When I make a "higher" speed gradual left turn (i.e. left turn through a roundabout). It doesn't do it if I turn left at slow speed from a standstill or at high speed when making lane changes. my engine hesitates about 5 seconds after the turn. The hesitation lasts a few seconds and then clears and off I go. I'm assuming its a fuel issue. Any suggestions, could this be a sign of a failing fuel pump? The issue only seems to happen when I'm running on diesel and not when running on WVO. Thanks for the help.

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'85 300td Frybrid WVO Kit

It is a fueling issue. Air is accumulating probably at your main fuel filter. Cornering hard causes a tilt in fuel level thus allowing a big gulp of air to be sucked into the IP, which is felt as a stutter.

Driving in a straight line you are still injesting air, but allowing only a little air at a time into the IP, which it can handle.

Start by tightening all hose clamps, look for cracks, etc. New fuel filter, gasket may be in order.

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Cheers!
Scott McPhee

1987 300D

...Air is accumulating probably at your main fuel filter....

Hmm... Not sure if I agree 100%. There is enough fuel in the lines/filter to go for 4-5 miles so I'm not sure that an immediate hesitation would occur.

Ironically, I have exactly the same problem when I'm running on diesel and not VO!!! I have the same question and wonder if it is not a failing fuel pump as you suggest.

And I'm also in Indiana...perhaps it is a Hoosier hesitation [bad, horrible, awful joke].

Bump for more!

this almost sounds like a fuel sloshing issue in the tank, does this model also have a manifold type setup in the fuel tank?

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Thanks for the replies. I don't think it would be a fuel tank issue because the hesitation happens a few seconds after turning and I think it would take longer for any air to work it way from the fuel tank all the way to the engine. Glad to know I'm not the only one having this problem IndyBenz.

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'85 300td Frybrid WVO Kit

When air enters into the picture things change immediately, regardless of what consumption calculations show for how much volume residing in lines should carry the car. Air deflates that theoretical bubble "right now"!

There's a big volume of fuel continuously flowing through the IP and only a little bit gets sipped as the engine demands it. The point is: anything in the filter gets moved to the IP in a couple seconds, especially air which collects at the top of the filter where the fuel take-offs are going to the IP.

A big gulp of air in the fuel filter gets released as some bubbles when cornering hard, and these bubbles enter the IP. Air immediately affects compressibility of fuel as soon as it enters the compression side of the pump, softening the pressure in the hard lines, affecting injector pop pressure, resulting in loss of power, or hestitation. Much before the fuel sitting in those lines gets consumed.

Interestingly, the volume flowing out of the IP on the returns side actually flows past the fuel filter again picking up air (there's a tiny internal passage inside the fuel filter lid to allow this) and carries this all back to tank to be vented.. as a continuous purge from the system. When this purge capability is outstripped by having too much air entering into the system (loose hose) you get a build up in the filter, that now affects performance, and can stall you completely in short order.

Alternate fuel systems that loop fuel from the IP output back to its input that have no equivalent air purge method (show me one that works and you have a market!) will experience this problem sooner while running on that fuel supply, because the air entering in that loop is trapped and has nowhere to go. But if your air entry point is outside of that loop, you're generally OK. It all depends on where your weak connection is and how you've done your routing. Generally it is better to force fuel by pumping from the tank side, rather than "lifting" fuel from the front side of the car as our IP mounted fuel pumps do in Mercedes. Air enters a system much more readily under vacuum (pulling fuel) than it does pushing fuel on the same line that has a loose connection. Pushed fuel oozes out of a loose connection, a pulled fuel just allows air to be drawn in... the devil for diesels. The reason MB's get away with lift is because they have engineered an air purge into fueling flows up front.

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Cheers!
Scott McPhee

1987 300D

So just an update, I tightened all my hoses and didn't see any change. The car has also become rather hard to start after sitting overnight (temperature doesn't seem to be an issue), so I'm pretty sure I have a leak somewhere. This morning before I started I decided to use the primer pump and see if that helped. When I pumped it it send a big splash of diesel onto my fingers (which it usually doesn't do when i prime). Seems like my primer pump may be leaking...however, I've read that some people just "live with" a leaking primer pump which leads me to think that a leaking primer pump doesn't cause starting/performance issues...is this correct, or may the leaking primer pump be the culprit of the air in my system. Oh and by the way, using the primer pump seemed to make starting the car much easier. Thanks for the help.

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'85 300td Frybrid WVO Kit

Your 1985 model should already have the "updated" primer pump but you might check anyway. You can "live with" some primer pump issues but it's is neither difficult nor expensive to replace the pump.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

This was happening to me in my '82 300SD a few years back, same hesitation after left turns. No modifications to the fuel system, however I was running homebrew biodiesel. Went away when I changed the filter, so I chalked it up to water accumulation in said filter. Much of the biodiesel I was getting at the time was not properly dried. Could also explain your hard starting.

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Mine has a white knob that has to be unscrewed in order to pump. It was my understanding that this was the old style which is often leaky..

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'85 300td Frybrid WVO Kit

That is the old style. In addition to being leaky most times, it also is a bit hard on the hands when pumping.

Definitely, get the new one.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

Yeah, after using it I usually have a few less layers of skin on my thumb

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'85 300td Frybrid WVO Kit

As a general rule anything substandard like your fuel primer pump should be replaced anyway. It may or may not be the problem. There is a strong chance it is though.

I have experienced this problem on left turning but on non mercedes diesels. Once it was even a non leaking but cracked water separator at the back of the car. Engine died out on left turns. Actually quit sometimes. Otherwise ran great with no fuel leakage on the ground while sitting.