'82 300D stumbles to start - UPDATE, PROBLEM SOLVED!

my '82 300D stumbles when starting in hot or cold weather. i replaced the glow plugs and reamed the pre-chambers. they had minimal carbon build-up. i checked engine (1 degree stretch) and IP timing (24 degress BTDC) and they are both ok. compression is 24+ bar across all cylinders with 96k original miles on the clock. injector release pressure is low (1750 psi) and i plan to replace the nozzles and bump the pop pressures to 1950 psi. could the low pop pressures be the root cause for the stumble starts, or is there something else i need to check? i have also considered replacing the fuel injection pump check valve thinking that the pump may be losing pressure over night (or whenever it sits for a period of time), but no one carries this part. any ideas?

many thanks,
john

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Diesel Engine Specific Aid

Chassis Model Number

W123

stumble like diesel hammer?

wow you have checked IP timing and degree of stretch is very involved and most wouldn't have done that. So things i mention are going to be simple. When checking pop pressure was the spray pattern good on all of them 1750 is not great but not bad. I balenced my injectors recently and one was really bad the psi was good but it started to pee before it popped. fuel tank screen ever been changed? Diesel purge and filter change is always good if it's been awhile or has never been done these are just the cheap and easy things to try. OH, is your battery strong? Glowing takes a good amount of juice and whats "left" over has to fight that 24+ bar of pressure. Is it stumbling while starting or just after starting till warm up?

'82 300D stumbles when starting

thx. for the reply. i have ordered new nozzles and a pop tester from kent and will be completing the nozzle change after the weather warms up a bit. at that time, i will be able to see the spray pattern. my guess at this point, is that if the nozzles have been changed within the last few years, they were incorrectly set at the non-turbo level which is approx. 200 psi lower than what is called for in the turbo models. i don't have history when the nozzles were changed, so I will start with fresh nozzles balanced to within 3 bar set between 1950 to 2000 psi. i will also do the purge prior to the nozzle change. i suspect a couple of the prechambers have some buildup. tank screen is unknown if changed before i bought the car. battery is new this winter and cranks the engine just fine. the stumble occurs while starting. warm restarting is just fine, as in i just touch the key and "marvin" comes to life.

UPDATE: today, i pulled all the glow plugs for inspection and all looked fine. none were oiled up and all had chalky white tips indicating that all are getting hot. so, i'm ruling out a glow plug issue at this point. on a cold start, after checking the glow plugs, the car stumbled to a start and the engine was missing on 1 cylinder for about 5 to 7 seconds...and then it caught and the engine smoothed out and ran silky smooth. with this observation, i really think that i have an injector tip clogged and not spraying correctly. as i mentioned earlier, i plan to replace the nozzles, now sooner than later. i will pop the injectors as i pull them and update this comment as to my findings and result.

marvin is well cared for

Tank screen is a good idea because the fuel system will loose it's prime anyway and nobody wants bacteria getting to the new injectors. I would replace injector return lines too and make them a little long so if you pull them off again you can cut them back 1/4 inch on both sides and put them back on so they seal properly or if they are fairly new and long enough cut them back dip in trans fluid and put back on. My SDL stumbled smoked hammered (long block has 50K on it) one injector was really bad pressure tested it peed off to the side before it popped (had bad spray pattern too) but I built pressure it would fall and I would hold pressure pretty steady to see (because I suspected) it was leaking down and loading up that cylinder and it was leaking diesel. So you may have same issue. Does marvin sit for days at a time like mine?

'82 300D stumbles when starting

hi noah, this is my daily (50 miles per day) driver. ok...so here's the update. diesel purge is done (2 cans), new nozzles balanced, car still stumbles (starts right up and runs, but misses on 1 cylinder for approx. 8 seconds). so, after completing the purge, i had to prime the pump. the hand pump leaked profusely after i unscrewed the handle and started pumping...but, i did get fuel primed to the pump. i tightened the white handle down after priming and it does *not* leak. do you think the cause for the stumble starting could be related to the lift pump?

'82 300D stumbles to start - SOLVED!!!

hi all:

i just wanted to post that i FINALLY figured out the stumble starting issue on "Marvin." the problem actually started getting worse! so, i started with the simplest things first as you have read above.

then, i decided to remove and thoroughly inspect the hard lines from the fuel injection pump to the injectors. i removed them and pulled the tightening nuts up on each line so i could inspect the flared ends...and there it was! on the #2 hard line there was a hair line crack at the flared nipple (pump side). i could see where it had been growing by the fresh metal. funny thing is, the line never leaked fuel. so, i went out to "Ivan" (my parts car) and pulled the #2 line off him and made the swap. night and day difference. i just touch the starter now and old Marvin purrs!

on this issue, the problem was something very tiny, but very simple. what i determined was that when the car would sit overnight, the pressure on the #2 line would simply drain off. so, when starting, it would take the pump a while to build pressure into that line like the other 4 cylinders. this is why it would stumble for 8 seconds (yep, i counted it off every time), which, incidentally, is the amount of cranking time it took when i pulled the hard lines to do the nozzle replacement and injector rebuild. what intrigues me is how at 135 bar of pressure the #2 line never leaked fuel. go figure. how did the line get cracked? well, i had my indy do a cylinder soak due to gummed up rings and he must have overtightened the line when he was putting the car back together. the stumble starts happened after i had this work done, so i know he must have cranked too hard. the rough starts are the primary reason i rebuilt the injectors. as a side note, when i pulled the #3 injector, there were 2 crush washers in the head. he had the injectors and pre-chambers out to do the cylinder soak, so i will be looking to replace my indy.

well, that's a wrap....

I'll check mine

I am still workin on my Idles fine but only go up 100RPM issue. (I am finally looking my age now (29) from all the stress of fixing this) I have a new lift pump coming. I did alot of other things in the past week but to no avail I will post all of those and what actually worked (something is bound to work) when I figure it out I will check the hard line nipples kinda sucks I have had those lines off like 5 times in the past three weeks so whats one more time to check the nipples especally if that's the issue.. thanks for the "straw"