When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi folks, low compression on a 2005 Ford Ranger 3.0L V6 RWD with 285,000 km / 178,000 miles on it. I can rustle up some photos if they're helpful. First suggestions from the mechanics (swap engines for $4-5k) was too expensive. I left Calgary, Alberta (Canada) Sept 26th on a US National Park road trip (WY, UT, CA, NM, etc.), and Sept 30th check engine light came on in Jackson WY. Got to Salt Lake City and got O'Reilly's OBD-II scanner to read a P0316 error code (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. Most likely solution identified was "Replace Cylinder Head Assembly." Fellow at O'Reilly's suggested ignition coil given the background, but we decided to do a compression test as a sanity check and we got:
poured some oil into 4, 5, 6 and got the following:
#4 - 100psi #5 - 120psi #6 - 100psi
Some background: we were driving up to the artic this summer (Hay River, Northwest Territories, Canada), and had a P304. Checked the spark plugs, and replaced spark plugs 4, 5, and 6 as they were eroded damn near down to the porcelain (1,2,3 were fine). This was after only 25,000km when all six were replaced (NKG). Found a scoring in the #4 wire, taped it with electrical tape, and the check engine light went away; realized something was causing premature corroding of the spark plug material, but didn't have time to dig in. 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). Maybe the wire short accelerated this (exhaust valve) issue? It does look like there's a TSB for exhaust valves.
Overall, the engine runs fine - plenty of power. It does seem to idle a little rough. 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). Right now the spark plugs look fine gap wise, and show nothing that indicates concern.
After the sticker shock of swapping engines, we decided to keep limping this baby along on our road trip as far as she goes, sticking to the main roads more than initially planned. Posting in case someone has some diagnosis suggestions - in a couple weeks / 1,500 miles I can get back to a buddy's in Salt Lake City (is it dumb to keep driving?). If I can confirm exhaust valves, I'd like to establish either a parts / tools list, or a machine shop that doesn't have a crazy lead time, or both. 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. For now plan to keep the RPMs low, drive easy, and see how far it gets me.
shows a fellow replacing the head and head gaskets without touching the fan clutch or AC compressor - I can take a closer look, removing the exhaust manifold looks like the worst part (aside from the overall number of pieces). If it is exhaust valves, I assume best to do both heads with new valves and whatever else is required. I've never touched an engine before, so doing this myself (and away from home / without my regular tool set) would be bit intimidating, but I have the time.
How do I best figure what the issue is? What do I need to 'get er done'?
Since adding oil to the low compression cylinder restored the compression, the low compression appears to be due to worn rings and not a leaking valve. I would just drive it because doing anything to the rings is cost prohibitive. Your spark plug problem might be caused by the type plug used. Your truck requires double platinum plugs which should have a PP in the plug number. If you use regular plugs 3 of them will wear out very quickly.
you will need to have your heads machined, valve seats , and new valves. most likely. you might get away with doing it yourself if it was just one valve. dont use oil right now to test compression, that is to test tor rings. i would test again. pull all plugs and cold motor. im not too sure but you want to see about 160lbs in all cylinders. so driving it 1500mi humm dont know, just dont push it hard. im sure the truck i have had some burnt vales for some time.before i got it and i had it a year before i fixed it.
There are a number of variables in compression test readings like starter cranking speed, throttle position, engine temperature, and altitude where the test is being run. I generally assume that the highest number is a good cylinder In your case the added oil ran your bad cylinder higher than the "good cylinder" which suggests that all rings are well worn. While I said I would just run it, there are several things that might help. A higher viscosity oil might seal worn rings a bit better. Valvoline has recently come out with an oil that is designed to remove carbon from rings and pistons which might help if your rings are sticking in the pistons. I think it is called "Restore". I have only seen it in 5W30 which is what my Ranger is supposed to run. I think I will try it even though mine has no known problems.
ok here this is the way i think, cold motor, all plugs out. test take a reading... then put the same amount of oil in each cylinder, test again, see if there is a difference, or much. oil will test rings. no oil will test the valves.
There's a chance the compression test was done incorrectly, the spark plug channels in the block require a very narrow fitting that some test kits don't have. The fitting might only seal on the threads. I'm not sure why, and this is totally anecdotal, but I had a harder time getting a good seal on cylinders 4-6 on my 2003. Just something to consider.
the difference in spark plug wear that you previously noticed is a good clue, though, that does suggest there's something happening there.
have you tried replacing the coil pack? If you can spare the money, it's a good simple place to start. I had a misfire caused by a very hairline crack.
if it is valve recession, my understanding (which could be wrong as I'm a total novice) is that you could get away with limping it for quite a while, unlike a head gasket. Since it sounds like you're not burning coolant or oil, hopefully nothing catastrophic is on the way. Good luck!
Hey folks. Thanks for the interest and replies. Few hundred miles down on the road trip. CEL has gone on and off a few times. Anecdotal, but it seems to be on more on hot days / long distance runs, and when we're doing small in city / just out of city runs it has gone away. I'm under no illusions I'm out of the woods. Nothing of note on the dipstick or fluid levels so far. It does seem to misfire at idle / lower RPM, but I don't think that's helpful diagnostically.
I wouldn't read too much into the "with oil" compression readings, I got a loaner kit from O Reilley's, though it didn't look beaten up. We were far from scientific when adding oil - on #5 we thought we spilled some so added more to be sure. Liquid being incompressible will simply result in higher numbers alone. I think a leak down compression test is the only real way to know where the loss of compression is going, and it wouldn't hurt to run the compression test a second time.
Knowing I had a spark plug wire issue (the insulation of wire #4 was very clearly scored where it was rubbing against a valve cover stud), I really should just replace the ignition coil pack and go from there. However, assuming there's an underlying compression issue, I should run (or pay someone to properly do when we get to Las Vegas area) a leak down compression test to have a much better idea of where the loss of compression is going. When it misfires, you can hear it at the tailpipe (I'll rerun the "dollar bill test" another time - trucks been running good today...); hard to say if there's reversion (air sucked in the exhaust) or not.
Pricing out replacing the heads it looks like a $1k parts job (heads, valves, head bolts, gasket kit, valve spring compressor tool, exhaust manifold bolts), and it looks like more than I want to take on in my buddy's driveway if I can avoid it. He's lacking in tools, and there's a few things I have that would make this go easier that I would rather not buy (in-lb torque wrench, ft-lb torque wrench, locking chain wrench to remove the fan, torx socket set, heat, serpentine belt tool, etc). Buuuut I've got like 10,000 miles before I'm home (I'll have places I can borrow tools / a workspace in under 5,000 miles). Thinking to do the ignition coil knowing the muddy history, monitor the fluids, and if it starts acting up past that do another compression test with a loaner tool and get a leak down compression test done.. at some point so I'm traveling forward with my eyes open.
I've had 'Old *****" for 15 years and 200,000 kms now, so I think I would (try) to do the head job (at some point) if it proves to be an exhaust valve issue - partly cuz I love the little truck, and partly cuz it's a great opportunity to learn.
Made it back to Canada. CEL continues to be on and off. Alternator / voltage regulator gave me trouble, and it definitely misfires on rare occasions, but otherwise its running reliably so far. Swapped a remanufactured alternator in when I was in Dripping Springs, Texas in O'Reilly's parking lot and took care of the ignition coil at the same time, although I don't think the ignition coil made a difference - but given the damaged spark plug wire insulation that went unnoticed for who knows how long, is wise to do.
Looking to get a leak down compression tester and do that to confirm, and putting a parts list together assuming its the exhaust valve seats. Rock Auto only has heads (not assembled heads) and if the issue is just the valve seats, it seems worth making a call or two to some engine machine shops when it comes time to see their turnaround time.
I'll be parking the truck in a month, and I think I'll deal with it when I'm back in the spring. I've got another 10,000 km or 5-6,000 miles before I'm "home" but I've got a few places I could hole up and deal with it if it acts up and needs dealing with before then along my route.
It would be interesting to see what your compression test results are now. Doesn't the fact that #4, 5,and 6 went >= 100psi with oil suggest that your problem is rings rather than valves, or are those numbers too low? With the air pressure fitting for the leak down tester you should be able to hear if pressure is leaking into the crankcase (oil fill cap hole) or out the exhaust (tailpipe) or intake (throttle body) valve.
Air was heard out the tail pipe when leak down testing cylinder 4 and 6, we ran out of time to do the others. Access issues resulted in only running a compression test on 1,4,5,6 with a diesel engine gauge (which would be less accurate at the low end of its span). Results in the link to my Google Drive (site won't let me attach a pdf!). Spent 6 hours, most of which was fighting with spark plug adapter fittings and shop hose adapter fittings at my buddy's to try and run both a leak down compression test and a compression test. An old spark plug was sacrificed, the welder came out.
I'm back from Thailand, holed up at my mothers while I prepare to drive 5,000+km back across Canada to finish up my road trip. I am no longer planning to keep the vehicle as I doubt it would pass an interprovincial inspection, but I want to have it drive reliably so I can visit people along the way. If I were to drive it in its current state, I would stick to highway and try to get back as soon as possible. I may source a compression test kit and run it for curiousity sake, but at this point I'm going to price out salvage heads / shop replaced seat rings / new heads and decide if the cost is worth the insurance or if I roll the dice and just drive.
A 160,000km salvage head is available, with gasket kit and head bolts it's about $500 including shipping. I have a few more leads to chase down first, like MAF and redoing compression test on all cylinders with a gas engine kit/proper fittings for access. I'm at sea level now, so numbers will be different, but should be useful. A couple buddies are adamant I should check the MAF sensor, so I'll try and see if I can salvage one of those, buying a new $70 part for something I don't think is my problem doesn't feel worth it. He says exhaust valves will leak, but not bad enough to throw codes. I've already done spark plugs (eroded tips), spark plug wires (noted damage on misfiring cylinder), alternator (tester at O'Reilley's said voltage regulator failed), and ignition coil (for good measure). Tired of chasing 'what if'.. at this mileage, what I've been reading and based on hearing air down the tail pipe it needs new seats and exhaust valves. Noise was not high pitch, suggesting a large leak - not that I have a trained ear. Might buy MAF cleaner and donate what I don't use to my buddy's shop for letting me spend time there to diagnose it.
I don't like being a cheap bastard and doing one side, but I just need 5,000km out of the old girl before I'd be trying to sell it. Engine issues - the one thing I hoped to avoid on this road trip, but I guess that's how ya learn.
Tried to clean the MAF sensor with CRC's MAF sensor cleaner, no noticeable change. Started the truck up from cold until it idled (~5min), then pulled spark plug wires from ignition coil - what I understand is called a power balance test. Almost no noticeable difference in RPM or audible noise when pulling wires for cylinder 4, 5, or 6. Significant RPM drop and audible change when pulling cylinder 1, 2, and 3. 1 seems to be doing the most work. Machine shop wants to see the heads before they'll price anything beyond a standard head job - I'm going to go ahead and ask they price valve seats and exhaust valves. Lowest mileage/cheapest heads I could get are off a 2003 3.0L with 160,000km. Cheapest valve seats and valves off Rock Auto are ~$200 delivered, doubt they'd let me supply them and they'd end up charging way more... we'll see.
El cheapo me wants to throw in the junkyard head on the LH side and go on, but the right way feels like swapping seats / valves in both heads. I won't get my money back in resale, but if this fixes it I'll be able to live with myself knowing I did the right thing.
Heads have been dropped off, should hear something tomorrow. All exhaust valves did look recessed, driver's head seemed worse. Cylinder #4 injector plastic body was also cracked, may or may not be related but intend to replace anyway. Only twisted off two exhaust bolts
$950 CAD to the engine shop plus $300 to Rock Auto in gaskets & bolts, a shipping mishap, one really really late night later and I'm 2,000km down the road. Engine sounds better than ever, but I lost AC. Shop confirmed it needed exhaust valve seats and seals. Guides were fine. I checked the reman head's valve installed free height which per spec and measuring reference indicated in Hayne's manual suggested the springs were short. Spec is 1.736 - 1.650 inch and they were ranging from 1.681 to 1.566, with most at or below 1.600. Did not raise this with the engine rebuilding shop. Codes have gone away, rough idle has gone away, no longer scared of red lights / stop signs.
My guess is the AC compressor was leaning over unbolted for a week and the seal in the compressor dripped dry and refrigerant escaped. Will double check a wiring hardness isn't missing, or a connection didn't get damaged on engine teardown/reassembly, but I think the system is low pressure and the compressor isn't kicking in as a result.
I will get around to doing a compression test of the cylinders and post the results, partly out of curiosity. The bores and cylinder heads looked good, particularly for the 300,000km odometer reading. If the numbers look good I might have to do some body work to get this thing to pass inspection now, used cars look expensive and I think I have an allergy to car payments.
