Misfire on cyl 3, low compression help

[silverbullet4]

1997 toyota 4runner ltd v6 with 341k mikes on the odo. On cold start, engine misses a little, and occasionally a little white smoke from exhaust. After it warms up, it runs fine for the most part, unless getting on the freeway, in which case it stutters a little. Code shows misfire in cyl #3. Wet and dry comp test confirmed low compression (133 psi compared to 155 psi in all other cyls). Pulled the cylinder 3 spark plug for inspection. Plug looks good, no signs of excessive oil fouling. Inspected the cylinder with borescope to check for any coolant or anything abnormal. No coolant in cylinder. Visual checks OK. Engine has 341k on it but was maintained very well by prev owner. Have not done a leak down test yet. what should I do next? Some people say I will just need a new head, other say, I should just get another engine. Looking for all insights and experiences here. Goal is to keep this thing on the road for another at least 30,000 miles as I only drive about 3000 miles a year.

 

[socal_99]

Have you tried testing your antifreeze for presence of CO? It uses a liquid which changes color in presence of carbon monoxide. I had a cracked head and a burned exhaust valve which had similar symptoms; light white 'fog' on startup and difficulty starting and rough idle but went away after few minutes. Would start right up if allowed to idle for few minutes. Most cost effective way to go is swap in JDM engine as you'll be getting alot of other things which will likely start to go bad in the next 5 years on your current engine.

 

[Devbot]

I'd check crankcase pressure or exhaust gasses in coolant. Sounds like a ring is on it's way out though.

 

[brillo_76]

When we're the valves adjusted? As these should be done 250 to 300k. If never it's possible the exhaust valves are too tight. Being your getting some white smoke that is never a good thing. Maybe boroscope that cylinder 3 and see if it's the head gasket or a cracked head.

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[JBurt]

Is it just me or does 155psi in the other cylinders seem like they're all too low.

I think a leak down test is definitely in order. I'd probably do that before checking valves. There could be issues with either, but I think the leak down test is easier.

I hope it's something easy. Good luck.

 

[gamefreakgc]

Is it just me or does 155psi in the other cylinders seem like they're all too low.

I think a leak down test is definitely in order. I'd probably do that before checking valves. There could be issues with either, but I think the leak down test is easier.

I hope it's something easy. Good luck.

It's smart that Toyota doesn't give a PSI value for engine replacement, just one that's more than a set percentage, 10% I think, less than the others. There's isn't an official PSI rating for cylinders on the 5VZ-FE. Lots of factors that can change the reading such as not pulling all 6 spark plugs at once, gauge inaccuracies and wet vs dry tests. I can verify that a low mileage 5VZ-FE is on average 210 PSI wet tested.

133 PSI isn't anything terrible though. I ran my engine with one at 90 PSI, with another at 120 PSI with the rest at 160-170 PSI for years and all of that was supercharged. There really isn't anything wrong with running with low compression in the cylinder and yours is not all that low. What does need to be addressed is the smoke at startup. Does the smoke smell sweet like coolant or foul like burning oil? Start it up and hop out and smell the smoke the next time it sits for a few days and let us know. Coolant smoke also looks more white while oil smoke is a bit bluish.

 

[MaineRunna]

155 for all cylinders at over 300K isn't that bad and the 133 will still run good. A leak down test isn't really necessary because you don't have a catastrophic loss of compression. A hydrocarbon test would be a good idea, but maybe you just have a bad coil boot.

 

[mtbtim]

Dude, you either have a bad head gasket but most likely a crack in head.

The fact that it's misfiring and smoking in the morning is a pretty dead give-away your engine is consuming coolant. You didn't say it, but I already know your engine is eating coolant.

Your compression numbers aren't great and you have a pretty high mileage engine. If you had less miles, I'd say roll the dice and put two remanufactured heads on and hopefully you get a lot more time and miles from it.

If it were me, and I knew I was going to keep the rig for a long time, I'd swap in a quality rebuilt engine and my suggestion would be to buy from Yota1 Performance in Riverbank, California. They ship to anywhere in the U.S.

My Timmy the Toolman channel has videos you can use for whatever route you choose. We have an engine replacement series and head replacement series.

You said you used a borescope but you probably didn't have the cooling system pressurized like we did in the video below to help confirm my buddy Sean had coolant infiltrating into the cylinder. It was the #3 cylinder too.

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