Hi all diesel aficionados

I'm a proud owner of a '92 300D 2.5T (W124) since last march. The car is approaching 180 000 miles and, although it has needed some efforts to heal what appears to be a recent lack of maintenance, it is in a very good overall shape.

I'm thinking about an injectors replacement job. I don't have any previous records for the car so I don't know if injectors were already replaced at some point. The previous owner was a long time diesel owner and when I bought the car, he told me that injectors would need some work though it was not immediately apparent to me.

But since I'm now more familiar with the car, I think that may be a needed job. First of all the glow plugs look to be Alright : the car always starts easily with minimum glow time with temperatures near freezing. It starts on all 5 cylinders and it is relatively quiet for the first 30 to 60 seconds. Then it gets noisier, misfires and emits white smoke until it gets warm (maybe 3 to 5 minutes when the temp is around 40 F). The misfire is more apparent when the engine is under part load at around 2000 rpm.

At first I was thinking about some kind of engine electronic management problem, but that system only works on egr and intake pressure, which neither seems to operate when the engine is cold.

An another clue that I believe points to faulty injectors is a very noticeable puff of black smoke when the engine is restarted after a few minutes stop (leaking injectors ?).

When the engine is warm, there is no apparent misfires, but the 5 cylinders rhythmic could fouls me. The IP timing looks to be good as there is no smoke driving in town or on highways. The average fuel consumption is around 28 miles per Imperial gallon, which I guess is about 23 mi / US gal. (50-50 town-highway). Highway only is around 28 mi / US gal. Those figures could be on the low side (wrong spray pattern ?).

Could some specialists confirm the diagnosis ?

__________________
DR
1992 300D 2.5T 351 000 km

Try the diesel purge route prior to changing the injectors.

__________________
Jim

Thanks Jim

Diesel Purge is not available in my area (Quebec city). I've used Stanadyne Performance Formula almost since I've got the car. The stuff seems effective in smoothing out the engine but not sufficient to get rid of misfires in cold weather.

Stanadyne was suggested by a nearby diesel shop : the manager never heard about Diesel Purge and had some doubts about its effectiveness. Nevertheless, it is clear reading the many posts on this site that Diesel Purge is almost a "magical potion".

__________________
DR
1992 300D 2.5T 351 000 km

Diesel Purge isn't just something you pour in the tank. You have to actually hook it up to injector lines and catch what comes back. Works good. Email Phil here at Partsshop.com and see if he can sell you some. It is worth a try.

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Jim

I've found an explanation for the 30 to 60 seconds period during which my diesel run smoothly before beginning to misfire : it seems that the glow plugs are still on even if the engine is running. At night, you see an increase in the intensity of driving lights when the glow plugs go off.

I knew that you could leave the starting key to glow position for an increase glow time when the glow plug light go off, but I always thought that glow plugs were shut off as soon as the engine started.

As for the Diesel Purge treatment, here is for those that don't already have it a link to a well illustrated procedure :

http://www.mindspring.com/~houlihan/merc/purge.htm

__________________
DR
1992 300D 2.5T 351 000 km

Sure sounds like bad injectors to me -- exactly what my 220D does.

Replacements are $50 US each from FastLane with exchange -- rebuild at a diesel injection service will be similar, as all they do is take the injector apart, put a new nozzle in it, and set the opening pressure.

Your milage stinks -- I'm getting 34 mpg on the highway with my 87 300D six cylinder!

Consider taking the injectors to a diesel injection shop for testing -- they will usually test for free.

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Hi

Have change injectors yesterday. Got them rebuild at a local diesel shop (new nozzles, recalibration). Tests on the old ones showed they were out of specs.

As there is no priming pump on that car, it was a little hard to restart. When started, is misfired a lot but I assumed that it was just air in the system.

The engine run more smoothly at middle and and high rpm (maybe I should not say that in this forum, but it run more "gaz like"). There is just a slight indication of a power increase.

The idle is stable but a lot more noisier than before, even when engine totally warmed.

But worst, the new injectors didn't cleared the main problem : when starting the engine cold, it misfires as soon as the glow plugs go out of power and until it warms.

Could it be a problem with the reverse damping valves on the IP ? If those were out of specs, could the higher opening pressure of injectors explains the noisier idle ?

__________________
DR
1992 300D 2.5T 351 000 km

Denrac:

Very possible -- you have the same engine I do, short one cylinder, and the same IP, ditto.

Noisier idle with new nozzles can happen -- usually indicates something else is wrong.

You won't see smoke on this car unless it is really bad -- US models (and Canadian, too, I think) have traps in the exhaust to reduce smoke.

I had a hard knock, rough idle, and miss (more like one cylinder not firing) at idle -- turned out to be the pressure valve holders in the IP weren't torqued down correctly. I replaced the seals and o-rings, but it wasn't really necessary.

This is a common problem with this IP -- if the pressure valve seals (reverse dampner valve seals) leak, fuel injection at idle is erratic and late. Miss and knock are the result.

Repair is simple -- obtain the special socket -- it is a multi-spline, not a hex. Remove the injection lines from injectors and pump and push out of the way. Plan on new plastic clips for the injection lines, they usually break when you take them off.

Remove the locking rings around the pressure valve holders -- there is a torx head screw holding them down. I had to use a pair of vise grips on one, it was seized.

Use the special socket to tighten each pressure valve holder -- the torque specification is 30 Nm, then 35 Nm. If you are not familiar with this amount of force, use a torque wrench or obtain some assistance -- it is possible to break the pressure valve seat if you get carried away.

The seal is a copper washer -- new ones are cheap, and all you need do to replace them is unscrew the pressure valve holder, catch the spring, lift the old one off, put the new one one, put the spring back in, and install the pressure valve holder.

Re-install the locking rings, then the injection lines, leaving them loose on the injectors. Crank until only fuel comes out of the lines at the injectors, accelerator to the floor. Tighten injection lines at injectors and start. You will have to crank for a while -- same drill as changing injectors.

My 300D runs like a top now!

Try this before you get excited. Otherwise, it is time to get the compression checked and a leakdown test done. If you are not using oil and have low compression, the valves are worn and need work.

Also, this engine has hydraulic tappets -- if the two little o-rings on the center bolt of the oil filter cap are bad, the oil leaks out of the tappets overnight -- they will rattle until they refill with oil, and compression will be low until they fill. If new o-rings don't fix tappet noise (tap tap tap/click click click instead of snap snap snap or crack crack crack for a noise description), you need to get the tappets replaced.

Injection timing being too fast will also make the engine knock and smoke at idle -- base timing is set with a drip tube just like any other MB diesel.

Remember, some noise is expected of a diesel at idle. The 601/602/603 seems to have pronounded idle noise/diesel rattle that goes away as soon as the accelerator is depressed, at least in all the ones I've seen.

You may also want to move the altitude compensation/idle speed adjustment -- it is a black "dial" -- actually a pull-and-turn then replace plug up by the booster on the bulkhead. Set to 5 if it is on 4 -- this helped mine considerably! Idle speed will rise a little, and noise should diminish.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks Peter

I'll try to find the right tools for retorquing the pressure valves holders. Cold engine maybe more affected by late injection if pressure valves are not set correctly.

When the engine is warmed, idle is very stable (no misfire, no smoke), just noisier than before. And, as you've said, the noise disappear as soon as the accelerator is depressed.

It seems there is no problems with hydraulic tappets : always silent. The engine consumes no oil (a gift compared to my previous 190E !).

When I started it after injector replacement, I didn't replaced immediately the pipe between the turbo and the intake. I was very surprised to see a lot of fumes coming out only tens of seconds after starting the cold engine. Maybe a stuck EGR valve ?

__________________
DR
1992 300D 2.5T 351 000 km

Denrac:

Could be a stuck EGR. That would explain the rough idle, but not the noise.

Don't forget, diesels always make blowby, much more than gas cars. Smells terrible, not like smoke or diesel exhaust. If you aren't using any oil, it isn't excessive.

Just how bad is the noise? Louder than, say, a Dodge diesel pickup? Terrible hard clack clack, sort of like a light hammer on the side of the engine? Or just a sort of muffled rattle?

Rattle, usually very even and consistant although not on every cylinder, is typical. So is a little vibration. No diesel will ever run as quiet as a gas engine at idle, due to the mechanics involved.

Higher opening pressure will give later injection. usually quieter, not louder.

My 300D rattles pretty hard when cold and first started, quiets in a minute or two. The old 220D snaps and cracks until it warms up -- nearly worn out!

A small puff of white smoke is typical, too -- takes a bit to warm up the cylinder to get good burn. Shouldn't last more than a few seconds. Worse when the temp is low -- how cold is it in Quebec now?

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Hi Denrac:

I wanted to mention that Diesel Purge isn't available where ANYONE lives.



Well, that may be a stretch - but I bet most of us get it by mail order or from an online site. If you are on EBay you can search for "diesel purge" and probably find it.

I've been going through my new CDROM manuals for the W124 and did notice that in the later 300D models with the 2.5, the glow plugs DO stay on for something like 30 seconds after the car starts. They call this "afterglow" I think and I'll bet it was done to make this engine run better on cold startups.

I recommend you do a more detailed check on the glow plug system. All it takes is one weak (not bad, weak) glow plug and the engine will make a ton of smoke on cold startup. It is because the fuel is not burning - and the car will run rough. If you do a search on my name here you should find some detailed procedures for checking your glow plugs. They need to be drawing the proper amount of current to get hot. One of mine was weak, drew less than 2 amps instead of 10 amps - and essentially did nothing to help start the car.

MCM Electronics has a multimeter on sale for $20 which has the 20 Amp DC current range (that a lot of multimeters don't have).

Ken300D

Where do you live? I mean since diesel purge isn't available where you are and all. I can get it off the shelf at two parts places near me. I haven't really checked very hard to find it though. A friend called me the other day and said that his local quality farm and fleet store carries it!

What I did was talk to the parts store manager and ask him if he could get it, he can and now he stocks it . ( I also have him stocking filters for the 300D) You know the "oddball" oil and fuel filters on the '76. Just a note, the oil filter is the same as what is used on Ford 9N tractors!

I was also wondering if anyone has a nice layout of how they purge a '76 W115? THat link above for the 123 was layed out rather nice Good Job! Tom

If your injectors have been misbehaving for a long while it can take several hundred miles of driving with new injectors, for the prechambers to clean up and and for things to start sounding better. You can speed things along with some sustained full load full throtle driving.

__________________
Bob D.
Parrish, FL
1 SDL, 1 D, 1 TD, 1 Mog

Ahhh Yes the old Italian tune up! I did that yesterday had to make a 100mile round trip to pickup 80 gallons of veg-oil. I had the '76 up to 92mph for a stretch going down US131. ( I was being teased bya snot nosed brat kid in a nice BMW 321i. I couldn't let him pass me, so I just "stayed ahead of him" until I got off the highway a couple miles later.

Honest officer I wasn't racing, I was just staying ahead of the other guy!

Peter : to qualify the idle noise, I would say it's the same tune as the Dodge diesel pickup, but on a dry guitar, without the concert loudspeakers ! When the cold start misfires are gone ( at an exceptionally hot 30 F at this time in Quebec city ) , the vibrations are those a well behaved diesel.

A mechanic at the shop where I had my injectors rebuilt told that the misfires could be related to air finding it's way in the gallery of the IP when the car is stop for a long period of time. Can't figure from where it could come from. The only indication of a fuel leak was at the heat exchanger just upstream of the fuel pump. It was just a wet spot (not dripping) and it was corrected with no effect. That mechanic suggested that it could come from the fuel pump : but I can't see any bubbles in the clear plastic hoses connecting the fuel pump, the injector pump and the filter when the misfires occur. There is no evidence of a leak at the pressure valve holders neither.

Ken300D : here, there is a song that says "if our ancestors had sailed on the wrong side of winter, we would have coconut trees on our streets", and maybe Diesel Purge at the corner store When the injectors were out, I checked the glow plugs and they were all bright orange when on. The engine always starts very easily, unplugged at freezing temperature. A detailed check of the glow plugs is on my agenda.

Fryerpowered : the quest continues (I mean diesel purge quest) and long live to the Italian tune up (Ah! mama mia!).

h2odiesel : maybe I'm getting used to, but you may be right, that noise seems to diminish.

__________________
DR
1992 300D 2.5T 351 000 km