Skipping/power loss under load. - PeachParts Mercedes-Benz Forum

winmutt · #1 07-26-2010, 02:23 PM

When accelerating in my car I am getting pops of power loss. I checked the fuel filter and there was plenty of air. Tightened up the lines in the back and now there is no bubble. Any other suggestions? As it is not happening at idle its just about impossible to diagnose. I have considered sticking a camera in there to see that is happening but that sounds like certain failure.....

Suggestions?

compu_85 · #2 07-26-2010, 02:25 PM

Sounds like the overboost protection could be kicking in. Unplug the single wire from the sensor on the intake and go for another quick spin. Would be good to have a boost gauge hooked up too.

-J

jt20 · #3 07-26-2010, 02:27 PM

would this be in the motor home?

if its the 123, try the primer - remove, flip washer, replace and tighten

is its the w124, try the fuel filter mount ( see the nailing thread by sasquatchgeoff)

winmutt · #4 07-26-2010, 02:27 PM

Quote:

Originally Posted by compu_85

Sounds like the overboost protection could be kicking in. Unplug the single wire from the sensor on the intake and go for another quick spin. Would be good to have a boost gauge hooked up too.

That problem was removed years ago

. If this was a gasser I would swear it was skipping.

1985300d · #5 07-26-2010, 03:44 PM

how long since you did the valves? wouldnt hurt to check the gaps

winmutt · #6 07-26-2010, 04:37 PM

Quote:

Originally Posted by 1985300d

how long since you did the valves? wouldnt hurt to check the gaps

I dont see how that could do it. Within the last year. I usually do them in spring.

winmutt · #7 07-26-2010, 04:38 PM

Quote:

Originally Posted by jt20

would this be in the motor home?

if its the 123, try the primer - remove, flip washer, replace and tighten

is its the w124, try the fuel filter mount ( see the nailing thread by sasquatchgeoff)

W123. Primer, you mean the hand pump?

This started occuring out of no where.

chasinthesun · #8 07-26-2010, 05:10 PM

Check your compression ,if you have a cylinder not pulling its load you feel it in the peddle.I drove a car with two low compression holes ,it eventually siezed after driving it a year.Heavier oil seemed to help it along for those last few months.

winmutt · #9 07-26-2010, 05:37 PM

Its not continuous, its completely random and not without load. Idle or revving parked does not bring the ailment. I am fairly certain its fuel delivery.

Volvo Diesel · #10 07-26-2010, 06:58 PM

I had an issue that sounds similar to yours that I initially feared might be fuel or transmission related. Your W123 is a 1985 like mine, so it should have a small switch on top of the valver cover which switches off the A/C compressor when the accelerator is depressed below a certain level. Maybe other years have this as well, but I thought it was an '85/KLIMA related addition. Try unplugging that switch and see if the problem goes away. The heat and age had gotten to my switch, causing the A/C compressor to engage and disengage at random times, seemingly always under load, causing a hesitation or skip on acceleration.

-Chris

79Mercy · #11 07-26-2010, 08:06 PM

About the only thing that makes sense is air in the fuel lines. Check all the rubber lines under the car leading up to the motor, replace them if they're old and use the correct MB hose clamps, some cheapo hose clamps do not clamp correctly.

jt20 · #12 07-26-2010, 08:24 PM

I am almost certain you have air getting in from some obscure location.

on the 123 re-torque the hand primer pump after flipping the washer. i just had the same issue and ended up swapping my lift pump for no good reason, only to find my primer pump jiggled itself loose. = total PIA

the fuel filter housing fiasco can happen to any model. It is characterized by intermittent 'popping' or 'nailing' after a period of high loading ..... this is unbalanced injector response due to air in the lines.

the engine keeps running because it is such a a small amount and there is enough inertia to keep it moving until the next injection event.

conclusion... you have checked the regular issues.. I dare you to swap your fuel filter housing.

layback40 · #13 07-26-2010, 10:10 PM

Air is difficult to find. Given its doing it under load, I suspect you need to start at the tank & work your way along the line checking everything. A weak primary pump could contribute a well.
I guess you have replaced the secondary filter & cleaned the tank strainer.

85chedeng300D · #14 07-27-2010, 12:40 AM

Quote:

Originally Posted by winmutt

That problem was removed years ago

. If this was a gasser I would swear it was skipping.

What about the switch-over valve? It could be intermittently switching on and off..... just a thought....

winmutt · #15 07-28-2010, 11:36 AM

I believe now it is a sticking valve causing compression loss. When I replaced my valve stem seals I noticed that one of the valves was sticking. Last night I heard what sounds like valve hitting a piston. Time to look for a new head.