We're STUMPED!
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Newbie
Joined: Nov 2012
Posts: 3
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300e
We're STUMPED!
I have just purchased a '93 300e with a problem that no one seems to be able to solve. It is immaculate and too cheap to walk away from. Now I have had the same mechanic for over 10 years for all my MB's, and while he doesn't say he can't fix it, he has had the car for 4 days with no solution yet. I really trust this guy, but am getting desperate. Here's the problem:
The car starts fine, and can run a little rough at first but once warm seems to idle fine. When accelerating the car does fine until somewhere around 1500-2000rpm at which time the acceleration drops out. If I back off the pedal and slowly start pressing it again it will accelerate until the same rpm point and then stop accelerating. I have repeated this until I have the car up to 65 miles per hour at which time she seems to run fine. But if I come to a grade, (uphill), she slowly losses speed and won't accelerate until the road becomes level again, at which time she will SLOWLY regain her speed by not pressing too much on the gas.
The previous owner alledgedly switched out the 'throttle body', and the 'computer' with no change, (the old ones were in the trunk when I purchased the vehicle, although I doubt new OEM parts were used as replacements). I figured the previous owner just didn't know what he was doing and was sure my mechanic would quickly diagnose and solve the problem, but so far no results. Before taking it in, I noticed the smell of gas as though the fuel mixture was too rich, also some VERY tiny black bits coming from the tail pipe. Car has no visible leaks
WE ARE STUMPED! Has anyone ever encountered this problem?? Help!
The car starts fine, and can run a little rough at first but once warm seems to idle fine. When accelerating the car does fine until somewhere around 1500-2000rpm at which time the acceleration drops out. If I back off the pedal and slowly start pressing it again it will accelerate until the same rpm point and then stop accelerating. I have repeated this until I have the car up to 65 miles per hour at which time she seems to run fine. But if I come to a grade, (uphill), she slowly losses speed and won't accelerate until the road becomes level again, at which time she will SLOWLY regain her speed by not pressing too much on the gas.
The previous owner alledgedly switched out the 'throttle body', and the 'computer' with no change, (the old ones were in the trunk when I purchased the vehicle, although I doubt new OEM parts were used as replacements). I figured the previous owner just didn't know what he was doing and was sure my mechanic would quickly diagnose and solve the problem, but so far no results. Before taking it in, I noticed the smell of gas as though the fuel mixture was too rich, also some VERY tiny black bits coming from the tail pipe. Car has no visible leaks
WE ARE STUMPED! Has anyone ever encountered this problem?? Help!
Junior Member
Joined: Jan 2012
Posts: 21
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1990 300 te
What do the spark plugs look like? Tap into the oxygen sensor with a DVM and check it's output. If the fuel injection system is working it will fluxuate between about 0 volts to almost 1 volt every few seconds. If it stays close to zero then you are running way lean. There are of course a number ot things that can cause that.
I had a similar problem when the can timing was a tooth or two off. Above a certian RPM the engine would just run out of power. Verify the timing marks on the crank and cam line up correctly. Or, you can watch the valves on #1 cylinder. Going past TDC every other time around you will be at the end of the exhaust stroke where the overlap of the valves happen. The intake should be just opening as the exhaust is just closing. If this overlap does not happen at TDC you may have jumped a cam chain.
I had a similar problem when the can timing was a tooth or two off. Above a certian RPM the engine would just run out of power. Verify the timing marks on the crank and cam line up correctly. Or, you can watch the valves on #1 cylinder. Going past TDC every other time around you will be at the end of the exhaust stroke where the overlap of the valves happen. The intake should be just opening as the exhaust is just closing. If this overlap does not happen at TDC you may have jumped a cam chain.
Junior Member
Joined: Dec 2012
Posts: 21
Likes: 0
From: Southwest Wisconsin
1991 190E 2.6
Hello Roggie!
I feel your pain, it took me several weeks to find that my friends '90 300E (that he couldn't get started) had a bad ignition coil.
Could it be possible to get a video of this car in action?
I wouldn't debunk that its the cats or any single thing right away until you do some diagnosis first.
If it is the cats, there is a way to test them;
Check the temp before and after the cat with a pyrometer or wireless thermometer.
The temperature should be considerable higher after the cat than before (like 200+ degrees F hotter)
The cats may appear OK, but the insides could be bad.
What else could it be?
I would recommend checking ignition and fuel.
If the engine is misfiring under acceleration, there is a good chance of the problem being in the ignition system.
Fuel: as revs increase, the engine demands more fuel pressure and flow. If there is poor fuel pressure (or flow), this could cause the symptoms you are experiencing (hesitation, poor accel, etc.)
Short and Sweet:
I would recommend checking the catalytic convertors like I said above with a wireless thermometer.
If cats are OK, check ignition system for faulted spark plugs or coil (Problems here are unlikely in this case)
Ask your mechanic about what they did about checking the fuel system. If it comes down to fuel, there are many things to look into. If it comes down to fuel, this can be discussed when we get there.
Best of luck to you!
Heres a video on checking cats: (ErictheCarGuy)
-201Freak
I feel your pain, it took me several weeks to find that my friends '90 300E (that he couldn't get started) had a bad ignition coil.
Could it be possible to get a video of this car in action?
I wouldn't debunk that its the cats or any single thing right away until you do some diagnosis first.
If it is the cats, there is a way to test them;
Check the temp before and after the cat with a pyrometer or wireless thermometer.
The temperature should be considerable higher after the cat than before (like 200+ degrees F hotter)
The cats may appear OK, but the insides could be bad.
What else could it be?
I would recommend checking ignition and fuel.
If the engine is misfiring under acceleration, there is a good chance of the problem being in the ignition system.
Fuel: as revs increase, the engine demands more fuel pressure and flow. If there is poor fuel pressure (or flow), this could cause the symptoms you are experiencing (hesitation, poor accel, etc.)
Short and Sweet:
I would recommend checking the catalytic convertors like I said above with a wireless thermometer.
If cats are OK, check ignition system for faulted spark plugs or coil (Problems here are unlikely in this case)
Ask your mechanic about what they did about checking the fuel system. If it comes down to fuel, there are many things to look into. If it comes down to fuel, this can be discussed when we get there.
Best of luck to you!
Heres a video on checking cats: (ErictheCarGuy)
-201Freak
