20% drop in fuel milage

[sergio7]

I have a 1989 MB 190D,,,I have noticed a 20% drop in fuel milage.I changed the air filter,changed the injectors(BOSH) with the only difference being,no more smoking and car is a little faster.I was told the engine has hydralic valves,so no valve adjustment is needed.Also changed fuel filter.The only thing I can think of is to get the injection pump timing checked,to get my fuel economy back to were it was.The car has 209,000 miles on it and been maintained very well.I used to get 35 MPG,I now get 28 MPG average city and highway.Please help, with fuel prices what they are.

[Knightrider966]

I don't have a car like yours, but a couple of local club members do and I would suggest you check your exhaust system for a restriction. This has happened to club members. If there is excessive pressure between your exhaust manifold and the muffler, there is your problem!

[Dee8go]

Where would that restriction come from? I can't think of how that could happen short of the pipe being crushed somehow, but doubt that's the case here.

[sergio7]

I checked the exhast no problem found.

[Knightrider966]

The muffler disintegrating internally would be one way. It doesn't happen often, but one of our club members had this very same thing happen to them.

[Knightrider966]

Originally Posted by sergio7

I checked the exhast no problem found.

The best way to do this is to drill a small hole between the exhaust manifold and the muffler and rev your engine up to 2500 RPM in park and report back what happens. If any more than a couple of pounds is eminating from here, that would be enough. A simple vacuum pressure guage works well for this.

[sergio7]

Does injection timing play a factor in poor economy,car runs very good,no engine vibration and no power loss that I can feel.

[arcticathlon]

I can backup Knightrider966.

i was getting lousy performance on my 1985 300D turbo and my muffler overheated to the point that it melted the bottom of my trunk mat. once i replaced it, it was faster and had better mpg. it was restricted and overheating.

[jbach36]

SOmeone mentioned he's getting less mpg too, suggested that the fuel they're selling us now has more "hamburger helper" fillers in it to stretch it further, meaning they're sort of watering it down (except it's not water, but you get the drift).

Just a thought, but I dunno.

jeff

[Knightrider966]

Originally Posted by sergio7

Does injection timing play a factor in poor economy,car runs very good,no engine vibration and no power loss that I can feel.

Yes, but injection pump timing being off would be accompanied by poor performance and vibration at idle as well as a low idle and if this is not the case, I'd look elsewhere! The only way pump timing would be off is if the pump gear jumped a tooth and this would be really noticeable!