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  #1  
Old 07-21-2009, 10:25 AM
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Rough Starting / Rough Idle...Ongoing Problem - Ideas please! (yes i've searched....)

let me start by saying that yes i have searched out this topic. i've read threads back to 2004 on hard starting 300Ds. i've been self diagnosing for months now based on what i've read and it's still an being an issue.

the issue: my '83 300D has a bit of a rough time starting. it kind of coughs or stumbles each time it's started after sitting for a long time (overnight) no matter how warm or cold the weather. it'll stumble and cough out gray/white smoke each morning and will idle roughly for about 5 to 10 seconds. if i give it a little fuel, maybe bring the engine up 100 or 200 rpms, it smooths right out. i'll usually feather the accelerator and hold it until things feel better and then it idles just fine. i feel like if i didn't give it a little diesel it might actually die out on me but i haven't let it yet. and boy does the engine shake when this coughing happens. i think i actually have to replace my motor mounts because of this issue wearing them out. the car runs and drives perfectly and will start without issue when warmed up.

the things i've done: all filters are changed at oil changing time, oil filter and both fuel filters new every three months. air filter is new last month. diesel purge done about 3 months ago. valve adjustment done about 3 months ago. all rubber fuel lines replaced under the car and under the hood. injector return lines replaced. all five glow plugs replaced with five new bosch glow plugs (and i glow them twice to start by force of cold winter habit). change over valve line from banjo bolt to ALDA new from dealership.

issues with the car: there is a small coolant leak (http://www.peachparts.com/shopforum/showthread.php?t=257036). i have the old style primer pump which may be leaking. it's always kind of wet around that area but it primes just fine. the new fuel line from the tank to the primary fuel filter (the one that kind of loops like a candy cane) seems a bit too long and thin and i think might be kinking where it bends. but the car runs fine without any fuel starving when driving it. there is a small vacuum leak somewhere. if the car sits for a bit the door locks won't open when the drivers door is unlocked. and the heater vents/floor vents have vacuum related issues too. those are the only things wrong that may have anything to do with starting or engine happiness.

this has been going on for months and i've been diagnosing and replacing without anything getting better. it was definitely worse in the winter but that was before i replaced the glow plugs so maybe it'll be better this winter but still a problem. i use 5W-40 synthetic oil and regular diesel at the pump. previous owner put some biodiesel through it but it hasn't seen any of that since last summer. in the winter i added stanadyne.

that's all i can think of.....what do you think?

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Old 07-21-2009, 10:37 AM
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I'm going to follow this closely, because I have the EXACT same symptoms with my '83 300D and have taken the same remedial action as you, except for replacing the fuel lines.
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Old 07-21-2009, 10:40 AM
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I would try to find out the health of the motor first by doing a compression check. White smoke could mean anything, but one of them is coolant from a leaking head gasket that shows up when cold. If that's possibility, You might want to send a sample of your oil out to a lab like Blackstone to see if coolant can be found.

Then I would check for timing chain stretch, then injector timing, and pop test and spray pattern test the injectors.


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Old 07-21-2009, 10:56 AM
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i don't like the sound of that......


as for all of those tests, i actually don't know what any of them mean. can i do them in my garage / front yard or is this the job of a better / professional mechanic? i assume a search here will show me....? i thought about new injectors, is it easier to just buy new ones and install them regardless or should i go through with those tests first?
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Old 07-21-2009, 10:56 AM
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I have the same exact problem. I decided it was bad injectors coupled with mediocre compression (I have some blowby) and a busted glow plug relay. I do the exact same thing, step on the pedal a bit for 5 seconds until it evens out, and I have replaced almost exactly what you have.
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  #6  
Old 07-21-2009, 11:13 AM
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Is your coolant level dropping at all? If not, then I would doubt any kind of head gasket problem.

It may be injectors but there may be a simpler, and less expensive, option. You mentioned leaking around the priming pump. If so, replace it for the new style for ~$20. Since this rough running occurs mainly at start-up, there may be air getting into the fuel system and it takes a moment to re-prime.
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Old 07-21-2009, 12:46 PM
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I know you said that you put in new glow plugs but it still sounds like that is where your problem is. I think you should check the plugs while they are in the car so that you are checking the wires at the same time. Did you ream the holes when you changed them? If the cylinder is not heating then it will start very hard and very rough and run rough until the engine warms up.
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  #8  
Old 07-21-2009, 12:49 PM
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Quote:
Originally Posted by DeliveryValve View Post
I would try to find out the health of the motor first by doing a compression check.




.
That's my thoughts as well. If the compression is low, starting issues will always be prevalent.

The only other possibility is valves that are too tight, but, I'm assuming that the OP did that job properly.

IP timing and injector spray patterns won't have any effect on capability to start unless they are wildly off the specifications.

A diesel needs the heat of compression and fuel.........and it starts..........
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  #9  
Old 07-21-2009, 12:50 PM
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Quote:
Originally Posted by SD Blue View Post
Is your coolant level dropping at all? If not, then I would doubt any kind of head gasket problem.

It may be injectors but there may be a simpler, and less expensive, option. You mentioned leaking around the priming pump. If so, replace it for the new style for ~$20. Since this rough running occurs mainly at start-up, there may be air getting into the fuel system and it takes a moment to re-prime.
Supplier of new style hand priming pumps 12.99 american including delivery. Current mercedes ebay diesel parts. Ordered a spare yesterday myself. Quick shipping out his door and he claimed to have five left.

The way it works in life unfortunatly. If I had purchased a few spare primer pumps at this price I would never need another . By not puchasing a few I will eventually need more.

Whenever there is any possible question or suspicion about that hand primer pump change it. Simply stated if fuel can get out air might be getting in. If that turns out not the issue then make sure you have at least some positive pressure in the injection pump fuel feed.

The beauty of old diesels is they only need compression and fuel basically to start. As another poster already mentioned.

I imagine somehow or other your fuel is back draining allowing air in during the process. Thats why the more time since the last run increases the difficulty of restarting. The longer the interval the more air may be entering for you to overcome before good fuel supply is established. Or in combination with supply pressure being so substandard it makes life difficult for the injection pump to do its function properly. At least this area is pretty cheap to work in.

Last edited by barry123400; 07-21-2009 at 01:10 PM.
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Old 07-21-2009, 01:04 PM
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to reply to all ideas:

yes, i think i need to just go ahead and buy the primer pump, mine is "bad" in some way right now and the new style is so much easier to use and easier on the knuckles. maybe that WILL fix it. (i'll look on e-bay but i prefer the reliability and helpfulness of Phil right here. though some cheaper shipping tiers wouldn't hurt, don't need to send everything UPS ground......hint hint!!! )

as for the coolant level, it's been impossible to monitor as i'm dealing with the obvious leak i have right now (http://www.peachparts.com/shopforum/showthread.php?t=257036). today seems to be the first day with no leaks so maybe i can start checking it regularly for loss of fluid.

yes, i reamed the glow plug holes, even bought a specific reamer for this purpose. how does one check the glow plugs and wires when they are in? what about that relay, can that be bad or broken and my glow light still comes on and they still glow and start the engine?

valves were adjusted to spec by my indy mechanic. this is the second time (second mercedes diesel) he's done this job for me and it's run better afterwards both times. what about injector nozzles that aren't off but actually gunked up or actually clogged? P.O. did run biodiesel, of quality i'll never know....

now, about this compression test, is this something i can head out to the garage and just do myself?

EDIT: did a quick search for the compression test how to and i think i found everything i need to check this out....never mind.....

thanks!!!
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Last edited by Squabble; 07-21-2009 at 01:10 PM.
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  #11  
Old 07-21-2009, 01:18 PM
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This is a good write up on testing the circuit.
http://www.dieselgiant.com/glowplugrepair.htm
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  #12  
Old 07-21-2009, 01:23 PM
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I am sorry but living in Canada I cannot purchase parts from the sites sponsor. I would if I could as this site is priceless. Since I generally pay more than Americans for parts and am a natural scrounger. When decent prices come along I tend to jump aboard. I imagine the primer pump would normally cost about 40.00 one way or another here.

Before moving on to other areas I would verify what I suspect is happening. A very simple test might be to elevate a fuel container as high as practical and feed the gravity output directly to the injection pump. Let the car sit as many hours as you like. If the car then starts instantly you have positive proof of where to start searching.

Many things could be leaking air in. Since I am pretty positive but not certain your problem is in this area. It is still where I would test by some method before moving to other areas. . You can do the gravity test prior to the arrival of a replacement primer pump for example.
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  #13  
Old 07-21-2009, 01:41 PM
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Quote:
Originally Posted by barry123400 View Post
Before moving on to other areas I would verify what I suspect is happening. A very simple test might be to elevate a fuel container as high as practical and feed the gravity output directly to the injection pump. Let the car sit as many hours as you like. If the car then starts instantly you have positive proof of where to start searching.
could you give a more detailed explanation of this test? do i need to buy a length of fuel hose and run the line to a container of diesel that's placed on the top of my car?
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  #14  
Old 07-21-2009, 01:44 PM
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Originally Posted by barry123400 View Post
Before moving on to other areas I would verify what I suspect is happening. A very simple test might be to elevate a fuel container as high as practical and feed the gravity output directly to the injection pump.
To get 7 psi at the IP, you'd need an elevation of about 15 feet.
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  #15  
Old 07-21-2009, 03:03 PM
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Brian is correct about height required to get even seven pounds injection pump base pressure. Since it has been established these cars will start and run at lower injection pump base pressures. For example some have removed the relief valve spring and their cars started. Fair to state as well that some pressure was perhaps available in the pump as the return orfice on the relief valve is small.

Others have watched their available base pressure drop to basically nothing when accelerating on the highway with a gauge monitoring the fuel pressure.

A modest elevation at least is still indicated for a gravity test. It does not have to run perfectly with this setup just catch and run easily. That would still prove or eliminate the fault type in my opinion.

You are right a length of fuel hose or something equivelant would be required. You are trying to supply the injection pump directly. Or a piece of your old fuel line and a rubber coupler for example. You may still have what you already changed out for example.

It just occured to me as you say the primer pump is still basically functional. A simpler and perhaps more or less conclusive test might be to pump the primer pump a lot just prior to trying to start after a prolonged down time. Hopefully expelling any air through the relief valve that may have accumulated as you get fuel flowing. Leaving the return line off the relief valve on the injection pump may increase or aid your observation of when solid fuel is flowing. Then screw down the primer pump handle and try a start.

I really like to keep things as simple as possible when troubleshooting. My limited intellect demands this appproach.


Last edited by barry123400; 07-21-2009 at 03:10 PM.
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