300SD rough idle/stalls on cold start - PeachParts Mercedes-Benz Forum

Don DS · #1 09-27-2006, 10:19 PM

I recently purchased a 84 300SD which I intend to convert to WVO. I've driven it about 200km and it runs fine once warm, but now that outside temp is down to 10 degrees C (52 F) up here in Ontario Canada, it starts harder and will stall after running for about 10 sec. Then it's hard to start the 2nd or 3rd time. Could it be poor injector spray? Valves needing adjusting? Low compression? I haven't checked these yet, but would like to tackle myself. I could use some basics hints where to start since I'm relatively new to diesels, particularly Mercedes. The engine also seems to "knock/rattle" a little more than I would expect when cold, but it totally quiets down when warm. Would love to hear any helpful suggestions?

SD Blue · #2 09-27-2006, 10:36 PM

Your problem in a couple of words.........glow plugs. Do you run them for the entire cycle until the relay "clicks"? They can be checked with a meter, about 1 ohm to ground with the relay disconnected. Or if you want, pull them and connect the wires in free air and see if they glow red hot.

CAUTION! They are extremely hot for quite a while after they stop glowing.

Motorhead · #3 09-27-2006, 11:58 PM

I second SD Blue on the glow plugs. The glow plug relay is mounted on the drivers side inner wheel well. Pull the black cover off and check that the foil fuse is in good shape. You can also find a small, five pin plug. Pull it off of the relay and you can then test each glow plug individually with an OHM meter.

DO ALSO check your valve clearances. The turbo 5 cyl engines have a habit of the intake valves tightening up.

Let us know what you find.

vstech · #4 09-28-2006, 12:44 PM

this is a nice pictorial on glow plug testing and maintenance.
http://www.dieselgiant.com/glowplugrepair.htm
He has put up several pictorials for repairing theese and other cars. his home page is pretty explanatory
www.dieselgiant.com
John

Don DS · #5 10-02-2006, 10:49 PM

Thanks for the suggestions. I have always cycled the glow plugs til the light goes out for 2 or 3 times and the rough idle/stalling still happens. It seems the relay and circuit is working so likely there are some faulty glowplugs. The dieselgiant site seems really helpful for this. When I get some time this week I'll check the glow plug circuit. Thank goodness I don't have a 6 cylinder . . .

Don

Don DS · #6 10-03-2006, 10:10 PM

You guys have been helpful, thanks. I checked out all 5 glow plug and wiring circuits and each one registers about .6 ohms. The relay circuit seems to be working with 12 v on each pin and stays on about 10 sec. Should I remove each glow plug and check how red they get? Should I attempt to check and set the valves? The dieselgiant site has a good explanation on this - no problem for me to tackle.

Any other ideas on what may cause rough idle, surging, stalling on inital cold start? On another note, the engine seems to have a fairly loud "knock" when it's cold. Sounds like it's the rythm of just 1 cylinder, but I haven't been able to isolate which one. This goes away if the engine speeds up or when engine warms up. Is this a normal "diesel knock" for a mercedes? I'm just not sure.

SD Blue · #7 10-04-2006, 12:04 AM

I think you are on the right track. Since you are into the glow plugs, it might be best to pull them and do a glow check in order to rule them out.

Usually the valves needing adjustment shows up as a slightly rough idle even when warm. Also, there is a lack of power. (At least that is what I saw on mine.) It is easy enough to check clearances and see what you have. You will need 27mm deep socket and 1/2" dr. ratchet to turn the crankshaft bolt. If you do it while the glow plugs are out, it should be pretty easy to turn. Also, you need (2) 14mm wrenches (one of them thin) and .35 exhaust and .10 intake feeler guage blades.

The knock is more than likely what we refer to as nailing. It is usually due to an injector with less than optimum spray or pressure. However, misadjusted valves can show up as the same thing. Try the glow plugs, then check the valves before venturing into injectors.

greasybenz · #8 10-04-2006, 09:22 AM

what kind of oil do you have in the engine? i know canada can get reallllyyyy cold so its best if you use a synthetic that allows better cold starting and wont give you that sputtering upon cold start-up.

OMEGAMAN · #9 10-04-2006, 10:45 AM

Quote:

Originally Posted by greasybenz

what kind of oil do you have in the engine? i know canada can get reallllyyyy cold so its best if you use a synthetic that allows better cold starting and wont give you that sputtering upon cold start-up.

Yeah and spikes in the tires so you can drive on the permanent sheet of ice that starts at the border and heads north

Check your rack damper pin. If it's screwed in too far it will stall cold but run just fine warm.
15/40 rotella will work just fine in the winter.

tenmaz · #10 10-04-2006, 11:12 AM

Quote:

Originally Posted by vstech

this is a nice pictorial on glow plug testing and maintenance.
http://www.dieselgiant.com/glowplugrepair.htm
He has put up several pictorials for repairing theese and other cars. his home page is pretty explanatory
www.dieselgiant.com
John

Thanks for showing us this site (dieselgiant) it has some great displays. I like to find more like this if you know of any please let me know at tenmaz@msn.com

Don DS · #11 10-04-2006, 05:08 PM

Actually, i don't know what oil is in it and it's definitely in need of a change. I'll use a good quality synthetic, but should I choose 15W40 or something thinner (5 or 10W40?) for the sub-zero frozen climate I intend to drive my tirestuds into

What is the consensus on the best oil for these babies? And just to be sure, it's 6.5 to 7 quarts right? What's that in the metric system? We buy in litres up here. I think 1 quart = 946ml. So that would be 6 to 6.5 litres for a fill?

Omegaman, you suggest checking the rack damper pin . . . Huh? What is this and how do I do it? Sorry for my naivete, I'm a newby!

greasybenz · #12 10-04-2006, 11:43 PM

a 5w40 synthetic will be good, im not sure what your local autoparts store carries but rotella 5w40 synthetic is just fine. Best choice is mobil 1 5w40 but is hard to find so 15w50 is the next best thing mobil 1 offers for diesels.

EDIT: my dads 78 non turbo took in 6quarts. My SD took in 8 and leaked about 2

Fill it up to 6 quarts/liters run the engine a little and check the dipstick, if you need more then put in more. Best if you buy 8 quarts just incase. My 87 takes 8 quarts exactly.

adrenelin500 · #13 10-05-2006, 04:57 PM

I had the same problem last year, i'd have to sit with my foot on the gas for nearly a minute before the car would idle on it's own. I checked all the plugs and it turned out that the furthest one away from the front of the car wasn't working.Not suprising because it's the hardest one to get at.Same with a friend of mines 300sd.This helped but not untill i changed out all of the injectorts did i have a flawless start. My suggestion would be to start out with some diesel purge before changing the injectors though. There is a product that you introduce into the line that goes into the large fuel filter from the injection pump .You place that line and the return line in the bottle and run it through your engine till it runs out.I believe it's called lubro-moly.Apparently hard to find but well worth the search.

dougk · #14 10-12-2006, 07:03 PM

Wow,
I just started having this same problem. My glow plugs took about 8-9 seconds to warm up before I could start, so I replaced 4 of my 5 glow plugs. I replaced four of them because that is all I could get at the auto parts store for the time being. I didnt get the furthest glow plug away from the front of the car. Now, my car had a hard time starting and stalled after a couple of seconds. I had to step on the pedal the second time to get it going and to level out without stalling. When it is warm it starts up right off. Could this be the last glow plug?

Also, could this have anything to do with the battery dying? I replaced the voltage regulator but the battery died again the other week. Could this be the glow plug relay messing up or does this not have anything to do with the rough starting issue?

Thanks

DK

adrenelin500 · #15 11-30-2006, 11:12 AM

I sort of had the same problem with my 82 300sd , Had a rough idle and hard start while below 5 degrees C. I checked the first four plugs manually with jumper cables and they were all good. Because the plug closest to the widshield was so hard to get at I left it alone. I did some more research and decided it would be easier to go back in and pull the last plug to test it. Turned out it was the culprit and it's no wonder. My theory is that when people change their glow plugs on these models they tend to leave the 5th one alone because it is a bit of a pain to get to.

Unfortunatlly that only solved my problem last year.The snow is down again and so are the temps at adout minus 5 C. I have 5 fairly new plugs , the preglow lamp works as it should but if I don't plug the car in it won't start.