I don't know what is going on with my 87 300D. The symptoms are as follows: Lot's of white smoke, even when warm, which reeks of unburned diesel, engine feels like a gasser with a bad miss, seems to not have as much power as it should, and doesn't get great mileage. It starts right up every time though. I took it to a shop, and they told me they thought it was a bad injector, so I pulled them all and took them to get pop tested. The guy said all were fine but one, and that one cleared up when he increased the pressure to it. There was a buildup of hard black carbon on the end of the injectors, so I cleaned that off and put them back in. No change. So then I figured I'd better check the timing chain, which I had replaced about 6 months ago. It was right on. Checked the injection timing, the mark was right on at 14 degrees ATDC. So at this point I pulled the injectors again, and sprayed some PB Blaster in the prechamber then filled each one with Seafoam. I also had to clean off even more carbon from the injector, although this time it was much softer and easier to remove. Put everything back, and again no real change. So now I am a little annoyed, and buy a big container of Marvel Mystery Oil and hook up the fuel lines so it runs straight on the stuff. Didn't see a whole lot of black smoke, but it did run pretty smooth while on the MMO. But now it's back on diesel, and back to running like crap with lots of smelly smoke. What else should I be looking at here??

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87 300D - Running on Veggie oil; 260,000 plus miles; Original #14 head