Injector test accuracy - PeachParts Mercedes-Benz Forum

mach0415 · #1 10-26-2010, 09:52 AM

I have noticed a lot of posts regarding people sending injectors off to have them pop tested and checked over for spray pattern, etc. My curiosity was sparked as colder weather is starting to creap in and more people are reposting possible injector issues, relating to misfire, smoke, etc. - especially when they mention that they recently had the injectors tested and they proved to be "good." When these injectors are tested , are they or should they also be tested at very low temps as well as higher temps? It would seem that with close tolerances inside injectors and spring tensions, etc. that an injector might test good at say 80-90 degrees F, but be on the near or far end of a threshold/parameter that fails drastically when introduced to 0-30 ish degree F temps, due to metal expansion/contraction with temp differences. What do you all think?

benzhacker · #2 10-26-2010, 09:44 PM

Quote:

Originally Posted by mach0415

I have noticed a lot of posts regarding people sending injectors off to have them pop tested and checked over for spray pattern, etc. My curiosity was sparked as colder weather is starting to creap in and more people are reposting possible injector issues, relating to misfire, smoke, etc. - especially when they mention that they recently had the injectors tested and they proved to be "good." When these injectors are tested , are they or should they also be tested at very low temps as well as higher temps? It would seem that with close tolerances inside injectors and spring tensions, etc. that an injector might test good at say 80-90 degrees F, but be on the near or far end of a threshold/parameter that fails drastically when introduced to 0-30 ish degree F temps, due to metal expansion/contraction with temp differences. What do you all think?

Interesting theory, more likely it's the fuel. You have two choices with low temperatures and a cold engine: thin the fuel chemically, or thin the fuel thermally. If you live in a domicile that has actual seasons, the fuel blends may be changed 2-4 times per year. The last tankful of summer blend #2 on a cold morning could lead to all sorts of difficulty even with multiple attempts to run through the glow process.

As long as the nozzles are clean, the opening pressure is right and the pattern quality is good, the injectors themselves aren't the root cause. There is a reason these engines have a fuel thermostat on them and further, there is a reason for winter blend fuel (more #1 in the #2 to thin it out). If it gets cold enough to gel the winter blend fuel, the only real fix is to use electric fuel line heating elements, maybe add some electric oil pan heaters (you plug in your car at night or when parked, coolant block heaters are another option) and there is also the option of further thinning out the fuel, though I wouldn't recommend it to the other options (adding kerosene, etc.).

I had cold start issues in the Winter in Colorado and again when in Mammoth and Lake Tahoe up at the snow line with my former '87 190DT car. This was a car I later converted to run WVO out of the second tank and added fuel preheaters and a block heater to it, the side effect was that I could then run any fuel without issue at all times of the year. There are a lot of fairly inexpensive accessories for fuel line/Injection Pump heating to do this, they are just better known to folks living in colder parts of the country; in Canada and Alaska and among the WVO/SVO crowd (we use much of the same stuff, sometimes in modified form).

Warm regards,

-bh

Diesel911 · #3 10-27-2010, 01:33 AM

The Injector on Mercedes is pretty much just a spring loaded Valve that opens at a set pressure.
I do not know what cold temps would do to a Spring.
I thing there is a give and take there. You would think cold weather would make the Metal in the Spring Stiffer. But, at the same time it might also decrease the Spring Length.
A stiffer Spring would tend to raise the opening Pressure while a shorter spring would tend to lower the opening pressure.

Cold temps have a bigger effect on your Battery (cranking speed and Glow Plugs), your Crankcase Oil, and the ability of the Engine to compress the cold Air in a Cold Engine enough to bring it to temp high enought to ignite the Fuel; then on the Injectors.

scottmcphee · #4 10-27-2010, 11:22 AM

Everything is rated at a temperature, so it might vary a little based on ambient. But the springs in the injector are so strong, and a spring has a "spring constant" value that is pretty much... constant.. I don't think the injector reacts mechanically much different regardless of what kind of fluid or cream cheese you put through it.

Now, the what comes out the nozzle is entirely dependent on what goes into it, that's a different story. The fluid properties are much more dependend on temperature.

mach0415 · #5 10-27-2010, 11:26 AM

Thanks! All good info to know.