PeachParts Mercedes-Benz Forum - View Single Post - Poor mileage on my 85 300D--replace Injectors or IP?

Shorebilly · #11 11-15-2006, 04:11 PM

Howdy,

First my 300D is definately getting between 26 and 27 MPG......

I drove to town today, and this thread popped into my head.....began thinking about LATE timing......we really can't gather enough info with the instrumentation on our carz....on my ship's engines I would know each cylinder's cooling (jacket) water temp in and out, Exhaust Temp, nozzle (injector) cooling water temp in and out, piston cooling water temp in and out (yup we had water cooled pistons), fuel temp, and had an indicator cock that we could attach an instrument to and find out compression and firing pressures.....and pull an out of phase indicator card and see what the pressure was inside of the cylinder as it fired and moved thru it's stroke.....however I got to thinking, if the injection timing was a tad late, the fuel would be burning a bit further after TDC....and thus not create as much HP....so it would require more fuel to develop the same power......

A bum injector can/will do many things.....it all depends on what it's doing....it generally shows up as inefficiently burned fuel...black smoke....and sometimes as a loud knock....with these little diesels, I don't have a clue....if you really suspect the injectors...get the other set, have them tested and set.....then swap them with the originals.....and then have those tested if ya really wanna know......

If the car is running smoothly, I doubt it's your IP...unless it's out of time....or really trashed.....you can also take the IP to the Injection Shop and have it put on a calibration stand.....ask if you can watch.....it will tell you exactly how much fuel is pumped for each stroke.....actually 1000 strokes..and you divide it out......you will see the actual fuel pumped in 5 graduated cylinders.....and will instantly know if one or more are not working up to par......I have already written way too much....It would be difficult to explain hoe an injector's plunger's helix works within the barrel here.....

Sorry, I got carried away......but if you're interested I could recommend some books that you may possibly find at a library.....

SB