300sd engine misfire - Printable Version

300sd engine misfire - Printable Version

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300sd engine misfire - kunasw - 04-13-2011

Hi everyone I am new.

I have a 1980 300sd turbo diesel with almost 200k miles with misfiring engine.

all five cylinders do not fire all the time, it feels like. normally it will be running on 4.5 and sometimes it will loose power drastically and it really feels like running on 1 or 2 cylinders. sometimes it stops on the road but usually i just keep on pressing the accel then others gradually start to fire again.

I am not a mechanic but wants to learn and work on my own car.
I had started with this one. i changed the oil, oil filter, both fuel filters, air filters, battery, glow plugs, and did valve adjustments.

I very much like this car and hope i can do some mods on it too like other members in this forum but still cannot turn it into a daily driver.
I got this one for like 2k if this problem is related with serious engine damage then maybe i need to get rid of it but i wish i don't have to.

Please help THANK YOU

RE: 300sd engine misfire - aaa - 04-13-2011

I'm starting to hate the word misfire, it seems to be a really bad way to describe these problems.

The "sometimes" part makes me think it's still fuel related. There is a filter screen in the tank itself as well. Any signs of black stuff on your old filters?

RE: 300sd engine misfire - kunasw - 04-14-2011

YES I had a problem with clogged up fuel filter. my mechanic told me i may need to clean the tank

RE: 300sd engine misfire - larsalan - 04-14-2011

Which filter? What was the clog?

RE: 300sd engine misfire - kunasw - 04-14-2011

replaced both prefilter and the spin on.
it used to hesitate when accelerating. i changed the fuel filters. no problem ever since. didn't really examined what the clog was..
since then i started filling up when i'm half way through the tank. recently i had noticed a significant fuel loss until 2/3 of the tank which is another problem.. maybe i need a new tank also..

replaced both prefilter and the spin on.
it used to hesitate when accelerating. i changed the fuel filters. no problem ever since. didn't really examined what the clog was..
since then i started filling up when i'm half way through the tank. recently i had noticed a significant fuel loss until 2/3 of the tank which is another problem.. maybe i need a new tank also..

RE: 300sd engine misfire - larsalan - 04-15-2011

A new tank full of fuel you mean? Maybe you can get a bit more stuff out of the tank it you swap the supply and return lines for a while.
I only mention it because I recently had some frustrating issues with this stuff myself.

RE: 300sd engine misfire - aaa - 04-15-2011

Again, there's a filter inside the tank itself, that can cleaned or bought new after the tank is drained.

Fuel loss? Notice any puddles of leaked diesel on the ground?

RE: 300sd engine misfire - kunasw - 04-15-2011

http://www.dieselgiant.com/Mercedesfueltankremoval.htm
maybe this is what i need to do! yes?

RE: 300sd engine misfire - aaa - 04-15-2011

I suppose... feels like overkill though. Drain the tank and remove the filter, not hard to do with the tank in place, as long as you don't mind diesel splashing all over you. I suppose if you removed the whole tank it'll only splash on your hand instead.

RE: 300sd engine misfire - kunasw - 04-16-2011

Thank you i definately should examine and really find out where the gas leak is first. hope its not the gas tank

or i can swap supply and return lines for a while before i start taking things apart..

RE: 300sd engine misfire - larsalan - 04-16-2011

Yeah, if you swap the lines you might just catch some gunk in your clear primary filter. I ended up going to the trouble of pulling out the in tank screen just to find that it was perfectly fine. Piece of mind I guess but, I spilled some fuel and wasted like 2 hrs of my life. And had to buy a $7 socket.

RE: 300sd engine misfire - kunasw - 04-22-2011

I swaped the lines and didn't solve the problem... hmmmm
This time when the engine was loosing power with a shake (it felt like it was firing only 3 cylinders) I opened up the hood then used the hand pump to feed more diesel into the engine which quickly let other cylinders to fire.
Is it safe to conclude that there is a problem with a diesel delivery than engine malfunction?
Do I have cloggled up injectors..?

RE: 300sd engine misfire - 300D50 - 04-22-2011

Seems like it's getting air into the lines, or the lift pump isn't keeping up with the fuel demand.

Have you noticed a "whoosh" when you unscrew the fuel cap on the tank right after shutdown? if so, it could be a clogged tank vent.

RE: 300sd engine misfire - kunasw - 04-23-2011

If I pump hard, it makes a tiny whisling sound around the injectors or injection pump. would this be the sound of air getting into the fuel line? How do I diagnose and fix? If its the lift pump, is there a way to test? and where can I find the tank vent?

Thank you for your help

RE: 300sd engine misfire - larsalan - 04-23-2011

there are 3 lines coming off the tank supply, return and vent. The vent looks like a bell.
[Image: snap_10.jpg]

It will open with minimal pressure going in either direction.
My pump would always make a 'wooshing' sound to so I can't say much about that.

RE: 300sd engine misfire - 300D50 - 04-23-2011

The "whoosh" is the fuel going past the relief valve in the IP, that's normal.

I'd check for a clogged tank vent first, if there's a "whoosh" from the filler neck, it's likely the vent is clogged.

RE: 300sd engine misfire - Captain America - 04-24-2011

My tank vent is clogged. But the vent line doesn't have the valve before the bell like in the picture...