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Discussion Starter · #1 ·
My Volvo S40's acceleration (turbo) is basically nonexistant at this point.

The dealer says one of the cylinders is misfiring and the compression is low on it. It doesn't need a new cylinder head (he checked) but he suggested I clean the PCV and get a fuel injection service ($800!)

I took it to my regular repairman & he says he doesn't see how cleaning the PCV will help the problem.

I'm trying to educate myself a little and it doesn't seem like cleaning the pcv will help that much but it's probably a good idea to get it done. Could it be that the o-rings need replacement?

Any suggestions would be greatly appreciated. It's sitting at the shop now & I doubt they'll do anything until I instruct them cuz they're baffled.
 

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I am not very familiar with your specific car, but I will give you some background on the 'basics':

The PCV Valve (Positive Crankcase Ventilation) sucks a small amount of air from the crankcase (meaning the area of air an engines oil pan, valve cover(s), lifter galley ('V' engines), etc...). This is done to keep pressure that escapes past the piston rings (as the pistons move up and compress air, a small amount of air can seep past the rings into the crankcase) from causing a leak in a gasket (oil pan, valve cover, etc...). There used to be a vent on a valve cover, but for emissions sake the air now gets sucked into the intake and burned (with whatever oil vapor might be in it) rather then put out into the atmosphere. If you think back to the old engines (like a 60's V8), you might remember seeing a ''breather" on a valve cover. If you cut it open you would would see a 'mesh' inside that was meant to catch the oil vapor and when enough accumulated, drip it back into the valve cover (engine). That being said, I cannot for the life of me figure how a PCV valve would affect only one cylinders compression (pernounced as "sounds-like-BS-to-me).

If you think of it, the dealership has stated that you have low compression in only one of your cylinders (I would REALLY like to see those compression test results, but I'd bet there aren't any). If that is the case (which would most certainly mean a mechanical problem), how is a fuel injection service going to help? How is allowing more fuel to get into a weak compression cylinder going to fix it? It wouldn't....

OK, Now here is what I would do (I have worked in dealerships in the past, and I do know that sometimes what the mechanic tells the service writer or service manager gets lost in translation). Inquire with the dealership on what I have already said, and ask about how their recomendations would correct what they have stated is wrong. I will bet you money, they will change the story and say that you mis-understood what was said.

Also, ask your local shop to do a compression test. It is a simple procedure in which the spark plugs are removed and a gauge is installed (screwed into the spark plug hole) and then when the engine is 'cranked', the gauge records the pressure that the cylinder is providing (through the action of the pistons going up and down and the valves opening and closing). Now, I won't pretend to know what a 'normal' reading is for that engine (turbo's typically have lower numbers, to allow for increases when the turbo forces more air into the engine), but specifics aren't truly important at this time. What is important is the comparison of all of the numbers. Low compression in one cylinder could be from a broken ring, a valve not seating, or the heagasket leaking pressure into the crankcase. Low compression in two cylinders that are next to each other usually means a leak in the head gasket that is supposed to seal them separately (could be a crack or could be a valve/ring problem in two cylinders that happen to be next to one another). Low compression accross all cylinders would mean excessive wear of the rings/valves (mechanical wear) or valve timing (mechanical defect: a timing belt that has jumped one tooth for instance).

"Could it be that the o-rings need replacement?", I don't know which O-Rings you are refering to, but I'd say 'NO'.

Ok, I know that was a long post! But, it does answer your questions, and it gives you a solid direction in which to go. I would have to say that a compression test would be about an hours worth of labor (so the total cost depends on what your local shop charges per hour). If you truly want to diagnose your problem, and someone has already said that there is a mechanical defect, then that is one way to go. If you don't want to diagnose a mechanical defect, then you could pay for a 'service' (like cleaning the PCV and Injectors), which will have no effect on a 'mechanical defect' and I doubt will fix your problem.

Cliff notes:
1) Reasons and education given for why I strongly dis-agree with what the dealership has stated.
2) Suggestions given for follow-up with the dealership.
3) Suggestions given for follow-up with the local repair shop.
4) Dismissed O-Rings question (still wondering which ones though...
).
5) Wrapped up with possible outcomes for the two logical choices: Diagnose further (or validate dealerships findings), or Pay for suggested service.

Remember: you said "I'm trying to educate myself a little", I did my best to explain fully, but it took quite a few words. Again, I am sorry for the long post.

As a final note: We have even touched upon the possibility that it is an electrical problem, fuel management problem, etc... Please let us know what you decide to do, and keep us posted on the outcome.
 

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I want to see the numbers as well.

Do you hear the turbo at all?

Is there a check engine light on?

Any other problems with the car at all?

If al else fails PM me and we can work something out.
I live somewhat near you.
 

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Discussion Starter · #4 ·
thanks for all of your help both on and off the list.

I took it to the Volvo dealership in Winter Park first. They diagnosed the low compression but recently the newest shop called the dealership for me and they said that the cylinders had uneven compression. It could be that's what they originally said.. or not. I don't really remember.

The newest place is called SKS Auto (something like that) in Maitland across the street from the Mercedes dealer. They seem to know what they're doing.

The SKS guy says the compression and poor performance are two separate problems. I'm gonna go ahead and get the PCV cleaned by the newest place. He's gonna call my extended warranty and see if they'll cover it. I imagine they won't.

Anyway they quoted me $450-$500 tops to clean the PCV that's about what the dealership wanted too. My regular mechanic wouldn't do it. Says he doesn't really know how.

The check engine light is on I don't "hear" the turbo but I don't think I know what to listen for. When it tries to go into turbo it shifts really hard.

I guess that's it. Thanks again for your help.

Tai
 
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