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Discussion Starter · #1 ·
Hello!

Any help here would be greatly appreciated. Having issues with this vehicle for two months now. I will do my best to lay out a timeline of the attempted maintenance and where the vehicle currently is.

This is the wife's vehicle. She has had it for the better part of ten years now. Not the original owner. Vehicle has 185000 miles on it. There are signs of previous owner maintenance, but we do not have a full history of vehicle maintenance, including after my wife acquired vehicle.

About two months ago, wife noticed that there was a decrease in engine power during acceleration, particularly prominent going uphill. The loss of power was gradual and became worse over time. Last month I pulled it into the garage for an oil change and started to dive in on the power issue. New fuel pump, fuel filter, and air filter were purchased and installed. New bank 1 pre-cat O2 sensor was purchased and installed. New spark plugs were purchased and installed. New spark plug wires were purchased and installed. The battery was five years old, so was also replaced during this time with a new battery.

After all these changes, there was still a power issue with the vehicle. Before the changes, my wife's brother scanned the computer for codes and pulled two codes: P0328 (Knock sensor circuit high input) and P1143 (Pre-converter oxygen sensor lean shift monitor fault (right bank))

The vehicle was still lightly used for the next week while we scratched our heads about the potential cause which we understood at the time to be a handful of things: low fuel pressure, clogged intake manifold, faulty TPS, faulty MAF, low cylinder compression, etc.

One morning recently, the vehicle would no longer start. The TPS was changed at this time, with no change in the start. After the vehicle was pushed into the garage, the intake manifold was taken off, fuel injector connectors were unplugged, the fuel pump fuse was pulled, the spark plugs and plug wires were removed, the distributor cap was removed and the connector for the distributor was unplugged.

Using a compression test kit purchased from oreilly's, I was able to test compression on the cylinders for the first 4 cylinders, as numbered by the Haynes manual, before the testing gauge's release valve went bad.

Compression read as such: Cylinder 1: 110ish Cylinder 2: 70ish Cylinder 3: 100ish Cylinder 4: 80ish .... then the gauge failed and would not hold any pressure readings.

From my understanding the compression test was done properly, all spark plugs pulled and the air intake open, in this case wide open with the intake manifold off. And if the testing gauge was to be believed, there is a significant lack of compression in bank 2 and a fair lack of compression in bank 1.

What are your thoughts? Are we right to assume that a lack of cylinder compression here is both the primary issue for the inability to start as well as the gradual lack of power that took place before starting failure?

In addition, I have photos for reference and a few additional questions.

On the bottom of the intake manifold, or more specifically the throttle body, there is a buildup of a grease type gunk. I don't know what it is and am unsure if it is a potential issue. It was also found to be dripping down on the bank 2 cylinder head.



Secondly, there is a thin pipe that runs underneath the intake manifold that I am unsure about. This pipe has holes on either end, but there were no hoses that were connected to it. What is this pipe? Is it needed in this vehicle? If so, what hosing and where does it go?





Some additional images of the engine here.




If it is to be believed that a lack of compression is the primary issue here, I'd rather like to know what the potential cost of a self repair would be, the cost of a mechanic to get involved (I can and will be calling myself to discuss local options) and lastly, whether or not this car has bit the dust or if the continued repair is actually worth it. I don't have any personal experience diving any farther into an engine than I have here, so a self repair would be a long tedious process with loads of learning, potential tool purchases, and the potential to damage interior engine components due to lack of experience and knowledge. Plus my garage is barely big enough to fit the truck and consequently I don't have much space to work in.

Thank you for any input in advance. Cheers!
 

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2004 Xterra XE 4WD Auto 3.3L NA V6
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I have to wonder if the timing belt may have jumped a tooth on one cam but not the other, causing the compression loss due to incorrect valve positions.

When was it last changed? Its interval is 105,ooo miles or 7 years.
 

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Discussion Starter · #6 ·
Timing belt is an unknown issue. Could have jumped a tooth perhaps. I am unaware however of how the belt jumping a tooth results in the valves being controlled differently. The cylinder state could end up being different from bank 1 to bank 2 given a jumped belt, but cylinder valves?.... how?

Are you suggesting that the inlet valve and the outlet valve of a singular cylinder are controlled independently by the timing belt, and a jump in the belt now results in one of those two valves not being completely seated while the piston is at TDC?
 

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The belt makes the cam wheel go 'round, which controls the timing of the opening and closing of the valves.

The belt jumping a tooth on one cam gear but not the other could cause it to alter the valve timing for the whole bank, not just 1 or 2 cylinders.

Compression read as such: Cylinder 1: 110ish Cylinder 2: 70ish Cylinder 3: 100ish Cylinder 4: 80ish .... then the gauge failed and would not hold any pressure readings.
Had you been able to keep going, cylinder 6 would probably have read 70-80 like 2 and 4, since they are all on the same bank, controlled by one cam. So long as the internet is not lying to us, here is what I found for the firing order and cylinder numbering.
 

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Discussion Starter · #8 ·
Since this post, we had the pressure gauge replaced. Re tested compression with similar values on 2 and 4. 5 and 6 were between 100-110. Each bank does have a cam shaft, so a jumped tooth would certainly change the relationship of cylinder positions from bank 1 to bank 2. Both the valves for any given cylinder however is controlled by just one shaft, unless I am mistaken. This means the only thing that could prevent both valves from being closed when a cylinder is in TDC (top dead center) is deterioration of the valve, valve stem, warped or damaged camshaft, etc. Even if the timing belt jumped, it shouldn't have an impact on the valves for a given cylinder being seated when cylinder is at TDC.

UNLESS, there are two camshafts independant of each other that are separately controlling the inlet valve on the outlet valve of each cylinder. That would mean there are for camshafts, two for each bank. And these 4 shafts would all have to be independently turning in relationship to the timing belt. If this were the case, you could easily have valves on a cylinder being in all sorts of various states depending on what happened with the belt...

As it were... I think for now resolving our compression issue is back burner. We still have a non starting vehicle. Up next is a recheck of all the systems involved such as, fuel, air, spark, etc.
 

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The 3.3L V6 is considered a SOHC engine. There is 1 cam in each head, so "S" for "single" means that they count only how many are in each head, not the total on the engine.

SOHC controls both intake and exhaust valves. DOHC controls intake separately from exhaust.

Your #6 being the same as the other bank means that it is not likely an issue with a jumped tooth. Up until that piece of very important data, the pattern seemed to suggest otherwise. Good that you got the testing finished!
 

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Discussion Starter · #10 ·
Thanks for the clarification. It is much appreciated. At the very least, the timing belt may as well be checked. At this rate I'll have the engine apart in no time. HA!
 
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