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Car Forum / Mercedes-Benz Cars / December 20071980 300SD cold starting problem
My 1980 300SD is having trouble with cold starts. I first noticed this at the end of last winter, but with warmer weather it disappeared. Was fine all summer. A couple weeks ago I adjusted the valves and after that it still started fine. Now the weather has gotten colder and as it got down to 45 deg it would start, but then run very rough. By applying some throttle and increasing the speed it would smooth out. Now that it's dropped into the 30s it's gotten worse and actually difficult to start, though it will fire up after more cranking. When it does start, sounds like it's not firing on all cylinders and shakes. The problem goes away after a few mins of running. Warm starting is smooth and OK. So, my first thought was that there must be one or two glow plugs gone bad. I pulled the connector at the glow plug relay and all wires to the plugs indicate 1 ohm. I thought they were supposed to be more like .5 ohm, but I checked a brand new one with the same meter and it also indicates 1 ohm. I get 12V to light a test light at all the glow plug terminals as well. The only strange thing was at first it seemed I didn't have voltage at the last 2 plugs. I was pushing pretty hard with the test light pointed tip and also tried hooking a test lead jumper to the plug and connected it to the test light For some reason, those 2 wouldn't light the test light at first, but now it's definitely there. It probably was just that I wasn't getting a good contact. When activated, the glow plugs have voltage for I'd say about a minute or so. The glow plug light on the dash goes out after maybe 10 secs, like normal and 12V remains on the plugs for I'd say a min after the dash light indicator goes out. Then there is a click from the relay and they go out. So, all this seems perfectly normal, So, I'm thinking I'm on the wrong track here. What should I check next? Could it be an injector problem? Is there any easy way to test them? I see in the shop manual they talk about how to test them in a test jig which sprays oil out of them, but lacking that what do I do? Also car has 125K miles and is in otherwise great shape. I did the timing chain test when I did the valves and there was no stretch, the timing marks line up at exactly zero deg. Any suggestions would be appreciated. Chet I own the same model and had a similar experience but had to look back in my log for the details. In '91 at 71,740 I replaced all the injectors to clean up the exhaust (it worked). In March '01 at 102,500 it stumbled at cold start so I replaced #2 injector. Slight improvement. Two weeks later I bought one glow plug and installed it in #1 - no difference so ex #1 was installed into #2 - no difference so ex #2 was installed into #3 and that cured it! I tested the glow plugs with a hot wire from the + battery terminal and a ground clip. They boil water on their surface in seconds - but even the weak one did so that "test" was bogus. The old SD is now at 111,500 and starts as it did in 1980 - with one new glow plug in 27.5 years! I also carry a spare 80 amp link for the relay - the original link is still in there! Hope this helps you. P.S. How old is your car's battery? If > 4 years it is suspect.  Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. >The old SD is now at 111,500 and starts as it did in 1980 - with one new > glow plug in 27.5 years! Wow! My glow plugs failed over the weekend. Started fine on Saturday afternoon. Went to a party. Several hours later getting ready to go home the glow plug light did not come on. But the engine was still warm and started right away. Car parked out doors until Monday morning. No light, no start. Called road service. No start even with his heavy duty battery and turning the engine over fast. No glow plugs, no start at 30 F though it will start with no plugs at 70F or more. Towed one block to local garage. I know this guy is going to charge me $800 to fix the problem. By the way, are the glow plugs in serial or in parallel? 1981 SD300 "Der Klunker" Did you check the 80 amp fusible link? $1 item, under the cover of the glow plug relay. Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. On Dec 4, 12:06 pm, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote: > Did you check the 80 amp fusible link? > $1 item, under the cover of the glow plug relay. > -- > (c) 2007 T.G.Lambach. Publication in any form requires prior written > permission. To answer Gogarty's question, the glow plugs are in parallel. Thanks for the advice TG. I've uncovered another problem. The hand fuel prime pump is leaking rather badly. Was loose, but tightening it didn't stop the leak. I wonder if air getting into the system could be contributing to the cold starting problem? I've ordered a new one and am assuming it's a straightforward replacement, which for $13 seems cheap. To further compound things, I'm not sure if it's been leaking all along or if maybe the diesel fuel conditioner that I put in last tank fill yesterday pushed the seal over the edge. Also, it seems to be idling just a bit low, even when warmed up, which could add to the rough running when started cold. I was going to adjust it, but reading the MB manual, their description and photos of the procedure are different than what's on the car. They show two cables connected to the throttle linkage. One goes to the cruise control. The other is the idle cable, which I don't have. I'm guessing that this went to some control knob in the dash on earlier models? Which makes figuring out the procedure confusing. Is it just adjusting the stop screw that is visible looking down at the injection pump? After fixing the fuel leak and tweaking idle, if problem persists, I think I'll replace glow plugs as TG suggested. These were put in some time ago, maybe 40,000 miles ago when I had a similar cold start problem. Also, how long do the fuel injectors generally last? These are the originals with 125K on the car. Could injectors cause only a cold start issue or would there be other symptoms? Car performs great otherwise. Perfect acceleration, no smoke, etc. Maybe a little rougher at warm idle than she used to be, but I think that may be that the idle just needs to come up another 50rpm or so. About the only other thing I've noted is that maybe a year ago the fuel economy seemed to drop a bit. Used to get 26 on trips, now its more like 23. As to idle, in the winter I feel my car's idle should be a bit higher (for better cold idle) and in the summer a bit lower after the motor is hot. I believe later models have an idle speed controller. We have some knowledge and a screw driver! The manual depicts the earlier models with the idle adjustment knob on their dashboard so disregard those pictures. The idle IS adjusted at the stop screw between the block and injection pump. I use a deep 5/8" socket to open the lock nut. Suggest you write down whatever adjustment is made so the original can be regained. Suggest 1/2 turn increments but adjust it after you replace the injectors for adjustment may not be needed. Suggest you consider Bosch remanufactured nozzles; the old nozzles are exchanged (core charge) for these. The motor will fire more smoothly. I use a deep 1 1/16" socket to remove the nozzles - they come out suddenly - like spark plugs - and have a conical washer inside the cavity that is supplied with the remfg'd nozzles and ought to be replaced as part of the job. Torque to 50 ft lbs. New bleed off hoses are part of this job. The nozzles are full of fuel so keep them upright until it can be drained off. My experience was not that the glow plug indicator lamp showed a GP failure but that a GP was simply not heating sufficiently to ignite the fuel. Glow plugs seem to get weak. When replacing the GPs have a 1/4" twist drill handy - twirling it inside the GP cavity with your fingers will cut any carbon that may prevent the new GP from going in. To limit dropping them I suggest using a small socket to remove / replace the electric cable nuts. Beru or Bosch glow plugs. Leaking 4 oz of fuel in 26 miles cuts mpg to 23. You know the culprit for that! Good luck with your project. Tom Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. In my experience (84 190D & 87 300SDL), cold start problem typically means bad glow plug(s). What I don't understand is your checking reveals all have normal resistance. Yes, the good one should be around (or slightly less than) 1 ohm. That will draw 12 amps of current per plug. 5 of them makes 60, which is within the fuse rating. Weak injector may contribute to rough running, but that is regardless cold or warm. Watch for the fuel leak. I once had leaking seals at injection lines (top of I/P). It was serious enough to draw too much air and cause no-running. I learned the lesson and replaced all rubber components at the same time (hey, the fuel lines are dry anyway :-) If I were you, I would double check G/P once more. Tom's method to replace the plug one by one seems to be a good way. I have another idea: disconnect G/P wire at the relay one by one. If one (or more) disconnect does not make the start worse, the plug may be in fault. By the way, checking the G/P resistance can be done without even accessing the plug. Just put one lead at the specific wire at relay, the other lead on any good ground. Hope you get it solved soon. It is cold outside! > On Dec 4, 12:06 pm, "-->> T.G. Lambach <<--" <"T.G. Lambach at > NoHamorSpamcomcast.net"> wrote: [quoted text clipped - 42 lines] > other thing I've noted is that maybe a year ago the fuel economy > seemed to drop a bit. Used to get 26 on trips, now its more like 23. Well, he did not charge me $800. He charged me $358.51. That included $118 for five glow plugs and $212 labor to install them and charge the battery. Total includes sales tax. He also told me the plugs were in series, not in parallel. He must be wrong,. In series "one not working, broken lead or something", makes noone working. Paralell. The one not working is the one and only. And you may start using the other ones. Surely not good but better than nothing. And I have problem to understand how it is possible to make a connection in series as long as you are using the same engine as the minus (-) for all the plugs. I would love to see that electric diagram. RD > Well, he did not charge me $800. He charged me $358.51. That included > $118 for five glow plugs and $212 labor to install them and charge the > battery. Total includes sales tax. He also told me the plugs were in > series, not in parallel. >He must be wrong,. >In series "one not working, broken lead or something", makes noone working. [quoted text clipped - 4 lines] >series as long as you are using the same engine as the minus (-) for all the >plugs. I would love to see that electric diagram. Hmmmm. Good point. There are MBs that have series glow plugs the earlier ones had them. The ground wasn't the block at eahc plug. They were in series and insulated at each plug. I'm sorry. I did not know this. I do belive you but do not understand what should be the reason for that solution. Having a chain that would break at the weakest point instead of several chains ?? Hmmmmmm. RD > There are MBs that have series glow plugs the earlier ones had them. > The ground wasn't the block at eahc plug. They were in series and > insulated at each plug. >I'm sorry. I did not know this. I do belive you but do not understand what >should be the reason for that solution. >Having a chain that would break at the weakest point instead of several >chains ?? Hmmmmmm. Do you not remember the old style Christmas tree lights? They were wired in series. One bulb went out in a string of forty bulbs and the whole string was dead. The only way to fix it was to remove each bulb one by one and replace it with a known good one. If the glow plugs were wired in series (the car is a 1981 SD300), then one bad one kills them all. If they were in parallel you would still have four good ones and the engine would start. So I am inclined to believe the mechanic since he charge me only for glow plugs, not fusible links, etc. Best to replace them all when one goes bad anyway. The GPs are wired in parallel. Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. On Dec 6, 7:24 pm, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote: > The GPs are wired in parallel. That's true for at least the 1980 and later vintage diesels. But I'm quite sure I've seen some discussion somewhere that some earlier MB engines had them wired in series. > -- > (c) 2007 T.G.Lambach. Publication in any form requires prior written > permission. Good news, I've solved the cold start problem and it's hard to believe what it turned out to be. I replaced the leaking fuel primer pump and then drove the car some more. On this drive, I noticed that it seemed rougher at even warm idle. Then later, when trying to accelerate from a stop, for a few seconds after I pressed on the accelerator, there was no response. This only happened once, so it was one of those things where you're left asking yourself "Did that really just happen?". After that I noticed that each time I stopped, at warm idle it was now running rougher as well. Over the course of a 12 mile trip with some stops at lights, it got so bad I had to put it in neutral or apply throttle to keep it from stalling. Now I started thinking it's some kind of fuel problem. On the way back, I took the highway and she went easily to 85 and stayed there with no problems. Which I would not expect if it were fuel, right? I was planning on changing the 2 fuel filters as they were over due. It's probably been 25K miles since they were changed. However, given the symptom at the time was only a running rough at cold starting problem, I would never have thought they could be the culprit. I replaced the 2 filters as well as the short hose from the metal fuel line to the fuel filter, which showed signs of cracking. Started right up and ran perfectly smooth. Smoother than it's been in quite some time. It past several start tests and driving around. As a final test, I left it outside and got it down to 21F. Started right up and idled fine. So, I'm very happy that it's fixed, but really amazed at what it was. Other than that brief failure to respond from a dead stop, there was no indication of what I would expect a fuel problem to exhibit. I would have thought I'd see problems on the highway at 85, rather than at idle. But maybe it's because with a partially clogged filter the fuel pump doesn't have enough power at idle to force fuel through, but as speed picks up it does? Or I guess it could be something in the filter that maybe came apart or wasn't made right to begin with that somehow blocks flow at low pressure, but gets shoved out of the way again as pressure increases? Or maybe that the fuel is thicker at lower temps, so it cools off with the car, but then is OK for warm starts? Anyway, it shows the importance of the basics. I would have replaced the filters right away or even months ago if I had one on those damn metal washers that goes on the spin on type one. That's a major annoyance. The filters don;'t come with the metal washer or the rubber O ring for the bolt either. One would think they would package them in. The oil filters always have several washers of various types for the oil pan drain plugs, which aren't even part of the filter housing. I've only found one online place that I think has the metal washers. And a couple months ago, prior to this problem, I ordered the washers at the dealer and they never called back to tell me they were in. And thanks to all here who offered help! Very interesting outcome; thanks for posting it. I suspect the short fuel hose that you replaced or one of its joints was leaking and allowing a bit of air into the fuel flow. At idle the air was significant but at high speed it was not material to the motor's performance. Similar to a gas motor's vacuum leak - creates a rough idle but is not noticeable when driving because its percentage becomes tiny as motor speed increases. Well, we all learned something! Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. Total agree. The leaking seal problem I previously described had very similar symptom: highway speed was OK while starting was difficult. However, the warm start was worse in my situation. The time when it finally needed a tow, a big puddle of diesel was on the ground. I guess the line completely drained. > Very interesting outcome; thanks for posting it. > [quoted text clipped - 6 lines] > > Well, we all learned something! |
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