300 sdl - intermittent hard starting - PeachParts Mercedes-Benz Forum

todd0765 · #1 09-27-2011, 11:34 AM

1987 300 sdl - diesel engine with new filters, injectors, injector return lines, etc., and good pump pressure. starts and runs good first cold start. after engine warms, requires two to three brief start cycles to start. will start on first warm restart with lengthy cranking, but does not want to "take" fuel when driving away. i am thinking sensor or relay somewhere. any suggestions??

compu_85 · #2 09-27-2011, 01:00 PM

So, say you drive for 30 minutes (engine fully warm), shut off the key, then try to re-start right away. Does it have trouble starting then? Are you sure the shutoff lever is working properly?

-J

todd0765 · #3 09-28-2011, 07:51 AM

time of running doesnt seem to matter. just restarting after first cold start. does not seem to matter if it is 5 minutes or 30 minutes. glow plug light comes on and goes off quickly cold or hot - but as i understand these plugs were some type of fast cycle units. i have not replaced them yet, but it seems to be more of being fuel starved than anything. how would i check fuel shutoff lever's operation? and i forgot to mention in initial post, the timing chain does not have play - it all seemed to be in very good condition. thanks

sixto · #4 09-28-2011, 01:48 PM

What compu_85 said. When you restart, have some turn the key to the glow position while you watch the shut off lever. It should pop smartly to the vertical position. It it lags or doesn't get quite vertical, you won't get full pressure to the injectors.

We don't measure timing chains for play, we measure for elongation. The tensioner is able to keep tension on the chain way beyond the elongation limit. You have to check the chain against various timing marks -

http://www.peachparts.com/shopforum/diesel-discussion/56836-93-2-5-turbo-timing-chain-replacement-interval.html

But I doubt your situation is a symptom of a worn chain.

Sixto
87 300D

compu_85 · #5 09-28-2011, 02:07 PM

In this grainy video you can see the shutoff lever move on my car:

Mercedes 350 SDL Diesel S-Class Cold start - YouTube

todd0765 · #6 10-08-2011, 06:24 AM

didn't mean to seem like ding bat, i did remember fuel shut off lever after i looked at your video. i will definitely check its function. i really think i need to replace glow plugs. i noticed by trial and error that if i cycle the glow plugs on, but do not crank engine until second or third cycle it starts and runs fine. hot or cold. so i am guessing it may have been glow plugs all along starting to get weak. hopefully not the glow plug relay

what puzzled me was that it would not take fuel after starting if i kept cranking. i'm talking very sluggish throttle, and top speed of say - 25 to 30 mph. i would just stop and restart if this happened, but that wasn't always ideal. i havent had this car very long and i am still learning all the little nuances of its running.

thanks for your help

buffa98 · #7 10-08-2011, 10:01 AM

When you turn to the glow position wait until you hear the "Click" of the glow relay turning off, then try to start. On mine the light goes out after 3 secs no matter hot or cold.

As far as the not taking fuel I am leaning to the shut off lever as well. Been there done that. Once you get the bugs worked out these are great cars.

Welcome to the forum

sixto · #8 10-08-2011, 01:53 PM

Next chance for a warm restart, pinch the return line to the fuel tank. Wrap a lot of tape over the jaws of vice grips and lightly clamp the line that collects the return from the injectors and IP and goes to the driver fender. If the engine starts quickly, the relief valve on the hidden side of the IP might be sticking open when hot lowering available pressure to the injectors.

This is only for diagnostic purposes. Shut off the engine as soon as it starts and remove the clamp.

Sixto
87 300D

86-300sdl · #9 10-11-2011, 12:48 AM

If the fuel shut off works ok may just be the glow plugs.

A couple of seasons ago I was sure my 603 was starving for fuel during start up....wrong...glow plugs were just tired. After just replacing #1 GP she fired instantly every time (of course after letting the gp's heat up). Did them all a week later.

Drove me crazy with all the "almost fire attempts, then fire and stumble" down the road until it warmed up...had to be fuel I thought LOL.