We have an '82 300sd that will start great and run great when cold, after it warms up , if you try to restart it , no go. cranks over fine, just won't cough. and now it is also shutting down when going down the road after getting good and warmed up.

I had posted awhile back ( just got around to checking the thing ) and had some suggestions about possible residual vacuum going to the shutoff valve and possibly rack dampner screw too tight and binding rack.

Today I tested it for vacuum... no vacuum going to the fuel shut off while cranking, good vac to it when turned off.

Made sure the manual shut off wasn't binding.

Backed the rack dampner screw out .

No change, still wouldn't start warm.

Cracked a few injector lines loose to see if it was getting fuel while cranking. Some fuel drizzled out around the fittings, but not with the gusto that I would expect.

Could I be looking at a failing fuel shutoff valve, possibly the spring inside it so worn that it can't kick the thing open when warm??
Any other suggestions?
Thing runs great other than that. fuel filters are new and injectors all rebuilt within the last thousand miles by a very good Bosch injection shop.

Thanks---------Robert

Sure sounds like a fuel supply problem. I would check the fuel pump first. Warm up the engine and get it to its failure point. Then operate the hand pump and see if you get a "buzzing" sound that would indicate it is functioning. If it is working OK, your problem might be in the IP. You did say that the filters are new, but you might try back flushing the fuel supply lines to make sure they aren't plugged. If that solves the problem temporarily you should probably drain and clean the tank.

Just suggestions. Others will jump in with more I'm sure.

Tank was drained and cleaned and new screen installed about 2000 miles ago, along with new primer pump.
I wouldn't think the lines could be clogged if it's running great one second, then I turn it off and try to restart and nothing..

The next time it is warm and you want to start it try taking the fuel cap off the fuel tank.
If that does not work go to Alldata.com and check the TSB titles... one for your car may say ' problems restarting when warm' or to that effect....

From what I have observed on this site.I would just check to see if valves have too little clearance. Once engine warms very poor compression if valves not able to seat properly. Only should take a short time to do a check. especially if not done since heaven knows when. Just a thought.

Valves were adjusted about a thousand miles ago. and I set them a bit on the loose side, They *shouldn't* be tightening up .
I cleaned out the tank vent lines a couple of thousand miles ago, but it wouldn't hurt to try the cap trick.

tightens up with use but can't make sense of that. Is this so and, if so, will someone 'splain it to me?

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

Wouldn't hurt to do a quick check on clearances....if you didn't tighten it down enough then may have closed up on you.....would hate to spend a few weeks chasing other possible things to find out it was this...

Usually its good troublshooting to look at what was done last when you have something that goes wrong not long after some work was done.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Not familiar enough with this type engine. Just a few other thoughs though and not meant to frustrate you as you may have covered already. I would warm up and shut down. Remove return line from injection pump and see if any fuel discharge when cranking hot. Just primarily verifys lift pump is not going down when engine hot I think. If your problem was quitting on road only would suspect back pressure (blowby) shutting down pump with perhaps semi obstructed bypass system as a possibility. I do not think engine can retain blowby pressure after shutoff when warm but you may want to verify again because it is so easy to do. Simple as removing oil fill cap prior to trying hot restart..

i am always looking for the simple thing... could be algae in the tank. you said you cleaned it but did you buy fuel again from the same place? perhaps too obvious a question but such a simple problem is easily overlooked.

good luck.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Tronteck, as the valve rocker pounds up and down if the adjuster is not tight the thread starts to travel in the tighter direction (less clearance) on mercedes gas engines. Mercedes used to specify clearence checks every 10k if i remember. Ignore this and pull head to change the burnt sodium cooled exhaust valve before another ten K was travelled in many cases. At some point mercedes made the interference fit of the adjuster threads much tighter and they became a bear to adjust but lessened the problem enormously. The diesel uses a different set up of two nuts pressured together with two wrenches to lock the setting called a jamnut arrangement i believe. If not tight enough the adjuster thread starts travelling again decreasing the clearance even on that design I believe. One might be prone to think the clearence would loosen and increase but the reality is it moves towards reducing the required operating clearence.

Barry, That sure sounds good as a reason ... but just isn't correct.
The reason has to do with the relationship of valve to the cam in the design. In old American engines with center cam valve train wear would develop at many juctions and thus would get looser...

But with valves which pretty much work directly from the cam the wear at the valve lip into the valve seat on the head produces the decreasing clearance.

The evidence that it is not the adjuster nuts situation ? Small engines in which the Valve end works directly off the cam ( the clearance is produced and determined by actually grinding the end of the valve ) have the same situation ( getting tighter with wear ) as our engines...

just visualize that the springs are always pulling the valve stem toward the cam. When the cam is not touching the valve stem, the only thing stopping the valve is the seat in the head itself. As this wears down (and the valve wears too) the valve stops deeper and deeper in the head. Eventually(if not adjusted) it will touch the cam all the time, not closing completely, and then it's valve burnin' time.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Thanks leathermag and pete for trying to give me some insite. I remember the increased and variable depth required to clean up seats on the older gas mercedes engines. The primary reason I felt the adjusters were perhaps slowley moving was that all exhaust valves should generally have been the same yet the clearances were different from each other. Yet they were all set say ten thousand miles earlier the same. Guess now just different wear patterns were in effect valve to valve. The second item that played into my thoughts was mercedes going to a much tighter interference fit on the adjuster. On the earlier engines I could get the adjuster moving with the crowfoot wrench but on the last ones I did had to remove the rocker and go straight onto the adjuster with socket and bar. Was kind of miserable since was trial and error. If i ever have to do another will set a dial gauge up and calculate the change required to return to spec. Rather than trial and error. the earlier engines were beautiful with no fan clutch. Just pull engine to four positions and get all the valves adjusted properly in about 10 minutes after you got the pan off. Loved those engines. But time does tend to move on.

Barry, It is certainly possible on any particular engine for the adjuster nut or the lock nut to be messed up to where they will not hold their position...
And the FSM suggests that if they won't hold their setting that new ones should be installed....But as a generic reason why our engines normally get tighter between adjustments it is the cam/valve train design.
Looking from the top of the valve, with right hand threads.... if the adjuster won't hold I think it more likely that it will get looser by traveling towards the big end of the valve with the pounding from the cam rather than defying gravity and getting tighter.