My 84' 300D-T (254,000 miles) has always had a bit of a shake which make my passengers feel like Kathryn Hepburn (parkinson's). When the car was converted to a two-tank Greasecar veggie system, the car actually got smoother. However it was discovered that my injection pump (IP) was leaking underneath. I'm pretty sure it was from using biodiesel in a car with over 230,000 miles on the original IP. So the internal seals got eaten up and now it leaks. I no longer use biodiesel because the station is too far from my house and frankly it's like 35 cents more per gallon.
The installer of the kit could never get the car to run smoothly at idle. He rebuilt an injector which was at that time the main suspect but it didn't help. So the verdict was that the IP was allowing air into the fuel system.
I dealt with this annoyance for eight months until recently it seemed to worsen.
The engine shakes from side to side at a really rough idle on either regular diesel or oil. It used to smooth out with the oil but not anymore.
I checked the motor mounts and although one is squashed, the shake seems to come from some inbalance. The motor doesn't move much from the torque of the engine.
I changed all the fuel filters and performed a diesel purge utilizing two full cans of the Lubro Molly cleaner directly into the engine using the fuel bypass system. Nothing changed.
So at this point I'm suspecting a faulty injector or the IP is finally dying.
I also wonder if the fuel booster pump the installers put in to help the oil flow toward the engine might have died? The shaking disappears at higher RPM's.
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