2004 4Runner - 1 cyl low compression

[AZjeff]

Got a call from a friend yesterday, their 2004 4.0 4Runner has been down on power some, took it to an indie who had been a Toyota tech, found low compression in 1 cylinder. They bought it 3 years ago with 180k, now at 230k, not sure how long this has existed, wife primarily drives it. It's a no rust car in great shape otherwise and they want to keep it for the long haul. Being advised a reman short block may be best choice for intended long term ownership, finding and fixing the exact problem was also discussed. So far the diagnosis is the weak cylinder (wasn't told the numbers). My friend thinks this indicates poor maintenance in it's history since it should run 300k trouble free and asked my opinion on course of action. I don't know these engines and am the wrong person to ask since I've never even owned a 180k car much less bought one at 180k intending long term ownership. I'm confused about the short block option, as that would require rebuilding the existing heads to use, no point putting 230k heads on a new short block is there? I'm sure he said short block.

This thread isn't a bash on the indie, he's a respected local mech and offered options. The short block option is being considered as a one and done fix rather than the potential of having this happen multiple times and dealing with being without the car for weeks again etc at a time moving forward. My only thought was if he thinks it's because of poor maintenance is he willing to replace the trannsmission, transfer case, differential rebuilds, etc as they would have received the same neglect. If he's lost faith in the car fix the exact problem and sell it and find another one. Thoughts from those with experience with these 4.0 Toyotas?

 

[MSCH]

poor compression can be one of 2 things, either a valve isn't sealing or the rings and cylinder are worn, or both.
only way to know is by disassembly although a mechanic can squirt some oil in the cylinder and see if the compression comes up
then problem is in the cylinder..

since I spent my life repairing engines, it has been my experience that by the time you take one apart
you are going to find other stuff wrong with it
and that is alot easier to go the long block route than it is to spend all that shop labor time
repairing it, but in the end the answer really depends on what it looks like on the inside.

as far as the other stuff, leave it alone unless it develops a problem.

 

[AZjeff]

Thanks. Hopefully he meant long block. What causes 1 bad cylinder, a maintenance problem or just happens?

 

[MSCH]

Thanks. Hopefully he meant long block. What causes 1 bad cylinder, a maintenance problem or just happens?

that I cant say... but poor maintenance would tend to show up in all the parts of the engine and not one area

 

[Astro14]

Sometimes, it just happens.

 

[Snagglefoot]

It’s time to retire that vehicle unless the OP does his own mechanical work. Toyota’s are legendary for high mileage but that doesn’t guarantee every one makes it to 300,000 miles. In fact, this one might make it, but with a bit of power loss.

 

[AZjeff]

It’s time to retire that vehicle unless the OP does his own mechanical work.

I agree and he's not a mechanic but that doesn't seem to be an option he's considering.

 

[Trav]

A leak down test will tell if it is leaking past the rings or valves.

 

[joegreen]

I guess the cheapest trial would be a piston soak for some stuck rings.

 

[MRC01]

Compression measurements can be variable and sensitive to the engine's condition when tested. Was the engine fully cold when compression tested? That can also be a factor. Don't jump into major work from a single low compression test with no other symptoms. If it's just 1 cylinder with low compression and there's nothing else wrong with the engine, try driving it for 20 miles, do a couple of smooth WOT freeway entrance runs to near redline, then cruise it for a while. Then test compressions again.

PS: this video on compression testing is for piston aircraft engines, though much of it applies to any piston engine

 

[SwampSurvivor]

Don't jump into major work from a single low compression test with no other symptoms. If it's just 1 cylinder with low compression and there's nothing else wrong with the engine, try driving it for 20 miles, do a couple of smooth WOT freeway entrance runs to near redline, then cruise it for a while. Then test compressions again.

With the original engine on my Marquis I tried all of that.

Turns out it was just a lot of carbon and possibly a bad helicoil job. I should have tried dumping water in it as a last ditch effort to break up the carbon in cyl 5.

 

[ARCOgraphite]

Slim chance it might be hot stuck. A soak (mentioned in post #9) would be a good and cheap first step if you don't have a compressor and adapter and gauge to do a leak down. I would fill that cyl with a couple oz of cleaner, plug it and turn the motor with a bar to just past TDC to force cleaner in to the rings and lands then pull that plug again after an hour. give it a overnigh soak and redo.

That 4 runner is past it's service life, so any more miles are just a bonus. Also just an EX valve could be stuck open and/or burnt - the cheaper fix than a bottom end reman.

 

[MSCH]

I'd lean towards it just being a valve in one cylinder.. but .

 

[dogememe]

Change the whole engine/long block if you're keeping the car. Otherwise time to drive it like it is til it dies completely or trade it in.

 

[Oliveoil2]

Not enough info. What does the plug look like???? Is it wet and covered in oil or oil deposits = bad rings. If not…..then look at a tight exhaust valve. Might adjust out as long as it’s not burned.

 

[Nick1994]

The low compression on that cylinder could cause it, do we know how low?

My dad had an '07 FJ Cruiser with the 4.0L, bought it at 60k and somewhere around 120k he was sick of it being so slow, so he hollowed out the 2 rear catalytic converters (had 4 total) and I have to admit, it was a lot peppier after that.

 

[ripcord]

Slim chance it might be hot stuck. A soak (mentioned in post #9) would be a good and cheap first step if you don't have a compressor and adapter and gauge to do a leak down. I would fill that cyl with a couple oz of cleaner, plug it and turn the motor with a bar to just past TDC to force cleaner in to the rings and lands then pull that plug again after an hour. give it a overnigh soak and redo.

That 4 runner is past it's service life, so any more miles are just a bonus. Also just an EX valve could be stuck open and/or burnt - the cheaper fix than a bottom end reman.

No way it's past its expected service life. That's rust belt conditioned thinking.

 

[ripcord]

I would repeat the test with and without oil added to the cylinder. If the compression doesn't go up with oil in the cylinder (assuming it's not zero), then it's probably not the rings. Also having a look down the plug hole with a bore scope could be instructive.

 

[Audiman]

As above, you can buy decent bore scopes from Amazon or elsewhere online for not that much, especially when weighed against the cost of labour. Get one and pull the plug and have a look. Turn the engine over and check the valve seats. If all is looking fine you could try following one of the many threads on here documenting piston ring cleaning to see if it makes any improvement.

Is your friend up for trying to save some money or happy to pay to get it fixed?

 

[AZjeff]

Got more info today, he was wound up yesterday. It's an 02 with the 3.4L if that matters, my mistake. One cylinder at 60 psi the other 5 at 140. That's as far as it got before options were discussed. I relayed the general thinking early in this thread that it needs to be properly diagnosed before he spends any money. This was echo'd by another mechanic he talked with this morning. It's got a slightly rough idle, runs okay but feels down on power. He can't say when the power loss was first noticed. He's not a DIY mechanic and will not be working on it at home. He's going to take it to a different indie next week to borescope it and pull a valve cover. He now realizes the shop he went to is a little bit too happy to put in a reman engine.

I said in the first post it's a rust free car, great exterior and interior that he wants to keep driving. Rustbelt guys can't comprehend that rust free really means no rust. 2002 cars with the original exhaust common. I'm still amazed and have been here 18 years.