300SD wont start and everythingi've checked seems to be ok - PeachParts Mercedes-Benz Forum

stephenc03 · #1 08-04-2008, 12:41 PM

My 85 300 SD intermitantly will not start. It cranks over but will not start sometimes and other times starts right up. I posted a thread earlier this week and got some feed back. One of you suggested that it might be the fuel shut off valve that is stuck and to remove the vacumme line. I did that and it didn't allow the car to start. She idles fine and has good acceleration. the fuel filters were replaced a few hundred miles ago and I treated the tank with algeside a month or two ago. I replaced the starter a couple months ago as well. I tested the battery last week and put a load on it and it held just under 12 volts. I replaced the glow plugs and I know that they work just fine. When I do manage to get the car started after a long time of turning it over, it puffs out a lot of greyish smoke. when it starts up with no problems it doesn't puff out alot of smoke...the exhuast is pretty clean. she does have a little bit of blow-by but nothing that concerns me as she has alot of power and idles smoothly. I am thinking it might be a clogged trap cataylist. the oxyidizer was replaced in 1997 with 100,000 less miles on it then what shows on the odomoter right now. What could these symptoms possibly be? thanks,
Stephen

Bajaman · #2 08-04-2008, 12:47 PM

Sounds like air is being introduced into the system. Check for air leaks. a quick check is to replace the cigar hose with a clear pvc hose and watch for bubbles.

stephenc03 · #3 08-04-2008, 12:57 PM

I noticed some moisture around the secondary fuel filter housing....is this suspect? I didnt think that would be a problem and the primary filter is full of fuel...no air.
-Stephen

LUVMBDiesels · #4 08-04-2008, 01:09 PM

Pulling the vacuum line off the shut off valve on the IP should not prevent the car from starting. It will keep it from shutting down when you turn the key to the off position. I would check the shut off valve itself to make sure it is not sticking in the 'off' position.

stephenc03 · #5 08-04-2008, 01:13 PM

Quote:

Originally Posted by LUVMBDiesels

Pulling the vacuum line off the shut off valve on the IP should not prevent the car from starting. It will keep it from shutting down when you turn the key to the off position. I would check the shut off valve itself to make sure it is not sticking in the 'off' position.

How do you check the valve it self? Just to make sure... we are talking about the circular metal housing on the side of the injection pump by the firewall right? how do you check it? do you have to take off the housing? thanks, stephen

Old Dies · #6 08-04-2008, 02:15 PM

Be very carefull about taking off that shut off valve. I don't think you want to do that. If it fails at all it will not shut off the engine and you would have to press that stop lever to stop the engine.
Without that shut off valve in place, of if it is installed incorrectly your engine can run away from you so fast you may not be able to stop it before it grenades. Bad scene.

kerry · #7 08-04-2008, 02:46 PM

What diagnostic procedure have you used to determine that the glow plugs are working? It sounds like your glow plugs are not working consistently. If it's spitting out grey smoke when it starts, that indicates it has been getting fuel.

Brian Carlton · #8 08-04-2008, 02:52 PM

When was the last valve adjustment?

stephenc03 · #9 08-04-2008, 03:01 PM

I dont know when the last valve adjustment was as I purchased the vehicle a few months ago. I can say that when it does run it idles smooth and has good acceleration. I replaced the glow plugs with bosche and tested them to see if they worked before I installed them. I have power to them. the car will start fine one morning and continue to start many mornings after that but about once a week it will not start. The temperature in sacramento california has been consistant for the last couple of months. I do not see why the glow plugs would be a factor given the symptoms. This is why i was thinking that it might be a exhaust problem like a clogged trap. After reading other threads, people have suggested that if I am getting alot of grey or white smoke out the tail pipe then I have fuel delivery to the cylinders. I dont feel that it is a fuel problem as I have alot of greyish white smoke coming out the tail pipe.
-Stephen

Brian Carlton · #10 08-04-2008, 03:07 PM

Quote:

Originally Posted by stephenc03

I dont know when the last valve adjustment was as I purchased the vehicle a few months ago.

Well, then I'll take a guess..........about 100K ago.

And, that's why it won't start...........the intake valves are not closing fully.

stephenc03 · #11 08-04-2008, 03:15 PM

Quote:

Originally Posted by Brian Carlton

Well, then I'll take a guess..........about 100K ago.

And, that's why it won't start...........the intake valves are not closing fully.

So even if the intake valves are not closing fully once I get it started, why does it operate good and idle smoothly and have power when accelerating?

One last thing. When I put fuel in it the last few times and taking off the fuel cap....it has a burst of air come out of the tank. I imagine that the vent is clogged. would a clogged tank vent have anything to do with my not starting?
thanks,
-Stephen

Brian Carlton · #12 08-04-2008, 03:18 PM

Quote:

Originally Posted by stephenc03

So even if the intake valves are not closing fully once I get it started, why does it operate good and idle smoothly and have power when accelerating?

One last thing. When I put fuel in it the last few times and taking off the fuel cap....it has a burst of air come out of the tank. I imagine that the vent is clogged. would a clogged tank vent have anything to do with my not starting?
thanks,
-Stephen

Starting is the most difficult task and requires the highest compression to achieve ignition temperature. A slight leak in the valve at cranking speed can cause this process to fail. Once started, the engine appears to run fine because the higher engine speed mitigates the compression loss thorough the valve.

That's another possible culprit. When it fails to start........next time.......remove the fuel cap and see if the problem is eliminated.

But, do the valve adjustment.........soon.........before you burn one of them.

stephenc03 · #13 08-04-2008, 03:20 PM

I was thinking of doing the valves this weekend. My friends are driving up and I can ask to use there special wrenches and feeler guages. I will definatly adjust the valves.'
-Stephen

Brian Carlton · #14 08-04-2008, 03:22 PM

Quote:

Originally Posted by stephenc03

I was thinking of doing the valves this weekend. My friends are driving up and I can ask to use there special wrenches and feeler guages. I will definatly adjust the valves.'
-Stephen

Print out the valve sequence and be sure you know when you're doing an exhaust valve and when you're doing an intake valve. Check off each valve on the printed page when you complete them.

It's easy to screw that up.

stephenc03 · #15 08-04-2008, 03:25 PM

Quote:

Originally Posted by Brian Carlton

Print out the valve sequence and be sure you know when you're doing an exhaust valve and when you're doing an intake valve. Check off each valve on the printed page when you complete them.

It's easy to screw that up.

yeah...been there done that. the valves are worse than when you started...it all worked out in the end.
-Stephen