I snagged a 300SD '79 for $500, but have some problems

[p5150]

So the guy I have bought it from had neither the time or means to fix this. The benz is in beautiful shape - slight oxidization on the paint (a quick buff will fix it) with no body damage. The engine is dirty, but all seems to be there......

Quick troubleshooting showed I had fuel pressure up to the injector pump itself, but no fuel was getting to any of the injectors. The car will not start. Yes, it turns over. I pulled the injector pump off today. And as far as disassembling that thing goes (to check for an obvious defect), well, it proved to be a touch more difficult than I thought it would be.

Could somebody school up this newbie Turbo diesel Benz owner?

[engatwork]

With the injector lines removed were you getting any fuel out of the ports on top of the injection pump while cranking the engine over at full throttle?

I wouldn't have pulled the ip off without a little more digging. What you need to do now is set the timing mark on the ip with the engine set at the specified degrees and re-install the ip onto the engine. I don't remember the setting right off the top of my head.

[Brian Carlton]

Welcome to the forum.


As Jim mentioned, most of the effort in getting an old diesel to start involves leaving the IP on the engine. Normally the IP is not the culprit. Getting all the air out of it is the typical problem.

If you have attempted to take the IP apart, in any way, the project can stop right now. It needs to go to a qualified Bosch repair facility to recalibrate it and ensure that it is working properly.

Be a little careful in simply taking things apart on a diesel. Some components are too complex for any mechanic other than a skilled technician with a test stand.

[boneheaddoctor]

I do hope you didn't take apart that IP....and it sounds like you might have....there are certain things you never want to touch....that can't be set correctly without it being in an injection shop....

Clarify that issue with us, and to what you may and may not have touched on it.

[p5150]

Yeah, I took off SOME exterior parts of the IP. Nothing too extreme that I wouldnt be able to put back together. I figured that there would be an obvious defect because I wasnt getting fuel to any of the injectors... Whats this about getting all of the air out?

[engatwork]

What I have had to do to get one to start that has been down awhile is remove the fuel lines between the ip and the injectors. Next you want to remove the fitting on the #1 cylinder (injector end) and remove the internals and spring while paying attention to their orientation. Don't be a bonehead and lose any of these items. Now screw the fitting back in place. Crank the engine over till fuel runs out of this fitting. I don't remember if I do it to all of them or not. Anyway, it won't hurt to do them all. After you get fuel coming up good remove the fitting and re-install the internals in the proper order. Screw the fitting back in place. Now connect the fuel line at the injection pump but leave it uninstalled at the injector in. Unscrew the hand pump on the fuel pump and pump it, crank the car over for a little while holding the throttle wide open then pump again. Pause every so often to keep the starter from overheating. Continue this till you get fuel coming out at the injector end. Whenever there is fuel coming at the injector end screw the fuel line onto the injector. On healthy engines it will crank up with just one cylinder flowing (and all of them connected) otherwise repeat until you have fuel coming out the other ones.

[boneheaddoctor]

Originally Posted by p5150

Yeah, I took off SOME exterior parts of the IP. Nothing too extreme that I wouldnt be able to put back together. I figured that there would be an obvious defect because I wasnt getting fuel to any of the injectors... Whats this about getting all of the air out?

I do hope you did not remove those two nuts to the left and right of where each of the injector lines screws onto...if you did plan to take it directly to a Bosche injection shop.

Try to do all work on level ground...if its on a hill these do like to air lock..

[JimmyL]

Originally Posted by boneheaddoctor

I do hope you did not remove those two nuts to the left and right of where each of the injector lines screws onto...if you did plan to take it directly to a Bosche injection shop.

Or try and get a used one from someone here.

[boneheaddoctor]

Originally Posted by JimmyL

Or try and get a used one from someone here.

That is the far cheaper option for sure.....recalibrations are not cheap.

[p5150]

No, I never took off the injector line feed fitting nuts. The only parts I took off were the fuel pump and diaphragms on the rear of the pump. Everything is back together as it should be. Here is what happened as Ive been told:

The car ran with a little bit of smoke and then one day it just wouldnt start. The previous owner said that he had changed the vacuum pump diaphragms previously - do you think some air might be locking the system up?

[P.E.Haiges]

p5150,

Vacuum system has nothing to do with the fuel system except vacuum shuts the engine off.

So you have fuel pressure up to the IP, but do you have fuel flow into the IP without air in it?

Air in the IP will cause it not to pump fuel. You might remove the outlet hose of the IP and see if air free fuel comes out of the IP when you pump the primer pump.

BTW, make sure you have the IP timed properly when you replace it.

P E H

[p5150]

hey guys thanks for your replies! Work on a separate vehicle has forced me to stop temporarially on the benz. I should resume this week. So would you guys venture to say that the IP is fine? That it is more than likely just some air stuck in the system? I guess Ill look into timing it and throwing it back together.

[t walgamuth]

it is fine.

you can start and run the engine on wd 40 to make it easy on the priming. just take off the air cleaner and spray directly into the intake til you can run it wo spraying.

good luck.

tom w

[SD Blue]

If you took the vacuum diaphragms off the back of the IP. When reinstalling, test with a mightyvac and then have a phone book, etc.. handy! Do a search for runaway diesel. Even a very experienced Benz owner accidently had an engine go into runaway!

READ the posts on runaway BEFORE YOU GO ANY FARTHER! If you do not, your engine and appreciation for this vehicle may be very short lived.

[p5150]

This is funny - Read my other post on the runaway situation. The vacuum shutoff switch was connected like its "supposed" to be - with the hook through the eyelet, then it ran away. I moved the hook out of the eyelet, now it wont start at all. (Small sputters) Maybe my injector pump is slightly off?