I find it strange you could have fuel coming out the return feed on the injection pump as you mentioned. Yet have no or very little fuel in the injection pump.

I pretty well know the reason it quit on you was the car was using the return line as a suppy source became above the fuel level in the tank. It also takes at least ten pounds fuel pressure to open that return valve on an average older mercedes.

For general knowledge what was the indicated fuel level when your problem occured? A lot of people thought the return line in the fuel tank was located somewhere below 1/2 the fuel tank capacity . No specific distance was ever mentioned to my knowledge.

I am only mentioning this as it is a part of the fundemental diagnostic proceedure for people that are unable/unwilling to measure the fuel pressure present in the injection pump. Plus my long standing desire to make the fuel system more understandable for some of us as time went forward.

I saw the need a year or so ago and wanted to try to diseminate what ever I could hoping others would fill in any of the voids.

Maybe I will have to further refine what I recommend as an approach to certain problems. Yet I always try to keep anything I recommend as simple as humanly possible at the same time.

This is still a problem for me. I can almost always design or engineer a follow up test usually. To expect everyone out there to deal with the ramifications or interpretation of them is not reasonable to me. There are too many variables usually to get into.

My almost constant lifetime working troubleshooting experience makes it almost automatic for them to assimilate easily for me when doing tests. I realise many people on our site or society do not have this developed mechanisim. Only heavy constant experience seems to develop it properly.

I am not a working auto mechanic either but have spent the majority of my working lifetime dealing with other peoples problems in several fields.

Anytime an injection pump element at the end of the line is not producing the fuel supply is immediatly suspected. Yet if solid fuel is pouring out of the return valve it cannot be the issue.

The follow up verification test normally is to run a clear hose into a container submerged in fuel. A lot of air should not be coming out the return and the fuel level in the recieving vessel should be rising.

You also have to have good amounts of fuel at pressure. Unless the relief valve is wide open. Then just pinching off the return line will supply high pressure to the injection pump to eliminate that possibe reason..Again as simple as possible consistant with users ability to quantify. I never mention delving into the injection pump unless certain tests have indicated the possible need. Even then there are steps to deal with the simpler issues.

As had ocured too many times in the past. People were sending good injection pumps out for service or replacing them and finding later they were not the issue at sometimes high cost. That had to be frustrating to say the least and has been reduced to some extent by following a sequence of easily followed testing I hope by now.

As for injection pumps not developing problems. Anything man designs or builds will either wear out or break eventually. We are dealing with older cars here in general as well.

Your issue has had no negative short or long term effects in my opinion with the engine.

When the pressure or amount of fuel is substandard for consistant very long periods of time there can be consequences in my opinion. I am still of the opinion that a metered check of the base injection pump pressure is a good ideal for cars with long term ownership in mind. Especially the 123s 616 engine.

Plus if you do not have a good permanent monitoring system of that pressure fuel filters should be changed at recommended milages. To only change them when noticeably obstructed may be very false economy.

These engines may be able to last a far longer time than average if one of those two things are done. As the fuel pressure to the injection pump becomes less from partial fuel filter obstruction. The car will still run pretty well usually.

Other dynamics are in play though effecting the life of the engine. Also with proper injection pump base pressure fuel milage will allways be better. The engine is running in a much better power balanced state. In otherwords the internal loadings and timing are then far more equal cylinder to cylinder..

I still feel the return line testing should have indicated the problem well. Especially with the verification test for air and volume. I really cannot visualise otherwise. Just my opinion that something abnormal took place here.

Well, it did. And upon reflection, can you guess why? ......

Because I checked the return feed that was really connected to the "out to IP" which, of course, produced plenty of fuel flow; I did not realize that the lines were reversed at that time. I just loosened the banjo at that had the injector return line connected to it!!!!! What a dumb-ass I am!

Yeah that would seem logical, but no. The car had been running with the tank near empty just a week prior to the problem occurring.


The tank was reading at about 1/4. Which was pretty accurate as I drove it to the station and filled it up last night and it took 9+ gallons.

Well that was really were I was going next. I was going to break out my fuel pressure gauge as I too was suspect of the fuel delivery, but then I saw that the lines were reversed.


Yes good idea.

Yes, true, but to quit so suddenly. It just didn't seem likely.

Well, like what? What should I be looking for?

Ex pagination of pictures plz
 

Is the way it is in the picture the correct way or the wrong way?