Hi all,

I might be looking to rebuild my injectors soonish, at the moment they are working fine but I don't know when they were last rebuild and want to make sure that the pop pressures are balanced etc.

I have read that the turbo OM606 injectors have a pop pressure of 135bar, Dieselmeken apparently sets his to 150bar. I am guessing this would mean that the injection timing would be slightly retarded vs stock - has anyone tried any different pressures and found any differences etc?

Just wondering what pop pressure I should aim for?

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UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!

I'm running mine at around 140 bar since the plan is to raise the boost level to a max of 3 bar.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Pop pressure isn't an exact science. Consider the fact most home gauges can have up to a 3% variation in accuracy.

Increasing the pressure alone is no guarantee of improved performance. When you increase the pressure beyond about 10% you have changed the characteristics of the spray. Too much increase and you no longer have proper atomization of the droplets.

As you noted, "balance" is the key, that and a consistent spray pattern. Get those even first before you consider increasing the pressure.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Thanks for the info, I know that if the pop pressure is too far out of specs it will retard the injection (as the pressure takes slightly longer to rise before the injector releases the pressure).

I agree with everything needing to be balanced - which is where the time spent on rebuilding the injectors is. The car is currently running really well at the moment now that there aren't bubbles in the lines!

Will report back when I get the parts for rebuild them, I know the NA engine has a lower pop pressure, will aim for 135 - 140 bar but balanced across injectors.

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UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!

I built a pop tester w/ electronic pressure sensor to record the instantaneous pressures (see post). Readings were comparable to what I noted on the needle gage. The time traces just show the fluctuating saw-tooth pattern as the injector chatters. If you do want to trim pops, I posted McMaster-Carr PN's for shim washers that fit.

I don't put much stock in the importance of balanced pop pressures, since I found that 3 of 5 injectors in my 1984 were labelled for an NA engine and did pop at 1600 psig (vs 1950 psig for turbo). But, changing them made no noticeable difference in how the engine ran.

I think that having a good spray pattern is most important. A streamer could even burn a hole thru a piston (people say). Higher pressures would give finer droplets, which is probably good, but that risks damaging the injection pump and cracking your injector tubes, and perhaps eroding your injector nozzles. I wouldn't go there, unless the car was just for play. I don't think you can go too fine. Modern common-rail diesels inject at ~20,000 psig, which is why they burn so efficiently. Electronic controls also allow tapering the injection flow so they reduce noise enough to not need pre-chambers in passenger car engines (more efficiency). I understand Fiat developed it (and gas direct-injection) and licenses it to M-B and V-W, which gave them funds to buy Chrysler.

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

Thanks for that, I will be looking at the spray pattern, I know that some of the higher pressure common rail injectors can make a mess of pistons, not sure if these IDI injectors could quite do it - more likely to just coke everything up with a bad spray pattern.

Mainly going to rebuild them due to ensuring that the injector nozzles are correctly spraying - might even look to see if there are any upgraded nozzles from AMG etc.

The car is a project car which will be used for drag racing (have posted up my project on a different thread) - but still want to make sure its all still driveable to and from the track and still usable when I do need to use it as a normal car.

Will see what the current injectors are like, now that I have fixed the air in the fuel lines there the car idles and drives really smoothly.

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UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!