Hard start after sitting overnight

[dragon16]

Hello all!

I'm seeking some advice that I haven't as yet been able to find by searching. My '85 300SD has recently developed a new problem: It requires a long extended crank to start, but only after it has been sitting untouched overnight. The first start in the morning always has me in fear of draining the battery (which is new), or damaging starter. Once it does start, it coughs, smokes, and generally runs rough for a period of 10-20 seconds. Then it smooths out, runs as nicely as ever, and has plenty of power. I'm speculating that this is fuel related, as it seems to have no relation to ambient temperature. It could be 90°F outside, and still has trouble with that first start of the day.

I'm hoping someone here can either direct me to an existing thread, or suggest a direction to run in. The car's recent maintenance history includes a valve adjustment about 1000 miles ago, fuel filters within the last 500 miles, and a diesel purge immediately before the last filter change.

I do notice some fuel collecting around the front two injectors, but expect that it is from leaky return lines. I'll be replacing these as soon as the new hoses come in. Glow plug relay is functioning properly, and all glow plugs show good resistance (<1 ohm) to ground. I have not yet removed them for a full test, but will be doing that soon, as well as reaming the holes.

Also, I do all of my own work, and am a fairly competent shade tree mechanic, however this is my first diesel, and my first Benz. I've only had it for a couple of years, and I'm still becoming familiar with its ins and outs.

Thanks in advance for any direction you guys can offer!

[charmalu]

Welcome to tne forum.

Even though you say the resistance is good to the Glow Plugs. I`ll place my bets that the Glow Plugs are your problem. You need to remove them, and put 12V to each one and see if the tips get good and hot (red). hold them with some pliers.

Also be good to get ahold of a GP Reamer and ream out the GP holes of Carbon.

Since you are new to diesels, Iam assuming you just bought this SD and working your way through the various systems. sounds like you have done your home work and ben doing some searching here for info. At the top right of the page is the Resource Tab, in there is the DIY Articles with pictures on various jobs, and DIY links listed in catagories.


Diesel Giant has a good write up on troubleshooting the GP system.

Mercedes Diesel Glow Plug Repair


Charlie

[dragon16]

Thanks Charlie! I'll get those glow plugs checked ASAP. I like that idea a whole lot more than replacing injector nozzles price-wise. Honestly, I was hoping that it would be that simple, but fearing the worst.

And thanks for the DIY info. You're right, I'm slowly working my way through the car, fixing problems and potential problems as I go. It's just going slowly due to funding, and some of the special tools required for certain jobs are a bit pricey!

[Phillytwotank]

If not the glow plugs i think it would be something fuel related.

I had the same problem with mine once and it turned out to be the lift pump. $10 kit from peachparts fixed the check valves on the lift pump did the trick.

[charmalu]

This line has me leaning towards GP`s.

"Once it does start, it coughs, smokes, and generally runs rough for a period of 10-20 seconds. Then it smooths out, runs as nicely as ever, and has plenty of power."


Add a little Never Sieze to the threads, helps later on when removing them. Looks like you live in the Salt belt.

Charlie

[Diesel911]

Just for the fun of it; before starting in the Morning start pumping on the Hand Primer until you hear a squishing sound and then pump some more.
If it starts up fast like that you have either an Air leak of the Valves in the Fue Supply/Lift Pump are allowing the Fuel to go back towards the Fuel Tank. It might be refered to as a Pump losing prime.

[dragon16]

@ Diesel911 - I forgot to mention it in the first post, but I did indeed try the primer. I get the squishing/buzzing sound from the IP on the first pump, but just to be sure I gave it about 10 strokes, then tried to start. No change at all. So I guess that pretty much rules out losing prime, huh?

@ Charmalu - I do indeed live smack in the middle of road salt hell. And the car originated from DC, which probably isn't much better.

I'm far from experienced with this, but it surprises me that a glow plug problem wouldn't manifest itself even after a few hours of sitting during the day. Do you think the block heater would produce enough heat to make a difference in the morning if the glow plugs have problems?

[whunter]

Originally Posted by dragon16

@ Diesel911 - I forgot to mention it in the first post, but I did indeed try the primer. I get the squishing/buzzing sound from the IP on the first pump, but just to be sure I gave it about 10 strokes, then tried to start. No change at all. So I guess that pretty much rules out losing prime, huh?

@ Charmalu - I do indeed live smack in the middle of road salt hell. And the car originated from DC, which probably isn't much better.

I'm far from experienced with this, but it surprises me that a glow plug problem wouldn't manifest itself even after a few hours of sitting during the day. Do you think the block heater would produce enough heat to make a difference in the morning if the glow plugs have problems?

YES.

Glow plugs link thread


.

[panZZer]

new nozzles

[dragon16]

Originally Posted by whunter

YES.

Glow plugs link thread


.

Thanks for the link! I needed some more good reading material. (NOT sarcasm)

Looking forward to arriving home from work and getting my hands dirty pulling some glow plugs.

And I'm not discounting the possibility that I may need new nozzles. Just working this angle first.

[dragon16]

Last night, in the absence of spare time to pull and test the plugs, I thought I'd plug in the block heater for a few hours, and see if it makes a difference in starting. Sure enough! It still took a little more cranking than I would consider normal for this car, but for the time being I'll attribute that to the fact that the battery was not well charged, and cranking was not as fast as it probably should be. But once it fired, it purred like a kitten right from the start. No coughing, no smoke. It sounds like a good possibility that I've got my answer. Going to get a whole new set of GPs ordered today.

So to that end, I gather that I should stay away from the Autolite brand plugs. Aside from that, my local NAPA carries NGK, Champion, Bosch, Echlin, and Beru. Any particular brand recommendations and/or warnings?

[gatorblue92]

Originally Posted by dragon16

Last night, in the absence of spare time to pull and test the plugs, I thought I'd plug in the block heater for a few hours, and see if it makes a difference in starting. Sure enough! It still took a little more cranking than I would consider normal for this car, but for the time being I'll attribute that to the fact that the battery was not well charged, and cranking was not as fast as it probably should be. But once it fired, it purred like a kitten right from the start. No coughing, no smoke. It sounds like a good possibility that I've got my answer. Going to get a whole new set of GPs ordered today.

So to that end, I gather that I should stay away from the Autolite brand plugs. Aside from that, my local NAPA carries NGK, Champion, Bosch, Echlin, and Beru. Any particular brand recommendations and/or warnings?

Bosch or Beru. You can buy them here on this site as well.

[dragon16]

Originally Posted by gatorblue92

Bosch or Beru. You can buy them here on this site as well.

Thanks Gatorblue. New Bosch plugs have been ordered from Fastlane.

I very much appreciate everyone's help. I'll update once I've changed the plugs out.

[kerry]

Purchase of new glow plugs could be premature. Did you confirm they were getting 12 volts with the key in the glow position? It could be as simple as a cracked strip fuse in the relay.

[dragon16]

Originally Posted by kerry

Purchase of new glow plugs could be premature. Did you confirm they were getting 12 volts with the key in the glow position? It could be as simple as a cracked strip fuse in the relay.

I did confirm this. The only thing I haven't done yet is remove the plugs and test them manually with jumper cables. But I figure this is $75 well spent even if they're not bad, just because I have no knowledge of how old they are. Can't hurt to be sure they're fresh, right? Need to pull them and do a carbon ream anyway.

Thanks for chiming in!