my engine seems to be in limp mode? also no tachometer, i can only bring the engine to life for 1 second , that is to unplug the overload protection rely then as soon as i stick it back in bingo it comes to life for 1 second then again kaput?????

Have you checked your fuel filters? Lots of times if the fuel filters or tank strainers are plugged, you will have problems. More that are familiar with this specific year will chime in..
welcome to the forum!

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yes all filters up front are good, its just a matter of unplugging that relay, i can plug it in and out really fast then the engine comes to life for a second, even if it is in and i shake it nothing happens i have to pull all the way out then in and all i get is one second of proper idle

I am not familiar w/ your year model, but I have read where the relays can be cleaned up a bit, then they work better. Maybe try unplugging and plugging it back in quite a few times. If there is corrosion maybe that can help

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Get a new ovp and see what happens.

I bought a new 1 and still same problem

Did this happen all of a sudden or slowly got worse??

As noted above - 3 filters total. Usually small inline filer in engine bay and large scew on filter. Be sure to fill with diesel before you install or there will be too much air in the system.

Try starting it with the gas pedal on the floor and a strong battery

Check all your fuel lines. There may be a crack somewhere letting in air.

May want to pull the return line going to the fuel tank (in engine bay) and see if you are getting return flow. That would check that the lift pump and IP is at least pumping a little. May not be enough pressure to pop the injectors open but eliminates one more thing.

Remove the air filter and check for obstructions.

Let us know

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1987 300TD 147,000 miles- Palomino leather interior, 1995 facelift and body cladding, E350 wheels, Rebuilt suspension and sport springs, rebuilt turbo, New Monarch injection pump and injectors....and the list goes on and on...

What do you mean by limp mode?
A diesel will run with fuel, air, compression. (No spark required). Electronics do very little with these engines. (The EDS will adjust idle but not required, can be adjusted at the injector pump.)
Electronics is another story.

What's the condition of the battery? Does the vehicle turn over quickly? Does the engine start run, can you press on the accelerator and keep the engine running?

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92 300D 2.5L OM602 OBK #59

yes this happened all of a sudden, when i say limp mode i mean really low idle, but aLl i have to do is unplug the overload relay then plug it back in and all of a sudden the engine runs like a million bucks for a 2 seconds then low idle again, good battery , turns over good, i can drive if but its running half staff, I HAVE NEVER HEARD OF THIS PROBLEM SOUNDS RARE AND CHALLENGING OMG!! AND ITS MY ONLY WHEELS FOR THE FAMILY RIGHT NOW

It is a pretty minor problem, and related to that relay. Not having the relay work will not stop you from driving, it just results in a really low idle (and turns off the ABS).

It will run if you keep your foot on the pedal. As a short term solution you can adjust the cable for the gas pedal pictured below, to give your foot a rest. Do not turn it too far, as it can make the engine rev too high.

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i tried that, i can get it to idle at 1000 rpm with adjusting the screw but but still at a 1000 rpm it sounds funky so i pulled the rely out at 1000 rpm then put it back in and then it gets smoth as butter, for 2 seconds them clunky and shaky effects start again,,,,,IT HONESTLY SEEM THAT RELY IS ONLY SENDING POWER TO THE IP PUMP FOR 2 SECONDS THEN SOMETHING SHORTS SOMEWHERE??

Hello,
do a google search on these terms:
602_603index.htm
07.1-2053.pdf

The first search should help in general, the second will assist in setting the idle.

You've got something going on, obviously, but hopefully a search will get you in the ball park.

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92 300D 2.5L OM602 OBK #59

what's the condition of the engine mounts?

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92 300D 2.5L OM602 OBK #59

ENGINE MOUNTS ARE IN GREAT SHAPE