'76 240d nailing
 

i have a 1976 240d (w115) with an automatic. yesterday it started nailing. it seemed to be been running a bit rough the last couple of days but it was so slight i thought it was my imagination, anyway, when i started the car yesterday it was quite rough at idle but didn't sound too different. i drove to work (25 miles on the freeway) and then it started to sound pretty bad. i listened with a home made stethoscope (a long screwdriver stuck to my ear) and i also cracked the injectors and it seems to be the #2 cylinder. i also noticed there is air in the return line from the ip to the fuel filter. of course it is blowing smoke that smells like unburnt fuel (grey and black). all the fuel lines look ok although some are pretty old. my question is what next? i would think if it had an air leak in the fuel line somewhere all the cylinders would be making noise not just one. could a clogged injector make air bubbles in the return line or is this two separate things going on at the same time.
john
p.s. i changed the the primer pump about 6 months ago because i thought it was leaking. the leak was actually an o-ring on the line out of the primer pump assembly.

something new
 

i just noticed that the cheap pre-filter looks kind of frothy inside. i have never payed attention to this before but that doesn't seem right. ???
john

If you get air in the system most often goes the highest point. 1 and 2 seem to be the most effected by air. Perhaps because the fuel inlet to the IP is close by.
Frothy fuel could be air but also fuel contamination.
Try putting the fuel inlet hose into a separate container of clean diesel fuel; loosen the injector hard lines and bleed out any air; run the engine and see if things improve.

You should check hose(s)/connections from the tank up to the pre-filter unless the pre-filter is higher than the lift pump and primer in whihc case those are suspect too.

'76 240d nailing
 

ok here is the latest. i changed the fuel line with the inline pre-filter. it looked old but was dry so i don't think it was leaking. i next bleed the system with the fuel filter vent cracked. all looked ok but when i started the car it still smoked and pinged, although not as bad as before. there is still air in the return line so i guess i'll start replacing more fuel line. i still think there is a problem with the number 2 injector because if i crack it the engine stops nailing and the idle seems to smooth out a bit.
john

found the problem
 

i finally got a little time to work on the bad injector in my 240d. i bought new monarch nozzles with the plan of rebuilding the injectors to get a little better performance than the old bosch units. it didn't look like they had ever been changed so with 168,000 on the clock i thought it was a good time. well i took the bad injector out and dismantled it to find what the problem was... a broken compression spring. has anyone had this problem? i could go to the junk yard to see if i could find and injectors to pirate the springs from but at this point i think it might be better to get new ones. i've been searching online but no one lists these parts. dealer only? i have yet to find a diesel shop by me (daly city, ca) that wants to do a pop test so i am kind of counting them out. any ideas?
john

try ******** in arizona. they If I remember have injectors, you can also find them on ebay if you look,, used you should be able to find a spring.

When I worked in a Fuel Injection shop before and maybe 2 times a year you would get an injector with a broken spring; so it dose happen.

Out here in CA a whole Injector at the Pick A Part is $5.00 so that could be a source. Also you can use the older VW Rabbit injectors that look the same as the Mercedes Injectors (The ones in my car now were rebuilt from VW Rabbit injector bodies with the Pop Pressure set to 135 bar).

You will have to ask him but maybe C Sean Watts would supply a spring.

Also I do not see why a local Fuel Injection Shop would not sell you a new or used spring.

I have some...
 

I have a good supply of 30mm springs but I'm very low on the 22mm. One other option is a new 'hollow' injector (everything but the nozzle) I also have some of those left.

76 240d nailing
 

thanks for the info. the pick-n-pull closest to me always has 123 300d's in it (i don't think i have seen a diesel rabbit there). do you think the springs would be close enough? i know the turbos run at a higher pressure.
john

The springs are not interchangeable unless they are the same length. Turbo injectors are just shimmed to a higher pressure, most everything else is the same. SOME VW to MB will work but not all.

76 240d nailing
 

i just got back from the junkyard where i found one 240d. it was a 123 but it had all it's injectors so i bought the bunch. they are rebuilt and really oily with a lot of carbon build up. they are actually a little shorter than the ones in my 115 but the springs are 22mm so i think the parts should work. 20 bucks for four of them. i am a little tempted to just stick them in my car to see how they work but since i only have one set of heat shields i'll just rebuild the 115 injectors and have them pop tested.
thanks to everyone for the help,
john

There is 2 body sizes of injectors. If you compare (but do not mix) the parts of the both types of injectors you will see the dimensional differences.
As long as the parts for the short ones are kept together with that Injector; meaning as a whole injector they can be used alongside the longer ones.
Take a good look at the spray nozzles of the pulled set. If they have a tiny central hole drilled down the middle of the pintel try to see if that hole is plugged up.
Until I bought a Mercedes I had not been to the junk yard often. I was surprised to find that the Injectors were only $5. These are the same injectors that Ebay seller pawn off as "running pulls" but charge a lot more for.