compression test

[LEOL]

Against my nature ill keep this short and simple as possible.

Did a compression test, (2006 5.4 3v, 172000k miles).

Results were 160psi accross the board, EXCEPT Cyl #2 (150psi) and #5 (150-155psi)

#2 cyl is known to have possible but unconfirmed damage or issues from a sparkplug meltdown/implosion of unknown cause.

have run vacuum tests, which do indicate issues, but dont seem to indicate valve or major ring problems, or head gasket leakage (though im still sorting out what exactly the readings are really telling me).

The compression range at which is "acceptable" by written diagnosing standards is 75%... which both #2 & #5 pass with flying colors, especially considering the mileage on the engine.

disregarding the vacuum test, and other things i've left out on this post... my question is...

in this scenario 10psi is roughly 6% of the allowed 25% ratio difference, so... under circumstances in which internal damage isnt already known, would a compression reading of 10psi in one or two cylinders be much cause for concern about possible internal damage, and/or being the primary issue with the current drivability power loss?

 

[USMCBuckWild]

Technically, no. In my honest opinion those are pretty good numbers for the mileage.

What are the vacuum test results? What else makes you think its an internal issue?

 

[docraymund]

Your compression test is acceptable. Though you might have excessive carbon buildup inside the combustion chambers which could cause preignition.

 

[1955moose]

Normally up to a 15 psi swing either direction is acceptable on a motor with that compression. Carbon buildup is usually an indication of carbon buildup on that one bank. The two cylinders that you have are more than likely leaky valves, and aren't enough to worry about. You didn't state in your post, what your problem is. I'm assuming loss of horsepower. Personally I'd leave it alone, and just enjoy your ride. As far as your vacuum readings, what are they? Anywhere in the 17-23 range is ideal, but a little either way is not a deal breaker. You might want to have your intake/ Exaust smoke tested for leaks. Let us know what you find.


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[Snag]

Moose,
LEOL Made a post last week I think it was. Fairly lengthy and in depth showing his problems and what his findings are. He had a spark plug melt down in that cylinder with the lowest compression. I think he again posted his compression readings post to get some ideas on those readings. I viewed his original post a few times and I have no idea what he can do next. His first post went 3-4 days with no responses and still not many, it has me stumped.

 

[1955moose]

Their are two scenarios where a partially or totally plugged Exaust will cause a vacuum drop. A partial clog will usually act up like yours when trying to hold rpm at 2,000 to 3,000 rpm. When a Exaust system is totally plugged like a blocked catalytic converter, your vacuum will start out normal usually around 15-17 inches then as it idles the needle will drop towards zero. Rather than get so technical in your posts, it does help some, I'd have the full Exaust checked out. Real common on these Suv's to clog up a cat or 2. I'm assuming your vehicle has lost power your trying to restore. Are the spark plugs that had the thread inserts fitting tight and square against head, and spark plug. If whoever installed the thread insert did a inferior job, or if pieces of the head are missing, you'll never get it 100 percent, and you'll be smelling fuel. That's my 2 cents.


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[LEOL]

sorry, been away havent been able to get to forums. anywho, i didnt think to actually inspect the threads to see if there are any thread inserts, but the plugs that were in it when i bought it all came out with zero issues... and actually as i recall one or two of them were barely hand tight. i haven't felt any threading problems, as ive taken the new ones in and out a couple times, so id be inclined to believe (assumptions are bad, i know) that there arent any thread inserts or issues in that department. i definitely haven't smelled fuel, so thats good.

as far as my goal, i have a few different angles im working with both my vehicle and my postings... but yes, lost power is the tangible issue at the moment, but Honestly the bigger concern is engine longevity... its got 173000 miles on it and its in good enough shape i want to get another 200k out of it, so something like a worn/damaged/burnt valve may not be a huge deal if the engine is performing just above acceptable levels, but in the long term, not so much. my philosiphy in this matter is by professional standards, doing what might seem not totally neccesary now, can save me from having to spend 3 times the amount replacing the whole vehicle in 2-5 years time. since im capable of complete overhaul on an engine, Id rather keep a vehicle 10-15 years or as long as the body keeps up.

as for the exhaust, i know its pretty common for these cats to clog even if to a minor degree, but (serious question) have you seen very many that clog for no reason at all?... i mean it just doesnt make much sense in my mind that a cat clogs even just a little bit without some kind of underlying cause. like i said in my super-post the bank 1 exhaust manifold has very obviously been recently replaced, and like you said an exhaust leak left unchecked can cause lean issues... so... given that the new one was seemingly done by a hack and is still leaking... perhaps that was and still is the catalyst. If so, i suppose carbon build up would be expected on that bank, which i didnt think about.... who knows how long it went with leaks.

as far as the vacuum tests go, i posted a shorter thread on that too, here

ive suspected all along that the cats are probably have at least a slight restriction, i just have my reservations about whether they were the actual underlying problem and i dont want to put a new set of cats on it, and end up eating those up too because i couldn't find the underlying problem without tearing the darn thing apart. Anyway, my next action is and was throwing a compression tester in the O2 sensors, i just havent had time to get the right fitting.

 

[1955moose]

One rich running incident can cause a problem with a catalytic converter. Theirs two ways to test. 1) use a infrared gun and check hot temps front and rear of all cats. Temp should be at least 25-100 degrees higher at rear of each cat. 2) use a gauge in the Exaust port of each cat where o2 sensor screws in.
Sorry don't know the reading on that one, should be available online. 3 rd way is vacuum gauge test while idling, and 2500 rpm.


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[1955moose]

Sorry I said two ways, oh well 3!


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[The Swagonmaster]

I just pulled some specs that might help on deciding if there is a exhaust back pressure problem.
First the tester, I had taken an old o2 sensor and broken the guts out of it and then jb welded a brass fitting in it that would allow me to hook up a vacuum/pressure tester to the exhaust in place of the front sensor. Leave your good o2 sensor attached to the harness, no sense causing more codes than we may already.
Ford says that with a warm engine there should be no more than 3psi back pressure at idle and 8psi at wot under a load.
You already know that you have a leak but this is a cheap way to see if there is enough restriction to be a problem.