This is called "drooling" and yes, it is a very bad thing, anyone who doesn't take pop pressure seriously or says it doesn't matter on a thirty year old vehicle, shouldn't be doing this important and delicate service .

It takes time and patience, two things very few seem to consider these days .

My old injector guy used to make them pop within 5 # and although it's a Metric car using PSI is fine, no worries / shame in it .

You have to try one set of on the nose properly done injectors to understand how much better your old engine will run and how much improved fuel economy plus easier starting cold or hot, smoother idle and better throttle response to understand .

I got one set of droolers that were perfectly balanced for my 240D, the engine ran strong but they drooled so it also smoked, not O.K., not ever .

Take the time to do it right ! .

The size of the dust that makes your injectors drool or pop off wrong, is smaller than you can see by eye .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

A few observations. If you do new springs you will need to check your PSI a number of times as it will take a while for those springs to settle down. Secondly, after rebuilding 1,000s of injectors I have never seen a broken MB injector spring. I have seen a few really rusted to the point where some of the metal was missing from the spring but it didn’t affect the injector. I would say swapping out the spring would probably be more headache than it’s worth unless you have a damaged spring. Like I said I haven’t seen one yet in 7 years. I have seen a total of 2 broken springs in other types of injectors (non MB)

If springs produce enough pressure to hold an injector nozzle in check (no bleeding of fuel) they can surely be trusted.

The most difficult part is creating a truly clean assembly. Submerge them in diesel purge and take the parts out one by one to be assembled. I've read there is no such thing as too clean. I believe that to be true.

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84 300SD
85 380SE
83 528e
95 318ic

Paragraph 4 of Mercedes Benz manual 07.1-135:
4. Test longitudinal bore (15) in throttle pintle. At slow, uniform downward movement of hand lever (approx. 4-6 seconds per stroke) a distinct, vertical cord-like jet (arrow) should come out of longitudinal bore (15). If no cord-like jet comes out, check longitudinal bore with cleaning needle 0.13 mm dia for unobstructed passage. If longitudinal bore is clear, the injection nozzle can be used again.
Note: Test procedure also applies to new injection nozzles.

I doubt that getting the pop pressure exactly right is terribly important. I say that because my 1984 300D "as found" had 3 injectors which popped at 1600 psig, i.e. for a non-turbo car. I changed to a set of 5 that popped at the correct 1950 psig, but can't say I noticed any difference in how the engine idled or performed. I think that having a good spray pattern and no early pee'ing is the most important thing.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Bill ;

Injector pop pressure directly affects cylinder balance so yes, it's very important .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

It also directly affects timing. Timing indirectly affects EGT's and power output. So yes, pop pressure matters.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

The 1981 240D Mercedes Benz injectors was never cleaned or replaced in 300,000 miles.

Some injectors have a consistent spray pattern whether the pressure tester hand lever is applied slow (approximately 4 -6 seconds per stroke) or fast (short partial strokes approximately 2 strokes per second).

Old injector from cylinder number three has a uniform spray pattern at any pumping speed even at the low end of the specification opening pressure of 1,450 psi.

Injector nozzle color from cylinder number two was gun blue indicating it was subjected to high temperatures. When tested, there was no fuel spray atomization, just a continuous vertical cord-like jet.

The most efficient method to update the injectors is to buy Bosch remanufactured units, acceptance test them before replacing the old ones.

CAUTION: Bought Bosch nozzles from the Mercedes dealer, half of them are defective, dealer do not accept returns for these units. Ended up as paper weights.

For a leak free injector installation, use a torque wrench with a high range of approximately twice the target torque. The high range for this installation is 708 in-lbf. Select a torque wrench with a range of 200 – 1200 in-lbf. Mercedes Benz specified torque range for the injector is 620 – 708 in-lbf, use 660 in-lbf.

Apply a light dab of engine oil on the injector nozzle holder bottom threads and sealing ring nozzle interface to reduce friction before installation to achieve the preload required.

The car gets 26 mpg when it was new, went down to 21 mpg at 300,000 miles, will update the mileage after a few thousand miles. Got 24 mpg after injector replacement with Bosch remanufactured units.

Thanx for this ! .

My '82 240D got well over 25MPG's even after the engine began to fail, since the rebuild it rarely gets over 24MPG, this drives me crazy ~ no smoke ever ~ the car still has the original white paint so I notice any Diesel smoot .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

A warranty claim and a "return" are two different things. It might be time for the dealer to get schooled in specifics of the Uniform Commercial Code.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

The opening pressure decreased after 300,000 miles which indicates the spring had a permanent deformation (spring rate changed).

The spring rate was calculated using carbon valve A230 for material, yields 300N/mm spring rate or about 0.068 lbf/0.00004 inch. Spring constant change for a spring oscillating at micrometers per second for thousands of miles is difficult to measure.

When the mean fuel injection pressure is close to the opening pressure, a consistent spray pattern is produced regardless of the hand lever speed application.

Selected Bosch remanufactured injectors which have a consistent spray pattern.

Attached Files

Test Data.pdf (174.1 KB, 58 views)

Someone just rebuilt there first set of injectors....

No nozzle lasts 300,000 miles. It was peeing at 150,000 miles and I’m really wondering how you really tested any spring? Those nozzles were pissing probably when you hit 1,200 PSI so how could that be a measure of spring fatigue?

You are stating a theory, but I doubt you or anyone here has ever tested this. My experience is that 1600 psig vs correct 1950 psig in 3 of 5 cylinders made no noticeable difference. Any effect on timing is very small. The IP injections are from a positive displacement cylinder. The only reason the injector will open later at 1950 psig is because of the very slight compressibility of the fuel and elasticity of the metal tubes, plus slight leakage past the piston if your IP is worn. Might give 1 deg timing lag, but I'll let somebody else run the experiments. I doubt a used IP is even that accurate between the pistons.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Well Bill ;

One degree ignition timing is one whole heluvva lot in fact .

Although you might not feel it in your butt dyno, it makes a large difference .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better