84 300D Why can't I keep this thing running!?
 

:o My 300D runs fine when it's running, but my injector pump seems to be sucking air from somewhere to cause me to have to re-prime the system using the hand plunger (for a lack of homework proper usage of part).every 15-30 minutes.

feed tube to primary and secondary filter clean, full and unobstructed at all times even after shutdown from issue. (changed multiple times while troubleshooting this issue!).

Return, (amber in color) see thru tube is never full and does have air bubbles even after priming.(not sure if never full part is normal, obviously air is not?).

After driving for 15 minutes or so she will start starving for fuel and eventually shut down. I am able to re-prime from banjo bolt and release the air (of which there is plenty of!) and go for another run! ooh! what fun!.

Smoke is minimal when running normally. smokes only when starting to starve and mostly of a more whitish color.

Temperature between 40-70o Celsius at normal operating temp.

Someone please help before I drive myself and this monster off a cliff!

Thanks,
Dave C.

Sounds you have a leak in your fuel line...or a loose connection.

Fuel lines are good! Have steady fuel to primary filter into pump. Always full! so do you have any idea where it could be sucking from pump and beyond!

Does your primer pump have a white plastic cap that you unscrew then pump? If so that is the old type and an easy R+R, they can leak air. Also was this a good running vehicle that this developed all of a sudden or a project type vehicle that you do not have much history on?

Maybe give a little more history, as it could be faulty fuel gauge and you are just low on fuel, clogging tank strainer, could also be a plugged air filter and you are associating using the pump to restart as a fuel issue.

If you're always having a solid fuel column to the secondary filter but the return line from the IP is always low or full of bubbles, I'd suspect a low output lift pump, some sort of internal leak in the IP, or simply a failure to burp all the air from the system.

Don't be fooled by the solid supply column though. If you have a tiny leak somewhere, you won't see the air, but it will be building up in your fuel system. If you have no history of it being done, replace the rubber fuel lines and clamps. When the rubber gets old, it can become porous or form micro cracks which will leak air.

Thanks Guys! Let me tell you a little bit more of what I have done so far. I have replaced all rubber lines both feed and return. This is the good Part! :) I have pretty much eliminated the tank and fuel lines as the immediate cause by building and installing with primary attached..(under the hood!..lol) an auxiliary 6ltr gas can therefore bypassing that part of the system completely temporarily of course! and still experience the same issue. This issue must be from the primary and beyond. It's a tricky one for sure! Primer pump is of the new type (Black metal head)

the car! 1984 Mercedes-Benz 300D

This is true, plus they do make rebuild kits if you want to keep everything absolutely original.

caswda, I bumped your post count up so you shouldn't get stuck in moderation anymore.

Thanks!

The newer hand primers are covered with Black Rubber.


There is some aftermarket companies like Flag that make the old style hand primers with the same hard plastic knob but it is black instead of being white. So a white knob is not always an indicator of a new style Hand Primer.


A long time ago one of our members had an issues with several of the new style genuine Bosch hand primers he got from the same store. He finally got his money back and decided that that particular store must have got a bad bunch of Bosch pumps.


He went to another one of the same companies stores and got what turned out to be a good one from there.


There is also copies of the real Bosch new type hand primer. Some by other legit companies and some may be fake.


The pic is of a new style Bosch however the part number on it may not be for a Mercedes.

The one that is installed now on my vehicle is the one you are showing in the pic. Definitely a good and inexpensive place to start.. Thanks!

There is more then one thread size for the new type Hand Primers so it is a good idea to be sure the one you get is the right size.

Some of them come with the smaller sized threaded area and also a threaded bushing so it can be used on pumps that need the larger threaded area. Sorry I have no part numbers to offer.

Yea, Thanks. I went ahead and ordered this inexpensive one

Diesel Primer pump,Bosch Upgrade 300D FITS Mercedes CUMMINS, MACK, NAVISTAR | eBay

and I'm hoping it comes with the adapter although I'm pretty sure the one I have is of the narrower or smaller od thread. I'll let you know!

Hey Diesel911 by the way, What about that vacuum canister that sits on the rear of the IP, does that have direct access to the pump? I have been experiencing run on's even with it connected!

it may be because its 33 yrs old,
either overhaul it or.................. you know. :(

The Vacuum Shutoff on the Fuel Injection Pump pulls the Fuel Rack into the shut off position. It won't work well if there is a Vacuum Leak in the system or the vacuum pump is not supplying enough vacuum.

Disconnect the hose at the Vacuum shutoff and see if there is Oil residue in it. If there is the diaphragm in the shutoof has holes and is passing oil through it. However, you can see oil and sometimes they still work normally.
As viewed from the drivers seat on the top right of the Steering Colum Lock is a vacuum shutoff valve. That could be worn out. Also the hoses on it need to go in the proper position. If you swap the positions it willnot work well.

You can have a vacuum leak anywhere in the vacuum system and it can effect the shutoff. To check the vacuum sustem you pretty much block disconnect one part of the vacuum system and plug the vacuum source and see if your vacuum situation improves. If it does the section you disconnected is the source of the leak.

For the under the hood you can visually look at and bend the rubber connectors and see if there is cracks in the rubber.

Note that the tiny plastic nipples that are on the main vacuum line snap off easily. Merely leaning on the line can break them (that happend to me during an Oil Change).