fuel system, engine not running?

1981 MERCEDES BENZ 240D
300,000 MILES • 2.4L • 4 CYL • 2WD • MANUAL
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HANDLEY
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Was running with very low power and very rough idle. I had set the idle a bit high because it was so rough. The engine would smooth out at higher rpms. But, the idle was still rough. I didn't want to set the idle too high. I needed 2ed gear on a moderately steep hill. I could get up to 65 or 70 on fairly level ground. I decided to replace the injectors and thought I had everything to do the task. I successfully started the engine and it was running a little rougher than it had been. That could be because I hadn't had block heater plugged in and the morning was a little cool. I shut it off and started the job. I had acquired a 27 mm deep socket to remove the injectors. I disconnected and removed the fuel line between the pump and the injector. I only disconnected one injector. I was then going to remove the injector but, it turned out the deep socket wasn't deep enough to fit over the upper part of the injector and I couldn't engage the wrench on the hex part of the injector. I put the fuel line back and tightened the connection. I reinstalled the return hoses. I thought all I needed was to find a deeper socket. Which I could do if I could drive the car. I hadn't loosened the injector at all. So, I cranked and cranked, no start. I loosened various fuel connections between the pump and the injectors and determined that fuel is reaching the injectors. I pumped the primer pump and also cranked the engine with the loose connections and saw fuel reaching the injectors. Seemed to be high pressure flow. The only different thing I noticed different from before I started the attempted repair was that when I pumped the primer pump, a small amount of fuel appeared on top of the primer pump button. It did this when I pushed it with my finger but not when I used a screw driver to push it up and down ( I was trying to see where the fuel was coming from by using the screw driver so I could see the top of the button). Could the problem be related to the primer? It looks like the lift pump is moving fuel to the injectors. The primer is also moving fuel and the leak on top, if it is one, is tiny. Could the primer button have a tiny crack? Is there a tiny vent hole of some kind in the middle of the primer button? It obviously had problems before I messed with it but, I don't think I changed anything when I put it back together. That's my best description of the problem. If any clarification is needed, let me know. Thank you for your help.
Mar 25, 2026 at 4:13 PM
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STRAILER
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The first thing I would do is replace the fuel filter, it sounds like you have air trapped inside the system right now so you may need diesel starting fluid to help purge the air out. If this doesn't work we need to do a compression test to see if the engine is any good still. Minimum compression should be above 247-255 psi, if it is lower than this the engine will not run no mater what. Or you can upload short video of the engine cranking from under the hood so I can see if it sounds normal or not. It can give us a clue.
Mar 27, 2026 at 8:46 AM