240D 27mm IP delivery valve stretch check-in. - Page 3 - PeachParts Mercedes-Benz Forum

barry12345 · #31 05-12-2018, 11:00 AM

Quote:

Originally Posted by Shern

Stretched the overflow valve spring a couple weeks ago and I've since noticed my engine running slightly cooler. It's hovering a hair above 80, whereas previously it sat around 85. Unless I'm getting some new combustion efficiency and stepping on less pedal, I can't figure out a correlation.

Likely a total fluke, but anyone else experience this?

Lower operational temperature never reported previously to the best of my knowledge. At the same time it could be reasonable as good fuel pressure gives a more balanced power loading inside the engine.

Theoretically it does increase the actual injector timing a small amount as well I suspect. Depending on just how low the fuel pressure was before correction.

I used to have access to very expensive and specialized testing equipment years ago. It spoiled me when investigating things. Not to have access to it since.

Another oddity was some reports of an increase of 1-2 miles per gallon when changing out a really old fuel filter. To detect that I figured those posters where really anal at checking their fuel milage.

Diseasel300 · #32 05-12-2018, 11:10 AM

Quote:

Originally Posted by Shern

Stretched the overflow valve spring a couple weeks ago and I've since noticed my engine running slightly cooler. It's hovering a hair above 80, whereas previously it sat around 85. Unless I'm getting some new combustion efficiency and stepping on less pedal, I can't figure out a correlation.

Likely a total fluke, but anyone else experience this?

Unless the spring were so collapsed that you had no fuel pressure in the fuel rack and had extremely late injection timing as a result (you would have been seeing a good quantity of grey smoke that disappeared when you stretched the spring), it's all coincidental.

If you had enough fuel pressure in the rack to fill the injection elements to capacity prior to the stretch, then stretching the spring did nothing to the injection quantity or timing.

All things considered, assuming that the spring stretch helped in some way, diesels burn hotter with more fuel injected.

barry12345 · #33 05-12-2018, 11:48 AM

Quote:

Originally Posted by Diseasel300

Unless the spring were so collapsed that you had no fuel pressure in the fuel rack and had extremely late injection timing as a result (you would have been seeing a good quantity of grey smoke that disappeared when you stretched the spring), it's all coincidental.

If you had enough fuel pressure in the rack to fill the injection elements to capacity prior to the stretch, then stretching the spring did nothing to the injection quantity or timing.

All things considered, assuming that the spring stretch helped in some way, diesels burn hotter with more fuel injected.

I have speculated that low fuel pressure also may tend to reduce the fill amount in a sequential fashion.. The available fuel pressure might just fall off a little with each elements loading. The lift pump replenishes the pressure only once per revolution.

I just suspect this might occur in certain cases. I do know that when calibrating these injection pumps at a service place. They have to verify the fuel pressure to do it at.

Shern · #34 05-12-2018, 01:59 PM

Thanks guys - I didn't think the two were related, just something I'd noticed.

The stretch was done along with a lift pump rebuild. The lift pump valves were hardly worn at all, almost felt like a waste of time until I found the little O-ring in the bore. Now that thing was pretty shrunken and brittle... was pretty happy to have replaced it.