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It looks like carbon is being blown out my muffler.

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.
1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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It looks like carbon is being blown out my muffler.

Postby Gregg Cain » 07 Feb 2010, 13:30

This website has benefited me immensely over the 3 years I have had my 850 wagon. Until now, any questions or issues I've come across were easily resolved with a little patience and research. Thank you. Now to my current car trouble. I parked my car and it was running fine. The next day I start it and the engine sputters badly, has little power, and will not idle.
The fuel pump is fine. Plugs and wires replaced. 2 fuel injectors were badly clogged, replaced all of them. At this point the car was drivable but still very weak, would not idle, and engine sputtered to the point it couldn't develop more than 4000 rpm. It did run better but a new issue arose. There was an overwhelming odor of gas coming into the cabin if I was driving and opened a window just a bit. The odor was not coming through the vents. Along with the gas fumes, what seem to be chunks of carbon started to blow out the exaust. (see attachement). I got a MAF code around this time, so I disconnected it. That stopped the fumes and carbon spray. Replaced MAF. Engine runs much smoother and stronger, still will not idol, and still has strong gas fumes from engine along with spraying carbon and smoke out the muffler. At one point it even blew oil over onto the top of the engine. I am hoping someone can help me to identify the problem and avoid any unneeded expenses. Thank you again.
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Re: It looks like carbon is being blown out my muffler.

Postby Ozark Lee » 07 Feb 2010, 16:22

I think I would start with the fuel pressure regulator on the end of the fuel rail. Take off the vacuum hose that goes to the regulator and look for signs of fuel. The diaphragm can rupture and it results in raw fuel being sucked into the intake manifold.

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Re: It looks like carbon is being blown out my muffler.

Postby Gregg Cain » 09 Feb 2010, 23:57

Sorry about the delayed response. No fuel in hose. Regulator was replaced at same time as injectors. Checked the intake air therm. it was bad. Wedged cold air side open. No difference. Any and all suggestions are welcomed. Thanks.
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Re: It looks like carbon is being blown out my muffler.

Postby JDS60R » 10 Feb 2010, 01:13

I see this type of staining from motorcyles when water condenses in the system or if the system is running so rich that gasoline in its liquid state makes it past the cat converter.

Are getting any 02 (oxygen sensor) codes and what oxygen sensor output voltages are you seeing?

Can you check the coolant temp sensor and see if it is working correctly?
and lastly

Please pressure test your cooling system and let us know what you found out. It is possible that coolant is making it into the combustion chamber, the car is compensating with more fuel and the unburnt coolant and fuel is wetting the inside of your exhaust and blowing out the carbon.
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Re: It looks like carbon is being blown out my muffler.

Postby FCPGroton » 10 Feb 2010, 01:38

I have seen this happen on my motorcycle when I start it up after it rains. Moister gets into the exhaust and condenses. Once the bike turns on and heats it up, it steams all the carbon off the inside of the exhaust and then blows it out the tail pipe. If there are no codes and the car is running fine, I would think it is just moister in the exhaust.
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Re: It looks like carbon is being blown out my muffler.

Postby charlyW » 10 Feb 2010, 15:35

See that all the time its just carbon in your exhaust being blown out when the inside of the exhaust condenses nothing to worry about

Also common on short run engines
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Re: It looks like carbon is being blown out my muffler.

Postby Gregg Cain » 13 Feb 2010, 10:41

i will check the O2 and coolant temp sensor. That makes sense about the blow out, but what about the very strong fuel odor from the front of the car? I don't notice it with the MAF unplugged.
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Re: It looks like carbon is being blown out my muffler.

Postby E Showell » 23 Feb 2010, 19:50

Had the same problem on my wife's former '96 850. Turned out to be a vacuum leak. Only the dealer was able to correctly diagnose. Leaking line was concealed under/near? manifold. Couldn't hurt to check that. Engine was throwing bad O2 sensor code, but that wasn't the problem.
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Re: It looks like carbon is being blown out my muffler.

Postby spensoft » 15 Mar 2010, 04:28

I just wanted thank everybody for the information posted here.

My son bought a 1994 850 Turbo with 145000 miles on it about 4 weeks ago. It was having a really hard time starting in the morning when it was cold. When it was warm outside, it was not as bad, but still hard to start. We checked all the normal stuff and we replace plugs, rotor, fuel filter and oil. We mostly did this because we had no idea when this had been done last. The only thing that helped was the plugs, but the car was still hard to start.

After reading a lot of post on this board, I came to the conclusion that this was definably an ignition related problem. When the car would start to kick over, there would always be black smoke coming out the exhaust. This appeared to be too rich of a fuel mixture.

So after reading this set of posts, I decided to pull the Fuel Pressure Regulator vacuum line off from under the throttle cable. This was the easiest place to get to it. I then tried to start the car, wow, it started right up (It had not been run all day). So I turned the car off and then tried again. Started right up, no problem and no black smoke. So I turned the car off and checked back under the hood and sure enough there was fuel coming out of the vacuum line the I had disconnected.

So we replaced the Fuel Pressure Regulator and now the car starts and runs like new. So thanks everybody for the info!!!

So now I have one question, with fuel being forced into this vacuum line, does anybody know if we should be concerned that any device connected to the vacuum like might have been damaged by the fuel?

Thanks
Brian
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