BNZ PWR

Hey everyone I am a proud owner of a baby blue 300SD. It has about 206K and has been largely running strong since i purchased it with 125K a few years ago. Unfortunately, I have been having some trouble that I really want your help with.

When I am merging onto the freeway, (or driving up a slight hill), i get a sudden loss of power when i shift from 3rd to 4th. This only happens when I have less than 3/8ths of a tank of fuel. As a result, I NEVER drive it with less than 1/4 tank. This also SLIGHTLY happens when i have a half or 3/4 tank of gas. I thought it may be the fuel pump, but my mechanic who is very good told me if this is the case, the entire fuel system needs to be replaced. My mechanic does not live near a freeway and it is almost impossible to replicate on surface streets, so i look crazy when i go over there. Otherwise, the turbo boosts strong and the transmission shifts well.

It feels as if the fuel cuts off. RPM's drop dramatically and i can step on the accelerator several times and eventually the power is restored. At first it was merely and inconvenience but it is becoming a very serious safety issue.

Any suggestions or advice would be appreciated!

carson357

have you changed the fuel filters?

BNZ PWR

i have changed the smaller one (the primary?) not the secondary one that sort of looks like an oil filter.

carson357

that primary is the metal one, the other plastic unit is secondary, the metal one usually becomes plugged by the smaller debris that passes the inline unit.
not sure how knowlegable your mechanic is, but these items are elementary when determining loss of power on mb diesels you might seek a more knowlegable garage. there may even be a tank algae contamination issue you may have. replace both filters and see how it goes

BNZ PWR

Im not sure how common tank algae is, I live in sunny southern california. As far as the metal fuel filter goes. Id rather change it myself. If i remove it, and when i replace the new one i should fill it with diesel fuel right? or should i simply use the block primer thats located near the secondary fuel filter?

The secondary filter was very dirty and needed to be changed. I had changed both the primary and secondary filters at the same time roughly 30K ago, but I do know that the ulta low sulfur has not exactly been kind to the older diesel motors.

carson357

i too live in southern california, and see algae contamination all the time on previous customers cars, it is best to fill the filter with diesel, those filters are to be changed every 15,000 miles, where are you? i am in san diego

BNZ PWR

i am located in los angeles in the san fernando valley, significantly more mainland.

RichardLSU

Go ahead and change both fuel filters, they're cheap. Fill the primary filter (the one that looks like an oil filter) with diesel before you put it back on. If it doesn't start after a few tries then pump the hell out of your primer pump. That should take care of it.

Dont lay on the starter and wait for it to start! If you have air in your fuel system it will NEVER start. Hence the primer pump.

I had the same problems and the fuel filters fixed it.

hineywineries

You may have fungus partially clogging the screen in the tank. Many people call it algae, but it is fungus, because algae requires sun light to grow. The process is called "photo synthesis". You can check it by removing and inspecting or run the fuel low, and pull up on your little hand pump. If it sucks back down, a restricted screen is causing a vacuum in the line.