Owner of a 1991 300E and looking for a cliff.
 

Not really but you get the point.

I have looked through previous posts and some of the symptoms match and others don't so here it goes.

My 300E (3.0 liter Straight six) is a 91 with 177,000 miles on it. I started having problems last fall stalling when I stop and sputtering and jerking once I do get going. I brought it in and it was the distributor cap which was replaced and the problem was solved... or so I thought. A few months later I started getting the same problems. it started with the occasional stall when I would come to a stop. But then turned into stalling every time I stop as well as jerking and slowly getting up to speed, as well as when I am going a speed and wanted to speed up it would jump and jerk and I would have to back off on the gas pedal. When I brought the car in before he indicated that the Spark Plug wires needed to be replaced. So I did that a couple weeks ago as well as changing the fuel filter with instant gratification but a day later back to square one. I can drive for about 30-45 minutes fine and then while holding the gas pedal in the same position the power just goes away and i essentially coast to a stall and engine shut off. I start the car and and can drive for only a mile after that with the same thing happening. http://www.peachparts.com/shopforum/...cons/icon8.gif

I have tried the whole fuel additive cures from seafoam to fuel injector cleaner, as well as Isoheet (I live in Minnesota). I got the car two years ago from an unknown owner (through a dealership that go it at an auction) The car had 161,000 miles when I got it I have always used premium gasoline 91 octane being the lowest that I have used. I've always changed oil regularly.

Any thoughts:confused:?

You replaced just the distributor cap, or the cap and rotor? You're getting no fault codes?

It almost certainly HAS to be in your ignition system if you replaced ignition components and that fixes it even temporarily... I think you are on the right path...

Pull the cap off and view the contacts--see what kind of wear they have amassed. Were the plugs changed with the wires?

You should also have the fuel pressure checked for good measure...

-GH

I replaced the actual plugs at the same time as the distributor cap.

I am not very engine savvy. What exactly do you mean by the ignition System.

I have no indicator lights coming on my dash if that's what you mean.

My car does that every once in a while...has the same straight six engine as yours. I get a check engine light every once in a while, I checked the error codes, and it came up as a faulty Air Mass Meter potentiometer. I haven't replaced it, because they car still runs fine, but it will throw a code every once in a while.

Is your engine consuming oil at all? It could be burning oil, and causing the spark plugs to foul, which would explain the strange running conditions...

But honestly, if you've already replaced everything in the ignition system (Spark plugs, wires, cap and rotor) then it could very well be a problem with the Bosch CIS fuel injection system. I would take a it to a competent Mercedes specialist.

Now by putting out "codes" what exactly do you mean? is this something that I can do or would i need a special computer hook up thing? AKA bring it to a MB dealership.

Do a search on how to check codes. No, you don't necessarily need a computer to check them. just count the blinks.

I can not speak for your W124 engine, however, a friend of mine had problems with replacement distributor caps on a 1986 190E 2.3. He finally went to the dealer to get a new cap and it ran fine. Just food for thought.

Thanks Nate but I used a brand new cap when I replaced it. And like I said before It ran Like a champ then started going down hill a couple of months after that.

If you replaced the cap only, and not the rotor, as now twice suggested, the rotor is very likely the problem.

Alright I will look into that. Thank you.

Pull your spark plugs and check them for oil fouling. I remember someone had posted about this same problem a while back and it turned out to be worn valve stem seals. That would not be unlikely on an engine with 177k miles on it.

Hi, I also had this exact same problem for 4 months. I have a 24-Valve 300E 1991. After many trips to the Garage, my mechanic changed the Distributor cap AND the Rotor Button that sits behind it. The rotor showed signs of corrosion and arcing that caused the rough idling and stalling intermittently. No problems now for the last 2000K's. If that doesn't fix it, you would need a very tall cliff!

Dont forget, these cars have oxyegn sensor that gets weak but still dont turn on CE light. My experience is to change these out as poor running engine messes up sensors and cat.

Kind of a bump
 

Well I brought it into a local guy who works on cars in his garage. Doesnt work on MB's much but he said he figured it out but I listened to his message a dozen times and cant make out the name of the part, he didn't sound too sure of the name either he did say however that...

+ It is located by the fuel pump
+ It lets air into the engine.

Any help deciphering? As well as finding the part he said that he has calls out to guys in the surrounding five state area with no luck. Any help would be great I just got done with school for the semester and WANT TO DRIVE!!

Sounds like an unsolvable riddle - anything letting air into the engine wouldn't be located near the fuel pump.

Called him back and he said it's the Jetronic. Anyone have one there wanting to get rid of?

Still a bit vague. Jetronic is the name for the fuel injection system of that era, which has many parts. "Lets air into the engine" sounds like maybe the air flow meter but you need to find out more.

300 e
 

if you have an electronic distributor it very well could be your pick ip coil that tell the dist which plug to fir. fuel pressure? shorted condenser in your dist. coil could be weak. chk for a bright blue spark from the center wire to eng block, you have to disconnect it and have someone crank it for you be careful its about 40,000 volts or higher. i really suspect you coil or the thingahmajig that replaces the coil. get you a cheap manual for your car divide and conquer.

Sounds like your crank sensor is going bad.Had a car like yours with the same problem.Needs to be OHM checked when car is not running ,although some times testing and wiggling wire at same time may get bad readings.If you test when car is running fine,you may get good readings.
One end of sensor is about a foot behind pass. headlight(test end) other is behind oil filter.Use ,search,to find the answer.You will get much more info in a much shorter time.
Pretty easy to test if you have an ohm meter,cheap at sears
Good luck
Rich

Thanks I brought that up to my mechanic and he said he hadn't thought of that but is going to check on it.

But...

He also said that he knows that this part is bad. Not sure what it is. Its under the air filter housing, a sort of plunger like thing. That whole part is bad. Can anyone help with the name of that part? Thank you all so much for your help. When I get it all fixed I'll let you guys know.

Are you referring to the part that is a round disc that moves up and down? If so, that is called the Air Mass Meter...and they cost around $800 new, IIRC.

Seems like usually the electronic sensor attached to those is the problem...not the meter itself.

How does the mechanic know it is bad? If he knows it's bad why can't he say what it is? You need a part number or a picture or to look at the EPC. It sounds as if you are describing the airflow sensor, aka airflow meter. It does have a replaceable potentiometer but they are no long in production by Bosch.

I took some pictures of the part but cant put them on here because of the size limit.

How about reducing their size?

Put them on www.photobucket.com then copy/paste the IMG Code into the body of your post.

Like this:

http://i179.photobucket.com/albums/w...d/IMG_0685.jpg

You can view the part at this URL

http://s285.photobucket.com/albums/ll41/300EforERIC/?action=view&current=AirFlow.jpg

Thank you for all of your help.

By the way How would I/My Mechanic be able to tell if it was just the Potentiometer and not just the whole part?

I reread your first post again and was wondering what your most recent problem was.
Is the car shutting off and comming to a stop?
Does it start right back up?
Or is it more of a rough running problem.
Maybe replacing the parts you changed fixed some things and this is a new problem.So what is the most recent problem you are having? I ask because this site may help your mechanic fix the problem as he may not be very familiar with Mercedes fuel injection.
Thanks
Rich

After driving for a half an hour or close to that I will be going, and with no warning the RPM's just drop to idle numbers and I slowly get to idle speed then it dies, And yes it will start right back up. Which is why he thinks that it is not the crank sensor.

Had a very similar problem - turned out to be the Fuel Pump Relay - refer thread - http://www.peachparts.com/shopforum/tech-help/210262-engine-cuts-out-high-speed-only.html

If it is the relay on the 1991 that would be the M.A.S unit. This does lots more than the fuel pump which makes it a little pricey.If I am correct it does the auto close and sunroof close with the key in door,the AC relay is in it,fuel pump relay and some think else If you have any good CD'S on the 124 you can bypass it to test it.Think it it pin 7 and 8 but please look it up first.
If you do decide to buy one tell me the part number.I should have one here.Also have a bunch of other 124 parts.
Thanks
Rich

How would I/My Mechanic be able to tell if it was just the Potentiometer and not just the whole part?

There's an old post here, at least 5 years ago, where someone had their throttle actuator rebuilt. Before sending it off they inspected it very carefully, and did so again when it came back, and concluded that the only thing the rebuilder did was to replace the potentiometer. I don't think there's much else that can go wrong on those old air flow meters.

I think you are going down the wrong road with the potentimeter.It would be cheaper to look for a fuel problem than the meter.The meter would not make the car stall.These cars can run pretty well with no power to the fuel distribator.Try taking out the OVP relay.Hard to start but runs ok when it starts.It won't die on you when driving,maybe a lousy idle.Bypassing the fuel pump relay is not that hard and you can drive it untill you are sure it is not a fuel pump problem.If not you have a crank pickup problem,which would make it die.Try the easy stuff first.Both of those problems are not that hard to verify
Rich

Fixed it awhile ago...
 

I finally got the car fixed awhile ago and I just wanted to close out this post and say thanks for all the help.

As some of you suggested it was the fuel pump. I broke down and finally brought it into a Merc dealership and had them diagnose it. The primary fuel Pump was, for some reason, overheating and shutting off I would then have to rely on the secondary fuel pump but that wouldn't get me too far. So with the Help of Phil i got a great deal on two new fuel pumps $128.00 each through all parts Express and and a new fuel filter (since I was gonna be under there anyways) And my girlfriends dad and I replaced the whole kit and Kaboodle. Car runs great! From the time we chocked the wheels till the time we set it back down it only took 45 minutes.

We took the whole assembly off and replaced the pumps and filters on the bench. It was really slick. Well thanks again.

Now onto the next Project, Those infamous dash lights...

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