1990 W124 300D Problem - PeachParts Mercedes-Benz Forum

TVRTASMIN · #1 10-20-2006, 02:57 PM

Hi.
I'm new to this website forum and hope i can get some friendly advice.

I have a W124 300 six cylinder diesel estate (UK term for stationwagon?).
Anyway, since filling with biodiesel several compression leaks have started from near to the injector bodies.The leaks (sounds like a chuffing noise) are from the same place.
There appear to be small holes in the head just next to the steel inserts that take the plastic heat shrouds, and the leaks appear to be coming from there.
The engine is running badly with plenty of smoke from the exhaust.
I also noticed that the coolant temp went higher than normal and i get a lot of clatter on tick over.
My thoughts on this are that the biodiesel is causing pre-ignition. The mixture is igniting in the pre-chamber for some reason.

Any help greatly appreciated.

Ian
England, UK

sixto · #2 10-21-2006, 03:14 AM

Given the cost and effort of replacing the heat shields, that's where I'd begin even if you don't agree with the logic.

Is this a SOHC or DOHC engine?

Sixto
93 300SD

TVRTASMIN · #3 10-21-2006, 04:13 AM

The engine is a 603.912 .
There is definately compression being lost .I cannot see that just by replacing a plasting heat shield, the problem will be solved.

The heat shields are made from a hard plastic which locate in this steel ring type insert in the head. The injector then slips between to screw it into the head.
The shield obviously is not a tight fit around the injector and could be classed as being cosmetic as i have seen on some engines these shrouds or sheilds are broken for the most part.

Maybe it is the injector sealing washers, and the compression is finding it's way up the back of this metal insert somehow.

The engine ran fine even from stone cold until i filled with 100% Biodiesel. Within 10 miles smoke was coming from the exhaust and this chuffing noise coming from this hole near to the injectors.

Gilly · #4 10-21-2006, 10:12 AM

I hesitate to transfer this thread myself as you have some answers already, but I heartily encourage you to start another thread on the Diesel forum too.
http://www.peachparts.com/shopforum/diesel-discussion/

Gilly

sixto · #5 10-21-2006, 02:49 PM

Could be a terminology issue. I don't mean the plastic shrouds around the injectors. I don't think those are heat shields but I don't know what they are. When they break in the US, the dealer doesn't replace them. I mean the heat shields between the prechamber and the firing tip of the injector.

These things -

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1UF05A51E1XC0VPIWH&year=1993&make=MB&model=300-SD-003&category=All&part=Injector+Heat+Shield

Sixto
93 300SD

Gilly · #6 10-21-2006, 03:27 PM

Sixto, those parts you linked to are the injector seals, those need to be there. The place I was at always replaced the plastic part too, but can't remember what they called them in the shop.
Gilly

riethoven · #7 10-23-2006, 04:06 PM

Quote:

Originally Posted by TVRTASMIN

The engine is a 603.912 .
There is definately compression being lost .I cannot see that just by replacing a plasting heat shield, the problem will be solved.

The heat shields are made from a hard plastic which locate in this steel ring type insert in the head. The injector then slips between to screw it into the head.
The shield obviously is not a tight fit around the injector and could be classed as being cosmetic as i have seen on some engines these shrouds or sheilds are broken for the most part.

Maybe it is the injector sealing washers, and the compression is finding it's way up the back of this metal insert somehow.

The engine ran fine even from stone cold until i filled with 100% Biodiesel. Within 10 miles smoke was coming from the exhaust and this chuffing noise coming from this hole near to the injectors.

Sounds like leakage around a prechamber. It will make that chuffing sound.

sixto · #8 10-23-2006, 04:17 PM

I guess there's two paths to lose compression - one on the outside of the prechamber the between the head and the lockring; the other on the inside of the prechamber through the injector seal and between the prechamber and injector. I'm not sure how tightly the prechamber taper sits against the boss in the head but I imagine the lockring imposes quite a force creating a seal. How that seal can come undone with just a tankful of the worst fuel ever is puzzling. Similarly I don't know how an injector seal can deteriorate over the course of one tankful.

Can you use drops of fuel between the injector and lockring then separately between the lockring and head to isolate the leak?

Sixto
93 300SD

TVRTASMIN · #9 10-23-2006, 06:29 PM

The leak is definately from the outside of the lock ring.
My injectors are the slanted orientation type.

When i said i had just filled up with Biodiesel, i meant just less than 10 miles earlier before the problems started.

I believe the leaks have been caused as a direct result of using the Biodiesel, there is no other explanation.
Somehow the fuel isn't being burnt properly as it is igniting too early in the prechamber or the fuel has caused a problem with either the injectors or the pump.

I have changed both the pre filter and the main filter. Both did not show any signs of blockage or foreign particles.

All the glow plugs are glowing fine as well as the run on period until they are timed out.

This is a link to the area of concern, the prechamber; Help: injector / prechamber / heatshield leak

I need to find the cause of the pre ignition to prevent the excess compression in the pre chambers occurring in the first place.