Poor accelration - PeachParts Mercedes-Benz Forum

lsmalley · #1 08-08-2014, 05:47 PM

As the title suggests, the acceleration on my car is extremely poor. I though the problem was remedied, but it has not gone away. I guess you could compare it to a plugged up catalytic converter. When I step on the gas, the car takes forever to gain speed. and If I am doing a decent 50-60 mph and say I want to pass a slow moving car, I step down on the gas to accelerate and the car actually starts to lose speed and power. Any help would be greatly appreciated.

oldsinner111 · #2 08-09-2014, 11:57 AM

I would check fuel pressure first.That will tell you if filltewr,regulator,or fuel pump problem.Next ignition.

lsmalley · #3 08-10-2014, 12:33 PM

fuel pressure is good, all ignition parts are good.Car runs super and idles smooth. only when accelerating.

oldsinner111 · #4 08-10-2014, 01:42 PM

Well my car is drive by wire,I had no problems when old engine was in.Now it doesn't open up as powerful.I will check when I have help,if throttle is opening all the way.Perhaps it needs lubing around throttle valve,or linkage from pedal is lose.Try that.

tbomachines · #5 08-10-2014, 04:53 PM

Have you troubleshooted the A/F ratio at all? The Bosch ignition systems are kind of a pain to do this -- I know at idle you can measure the duty cycle using a multimeter. I imagine if you ran longer wires you can get it into the passenger compartment pretty easily, but keep in mind it will fluctuate under load. I would also make sure that the MAP plate depresses and returns to its rest position without binding or resistance (it requires a little bit, but should be even throughout its depression). I would not think ignition is the issue unless it is clearly misfiring.

One other thing to consider is that the M103 is not a powerful engine by todays standards, and relies pretty heavily on gearing to get it going (esp. the 2.6). I would make sure the trans is kicking down correctly in addition to troubleshooting the AFR.

ps2cho · #6 08-10-2014, 09:38 PM

Fuel pressure is practically worthless to chase once you know its to spec. Check it and forget it. You need to do a fuel volume test if you actually want to diagnose -- Providing the correct amount of fuel at WOT will tell you where the issue is and you can work backwards. Unless you've been burning a quart a week for the last 5 years, its fuel related so forget about the cat its fine.

Basically this is it -- if you get the correct fuel quantity in 60 seconds, its the EHA and/or distributor, but most likely eha. If you don't get the specific quantity, its downstream either filters or pumps. Don't take this as advice to start with replacing parts. Do the test and report back.

lsmalley · #7 08-19-2014, 08:01 PM

EHA is working, fuel pressure is good. Also had the cat inspected by the shop that instsalled it. Guy cut a hole in it and looked at it and all was well. I'm jus taking a random guess, but could something be wrong with the throttle, throttle body, throttle body sensor? I am barely able to get up to freeway speed (70 mph), it takes a good 45 seconds to 1 minute to even reach 70 mph. If I try to floor it, the economy gauge goes all the way to the red and the car rapidly loses speed. If I easy up off the throttle some, but not all the way the it will slowly pick up speed again.

mpolli · #8 08-20-2014, 03:10 AM

Fuel filter? That would cause the symptom. Longshot maybe.

Ferdman · #9 08-20-2014, 06:40 AM

Ismalley, a bad Oxygen sensor could be causing your acceleration problem. Had a similar experience with a 1991 300CE.

Hirnbeiss · #10 08-20-2014, 07:03 AM

Is it downshifting correctly?

lsmalley · #11 08-21-2014, 05:19 AM

It is down shifting correctly. Just went and put in a new Bosch 02 sensor today and still have the same problem (and as a side note, if I seem to be throwing parts at the cat because someone makes a suggestion, it's because I get the part free under its warranty.) Vacuum is at 18 hg. Actually now it seems like the throttle plate isn't opening correctly

Skippy · #12 08-21-2014, 06:43 AM

If it's a regular mechanical throttle linkage, it should be easy to check. However, economy gauge in the red when you floor it is a good sign. I'm thinking it's most likely a fuel issue.

lsmalley · #13 08-27-2014, 02:00 AM

Quote:

Originally Posted by Skippy

If it's a regular mechanical throttle linkage, it should be easy to check. However, economy gauge in the red when you floor it is a good sign. I'm thinking it's most likely a fuel issue.

How do I check the throttle linkage? Also, with the air cleaner housing off and the distributor exposed I can start the car and give it gas by had and what I notice is that the plate seems to pulsate some and not open all the way (the plate connected to the fuel distributor, not the actual throttle body). Also, I am getting a CEL code #17, which is O2 sensor shorted to positive or ground. O2 sensor is brand new, maybe a week old. Could this be the OVP? This acceleration problem is really annoying and very unsafe. I can't get above 60-65 mph and it takes at least 15-20 seconds to get to 40 mph from a stop.

mpolli · #14 08-27-2014, 03:07 AM

Did you ever do the fuel volume test that was suggested? A clogged filter would have good pressure at idle and only lose it when more fuel was needed. Or is the filter new?

Skippy · #15 08-27-2014, 06:39 AM

That code would make me tend to think the sensor was bad out of the box (It happens.) or there's a problem with the wiring.

As for checking the throttle linkage, remove the air filter and whatever else you need to see the throttle butterfly, then floor the pedal while a helper looks to see if it goes fully open.