The injectors I purchased for my 240d are popping at ~ 130bar. I have a smoking issue with the car and hope this is the cause. The injectors are India bosch remans. My old ones are now in India, I got a good deal on the new ones and so must solve the problem one of two ways. I can: A)Buy a pressure tester and shims online. or B) Adjust timing to compensate.
Assuming option B: Is there any way to calculate the number of degrees advance which would have to be introduced to satisfy a difference of 15 bar if all things are equal given a correct flow rate and pressure from the mw pump? I have read that some have used 135bar injectors in a 240d by advancing timing. I would not feel comfortable doing timing by ear given my lack of experience with these cars. I would not feel uncomfortable adjusting the timing if I had a number to shoot for. I have somewhere else to put the $200 right now on the car and much as I would like to have a pop tester, there are these bushings.
I am no mathist, so could use some specific help on this one.
thanks

Where is your injection timing presently set?

I had a set of 603 injectors cleaned and pop tested for $85 a few years ago. That'll leave enough to do one bushing for now

Sixto
87 300D

The timing is at 24*btdc, valves, chain etc is as per specs. Assuming pump is operating at correct pressure and flow for now.

These are new remans which do not require cleaning. The only reasonable way for me to set pop pressure lower is to do it myself purchasing shims and a pop tester. I live in Utah. There is not an indy mercedes mechanic within 50 miles of me nor is there a bosch service center. The mechanic who pop tested my injectors has no shims and if I needed to purchase them to have him shim the injectors, I might as well spring for the pop tester and do it myself. In any case, I'd as soon compensate for the higher pop pressure by advancing my timing if I could find a timing number based on the math if that is a workable solution.

I don't know enough about these fuel systems to appreciate what you're trying to accomplish but Gus Pfister at Pacific Fuel Injection in South San Francisco, where my injectors were cleaned and balanced, services a lot of Bosch fuel injection equipment that arrives by mail. Hopefully you have another vehicle to use while waiting.

Maybe building one of these will be easier than flow calculus http://www.peachparts.com/shopforum/general-information/224334-how-build-diesel-injector-pop-tester.html

This thread is like a science fair - http://www.peachparts.com/shopforum/diesel-discussion/123573-anyone-know-how-use-diesel-pop-tester.html

Unfortunately you need thicker shims to lower pop pressure and you don't know the thickness of the shims you have. I don't know a way around that.

Sixto
87 300D

I had not thought of sending the injectors out to be reset. Thanks for the referral. If I cannot find an answer about the timing adjustment, I will look them up.

Hmmn I thought it was the other way around, i.e. thinner shims to lower pop pressure. Someone else who knows for sure please chime in.

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So, you have four new injectors and they are all popping at the same approx pressure, but said pressure is 15 bar high. I would be at least a little suspicious of the gauge and/or technique.

Considering that the typical OM616 on the road is 8-10 degrees retarded without major symptoms, I highly doubt that the reported symptoms are solely a function of over-spec pop pressure. How were the spray patterns and chatter during testing?

These are newly refurbished injectors aren't they?

They are all popping at 130 bar right?

And that's mean to tbe 15 bar too high or something like that? It that what "we're saying"?

I can't find the specs in the FSM - only chap 07-135 that says used injectors should pop above 100 bar...

...it does, however, say that they should all be within 5 bar of each other.



When I bought my refurbished injectors I was told that the pop pressure was set 15 bar higher than the prescribed pressure because after initial use they bed in and you get back down to the correct pressure "quite quickly".

I bought my injectors from a well respected firm in the UK.

(I've now bought a pop tester and will be doing them myself in the future though)


EDIT:-

List of pressures here

http://www.peachparts.com/shopforum/diesel-discussion/198995-diesel-injector-pop-test-pressure.html

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Don't leave that there - I'll take it to bits!

1983: All fuel hoses/ lines replaced , primer pump replaced. Valve adjustment , chain elongation corrected. injector timing set at 24*btdc. ADA adjusted incrementally to no effect after 1/2 turn clockwise-slight smoke reduction at 1/2 turn. New delivery valve sealing rings. Vacuum pump is putting out ~20in.
I'm trying to rule out the injectors as a possible cause of the smoke. The smoke is light grey. It appears after the glow plugs cool and is a substantial volume.
The smoke stays constant when injector lines are cracked in turn. The car idles smoothly and quietly.
When I rev the engine, It seems underpowered.


I do not know, but have assumed that when rebuilding injectors, people would set them for the pop pressure indicated. In the case of the 115bar injector, expecting it to settle 15bar to 100bar would put it at the lower limit for popping effectively.
This is the second set of India remans. I returned the first ones after they tested at 1950-2000psi (that's in the low 130's bar range). This second set I have had tested at a shop which does foreign only work. He does not have shims and understandably is working on more relevant cars now. This second set is in the ~130+bar range. The units are stamped with the housing number for the turbodiesel injector, but have a 115bar stamp as well. This is two shops, two sets and same result. The current set reportedly has a "good" pattern of spray.
The only other thing I can to do is to replace the ip with a junkyard unit or classifieds on here. I would like to rule out the injectors first. This brings me to my question: Is there a reasonable estimate or proof regarding the relationship between pop pressure and ip timing in terms of degrees?!

Answering that question would require that the time delay (probably nanoseconds) attributed to the additional actuation pressure be accurately measured. And you do that with a bottle jack and a stop watch.

I have understood in my research of this issue that if the pop pressure is too high, it can be compensated for by advancing the ip timing. My timing is such that I would have to dismount my pump again to advance much beyond 24*btdc. I am therefore wondering if there is a degree I could shoot for to see if this is the problem. If it were say 26* btdc, then I could reach that and probably have while monkeying. If the number was 30 or so, I'd have to reset. While I understand that I could just get the injectors redone, my finances suggest to me that I should try the adjustment of timing as a diagnostic tool.
I just have not been able to find the amount of advance people use to compensate when they use turbo injectors on an n/a engine. I am willing to put a new heart in an old man, but can't do a hip and knee replacement if the heart wont work. I need my funds for the suspension that I cannot accomplish on my own.
I understand that the question I have seems esoteric, but I think if it were solved, would be of benefit to the community here. Again, what would the relationship be between ip timing and injector firing assuming the rate of flow and pressure in the mw pump is nominal. I assume one of these old pumps is much like the other in their natural state- otherwise, there would not be a fixed degree of timing in the fsm.

Originally Posted by fochs
This brings me to my question: Is there a reasonable estimate or proof regarding the relationship between pop pressure and ip timing in terms of degrees?!



You would want a fast stop watch !!!

The change required would be dependent on how fast the motor was revving.
It is true that retarded timing may cause smoke at idle. It normally goes away when the motor is revved up as the timing device advances.
If you are getting smoke with the new injectors, I would go as far as to say that its not the injectors, being off by that much on pop pressure is unlikely to cause smoke.
What is the history of the motor?

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