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Discussion Starter #1 (Edited)
06 s40 t5 awd m66

Ok, so within the past 2 months or so ive been having some problems with my 2006 volvo s40 t5, its AWD and has the m66 6 speed manual transmission, its all stock too. I cant seem to be able to pinpoint exactly what is wrong. A couple months ago it started hesitating then it got worse. After a bad shop experience and needless parts and money the problem persists. I decided to look at the plugs becuse it threw a couple misfire codes for cylinders 2,3, and 4 and listed plugs as the probable cause. The plugs were burned and corroded so i replaced them. Packs looked fine. After replacing the plugs the problem went away. But now, its back. It happens right after i shift and get on it. It hesitates and shutters. It hasnt thrown a code yet. The one time i want to see the light, it doesnt come on! I can also hear the turbo spool up and sometimes it doesnt sound right. Like it spools but then it misfires, stops prematurely. So anyway, i was thinking it might be coil packs, bad cat, tcv, turbo, vacuum leak, clutch, im just not sure anymore. It also seems to be better the closer to an empty tank i get (usually around a half tank it performs better). I would really appreciate any and all help or ideas and thoughts. I am also in the US.
 

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Sounds very fuel pressure sensorish to me...the hesitation that you feel is a symptom as well as loss of gas mileage and performance, so you may want to start investigating that as a potential source. It may not throw a code at first, but eventually it probably will. I think if it's a P0193 if I remember, but I could be off. Regardless, this is pretty common with these and there is a lot of good info out there to help you see if this is a possible cause - if you just do a quick search you'll likely come across something here. It's a relatively easy fix that you can do yourself.
 

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Discussion Starter #3
Hey, thanks for responding! I appreciate the help. When we took it to the shop that was one of the parts they replaced. Could it have gone bad again and that quick? How can i test it? I still have the old part. Maybe ill get lucky and they just forgot to put the new part in lol (wouldnt surprise me with this shop)
 

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Well, I wouldn't think that the case. Provided they actually did install the new one, which could be determined with a quick inspection this may not be the source. You say you changed the plugs recently do you know what they were replaced with? Could there be a possible gap issue? Did you inspect to see if there is any oil leaking around the area that could be leaking into the holes?

Besides the OEM Volov plugs, a lot of us are using the Denso's & NGK's with no issue. I've been using the NGK's and have had no problems whatsoever. In fact I recently changed mine and it fixed a little hesitation issue I was experiencing at higher speeds in the lower gears.

Also, this may sound dumb to ask, but are you running premium fuel? I've read people having issues like this by running a lower quality fuel. I'm sure some of the guys around here will have some more ideas that I'm not mentioning as well.
 

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Discussion Starter #5
Yeah, im using premium fuel. I checked and yeah they did put the new part in, i said that more as a joke because of how bad the service was. The plugs i used were NGKs. Same gap.I filled up this morning and it seemed fine but that can change
 

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Hmmm...well that's a bummer, so what about cleaning things like the MAF and/or TB?

Also, came across this thread...does any of this sound like what you're experiencing?
 

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fuel rail sensor...or fuel control module... the module gets its info off the rail sensor and tells the fuel pump the pressure output kind of weird, i would have just stuck with the reliable fuel pressure regulator if i were the engineer......
 

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Discussion Starter #8
Thanks for sharing! Well, it kind of does but not quite. I do drive the highway every day, about 120 miles a day. So i can see it being the problem. Plus the car has 143,xxx miles on it. Ill check the sensor and see how it looks. It doesnt really stall it just kind of hesitates when i get on it to try to pass people or get on the highway. Then at highway speed if i let off the gas it goes from 80 to 60 in about 5 seconds flat (should be some kind of record LOL)! I do need new brakes but they dont make any noise and theres no dragging noise when it starts to slow down. also idles a little rough too. Going against the wind or uphill is like pulling teeth! But its definitely something ill look at!
 

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Discussion Starter #9
fuel rail sensor...or fuel control module... the module gets its info off the rail sensor and tells the fuel pump the pressure output kind of weird, i would have just stuck with the reliable fuel pressure regulator if i were the engineer......
any way i can check the fuel rail sensor or module to make sure?
 

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I could be wrong, but I believe the fuel rail sensor is another name for the FPS. The control module is not something that you don't really want to replace or should have do...they typically aren't an issue from what I've read.
 

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Just tossing this out there but there's no way you can look at a coil pack and deem it to be fine. My experience with multiple cylinder misfire codes has usually pointed towards bad coils, and even then it usually is just one coil. I would buy one or two new coils and start doing some troubleshooting. Do you have a Vida/Dice unit? Also make 100% sure your NGK's are gapped right for Volvo at .028 because they aren't out of the box (at least the ones I have used). I usually run OEM plugs, but have NGK's in the S60. And by the way, I had a very similar problem to yours in my S80 last year, getting on the gas between 50-70 it would sputter and run like crap but idled fine and had no issues under 50. Turned out my coil on cylinder 1 was bad, no codes. Pretty frustrating sometimes, but take care of the small simple stuff you can do yourself first before diving deep into the really expensive stuff. At 143K the coils could definitely be getting iffy.
 

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Ya, I think beachnut has made some good points. Unless you are 100% sure it's never safe to assume that a part is free and clear. These are much cheaper fixes than throwing a bunch of money at the problem hoping it will fix.

I'm pretty sure you can also test the functionality of the coils by using an ohm meter. A quick search should yield many results on how to do this. I guess you could also try to verify that there is no problems with the fuel injectors as well while you're at it.
 

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Discussion Starter #14
Update: Thank you to everyone who has commented and helped with my vehicular problem. Today i discovered what was to blame for the lengthy and stressful issue. The expansion tank. As weird as it may sound that is what was wrong. My expansion tank had a large, deep crack in the top about 3 inches long that did not allow for the cooling system to build the pressure needed to efficiently cool the engine. I had put an epoxy patch over it but it heated up so much that it eventually soften the epoxy enough to blow the patch off. While the patch was in place my car ran much better, though it still had small, slight hesitations. When the patch finally blew off this past week i noticed the hesitations even more. I was unable to link the tank to the problem because i was focusing on bigger things. I had ordered the tank some time ago but i didnt put it on because i had patched the old one. So, today i put the new tank on and ran it. It ran beautiful!! Absolutely no hesitation at all! Its as quick and agile as ever! The problem was that the engine was over heating just enough to keep it from running smoothly. I had suspected the tank to have something to do with it but denied replacing it. Always go with your gut. When i had removed the tank i could see dried coolant all over the engine compartment. It has a smooth idle and runs great. Plugs were neccesary but the tank if left untouched surely would have corroded the new ones too.
 

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thanks for sharing your solution! wow, these coolant expansion tanks really are weak link...and, unfortunately, also pretty critical....
 

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Wow...what a random solution. I though having it cracked would require attention, but not the cause of your problem. We've all had these go and I don't think I've ever heard your problems being a byproduct. Glad you got it worked out and hopefully this helps someone else in the future.
 

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Discussion Starter #17
Yeah ive never seen this happen either, but theres always a weird crazy case. Seems to always be me lol. Hopefully this will help others from spending needless time and money! Moral of the story is, if you have a cracked tank, REPLACE IT! Thanks to all!
 

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im not convinced it was the expansion-- hope thats all it was though.
 

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Discussion Starter #20
It did when the patch finally blew off yeah but it went back down. Every now and then i could hear the tank lose pressure. Ive gone through a full tank with no problems. Ive run it though the paces too. It could have been burning coolant too
 
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