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Discussion Starter #1 (Edited)
Update: I guess I need a new engine sadly. Where should I buy one? How easy is it to remove and replace?

Or would it be cost effective to repair this engine?

Hey dudes,
I need your big brains on this one. I have extremely low compression on some cylinders. Trying to diagnose what is going on. Here is the history of the truck:
-I noticed a sharp reduction in fuel efficiency 15->10.5 mpg
-Then misfire in cylinder 3 with rough shuddering, usually when warm
-It then began to die at stoplights under idle, usually when warm
-I ripped the whole thing apart and changed the timing belt and front oil seals
-I discovered 2 of my fuel injectors were faulty in testing (possibly causing misfire)
-I accidentally spun the RH camshaft sprocket 90 degrees counterclockwise when removing (I've seen this posted here, but others haven't seen much effect as far as valve damage)
-I then compression tested the engine...
#1: 150 psi
#3: 55 psi
#5: 33 psi
#2: 90 psi
#4: 150 psi
#6: 125 psi

This is absurdly low right? How was the engine even running? Have I been driving it like this for years and it only now just started dying at stoplights? Do I really only have 2 good cylinders?

Tested it again with oil added to cylinders:
#1: 178 psi
#3: 80 psi
#5: 45 psi
#2: 100 psi
#4: 170 psi
#6: 145 psi

My first time doing a compression test, but I don't think I've done anything wrong. Used battery on the starter with all accessories removed, no belts, intake plenum removed. What should I do to figure out this problem?
 

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Well if the timing belt is installed correctly and you failed a compression test and you want to figure out why then the next step would be a cylinder leak down. You could potentially identify worn rings or valve damage with this. If those are indeed accurate numbers, you probably want to start engine shopping. Best case scenario would be bent valves but removing the head to repair it is a lot of work
 

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2000 Xterra XE 4x4 3.3L AT
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Yeah that’s not good.

Without a leak down test pointing towards where the leak is I’m going to guess timing belt slipped and you now have some slightly bent valves causing the loss of compression. This would also explain the sudden change in fuel economy.
 

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Discussion Starter #5
@Blackberry Do you think my compression test could not be accurate? How so? Anyway, I can try the leak down and listen for air seepage. If it is piston rings or valves, how practical would it be for me to do the work myself? Maybe a lot of work as you say. But could it be done in my garage? I've never torn into the heads, but I'm willing to if I can get this thing running again. If it's piston rings, that sounds more complex. What would you do?

@RacerXXL Old timing belt was in great condition and timing marks were perfect when I took it off. Could have bent valves with the RH cam sprocket turning though.

@mhamor RH is passenger and referenced from the perspective of the driver.
 

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Lots of things result in poor compression tests. Spark plugs seat contamination or a sticking check valve come to mind first. DIYers have removed heads in their garage. It probably calls for at least a dozen hours of work.
 

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@Blackberry Do you think my compression test could not be accurate? How so? Anyway, I can try the leak down and listen for air seepage. If it is piston rings or valves, how practical would it be for me to do the work myself? Maybe a lot of work as you say. But could it be done in my garage? I've never torn into the heads, but I'm willing to if I can get this thing running again. If it's piston rings, that sounds more complex. What would you do?

@RacerXXL Old timing belt was in great condition and timing marks were perfect when I took it off. Could have bent valves with the RH cam sprocket turning though.

@mhamor RH is passenger and referenced from the perspective of the driver.
yeah, i'm suspecting bent valves after reading this, with that accidental turning of the RH cam sprocket.
 

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If it accidentally turned with the belt off, I wouldn’t suspect the force would be there to bend a valve. Especially not on multiple cylinders.
 

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I have done head gaskets on 4 or 5 of these and its somewhat of a common problem, but on every one it has been cylinder number 5 that had the issue. I would check the coolant level and look at the spark plug from cylinder number 5 to see if it looks any cleaner than the rest. how many miles are on it?
 

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Discussion Starter #11
The leak test was very informative. I did not do a traditional leak down test. I didn't use gauges to measure percent leakage. I just ran some compressed air around 50 psi into the cylinders. I was able to hear all the leaks clearly. Results are as follows:

1: very slight leak from oil dipstick tube
3: rushing air out of intake
5: rushing air from dipstick tube and crankcase
2: air from intake
4: very slight leak from oil dipstick tube
6: slight leak from intake

Compression numbers for reference:

#1: 150 psi
#3: 55 psi
#5: 33 psi
#2: 90 psi
#4: 150 psi
#6: 125 psi

Looks like some intake valves are not sealing well at all. The worst cylinder (5) probably has ring problems and associated cylinder wall damage.

So what is the best way to get my beloved truck up and running again? Should I get some shop to work on the block and I can pull my heads and do valves? Should I get another engine? I feel like a junkyard engine may be cheap, but it could be a gamble. What do you guys know about the young imported engines from Japan?
 

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Just for my own piece of mind:

You ran the compression test with the timing belt installed?
Did you rotate the engine to ensure both valves were closed during the leak down test?

I usually don’t use a leak down tester unless someone specifically asks. I usually just pull the valve out of my compression tester and hook shop air up to the hose.

I installed a JDM engine in my Xterra. It’s been about a year and it runs great. It’s a lot of work. Book time was roughly 24 hours. Don’t recall exactly how long it took me but it was three full Saturdays. I also did a number of other repairs at the same time though.
 

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Discussion Starter #13
Yes I put a brand new timing belt on before compression test. Yes I found TDC for each cylinder when I did the leak test. Used a compression tester hose.

I'm pretty amazed at the condition it's in. I was just driving this thing a few months ago, despite these terrible compression numbers. I don't even know how the damage happened. Maybe it was existing when I bought it used.

Anyway, I'm guessing repairing this engine is not a good idea? I've never done anything like replace an engine before. I'm guessing you need some special tools. I don't even know where to look for an engine. Please share any experience and recommendations you have.
 

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You will need at least an engine hoist and some jack stands. It’s quite the task. I bought a JDM engine off of eBay which I still feel is a total dice roll. The engine was very much Japanese and all of the accessories were backwards, the oil pan and oil filter were different and the thing was scary clean on the inside. Not even a drop of old oil. Heard rumors that some of these engines are trash because some people don’t take care of them knowing they don’t have to live past 50,000 miles or whatever it is. Tore my Japanese engine down to the long block, tore the American one down to the long block and chose the better of whatever parts I had. American intake, Japanese throttle body and distributor, etc... I put it together with a new timing belt and water pump and all new gaskets and the truck has been running great and now I even have spare parts for almost anything I need. I did some steering work and other things at the same time and it took me three full Saturdays before I could drive the car. I work on nothing but Nissans for a living too. It’s a lot of work but you’ll never get a great running engine with all new maintenance parts for $1000 any other way
 

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i just bought a 2001 V6 xterra in august 2019, it ran okay but felt a little under powered. i did the compress test and had about the same results. I'm currently rebuilding the engine, the passenger side head gasket had blown on the middle cylinder. the driver side was basically running the whole show.
 

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@FatherSavage Sounds like you got lucky if it's just the head gasket. I wish mine was just a head gasket. Haha.
man i think a jdm crate engine will serve you best that engine of yours like has more miles than is worth to repair it.
 

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Discussion Starter #18
Yea I think I'm going to have to find one. Anybody recommend any of the online JDM dealers to buy from? I would love to hear from someone here who has done it.
 

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Yea I think I'm going to have to find one. Anybody recommend any of the online JDM dealers to buy from? I would love to hear from someone here who has done it.
yeah it can be hit or miss, might check out mazda-nissan heaven in fort worth and see if they have any good low mileage ones that can easily be redone gasket wise they ship nationwide, - Mazda Nissan Heaven
 
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