Next step looking for air leak
 

Good Morning,

I hope I got the title close to what I'm doing. Next weekend I will take out the sending unit in my fuel tank, and change the strainer. The fuel gague bounces around, and recently I've lost a little bit of power, and she misses just a tad bit at around 60 mph. I've changed both filters looking for an air leak that might be causing loss of power, but that didn't help. I'm thinking now that the problem might be in the tank area. Is there a gasket that I should replace when I take those parts out? I guess all that I will see is the sending unit & strainer - right? I hope it doesn't have an in tank fuel pump. From what I've found out so far is that I'll remove the back seat to get to the point where I can access the tank top, and take out the sending unit with channel locks. Then I'll clean the sending unit with brake cleaner, and replace the strainer. I sure do hope I get it straight. If there is a gasket involved what would be its name so I can order a spare? Thanks for reading this & Happy Thanksgiving.

Hugh Sr
1984 W201 (190D 2.2L) 147,543 5 speed

The Tank Strainer can normally be cleaned instead of replacing it but, it will need a new O-ring.

If your Fuel Outlet hose attached to the Tank Stariner has a crimped on Brass Collar and your Hose is old and needs replacing you can cut or filte off the Brass Collar and yank the hose and collar off. If you are using Diesel Fuel you can replace the Hose with SAW 30R7 Fuel Hose that is also rated for Diesel Fuel and is sold in just about any Auto Parts Store and a Hose clamp.

Replacing the Fuel Inlet Hoses under the hood also eliminates sources of Air leaks if the hoses are old as well as replacing the Old Style Aluminum Bodied Hand Primer if you have one.
If you have the old style Hand Primer replace it with a Bosch one as some members have had leaking problems with the Febi made ones and Bosch claims to have a Viton Seal inside; copies by other companies may not.

I doubt if there is a in Tank Electric Fuel Pump.

IF you are SURE you have an air leak...
I know several times people have found theirs coming from the hand pump... it's design makes it an easy place to , after deterioration , suck air into the system.

Air leak
 

My 1984 190d does not have a hand pump. I had a 1985 Volvo 240GL, and drove it for about ten years. It had a in tank fuel pump. Thanks for your help.

Hugh Sr

My Volvo Diesel 244GL has no tank pump. However, tank pumps are common on Gasoline Fuel Injected Cars.

I a way it would be nice if Diesels also had the Fuel Supply Pump located in the Fuel Tank as it would eliminate the chance of an Air leak.

But, since Diesel Fuel is often contaminated it needs to have some filtration before the Reaches the Fuel Supply Pump and to that end it is better to have the pump located some place where a filter can be easily changed.

Continuation of air leak
 

You do get to the strainer when you pull the fuel sending unit - is that right? I was just under the tank & noticed toward front middle of the tank some sort of rubber hose attached to the tank. What could that be? Thanks.

Hugh Sr
1984 190d 2.2L 5 speed

Hugh,

A leak in the tank area will not directly cause missing at some speed / load. This will only cause the air bubble in the clear filter to become larger and eventually starve the injection pump. Next time you notice this failure, quickly inspect the clear filter and take note of the fuel level inside - there should only be one tiny bubble.

If you suspect that air is problem, begin with the first easily replaceable hose - from the clear filter to the lift pump. This hose is the only hose that experiences vacuum / suction after the clear filter.

the strainer is at the bottom of the tank since it is the supply for the pump.

If the sender is out you might be able to get at the strainer with a really long pipe brush... but won't be very effective.

Sucking air = power loss?
 

Good Morning,

From what I've been able to learn so far from my power loss problem is that its probably a vacuum leak. I've been thinking about that trying to see in my mind how that would work. What difference does a little more air make? When a valve opens in he cylinder doesn't it let a measured about of fuel and air in? And as far as pulling the fuel fuel through the lines when I purged the fuel system the other day I noticed that the return line was really putting the fuel back in the jar I had the Molly in. Just though someone could put some light on this so I can understand the mechanics behind what is going on. Thanks. Happy Thanksgiving.

Hugh Sr

Sucking air = power loss
 

I forgot to tell you that I have a 1984 190d. 2.2L 5 speed.

Hugh Sr

The vacuum system and fuel system are separate and never mix. There are a few related components, but it is almost improbable that a vacuum leak would cause sluggish performance.
none
it isn't very accurate, but yes. Adding more air would do no harm.

*also, this isn't a gas engine, only air and exhaust go past the valves. Fuel is shot into the cylinders for mixing.

The fuel system system always provides more fuel than that which finds its way through the injectors. It is sent back to the fuel tank via the fuel filter housing connection.