91 350sdl hard/no start when hot - PeachParts Mercedes-Benz Forum

Mjrchode · #1 08-08-2013, 10:12 AM

Hello Forum,

I recently passed my SDL to my son and as he drives it a lot more than I was and a small issue has shown up. The engine is from a '87 300td and has ~230K. Over the past few weeks it had become increasingly harder to start cold and was smoking like a train. Glow plugs work fine (manual glow plug relay setup). Noticed the typical leak on the top of the injection pump around the output ports and ordered the seals, O-rings and socket.

On Saturday we went to start it and move it to the shop and almost killed the battery trying to start it. He had driven it the night before. Would not start. Turned out the lift pump was moving almost no fuel. Re charged battery. Replaced both filters. Replaced all rubber fuel lines under the hood with new. The fuel thermo switch was removed several years ago. Still no fuel. Determined mechanical lift pump is almost dead. Installed an electric lift pump (Airtex E8153). Starts much better. Almost zero smoke when idling. Runs better as well. Barks the tires again when shifting between 1/2 and 2/3. Still leaking at injection pump port seals.

Changed injector pump seals and orings. Purged and starts right up. Runs great. Son drives it 15 miles away. Stops to get fuel. Will not start. I drive over and check it out and there is fuel at filter/pump/injectors. Electric pump humming away. Weird. So we are standing there talking for a few minutes and try to start it and it fires up. Off he goes.

Yesterday it does the same thing several times. At gym, at friends house, and store. Starts fine cold. Drive anywhere you want to go. Turn it off and you have to wait 20-30 min before it will restart. Like it needs to cool down. Very strange.

I'm working through Sunday and will not be able to get to it until then but can yawl shoot me some ideas? I have no idea where to start with this one. Got any ideas why it will not start hot? I figure it has to be air somehow. But why does it clear up in 20-30 min?

sloride · #2 08-08-2013, 10:57 AM

Just throwing this out there as I do not know if the 91sd has a fuel tank vent like a 123, try starting with the fuel cap off. Possible there is a vacuum from an inoperable vent that does not equalize to normal pressure and not a vacuum.

NJ300sdl · #3 08-08-2013, 06:39 PM

Shut off valve may not be going back to the run position.

Diesel911 · #4 08-08-2013, 09:02 PM

Like NJ300SDL said.

When it is hot disconnect the Vacuum Line at the Vacuum Shutoff on the Fuel Injection Pump and see if it starts. If it does start every time like that it is likely the Vacuum Switch on the Steering Colum Lock is not relieving the Vacuum right away like it is supposed to.

There is a rebuild it for your Fuel Supply/Lift Pump.
Newer Model Lift/Fuel Supply Pump Rebuild
Anyone ever replace the valves in the fuel lift pump? - PeachParts Mercedes ShopForum
606 Fuel/Lift Pump Rebuild
OM606 Fuel Pump Rebuild - PeachParts Mercedes ShopForum

Brian Carlton · #5 08-08-2013, 11:07 PM

I once suffered similar problems with a 603...........resulting in a 10 hour adventure to go 100 miles.

Eventually found the problem to be a bad aftermarket primary filter............one that could not be diagnosed by looking at it. The outlet port was partially clogged, but the clog would "cure" itself when the engine was shutdown.

Very frustrating and expensive lesson. Originally diagnosed a bad fuel pump because the output was not to spec. Can you see why?

The simplest things can ruin your entire day.

Mjrchode · #6 08-25-2013, 09:49 AM

Hey Guys,

Thanks for the feedback.

Been slowly working our way through this list of suggestions and several we came up with. Replaced inline filter again with "correct" style. Shutoff lever/solenoid, etc seems to be working correctly. Removed in tank screen (cut it off) which helped and we replaced the tank vent valve which cured the hot start issue. He still has to crank about 8-10 sec to get it to fire off when cold but hot start is a non issue now.

Regards,

Mjrchode · #7 08-26-2013, 11:45 AM

Whelp,

it shut off on him again yesterday on his way home from a friends house. Can floor it and no increase in RPM/power. We were messing around with it after we finally got it home and pinched off the return line and started it. Ran like a champ so I guess the fuel pressure check valve in the return banjo fitting is bad. Cummins refers to this as an overflow valve. I have a small spring tension tester at work so I'm gonna go get a handfull of 20 cent springs and see if I can find one that works instead of paying MB $65 plus shipping for a new one.

Thanks for the help again,