I just bought an 85 300SD last night that supposedly had a new motor put in 100K miles ago. Total miles about 300K. It started up fine both times I looked at it. I think the turbo is bad, it has lots of power at startup but none after that. The owners said they never replaced the trap oxidizer, so I am hoping I can get a new turbo installed due to the recall on the oxidizers. Anyway, I put a new air filter in today, and went to start it. Nothing. It took me about 2 minutes of solid cranking to get it started. I left it run for 5 minutes, and shut it off. Went to start it 15 minutes later and the same thing. The previous owners said they had a recent valve adjustment, and replaced most of the glow plugs. The glow plug light comes on. The battery seems good, as the engine turns over quickly. My concern though is that perhaps it turns over too quickly and might have low compression? The only other issues I noticed are that there is smoke that comes out the top of the air filter, and oil is getting into the filter. Also, one of the fuel lines leaks a little at the injector, and the prime pump seems to have a leak. I am really concerned that the compression is shot, but like I said, it has lots of power up to about 30 mph, so I don't know if that means the compression is good or not. There is lots of fuel coming through the prefilter. The big fuel filter seems a little old, but haven't been able to locate a replacement yet. Any advice on how to tell what the problem might be would be greatly appreciated!

I would try a compression check first thing. Is it a CA model? Replace both fuel filters. Oil and smoke coming through the air filter sounds funny. Something in the top end may not be kosher.

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

Jmana,

Low compression will cause hard cold starting more than hot starting. SO if it starts easy cold, the compression is probably OK.

The dash GP light coming on doesn't mean the GP are working. See if the cabin light dims when you turn the key to the GP (run) position. That will tell you if the GP are working.

P E H

Good advice from P.E.

If the GP are fairly new maybe the relay could be bad?

Also, please don't take this the wrong way but I don't know if you are new to diesels. Are you waiting for the light to go out before you try to start? Sorry, but I had to ask.

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

Yeah, this is my first diesel, but I am waiting for the light to go out. I have done a little research, and I have found someone saying that the smoke coming from the air cleaner could be from the egr valve. Anybody hear of this, and what's the best way to remedy this? I noticed one person fixed it by plugging up the vacuum, but from what I can tell there is more than one hose coming out of it. By the way, I looked at several diesels before I bought this one, and this wasn't the first that had the smoke out of the air cleaner, in fact one was blowing smoke out the dipstick tube, which I don't think is a good sign. Anyway, I am going to try and find a fuel filter tomorrow to replace the old one. Also, does the plunger have to be screwed in tight? Today I was messing with it, and I didn't realize that it wasn't screwed down the whole way. Could that have left enough air in to make it hard to start? I guess I will know the answer when I go to start it tomorrow morning. I hate to be a pain, but one more question: If the valves really were recently adjusted as the seller said they were, could it have been that there was a bad compression problem before, and they tried adjusting the valves to correct it, but it didn't? I am going to call the seller tomorrow, and ask her how long it took her to get it started when cold.

Yes the primer pump should be screwed in all the way
If fuel leaks air can get in and make it a big pain to start
And I believe it will decrease performance as well
EGR check this
http://www.peachparts.com/shopforum/search.php?searchid=445048

i think if the compression was bad you wouldnt be able to start it. if you are running out of power at high rpm then you are lacking fuel for some reason. start by changing both fuel filters. also i would put some fungicide in the fuel and let i t sit over night. if it starts poorly but then runs rough for a minute after starting then smooths out then you prob have one or more glow plugs out. after you are sure all fuel related maintenance things are done, then you may have a fuel enrichment problem where it is lacking enrichment when coming under boost. this is not a difficult problem but i am lacking in personal expereince to tell how to fix it.

others on this site can tell you how.

good luck.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

If the engine won't start after it has been fully warmed up, then it's not getting fuel. The answer lies in your statement above. If fuel can leak out of the primer pump, air can get into it. You need to replace this primer pump before you do anything else. Make a careful analysis of the fuel lines and replace any of them that are cracked or might be leaking fuel or air.

The engine is intolerant of air leaks and you must crank it to get the air out of the system.

Changing the secondary fuel filter is also advised to rule it out.

Then, after this is done, let's see if the problem remains.

It very well could be that the boost pressure line from the back of the intake manifold is plugged or the oveboost senso on the manifold is stuck and therefore you are not getting sufficient fuel under turbo boost.

Both of these issues are easily corrected. As to the "new" GPs it is possible that you may have one or more failing which would explain the hard starting. One of my cars is not at all tolerant of even one bad GP. The other doesn't seem to mind so much as it starts when really cold every time. I highly recommend the investment in the new GP controller available via Fastlane at the top of this page. It comes with 4 GPs and that controller has improved the starting on my cars dramatically.

I would try to clean the banjo bolt on the back of the intake manifod. Then check for continuity between the overboost switch pin (top of the switch on the top near the rear of the intake manifold) and ground. If the banjo bolt is plugged or the switch is crudded up on the inside and sensing overboost then you will have no power when the turbo spools up.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

I cleaned out the line coming out of the intake, didn't seem real dirty to me. Also checked for power at the switch on the top of the intake, with the key on there is power to the wire. Cleaned this off also. No difference in the amount of power, still sluggish when you step on the gas. I did get the starting problem corrected, all the glow plugs were shot. Wish I had something to clean the holes out before putting the new plugs in.

Just an additional not eon checking that switch. Yes there i spower to the switch but the switch is actually a negative ground switch meaning when it is "on" or sensing overboost it completes the circuit and tells the switch feeding the alda to reduce fuel and therefore power.
Pull the connector off the top of the sensor and then check for continuity to the manifold. if the circuit is open then the switch has failed and therefore you wil get no power.

Glad you're wrokgin through things on the car though.

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

I checked both the switch terminal and the wire. The terminal didn't show anything, but the wire did have juice. Don't know if that means anything.

I got it working!! I put a new screw on fuel filter, and dumped in some kind of stuff the Mercedes guy sold me, now she runs like a race car! I don't know if it was the new filter or the (expensive - $25 for just enough to fill the empty filter!) additive the repair guy talked me into buying, but now she works like new! The previous owners must not have done any maintenence on this car, all glow plugs were bad and now this. Now I just have to get it repainted, new timing chain, and the AC working and it will be in good shape!