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  #1  
Old 03-19-2009, 10:16 PM
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'90 300SE fuel smell under hood

A co-worker has a '90 300SE with the same engine as my '88 300SEL and had asked me this, but I have no clue. He said the other day he faintly smelled gas and smelled between the crack of the fender/hood and could smell some gas fumes... not bad though. He said its been like this for awhile, but there are no fuel leaks to be seen visibly and the car gets about 21 mpg. I did a search and seen where some people with 300E models mention something of a EHA valve that sometimes leak on these cars, but I looked and it looks like a relay of some sort to me? Looks quite costly as well. His mechanic told him that it looks like the way these engines are designed that a fire from a fuel leak is low, because the exhaust manifold is on the passenger side of the car and there is nothing on the left side of the engine that really would get hot enough to spark a blaze, but nevertheless, he does not want a fuel leak if something is occuring. The mechanic also said, "of course you smell gas, what do you think this car runs on, coal"? lol. I have yet not to smell a little diesel fumes under the hood of a diesel engine, so I guess some gas fumes on a gasoline engine car (especially older) is not really that uncommon or cause for concerns?

I looked around my M103 engine today and I did not smell raw gas fumes, but if I get close to the air cleaner I can smell some gas fumes (when the engine is fully warmed), but it seems to be coming from the hole in the center of the air cleaner cover... I guess this is normal? I also thought I would smell around mine and after a 40 mile trip, I pulled in the driveway turned the car off and went to the front and smelled in the grill area and faintly smelled gas fumes, but not major and I do not see any fuel leaking on my car either. My old '85 380SE had some sort of a canister by the radiator that always omitted gas fumes. No one knew what it was though.

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Old 03-20-2009, 08:25 AM
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As you mention the EHA valve bodies sometimes develop a hairline crack and leak. It's easier to detect if the engine is cold because engine heat evaporates any slight weeping. From my experience it was a very strong gas odor. It would be worth pulling the air filter when the engine is cold, then starting the engine and closely examine the EHA valve for any leakage.
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  #3  
Old 03-20-2009, 08:53 AM
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A slight fuel odor probably isn't much of a concern....but I'd look things over. A strong fuel smell is bad.

FYI none of our diesels smell like diesel under the hood at all. If all the lines and clamps are in good shape and not sweating or leaking....there should be 0 diesel smell.

My brothers 300D did smell like diesel last week, because his cigar hose split at the top and was pulsing a steady stream of fuel down the hose, onto the car, and onto the ground. Replace the hose....cleaned the fuel up....no more smell.
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Old 03-21-2009, 01:40 AM
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I am not sure about his car, but on my car, I cant smell any gas smell at all when the engine is cold.... only a faint smell with a hot engine and I smell between the "cracks" or the left side of the grille. Hey, isnt the air intake on that side and perhaps one reason why a faint fuel smell can be smelled there when the engine is hot and turned off?

Quote:
Originally Posted by Ferdman View Post
As you mention the EHA valve bodies sometimes develop a hairline crack and leak. It's easier to detect if the engine is cold because engine heat evaporates any slight weeping. From my experience it was a very strong gas odor. It would be worth pulling the air filter when the engine is cold, then starting the engine and closely examine the EHA valve for any leakage.
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Old 03-21-2009, 01:42 AM
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Yeah, its only a minor smell with my car, alittle stronger with his.

My '84 190D diesel didnt have a diesel smell under the hood either.... only occasionally and very faintly, but there was a canister/filter type part on the left front of the engine that had a couple of cracks on it. I guess it was from that. I sold the car before I got around to replacing it. I guess the new owner took care of that. Strange, the MB had been serviced at a Mercedes dealer only 3 months before I bought it. Not sure why they did not catch it. They were instructed to go over the car with a fine toothed comb and service anything it needed.

Quote:
Originally Posted by pawoSD View Post
A slight fuel odor probably isn't much of a concern....but I'd look things over. A strong fuel smell is bad.

FYI none of our diesels smell like diesel under the hood at all. If all the lines and clamps are in good shape and not sweating or leaking....there should be 0 diesel smell.

My brothers 300D did smell like diesel last week, because his cigar hose split at the top and was pulsing a steady stream of fuel down the hose, onto the car, and onto the ground. Replace the hose....cleaned the fuel up....no more smell.
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Old 03-21-2009, 09:40 PM
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Just run your finger along under the EHA module; if it's oozing there will be a buildup of gas/dirt residue. My '91 has no gas smell at all.

DG
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Old 03-24-2009, 01:07 AM
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Thanks. I will check this on my car and his as well. Can it be felt without removing the air cleaner?
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Old 03-24-2009, 01:09 AM
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Quote:
Originally Posted by Ferdman View Post
It would be worth pulling the air filter when the engine is cold, then starting the engine and closely examine the EHA valve for any leakage.
Will the engine even start with the air filter removed? Some cars with FI wont start with this removed.
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  #9  
Old 03-24-2009, 09:20 AM
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My 1991 300CE starts and runs fine with the air filter housing removed. It would be very difficult to determine if the EHA valve is leaking with the air filter housing in place. You would need a mirror to even see the EHA valve, let alone feel for a weeping gas leak. Of course, that's a 104 engine ... the 103 engines may have more clearance.
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Old 03-26-2009, 01:11 AM
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Thanks. I will check mine when I get a chance and I will relay this to him as well.

Someone told me if it was leaking then the car may be hard to start... my car is easy to start and AFAIK, his is as well.

I am starting to panic because my Lexus has broken and I may need to start driving the MB regularly and dont want to if there is a fuel leak issue.

I guess its not like it spews gas or anything does it? I cant be losing much fuel, as I get about 20-21 mpg in city driving. As mentioned, the smell is so minor, I was thinking it was just fumes coming from the air cleaner housing.
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  #11  
Old 03-26-2009, 08:07 AM
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There's no risk driving it, it doesn't leak much fuel even if it is leaking.....just take a look at it to be sure, its pretty easy to check.
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'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
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  #12  
Old 03-26-2009, 07:49 PM
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Quote:
Originally Posted by pawoSD View Post
There's no risk driving it, it doesn't leak much fuel even if it is leaking.....just take a look at it to be sure, its pretty easy to check.

Thanks. I started to check mine today, but about as soon as I got the hood open, it started to rain. I was able to smell first and the smell is not coming from below the air filter it seems, but from the hole in top of the air cleaner. Could that mean something different, or still possibly a leaking EHA? I will check it more closely on my next day off and if its not raining.
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  #13  
Old 03-26-2009, 09:52 PM
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Don't forget to check the Fuel Pressure Regulator vacuum line. I had mine leak gasoline back in the engine through that line on my 560SEL.
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  #14  
Old 03-27-2009, 06:21 AM
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Professor, as far as I know that line running from the fuel pressure regulator to the breather hose is a vent line. If the FPR diaphragm fails it directs leaking fuel to the valve cover to prevent an under-hood fire.
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  #15  
Old 03-27-2009, 03:32 PM
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Quote:
Originally Posted by Ferdman View Post
Professor, as far as I know that line running from the fuel pressure regulator to the breather hose is a vent line. If the FPR diaphragm fails it directs leaking fuel to the valve cover to prevent an under-hood fire.
It serves as a vent line in case of failure but when operating I think it may actually help the regulator figure out it's reference to regulate pressure by comparing the fuel pressure to that of the manifold. I might be wrong but that's my guess.

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