Engine cutout/sputter above 4300 RPM - PeachParts Mercedes-Benz Forum

#1 09-21-2002, 06:25 PM

All of a sudden my 220SEb cabriolet engine has gone from running like like a fine timepiece to missing/sputtering/cutting out whenever I am accelerating hard and after the RPM reaches 4300. It runs fine above 4300 if I am not accelerating. If I am cruising smoothly above 4300-5300 and punch the throttle, the problem will surface. It almost sounds like it starving and not getting enough fuel or air. I thought it might be a faulty advance but why would it run smoothly when not accelerating above 4300 if that was the case? Changing the fuel filter attached to the engine was no help and inspection of the old filter revealed it was in good condition. Is there an internal filter in the tank? I am assuming that the fuel pressure is ok if it can provide fuel to run at 5300 RPM. Any suggestions on what the problem could be? Thanks, Gregg

psfred · #2 09-22-2002, 12:50 PM

Gregg:

Sounds like a fuel supply problem -- you aren't using all that much at low throttle at high rpms, but when you open up, there isn't enough fuel.

I believe there is a tank screen, could be full of crud or rust.

You should probably test fuel delievery from the pump -- don't know the specs, but the usual is about a liter in 30 sec, 1.5-2.5 psi delivery pressure. Test by running car at idle on the fuel in the carbs with the fuel line disconnected and diverted into a large container. Be careful, fuel is very flammable ----- need I say more?

I'd bet you have either a tired fuel pump or a plugged tank screen.

Peter

#3 09-22-2002, 10:51 PM

Peter,
Thank you for your reply but my car doesn't have carburators. It is a 1963 220 SEb Cabriolet with an M127.984 fuel injected engine. Do you know if this model has an internal gas tank filter? Thanks, Gregg

psfred · #4 09-22-2002, 11:09 PM

Gregg:

Will still have a fuel screen in tank. Fuel pump should definitely produce a liter or so in 30 sec when jumpered at the relay and hose disconnected from IP. Should produce considerably more pressure, though.

I still think you are showing signs of fuel starvation, especially if you are getting good to excellent milage.

You can also check the resistance of the coil -- should be 0.8 ohms, I think. If the coil is bad, you can get loss of spark at high speeds, ditto for high charge density -- the spark won't jump the gap when the pressure in the cylinder is high on compression, as it is when the throttle is open.

Peter

cth350 · #5 09-23-2002, 01:57 PM

Fred's basic's are right. The pump spec is a bit off for the mechanical fuel injection motor. The 220se fuel pump delivers lots and lots of fuel at about 18psi. Though I don't have the specs either. The screen setup in the tank is exactly the same between a fuel injected and carb'd car.

You'll find that 4300 rpm is about the point where the advance weights in the distributor are fully extended. Any chance you recently replaced a screw on the housing ? I used one once that was a bit too long. It tore off a weight. Oops.

Rather than spending time guessing, bring the car to a shop with an engine scope. It will tell you precisely what's wrong.

-CTH

#6 09-23-2002, 05:59 PM

I checked an old manual and it depicted the gas tank as having a strainer. Since I had almost a full tank and it looked like one must have an empty tank to get to the strainer, I choose to check the fuel pump flow volume first. I unhooked the fuel line between the tank fuel pump and the engine fuel filter. After connecting a hose from that point to a container, I turned on the ignition for 30 seconds. In that short a period I was able to fill the container with 3/4 of a gallon of fuel. So I must assume that it isn't my electric fuel pump. What I didn't mention in my initial thread is that I had modified my distributor by installing a Perlux electronic ignition module and coil. The previous contributer jogged my memory to recall that my problems started after that installation and maybe my advance is being restricted because of that modification. I'll check that out next, although I still am puzzled as to why I can attain 5500 RPM without a miss as long as I am not accelerating hard? I appreciate those of you that have offered your advice. Gregg

Rackne · #7 09-25-2002, 10:53 PM

Check the screws on your new Pertronix they may be intruding on the vacuum advance. This occured on my XR-700 conversion due to the thinness of the replacement components, add a washer or two. The assembly should rotate freely within a couple of degrees.

#8 03-25-2003, 07:53 PM

At last! After fiddling with this problem for months in hopes of avoiding having to take it to a real MBZ mechanic, I have solved my RPM restricted acceleration delimma. It was not the fuel, fuel pump, fuel line, fuel filter, injection pump, injectors, spark plugs, spark plug wires or distributor mechanism. It was the timing! After installing the Pertronix solid state module, I had set the timing according to the no vaccum specifications specified in the Mercedes Manual. It turns out that the timing marks on the damper were either inaccurate or not compatible with the Pertronix installation. Simultaneous with the use of my timing light I was moving the distributor around and just trying to get it to "sound" right. It sounded right at what looked like 45 degrees of advance. I took it out for a road test and it accelerated like never before without a miss all the way to 6000 RPM. How can this be? Could the damper be mismarked? Could an earlier timing chain replacement cause a mismatch in timing? Any clues out there?

psfred · #9 03-25-2003, 09:51 PM

Check to make sure you are using the correct spark plug wire (I know, too easy, but 45 out is about right for the next plug back in rotation.....).

It is possible for the damper to slide if the rubber goes bad. This means replacing it, of course.

Should be no difference in the Pertronix and point timing -- the Pertronix is only the pickup that switches the coil to replace the plugs, and if you got the wiring off, it wouldn't run.....

Very late timing will indeed limit top rpm!

Glad you found the problem.

Peter