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mralexc, ASE Certified Technician
Category: Car
Satisfied Customers: 25
Experience:  ASE certified Master Automotive Technician, Vocational Degree in Advanced Automotive Technology, Nissan dealership training,
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Volvo XC90 2.5T: I have a 2005 XC90 D5 (163) which has recently

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I have a 2005 XC90 D5 (163) which has recently has the injectors cleaned (one replaced, 4 overhauled/cleaned). Also the EGR valve and inlet pipe were cleaned (there was a lot of carbon build-up). Now the car is smoking (much more exhaust smoke than normal) on idle, and big clouds of smoke when accelerating.

Any ideas why it's got worse now that the injectors are working better?


Hi my name is XXXXX XXXXX i am going to try to help you out, there can be several reasons your vehicle is blowing smoke, if it is a black or dark gray smoke then what is going on is there is either too much fuel,improper fuel spray or there is an insufficient burn process going on in the combustion chamber, most times when you clean the injectors you use a chemical process to clean them while they are on the vehicle, what happens is that these chemicals not only loosen up the carbon slag on the injectors but on the valves and piston face as well, and it usually burns off sometimes it doesn't it coats the spark plugs and causes an insufficient burn which causes black smoke, the best advice for this scenario is to perform a compression test on your engine and replace the plugs and let it finish burning off the carbon, white smoke is water it can come from humid air or a leaking intake manifold gasket ,cracked block or head etc and will usually have a sweet smell, big clouds of white smoke would be coolant and accompanied with a sweet smell. blue smoke is oil which can happen if the engine has excessive wear and the carbon cleaning removed the carbon buildup that was around the piston wall and was actually acting like another piston ring preventing the oil from being burned in the chamber to test for this you need to perform a cylinder leak down test. i hope i have been helpful if you have any further questions do not be afraid to ask i will do my best to help you.
Customer: replied 4 years ago.



Thanks for the answer. Can I confirm the following please? You say:


"the best advice for this scenario is to perform a compression test on your engine and replace the plugs and let it finish burning off the carbon"


Is this something you would expect the garage who did the work to undertake at no extra cost? Is it a normal situation?


And one final question, how long would you expect is needed to burn off the carbon slag that was loosened by the cleaning? It's been driven for a 150 miles or so since the work (keeping revs as high as practicable) and it's still happening.


Thanks for the feedback.



it all depends on what type of smoke is coming out of your exhaust.

if it is black smoke then yes i would recommend doing a compression test to make sure there is no issue with a loss of compression, a shop might also wish to re-pull the injectors to see if they are properly spraying.

if you went to the technician with an initial complaint of smoke coming out of the exhaust then the repair that they provided did not fix the problem and they should cover the additional labor for a compression test and possibly a leak down test, and fuel pressure test, and check the spray pattern etc...
these tests usually only take 30 or so minutes to do, and pay only an hour but the shop could absorb the cost easily as a good faith gesture to a customer.

just be nice to the technician, in this case the old adage about flies and honey is a good rule but don't be afraid to be firm you brought them a problem and they did not fix it completely.

if you as a customer off the street said hey my vehicle is running rough whats wrong and did not mention the smoke then there is less of a liability on their part but the good faith should still be there and there might be a minor charge for them to look into what they would see as a new problem,
to avoid this you might say, hey since you did the repair my car is smoking badly could you take a look i gave it a few days because i thought it was just something burning off but it hasn't gotten any better. then they would be liable for the testing however if their are additional repairs you are going to have to incur some costs like if it is the plugs you are going to have to pay for them or let them diagnose it and you replace their diagnosis yourself.
it would be the same as if your problem is engine oil blowby, the shop should have diagnosed the repair in the first place but they are going to say that the repair that they performed is only one of several issues you have and sometimes fixing one problem brings another to light. which is unfortunately true.

I once repaired a upper intake manifold gasket on a camaro that was leaking, so it did not run before i got it. the coolant was leaking into the cylinders so it ran rough and i told the customer it might do so for a day or two until it burned off all the garbage and that i would recommend replacing the spark plugs and 02 sensors when it finished cleaning itself out but it should be ok, a few days later it was still running rough, the vehicle because of the misfiring and the customer trying to race the vehicle like that it jumped time, which is also another possibility for black smoke but usually the engine runs badly. i had to do the diagnosis for free but i was able to charge for the additional repairs.
no technician is perfect but they should look at the car and try to figure something out without charging you. any additional repair though unless it was something that they did or repaired will be extra.

I hope this was of some help to you, if you have any more questions do not be afraid to ask i will answer as soon as i can
and don't forget to rate me if i you feel i have thoroughly helped.
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