82 300sd hard to start - PeachParts Mercedes-Benz Forum

isc62 · #1 02-26-2008, 11:45 AM

My 300sd is hard to start and is getting worse as winter starts to wind down. Here is what I have done so far. Changed fuel filters, added radiator hose heater, adjusted valves replaced fuel lines on engine. Once I get it to fire it will start the rest of the day no problem. I have jump started it just about every day the last 2 weeks. Had the battery checked at advance with there electronic battery checker it shows Good Battery. The cranking speed is plenty fast. The only thing I have noticed is while cranking I got no to very little fuel out of the injector line at #5 cylinder. I cracked the line while running and the cylinder imediately went dead fuel sprayed out of the fitting. This prompted me to take a look at the fuel lines. So I changed the existing hardend and discolored used to be clear lines with new vinyl hose. Now I can see that I have fuel in the lines going to the ip. I do not see any air bubbles. When I pump the primer pump I do see some tiny bubbles if i pump it fast. I have a new style primer pump coming this week. Hopefully I am on the right track.

I believe my original problem of hard cold starting has been fixed and a fuel problem has replaced it. This last weekend I had the block heater plug in a magnetic heater on the oil pan and a small electric heater under the hood. I shot temperatures on the valve cover and block of 75 degrees. Still fought to get started. Finally a shot of ether and it took off.( I know ether is a bad thing) The car runs great when once it is running. The car has 198,000 on it it does have some blowby nothing excessive. and a few oil leaks the turbo return o ring being the worse right now. Right now I don't have the equipment to to a compression test. Judgeing from the way it runs I would expect it to be good.

Now my questions.
Am I on the right track with the primer pump?
I see the Primer ump assembly listed, Is this also a mechanical fuel pump? I see a cam follower in the pictures of the backside. If so are they a common failure item?
Is vinyl safe for use on dino diesel? If not what should I use?
Am I missing something obvious?
Thanks
Scott

vstech · #2 02-26-2008, 11:50 AM

um, ... glow plugs?

isc62 · #3 02-26-2008, 11:53 AM

Yes replaced glow plugs also back in December. Forgot to list that. Tested them this weekend again also all tested good for resitance and voltage to each plug.

hangit · #4 02-26-2008, 11:56 AM

I was having many of the same problems with my 240D and followed your lines of detective work also. Finally broke down and changed injectors. Solved my problem.

John

SD Blue · #5 02-26-2008, 11:58 AM

How long are you letting the glow plugs cycle?
If it is very cold out (BTW, you don't mention the area you live in.) then first start I would let it glow until hearing the relay trip.

isc62 · #6 02-26-2008, 12:06 PM

Sorry I am in Indiana. I have let the glow plugs run the whole cycle twice and tried to start without any success on a number of occasions. Even on days of 30 degrees or more it is doing the same thing. I guess I need to update my profile. Thanks

SD Blue · #7 02-27-2008, 10:03 AM

What brand of glow plugs did you install? Many folks have reported problems with particular brands, such as Autolite. Also, did you use a reamer? If you have a significant carbon build-up, the new plugs may have difficulty heating the prechamber. When I replaced my glow plugs in December, they appeared fine by resistance measurement but would not heat significantly. When I pulled them, they had a layer of carbon on them that I believe caused the problem. I'm not sure, but maybe cleaning them with a brass brush may have helped. With the circumstances at the time, I just changed them.

When it does start, do you have a smooth idle?

isc62 · #8 02-27-2008, 01:57 PM

Quote:

Originally Posted by SD Blue

What brand of glow plugs did you install? Many folks have reported problems with particular brands, such as Autolite. Also, did you use a reamer? If you have a significant carbon build-up, the new plugs may have difficulty heating the prechamber. When I replaced my glow plugs in December, they appeared fine by resistance measurement but would not heat significantly. When I pulled them, they had a layer of carbon on them that I believe caused the problem. I'm not sure, but maybe cleaning them with a brass brush may have helped. With the circumstances at the time, I just changed them.

When it does start, do you have a smooth idle?

I used Autolite as they were what was available on short notice. The old ones came out clean, had 2 bad out of the 5. I didn't ream the chambers. The car was starting better after the new plugs. The new plugs still test fine with only about 2500 miles on the engine since I changed them. When it does start It has rough idle for about 20-30 seconds after giving it some throttle it staightens out and idles fine afterwards. The car performs well after it is started. Adjusting the valves a couple of weeks ago made a big difference in the way it runs.

Yesterday, After sitting about an hour it didn't start easy. Temperature was about 30 degrees out. I'm putting my money on a fuel problem at this point. I do have a new style primer pump coming this weekhopefully in the morning. I will see if it helps. I noticed some tiny air bubbles when pumped it fast the other day. If that doesn't work I'm thinking about looking at the lift pump. I don't have fuel at the injector lines while cranking. But plenty while running.
Scott

junqueyardjim · #9 02-27-2008, 02:07 PM

I sure have heard a lot of complaints about autolite glow plugs here on the forum. Matter of fact, I have never heard any thing good about them except that they are less costly and available right now. Dollars are dollars, and if that is what we are fighting, that has to be considered. But if time is the only factor, then order the Bosch plugs from FastLane here on the forum. I often get my parts the next day. Not always, but often.

vstech · #10 02-27-2008, 02:31 PM

if you are not getting fuel at the injectors while cranking, then you have a worn IP... it may have been run on wvo with a lot of water in it in it's previous life. very destructive on an IP. my bet is still on the Glow plugs, you describe classic GP problems.
do a digital meter resistance test, all glow plugs on a cold engine should show exactly 6 ohms of resistance. if it is more or less, then you have bad plugs.
autolite Glow Plugs are total junk. more than a month out of them is rare.
a good set of Bosch plugs and I bet your motor cranks on first try.

Magoo · #11 02-27-2008, 02:34 PM

Autolite or not, if the resistance reading per plug is correct and 11-12 volts is supplied to the plug, it has to glow.
My money is on a fuel delivery problem or low compression.

rrgrassi · #12 02-27-2008, 03:41 PM

IIRC, the correct resistance is .6 ohms. I bought Bosch plugs at AutoZoo because I was also in a "need them now" situation.

Diesel Giant has an excellent write up on the GP system.

isc62 · #13 02-27-2008, 06:00 PM

All glow plugs read .6 ohms and each has voltage to them when the GP relay is energized. I wasn't nuts about buying autolite gp's Not nuts about buying anything branded autolite. Sometimes situations dictate to buy from the local jobber. I definantly have a fuel problem now. It still may have another problem besides that. I do not have fuel coming out of the injector line while cranking. When I pump the primer pump fast I see that it as introducing air to the fuel system. So I pump it nice and slow and I don't see any bubbles. I do have a new style primer pump on order (local jobbers don't have any). I will see if this helps with the fuel delivery problem.

Just got of the phone with the PO he said no wvo or bio in the time he owned it,10 years and 100,000 miles. Wouldn't low sulfer dino diesel with virtualy no lubricity be harder on an ip than wvo or bio?

Robert Squires · #14 02-27-2008, 06:15 PM

* When was the last time the valve clearances were adjusted? They're mechanical, not hydraulic. Valve clearances will affect performance as well as starting. Should be adjusted once a year.
* You've measured the glow plug resistance. Are you getting current to all the glow plugs during the preglow? And for long enough? There's a temp sensor, like a thermal timer, for that preglow.
* What is the fuel pressure, both while the engine is cranking and when it's running? Weak pump? Filter "sock" in tank partially blocked?

isc62 · #15 02-28-2008, 12:05 AM

Valves were adjusted Feb 10th on the loose side of spec. .004 intake .014 exhaust. according to dieselgiants guide. All but one valve was tight before adjusting. Performance improved dramaticly after adjusting.

All glow plugs have power to them during glow cycle. Was checked on Feb 17th. I let it glow through one whole cycle then during the second cycle try to start it. I would say the relay picks up for around 50 sec to a minute. I cleaned and greased all the connectors last summer. Silver plated contact points are prone to tarnishing. (15 years of repairing mechanical circuit breakers in the power industry)

I did not check fuel pressure yet. Cracked the banjo bolt on the inlet then outlet sides of canister filter had fuel flow during cranking. Cracked incjector line after bleeding the system and no fuel at injector. I only checked number 5 cylinder. I atached the line and finally got the car to run cracked the fitting on number 5 and cylinder imediatly went dead and fired when fitting was tightened. In my close to 30 years of wrenching a plugged sock would be more detrimental during acceleration. I'm not looking forward to messing with the tank if I don't have too also...I'm leaning towards the weak pump idea. I will build a jig to test fuel pressure tomorrow. What would good pressures be for cranking and running?

I'm assuming the lift pump is a piston pump with a check valve at the inlet and outlet. These kinds of pumps have a low failure rate. I guess I could take it apart when and make sure the check balls are not gummed up and check clearance. I'll report back what I find.

I'll admit I'm working on a shoestring budget here. My ex got all my tools in the divorce. Went from a 3 fully equipped shop to working in a leaky carport in the cold. It was worth it lol.

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