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help me diagnose my1993 Mercedes 300e


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stphnhrrll
New User

Apr 10, 2014, 8:56 AM

Post #1 of 6 (886 views)
help me diagnose my1993 Mercedes 300e Sign In

3.2 engine
210,000 miles
Engine was rebuilt May 2013 (not by me)

I've only owned this car less than 2 months. Usually it runs great, but every now and then it acts up. I just replaced the O2 sensor and it ran great for about 100 miles and then this morning it started again.

Here's what it is doing...

Even when it's running well, the idle lopes the tiniest amount (it doesn't concern me, probably a small vacuum leak I'll get to it later) when it's running poor it lopes hard. Between 500-1000rpms. When I drive it, it also lopes. It accelerates itself, but in a pulsing sort of way and not more than an extra 1-2 mph. If I were to coast in drive the car would sporadically inch forward on its own. When I gave it some gas, I could actually feel my catalytic converter vibrate underneath my feet. The car exhaust smells of gas, but only when it's running badly.

I hope I'm explaining it clearly. Anyway,I thought the problem was the o2 sensor, I was obviously wrong. I know it has to be in the fuel system, but I don't have a lot of money to just start replacing everything.

Please help!


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Apr 10, 2014, 9:45 AM

Post #2 of 6 (872 views)
Re: help me diagnose my1993 Mercedes 300e Sign In

You have to care about vacuum leaks you suspect and get any out of the way.


What I read into this is smelling gas that can quit and might just be leaking and delivering proper pressure gets messed up because of it? Just let fuel pressure up and go hunting for anything that carries fuel under pressure if only running a finger under assorted fittings and lines.


Generally that wouldn't be burning thru exhaust if so but would throw off everything and waste fuel, harm or kill O2 sensors, converters in time up to excessive back pressure then the car can't behave if not within parameters it can self adjust to cover.


Start looking for the obvious. BTW and it's IMO "rebuilt" engine doesn't mean it's new again at all,


T



stphnhrrll
New User

Apr 10, 2014, 9:58 AM

Post #3 of 6 (864 views)
Re: help me diagnose my1993 Mercedes 300e Sign In

Where would the leak be coming from though?

Could it possibly be the cold start valve? I have no issues with starting the car, but maybe it's just leaking?


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Apr 10, 2014, 10:13 AM

Post #4 of 6 (859 views)
Re: help me diagnose my1993 Mercedes 300e Sign In

Vacuum originated from intake manifold so anything sealing that, hoses, gaskets, diaphragms up to possible ducts for climate controls use it. If violated it sends along wrong information as manifold vacuum is a dependable way for things to know what load the engine is under. If too low it might think you are accelerating or going up a hill when you are not kind of thing.


Just rule out that. Engine should know if it's cold or not and would think by '93 it doesn't need (who knows what MB was thinking?) an extra something to deliver more fuel than the injectors for a short while when cold. I thought that ended ages older than this and you may know better. Little info on these cars from me and not going to pay for data on them in specifics,


T



stphnhrrll
New User

Apr 10, 2014, 1:58 PM

Post #5 of 6 (840 views)
Re: help me diagnose my1993 Mercedes 300e Sign In

I just checked for leaks and I couldn't find any, but when I pulled open the air filter cover there was no air filter. HUGE facepalm.

Just curious if that can cause symptoms similar to a vacuum leak?

Still no check engine light and when I started it again, it idled fine.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Apr 10, 2014, 2:54 PM

Post #6 of 6 (833 views)
Re: help me diagnose my1993 Mercedes 300e Sign In

Hmmm? Not a good sign and it probably would make more noise if missing. The question is why? Was it just too dirty to run somehow and taken out? Is it oily in where it belongs now which is not a good sign and how much junk may have been sucked in without one there.


Will it run differently without if all else is fine? Hard to say for sure.


For now get one and check everything to do with air intake parts that all is in place, plugged in.


IDK sport. If someone could have just missed that in the course of service I tend to doubt it. It may have run better enough to sell it with it missing so makes me wonder what else could have been hacked?


I suggest you do as much looking around as you can and find a shop that has a Benzo tech as they are to me a total pest for parts and prices. Special tools for some things likely so not a good DIY car for most people. One of the cars that if you have to ask the cost it's not for you IMO,


T







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