Zero fuel pressure? - PeachParts Mercedes-Benz Forum

Stevo · #1 01-28-2012, 03:45 PM

I finally got around checking into this fuel pressure issue simply out of curiosity as my 240D with only 45K on the rebuilt engine, runs like a champ. I pull the banjo fitting off the inboard side of the IP (return fuel to filter) and its just a plane banjo, no spring, no small ball bearing. I rebuilt this engine 8 or 9 years ago and so it must have been me that put things together, but why is my engine running so well with NO check valve in the return? I received the fuel pressure checking kid from a member here but the gauge which I've ordered hasn't arrived yet. Will the pressure show zero?

Stevo · #2 01-28-2012, 03:58 PM

I took the proper check valve out of a spare IP and left everything sitting on the work bench until I decide to put it back together like it was since it runs so well or install the check valve. keeping in mind, "never disturb a sleeping dog" or "don't fix it if its not broke", Or did I miss something? 1980 616 engines didn't have check valves?

barry123400 · #3 01-28-2012, 04:07 PM

They all have them for sure. Some 616s will run with no pressure or almost none present in the base of the injection pump has been proven unfortunatly.

You should get a real suprise when you restore the system to what it should be. You want about nineteen pounds present. When you get the gauge delivered make it happen. The manufacturere states about fifteen but nineteen is better and proven over the years. Do not leave the system as it is over the long term. Personally I would install the complete relief valve now rather than later. Do you have any ideal of what kind of highway mpg you have been getting without the relief valve?

My best guess has been that the restriction although very small of the return system allows a slight operational pressure to be present when the engine is running in the base of the injection pump.That is about the only variable that I can think of so far. Or why some will run with an open relief valve and some will not.

One last possibility without looking under a hood. Could the relief valve be installed further down the system by accident perhaps. Like the input to the filter block from the return line? I suspect not though or it would be backwards and you would have excess pressure and the car would really preform if the lift pump is in good shape. This could be your sleeping dog if the car seems very fast for a 240d. The lift pumps on the 240ds put out less pressure than the 300d turbo lift pumps do and perhaps still less than the 300d non turbo or the same as well.

I just noticed you have a euro 240d in your signature. The injection pump is different on them and the relief valve may or may not be the same on them.

Stevo · #4 01-28-2012, 04:25 PM

Quote:

Originally Posted by barry123400

They all have them for sure. Some 616s will run with no pressure or almost none present in the base of the injection pump has been proven unfortunatly.

You should get a real suprise when you restore the system to what it should be. You want about nineteen pounds present. The manufacturere states about fifteen but nineteen is better and proven over the years. Do not leave the system as it is over the long term. Personally I would install the complete relief valve now rather than later.

Thanks I hopped you would see this. Its been running with the same checkless IP for the last 8 or 9 years and, like I said the car is very zippy, I have had many 240Ds in the last 10 years and know what to expect from a 616. I will put in the proper check and see what happens, but if shes any zippier I'll be up for a 240D speed record

I will stretch the spring to 27mm?

compress ignite · #5 01-28-2012, 04:33 PM

With your I.P.'s serial number in hand.

I believe you'll be told that the Fuel Pressure Relief Valve is a Venturi type.
(No Ball and Spring)

Stevo · #6 01-28-2012, 04:47 PM

Quote:

Originally Posted by compress ignite

With your I.P.'s serial number in hand.

I believe you'll be told that the Fuel Pressure Relief Valve is a Venturi type.
(No Ball and Spring)

Well It must be the Venturi type if its been running for years as I've described, NO

barry123400 · #7 01-28-2012, 04:50 PM

Quote:

Originally Posted by compress ignite

With your I.P.'s serial number in hand.

I believe you'll be told that the Fuel Pressure Relief Valve is a Venturi type.
(No Ball and Spring)

Thanks I just learnt something. When I noticed very late that he had the euro 240d in his signature all bets were off. I know nothing about those injection pumps not sold in north america as well.

I did suspect something might be different though. If it has a venturi type constant restrictor is another possible component of a suspected difference.

Any tuneup of the fuel supply system might require some thought. When he gets a gauge installed there may be something to learn here. If the car is running extremely well I doubt that I would change the relief valve system. I still would want to know the operational pressure on an ongoing basis though as well as currently. Theoretically a venturi can wear so the recommended base fuel pressure from the factory on those pumps should still be checked.

What really got my attention at one time. The lack of a cigar hose or obvious pulse expansion device on the majority of the euro version cars injection pumps. If you fill the fuel tank up past the half way mark and remove the cigar hose from the system and substitute a hard hose there is a big change on some 300ds with the north american injection pump. It runs poorly or differently until the fuel drops down past the entry point of the return line to the fuel tank.

So as a general thing especially in the south. If the cigar hose has gone rock hard consideration should be given to changing it out. You may or may not see a noticable diference. It has a function other than noise supression as was propagated for along time.

As the poster may or may not know. The 616 engine with the euro version fuel injection pump does not have the first cylinder rod bearing issues. For certain it is the same block though.

Or at least posters from europe state the issue is not known over there. It is well know over here. They had a lot more 240ds in service at one time as well in europe. I often have wondered why there was an export to north america version of injection pump and a euro version pump on those cars sold there. There must have been a reason.

Stevo · #8 01-28-2012, 05:34 PM

Sorry about the confusion, I am talking about my (US spic) 79 240D. The engine is a 1980 US spic 616. I will check the pressure when the gauge arrives, and post the results. While we are on the subject, I do have a couple Euro cars and was going to check the pressure on those "M" pumps. I wonder what the spics for the spring length is (617&6), assuming I will find a spring.

barry123400 · #9 01-28-2012, 07:03 PM

Quote:

Originally Posted by Stevo

Sorry about the confusion, I am talking about my (US spic) 79 240D. The engine is a 1980 US spic 616. I will check the pressure when the gauge arrives, and post the results. While we are on the subject, I do have a couple Euro cars and was going to check the pressure on those "M" pumps. I wonder what the spics for the spring length is (617&6), assuming I will find a spring.

There are a few things to check before stretching a spring once you have a gauge. If we are talking about the north ameircan version of the injector pump they all had regulation of fuel pressure. If you had the original fitting off the pump when the engine was rebuilt. It again may be installed elsewhere if it is possible. It is also a possibility that someone may have installed a venturi type regulator on the american pump at one time.

Since you are experienced with other 240ds. If this one is quick you probably have fuel pressure I believe. They can be a little doggy without it.

Sorry for the confusion as I went back at the initial post of yours.Read your list of cars at the end of the post and added a little amount to it as a result. This was the first time I had heard of a venturi type regulator from a poster on your thread as well.

Stevo · #10 01-28-2012, 07:47 PM

Sounds like there is still some mystery here. I have several 616 IPs around (all US sic). I will compare IDs. The IP I got the relief valve off was from a later 616 (post 81+-) i think

Or I can do what compress ignite suggested, call that shop in Seattle. So the question is 'do all or any more US spic, 1980, W123, 240Ds have the venture type IP fuel pressure regulating system.

barry123400 · #11 01-29-2012, 01:43 AM

Since one has never been reported before on an american version pump.
at least to my knowledge that is quite limited. It would not hurt to check it out.

If it was stock it still sounds unusual to me. You might have a look to see if the cigar hose is present when you get a little time as well.

funola · #12 01-29-2012, 10:33 AM

Without a pressure relief valve, you'll get max pressure, not zero pressure.

funola · #13 01-29-2012, 10:36 AM

Quote:

Originally Posted by compress ignite

With your I.P.'s serial number in hand.

I believe you'll be told that the Fuel Pressure Relief Valve is a Venturi type.
(No Ball and Spring)

By Venturi type, do you mean the ones with a tiny orifice? If so, I've only seen them on VE IP's, not inline.

funola · #14 01-29-2012, 10:44 AM

Quote:

Originally Posted by funola

Without a pressure relief valve, you'll get max pressure, not zero pressure.

I take that back.

Stevo · #15 01-29-2012, 11:36 AM

Later this morning I'll got out to the shop and get some numbers off the IP in question along with numbers off other IPs of the same vintage. I would think that someone else would have reported this anomaly by now or else not that many folks have checked fuel pressure on an 80 616 IP.