Loss of power/white smoke 992 300DT - PeachParts Mercedes-Benz Forum

mikenpike2000 · #1 07-23-2018, 03:52 PM

My 92 300DT has had another issue. I recently noticed a puff of white smoke when starting. Is this unburned fuel? Could I have bad glow plug(?) On flat ground the old car cruises right along, 60-65 on the interstate no problem. Hit a hill, and no power. Its never been a powerhouse, wasn't intended to be, but it was better than this. Didnt't think I was going to make it home today, she topped the big hill (mountain, I'm in Kentucky,y'all) at 35 and that was all she had, and I'd downshifted to 3rd. I was afraid to push it so I just put-putted on home. It seemed like I felt some surging in the engine for a second or two. Didn't overheat or smoke, didn't vibrate or rattle. Once on flat ground, seemed fine again. Stopped at the drug store, and the engine seemed to turn over more than normal before catching. Dropped Mom off, and was really noticeable that the engine wasn't catching as fast as usual. It usually turns twice, and catches. Ideas? Opinions? Thoughts?

Diesel911 · #2 07-23-2018, 05:56 PM

In Diesels in general loss of power is attributed to restrictions in the Fuel Supply System. Fuel Tank Screen and Filters.

Then there is the Fuel Pressure Relief/Overflow valve that has plastic parts inside that warp of fall apart that would reduce the Fuel Pressure.

On the older models a plugged fuel tank vent can cause issues. If you Fuel level is low enough for you to drive around with out the Fuel Fill Cap on the tank you can drive without it and see if there is better performance.

The Fuel Supply/Lift Pump could need to be rebuilt.

Look for signs of a Head Gasket issue like Oil or combustion smell in the Coolant Tank and a upper Radiator Hose that remains hard/inflted 1-2 hours after the Engine has cooled off.

On the older models you can swap the positions of the Fuel Inlet Hose and the Fuel Outlet Hose to bypass the Fuel Tank Screen but you need to have at least 1/2 tank of Fuel. I am not sure if that can easily be done on yours.

If you have noticed your performance is better with a full tank of fuel then with say 1/4 tank of fuel that is some indication of a fuel supply issue.

Diseasel300 · #3 07-23-2018, 06:02 PM

I really wish the old myth of the overflow valve on the 60x engines warping and affecting fuel pressure would just die already. They're a drilled orifice, the spring and plastic components are only part of the check valve assembly. Their failure will affect air ingress during a rest, but not fuel pressure. The fixed volume pump acting against that drilled orifice sets the fuel pressure.

I'd be checking for air ingress somewhere. Look for "sweaty" fuel lines. If your car has the fuel preheater thermostat on it, they're a very well known source of air leaks. Air in the system will cause power loss, white smoke, nailing, hard starting, you name it. Also worth checking and/or replacing the fuel filters, especially if it hasn't been done for a long time.

mikenpike2000 · #4 07-23-2018, 08:35 PM

You folks on this forum are really helpful and appreciated. So much combined knowledge. You've saved me untold work, worry and money. I appreciate you all. "Diseasel300" I thought of the possibility of fuel filters also. This car has been lifetime serviced at Mercedes. I am NOT impressed. The engine was so filthy I was actually afraid the car would catch fire. Took 4 cans of engine degreaser and liberal applications of pressurized hot water and 2 days to get it cleaned. I think the previous owner was elderly, female, widowed, and Mercedes service just didn't bother. Many things should have been seen to service wise, but were ignored. I've been playing catch- up since I bought the car. Typical things. Wiper motor. Tires. Auxillary fan. A/c system. Air filter. Badges had fallen off the trunk. Blown fuses. Multiple small things that were easy enough to repair ( once I found y'all) that the previous owner would have had done. She is living still, drives everyday, in her right mind, and quite comfortable financially. This is a '92 with 81,000 when I bought it. 81,000 for a diesel is still new, in my opinion. From the service records book that came with the car, a labeled Mercedes service history, they changed the oil, a few bulbs, and converted the a/c to 134. That's all the history that was recorded. Service records are up to within 6000 miles of my purchase. I couldn't do this without y'all. Just wanted my appreciation known. Thanks A LOT.

Diesel911 · #5 07-23-2018, 08:51 PM

Quote:

Originally Posted by Diseasel300

I really wish the old myth of the overflow valve on the 60x engines warping and affecting fuel pressure would just die already. They're a drilled orifice, the spring and plastic components are only part of the check valve assembly. Their failure will affect air ingress during a rest, but not fuel pressure. The fixed volume pump acting against that drilled orifice sets the fuel pressure.

I'd be checking for air ingress somewhere. Look for "sweaty" fuel lines. If your car has the fuel preheater thermostat on it, they're a very well known source of air leaks. Air in the system will cause power loss, white smoke, nailing, hard starting, you name it. Also worth checking and/or replacing the fuel filters, especially if it hasn't been done for a long time.

I got the info from another member and his thread is somewhere who had that issue. Apparently replacing his fixed the problem. Note that no one has to believe me.

sixto · #6 07-23-2018, 10:14 PM

Can you tell if the turbo is boosting? The wastwgate default is full open (no boost) unless the ECU grants it a vacuum signal to close and generate boost. Lack of boost in and of itself won’t cause white smoke.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Mxfrank · #7 07-23-2018, 10:44 PM

602/603 Turbos tend to bog down when the Alda port clogs with soot. It's easy enough to clean. Yes, this little thing can make your dinosaur feel extinct. See photos.

barry12345 · #8 07-25-2018, 04:23 PM

Any diesel performance problems. Change the fuel filters usually before looking elsewhere.

Was a constant standard to do this years ago. Perhaps the fuel Is cleaner today in general. Yet you can still pick up a tank full with a lot of dirt or other issues.

I do not see this as a waste. If doing the filter change does nothing. Take the old one and put it into a fuel proof container and keep it in the trunk.

It may be needed as a spare someday. Especially while away from home. Your loss of performance could also be you have a real fuel quality problem. Being very careful where you fill up can save you many problems over the years.

In general I like large truck stops. If they tank bad fuel it really hurts their business. So the have systems in place to avoid those issues.

Where small stations do not monitor their fuel. Some of them are also supplied by independent bulk carriers. If they neglect to clean out whatever their last load was. It gets mixed in with the diesel fuel. Getting water is all too common as well at low volume places.

When you make sure those possibilities are covered. Then I look around. Unless something else is pretty obviously the cause.