gas. You can check who sells top tier gas in your area by going to toptiergas.com and entering your zip code. Techron is a good fuel system cleaner as well.

 

I have a 2005 Ford Ranger 3.0L V6 RWD with a P0316 (misfire detected on startup - first 1,000 revolutions), with the following codes stored: 1) P3000 random misfire detected, 2) P304 misfire in cylinder #4, 3) P0306 misfire in cylinder #6. Talked to three shops in Salt Lake City who suggested $4-5kUSD to swap in a used engine, with a similar number of miles. My buddy in SLC isn't setup for me to do mechanic work, so I think I'll just keep limping this baby as far as she goes. Posting as a long shot in case someone has some wise thoughts I'm missing. I can rustle up some photos if they're helpful.

Some background: we were driving up to the artic this summer (Hay River, Northwest Territories, Canada), and had a P304 - found a scoring in the #4 wire, taped it, and the check engine light went away. Replaced the wires when I got home (Calgary, AB), and hit the road again (quit work to travel for a year, did a bunch of preventative maintenance assuming engine was solid past 300,000km / 200,000miles). Hit Jackson WY and the engine light came on, tickled some spart plugs, saw nothing obvious and decided to drive on to Salt Lake City (where I am crashing at a buddy's). O'Reilly's OBD-II scanner gave the codes above, and lent me a compression test which we did this morning:

#1 - 90psi #2 - 98psi #3 - 80psi #4 - 65psi #5 - 75psi #6 - 80psi

poured some oil into 4, 5, 6 and got the following:

#4 - 100psi #5 - 120psi #6 - 100psi

I was hoping it was the ignition coil, given the spark plug wire insulation issue but that seems like a tired engine with some tired piston rings. Overall, the engine runs fine - plenty of power. Oil level/colour looks fine, although it looks like it dropped from mid to low in the last 3,000km (hard to know for certain). Coolant level holds (it was leaking via timing cover to the point of dripping on the ground late 2024, which I sealed up along with replacing the timing chain last winter). When I replaced the spark plugs last winter in preparation of this trip #4, 5, and 6 were all corroded almost down to the porcelain. 20-25,000km later the same thing happened while trying to sort out the P304 code in Hay River. Right now the spark plugs look fine gap wise, and show nothing that indicates concern.

I've got 10,000km / 6,250 mi approx to go (plan to check out National Parks in California, stop in Austin, check out Louisiana, and head for Ontario where I have family) before I make it to my mother's on the east coast, after which I don't super care how it runs - ideally it makes it back to Calgary, AB and offload it somewhere. I've got it setup to sleep in the back, and it has a kitchen/gear storage setup drawer system so it has a greater level of utility than just a vehicle for me for the next few months that would be inconvenient. I feel like shipping my worldly goods back (or shipping the whole truck) is probably cheaper than swapping the engine, unless I can find somewhere with more competitive labour rates. Plan to keep the RPMs low, drive easy, and see how far it gets me.

 

it would be better to start a new thread. so how many miles on the motor. they are prone to have burnt valves. its not too hard of a job and if theres a good machine shop around. i had the same issue. misfires and low compression. i got mine online from Rock Auto for under $1000 no machine shop close to me. i did a new water pump at the same time. i had 160k on my motor they will go 300k if taken cared of. runs great now.

 

OK - started a new thread here. It's 285,000 km / 178, 000 miles on it. Is there a way to test if it's a burnt valve? What parts does a fellow need - new heads and valves? I'm on the road, so if I need a bunch of specialty tools it might be tricky to do myself - but I have the time. Expect it would be cheaper to buy the tools I don't have than pay the labour for someone else to do the work.

Just hoping she limps at least 1500 miles to where I can hole up for a week.