98 E300 Turbodiesel "hiccuping" - Page 2 - PeachParts Mercedes-Benz Forum

cessna5354 · #16 10-01-2009, 07:13 PM

I have the same symptoms at hiway speed with cruise on, I thought for a while it was the cruise cutting out, very very briefly, but later the car was stalling when decelerating to a stop.
I replaced the lines, O rings, DV washers & Orings. Car ran like it did at 50K miles.

BTW, been quite a while since I have hear the phrase Butcher Paper, relatives were real butchers.....I like it.

Good Luck

John Doe · #17 10-01-2009, 11:06 PM

I'm going to have to go with the alternator explanation because it quit doing that after I had the new $700 alternator replaced. I've put the car out to pasture so to speak at a house that I only use 4-5 times a year because the rentals are kind of pia as the closes airport is 70 mi. away. I had a new alternator, radiator, turbo hose, new AC compressor and new motor mounts installed in the summer at MB of Richmond. $3-4K iirc. The car doesn't hiccup anymore. It was near perfect for a car that age..........until I was up there week before last and noticed the @##$$$#@$$#@damm headliner on the ceiling and sunroof are sagging--I am storing it in my boathouse and I guess it is the humidity because the boathouse is kind of a garage with water access, if that makes sense. Thanks for the info about the steering wheel--but make no mistake--I wasn't intending to do that myself--I'll get the guy doing the headliner to take care of it/

leszek · #18 10-05-2009, 01:08 PM

To the first question is the string of replies, mine is a turbo.

I have not thought of the Alternator scenario, but, I can honestly say that this problem was ever so slightly visible about 3 years, 100,000 miles ago. got more noticable about 30,000mi ago. I changed out all the 6 plastic fuel lines about 10,000 ago, and it actually felt a bit worse, but I had a friend helping me that day who, though I always appreciate his help, is by far the most careless person I know, by careless, I mean, not carefull literally. He breaks every tool I lend him etc, but man is he helpful, so I choose my battles (i.e., he has done way more work around my home than what the broken tools cost to replace). Anyhow, I just replaced all the lines again a week ago, and it's definitely better, but certainly still there. I would say about a 50% improvement. For those reasons I kind of doubt it's the alternator as I feel it probably should have failed by now if that were the root of the problem, and it should not have improved by changing the lines "carefully" if it were. I don't see air in the lines while at idle or standing still just above idle, but it also deos not stumble at idle under no load. I was contemplating putting a small reverse camera under the hood aimed at the lines so I can see while I am driving and causing the symptoms, but I am almost convinced that this air I am getting is not coming through these lines because I would imagine that in order to cause a hiccup, the air itself would have to be at the combustion chamber at that very moment in order to cause it. THis hiccup is very predictable, meaning I can make it happen right at the very time I roll into the throttle. So, the air bubble, if there is one, would have to be quickly working it's way to the injectors as I pull my foot off the gas to decelerate and then be right there at the injectors (or one of them) when I slightly roll back into the throttle, causing that momentary hiccup.

There are a couple of black plastic looking things attached to the injector pump which the clip on plastic fuel lines go into. What are there? I understand one is a heater? I also understand that these have "O" rings behind them??? Could these suck air?

TMAllison · #19 10-05-2009, 04:29 PM

Quote:

Originally Posted by leszek

There are a couple of black plastic looking things attached to the injector pump which the clip on plastic fuel lines go into. What are there? I understand one is a heater? I also understand that these have "O" rings behind them??? Could these suck air?

Attached to the IP is the shut off valve (black plastic) and the metal lift pump further back. The SOV has an oring between it and the IP; they fail. Lift pumps dont fail often, you can prob ignore it except to check that the lines are well sealed.

The fuel thermostat is in the cyl head and is at the start of the fuel path. Again not a high fil part.

leszek · #20 10-06-2009, 07:50 PM

So by the fail do you mean that its the "O" ring that I should consider or the entire SOV? Would it be possible for the SOV itself to be causing the problem? I am trying to make sence of it but I have no idea how they function other than possible some sort of needle valve. I know mine does shut off very well with a notable "klunk", but could there be some sort of "meandering" of that valve that causes it to interfere with flow??? Or, am I just letting my mind run wild and you are simply suggesting I replace the "O" ring behind it (of course it would make sence to try that first). Would a failure of that "O" ring tend to cause air in, or fuel out (I have no leaks what-so-ever).

TMAllison · #21 10-06-2009, 09:04 PM

A bad SOV oring usually leaks. Requires a mirror and light to see up under there. A leaker sometimes causes a delayed shutdown; you turn off key, its in your hand and the engine turns off.

The clunk you hear is prob due to failing motor mounts. Puts stress on the serp belt pivot arm which causes the clunk you hear.

hobbitss · #22 10-06-2009, 09:49 PM

Check the rubber fuel line in the engine compartment where it meets the metal line from the tank... Mine was dried out and leaking air into the fuel flow, it caused hesitation at highway speeds... The Indi who worked on my 98 trimmed the end of the rubber line and clamped it onto the metal line... No more problem...

leszek · #23 10-07-2009, 09:17 AM

thanks hobbitts, I will check that rubber hose. Are you aware if that caused visible air bubbles in the clear fule lines?

As far as the clunk, I don't think it's that motor mount again yet. I did change those once. The prvious ones had totally collapsed. New ones made it feel like I traded the car in for an entire new vehicle. I had a interior vibration at idle causes by the steel against steel. THe clunk I mentioned is much more of a "clack" I guess. Best comparison I can make is that it sounds like a rather loud starter solenoid.

hobbitss · #24 10-08-2009, 09:33 PM

Quote:

Originally Posted by leszek

thanks hobbitts, I will check that rubber hose. Are you aware if that caused visible air bubbles in the clear fule lines?

As far as the clunk, I don't think it's that motor mount again yet. I did change those once. The prvious ones had totally collapsed. New ones made it feel like I traded the car in for an entire new vehicle. I had a interior vibration at idle causes by the steel against steel. THe clunk I mentioned is much more of a "clack" I guess. Best comparison I can make is that it sounds like a rather loud starter solenoid.

I was informed of this issue while having my original plastic lines & o-rings replaced as I thought they were the source of the hesitation... My lines were to old and yellowed to really see thru'... I was told that only one of my o-rings was weaping and not the air source...

After the work was done the hesitation was greatly reduced and totally gone after running thru' a couple of full tanks...

TMAllison · #25 10-08-2009, 10:46 PM

Quote:

Originally Posted by hobbitss

My lines were to old and yellowed to really see thru'... I was told that only one of my o-rings was weaping and not the air source...

Your fuel line form the tank may well have been bad but, fuel molecules are larger than air so any seal that leaks fuel out can let air in; and some leaks can be small enough to let air in but not fuel out.