Tips for fuel economy, 300D. - Page 3 - PeachParts Mercedes-Benz Forum

argus445 · #31 05-09-2009, 11:34 AM

Quote:

Originally Posted by JonL

I'm curious about this as well. I imagine the EGR will have some effect on fuel economy, but I'd love to know how much. Perhaps after I rebuild my injectors I'll do a test. On the '87, the EGR doesn't function at highway speed, so the effect will only be in city driving. I've left my EGR intact because I'd like to keep my environmental footprint small, and the difference in performance isn't important enough to me. If the fuel economy were significantly different I might reconsider... trading less CO2 against more NOx.

I got about 6 mpg difference and i tested all the parts seemed to be all functioning and setup right tho. I just wonder how much volume of exhaust it actually adds and if it equally gets distributed with how the egr valve dumps it in the front like it does? In 1982 did they even have Nox restrictions in USA? I'd assume if they did vw would of had that mess on they'res?

JonL · #32 05-09-2009, 01:33 PM

I'm pretty sure the US had NOx regulations in '82, but they were probably very lax. All the emissions limits have become progressively more restrictive over the years. VW might have been able to get around it differently, perhaps with injection timing. VW uses a VE distributor pump that I believe has more timing control flexibility than the inline MB pumps.

On the '87, there is an air butterfly valve (like a throttle plate) that closes when EGR is called for to create enough manifold vacuum to draw in the exhaust gas. As I recall, the exhaust goes into an intermediate chamber in the air box and I think will be distributed evenly amongst the five intake runners. If there's MPG to be gained, I think it probably comes more from eliminating the intake restriction rather than eliminating the exhaust itself.

6 MPG is a huge improvement. I'd go for that!

#33 05-09-2009, 04:15 PM

6mpg means the EGR was leaking exhaust past the seat and needed to be cleaned/replaced even if you wanted to keep it. Improvement should be more in the 1-2mpg range. Power at WOT shouldn't change since the EGR is inactive at that point.

argus445 · #34 05-09-2009, 04:37 PM

Yah the improvement was from unhooking it 1-3mpg and cleaning up the intake too 200K miles of egr junk had collected as well. I dont really do much WOT which is another killer if u have the egr still running.. same thing happens with vw TDI engines it's a mess.