Loss of power up hills - PeachParts Mercedes-Benz Forum

Veloce300DT · #1 06-04-2006, 08:58 PM

My 300D Turbo has started acting up. Im going to be cleaning the banjo bolt out tomorrow to see if it helps any. Here is what the problem is.

Resistance to acceleration on hills, grades, and steep freeway onramps.

Acceleration on level ground is fine most of the time.

When I am traveling on the highway at any speed, once I start climbing a grade or hill, the car decelerates dramatically- and feels as though its starving for power- at the same time i feel some light vibration in the accelerator pedal... in an oscillating pattern. I have to floor the car to keep it moving.. even if I am traveling at 85mph. Usually my car has had PLENTY of power for hills and grades- I used to be passing everybody in the fast lane. Now I am stuck in the slow lane hoping I dont get rear ended.

The same thing happens when traversing steep freeway on-ramps... at full throttle there is no power- the car stays at a stagnant speed, and once the climb is over, it resumes accelerating.

And sometimes when I am on flat ground, my car will accelerate to 85mph and will nto go anny faster unless I start going down hiill. It used to pass 85mph with the blink of an eye, without having to floor it.

Any ideas?

The fuel system is fine... clean and flowing well. My injectors are tired. They neeed replacement. Other than that my only guess is a clogged banjo bolt, or maybe an EGR problem. Im thinking banjo bolt only because when the car exhibits the symptoms described- it feels as though there is little boost from the turbo. Its relatively fine otherwise.

d.delano · #2 06-05-2006, 01:05 AM

bypass the overboost solenoid on the firewall, the one the ALDA hose goes through
see what happens then
if you have a boost guage check your boost pressure while you're at it

Steve300 · #3 06-05-2006, 11:54 AM

I have the same problem. In my case, the intake /exhaust manifold gasket is bad (leaking lots of oil around that area). So I thought that may be the casue for losing power.

To: d.delano:
You said: "bypass the overboost solenoid on the firewall, the one the ALDA hose goes through
see what happens "

Would you please explain in details exactly how do you "bypass" the connections?

Thank you
Steve
1985 300D Turbo

Veloce300DT · #4 06-05-2006, 12:14 PM

Im glad to hear im not the only one with the same problem.... steve, have you repaired the intake exhaust manifold and gasket? it would be interesting to see if this is a fix. I'll know by the end of the day if cleaning the banjo bolts and alda valve restores the power loss on grades etc.

Mismost · #5 06-05-2006, 12:35 PM

When is the last time you changed the fuel filters? I know you said the fuel is fine.....but it sure sounds like the filters are starting to get plugged....enough fuel to run 85 mph, but not enough to pull the hills...feels like it's starving for power....sure does sound like the filters to me.

d.delano · #6 06-05-2006, 01:56 PM

I had this problem when I first got the car, and my overboost solenoid was rusted shut, so I just kinda figured you should look at it. Look at the driver's side firewall, to the left of the brake booster. You will see a device that has the ALDA hose going through it. Disconnect both ends of the ALDA hose, and splice them together using a spare length of generic rubber vac line. Then get in the car and see if it feels any different. You should feel the turbocharger spool at around 2k. Put your foot halfway in it, keep it there, and feel for an uptake in power at around 2k. Not a tremendous whoosh but it's fairly obvious.
The turbo sends a pressure signal via the clear plastic hose. This signal tells the IP to increase fuel delivery in sync with turbo boost. If the hose is plugged or the signal chain is otherwise broken along the way from the intake manifold to the IP, something from A to B is blocking the signal. Worst case would be the turbo isn't even boosting, but that's really not likely. Intake manifold has a sensor that senses overboost, then tells the overboost solenoid on the firewall to close up. This is how the overboost system works in a nutshell.
Steve- do you hear a loud whistle when you let off the accelerator? I do. I may have a pinhole in my intake/exhaust gasket too. I adjusted the turbo up to 12psi, and when I replace those gaskets, I may have to turn it down to compensate. Depends on how much pressure was wasted by that pinhole. Just something to think about.
If the fuel filters have not been checked you should check them first though, re: sudden loss of power.

Veloce300DT · #7 06-05-2006, 02:33 PM

In my case, the fuel filters should be fine. They were recently replaced, and I run BG fuel cleaner every other tank. Im sure that clean banjo bolts will boost power, but I wont be surprised if the hesitation is still present on hills.

Steve300 · #8 06-05-2006, 05:33 PM

Nate:
I have not done the repair work on the manifold gasket yet. I do not think I have the courage to do it myself. I wonder how much it will cost if I bring it to the shop.

d.delano:
Thanks for the explanation of "bypass overboost solenoid".
Yes, I do hear a distinct "whistle" when I let go the accelerator pedal during high speed.

Steve

Veloce300DT · #9 06-05-2006, 07:39 PM

Im crossing clogged banjo bolts off of my list as a problem. Clean as a whistle.
Wet dreams.

The intake manifold is fine, overboost was bypassed, boost is fine. Problem still exists.

Next step will be double checking fuel lines, filters, and the TANK SCREEN which has NOT been checked. Primer pump etc is all current. So IF there is an issue in the fuel system, its going to have to be either a restriction or a leak somewhere, or a clogged tank screen.

If the problem does not exist in the fuel system, then the only logical cause could be my tired.... injectors?.... if I am accelerating up a hill, at full boost, with an entirely free flowing fuel system and i still get the hesitation to accelerate, then would it make sense for the problem to be caused by tired injectors? I would think that poor injection esp under pressure from full throttle combined with an incline could cause hesitation... am i right?

If the fuel system is clear of leaks/blockage and thhe tank screen is fine, im going to be cluless and depressed. I want the old powerful torquey car that I knew to come back!!

Hatterasguy · #10 06-05-2006, 09:23 PM

Before messing with the injectors chech the tank screen. Also just change the fuel filters again for the heck of it. Its better wasting $10 on a spin on and fixing nothing then $300 on injectors and being back at square one.

This problem does not sound injector related. It's acting like its starved for fuel, do the 617's have an engine driven lift pump like the 603's?

#11 06-05-2006, 09:29 PM

Quote:

Originally Posted by Hatterasguy

This problem does not sound injector related. It's acting like its starved for fuel, do the 617's have an engine driven lift pump like the 603's?

I agree, the 617 lift pump looks like this:

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ41TI19Z2U9&year=1982&make=MB&model=300-DT-001&category=All&part=Primer+Pump+Assembly

Hatterasguy · #12 06-05-2006, 09:33 PM

Hmm the little Yanmar's have a similer lift pump. They work in a similer manner to the fuel pumps on Ford and Chevy V8's. Ie their is a diaphragm inside that pumps the fuel.

The symptoms sound very much like a Chevy BB with a bad fuel pump, or a Yanmar with a bad lift pump.

Veloce300DT · #13 06-06-2006, 02:46 AM

Thanks for the continued advice guys!

I am definitely going to replace all the filters, check for leaks etc. before I tackle the injectors to pinpoint the issue at hand. I replaced my primer pump not too long ago. I have heard that bosch products can be sketchy sometimes... or better put- DEFECTIVE. So the primer pump will also be checked. If there is anything wrong with the fuel system I am going to go all the way and replace EVERYTHING in the system. lines, filters, tank screen, primer pump. If this doesnt fix the problem than it sounds like new injectors are the next step. I need them anyways- I have been putting it off and dealing with the rough idle and slight over all power lag for quite some time- the current injectors have been tested and are on their last leg.

Im going to run the tank as close to empty as possible, and start on the fuel system. Probably in a couple of days. I'll post results back here. Hopefully I will be able to guide steve300 in diagnosing his similar problem. But on a 20+ year old car symptoms like this can be caused by a multitude of things.

If anybody can think of any other things to check, let me know!

dieselnut14 · #14 06-06-2006, 06:46 AM

To check the tank screen you do not have to take it out, just undo the fuel line at the tank and if the fuel runs out in a steady stream your fine, also check that your tank vent is clear and that your cap is not full of dirt. The vent on the 123 is located on the left side near the rear wheel and the end has a cone on it. You could check by blowing air thru it to the tank. make sure your fuel cap is off.

Good luck
Peter

1984 300d 262k mi.

Veloce300DT · #15 06-12-2006, 01:50 PM

New news to report here on my problem... I am pretty sure, 98% sure, that the problem is definitely a fuel delivery problem caused by a restriction somewhere in the line. I ran the tank nearly dry until the fuel light lit up on my instrument cluster. With the fuel level being low, the car is exhibiting the same loss of power characteristics- but more so, with the vibration and loss of power being greater now at full thottle, or under full load. The car struggles to make it up the freeway on ramps, and barely hits 45mph without a fight. Once on the freeway acceleratiion resumes, although staggered by more hesitation and vibration. Once a constant speed is established, say 75MPH the car will cruise there, but will occasionally loose power, gain power, loose power....
Last night the car would not top 75MPH no matter how I applied pressure with the gas pedal.

Because the issue has gotten worse with a low tank of gas, I am very hopeful that cleaning the tank screen and filters will resolve the problem.

All fuel filters and tank screen being changed today, and any leaks or bad hoses will be replaced as needed if there are any. Will post results as soon as I have it back on the road.