rough idle fuel related

[digieditny]

well many of you helped me replace my fuel tank strainer. I really thought that was my issue... I drove the car for the first time today below the halfway mark and the rough idle still occurs. It just has to be fuel related... I can't imagine what else it can be. When I fill the tank, it idles perfectly. No issues. Around the halfway point it starts to give me issues.

Could the lift pump be an issue? Does it start acting up when there's less fuel? What else can be related? Can it be something unrelated to fuel even though it acts up depending on fuel level?

The primary, secondary fuel filters and tank strainer have been changed. One of my injectors was leaking so I thought that was it. I changed the hose and still not fixed.

EDIT: Just wanted to add that I still have the old style primer pump. Could that be the issue? Is there a way to test it?

[Stevo]

You NO longer have the fuel supply and return lines switched right? Because if you did that would cause a problem at -+ 1/2 tank. Not sure if that applies to the TD but I suspect so.

[digieditny]

I don't have them switched

[barry123400]

If this problem has been ongoing since you aquired the car. Try to establish if the injection pump has been replaced with a north american version. If it has the euro injection pump ignore this. Or if the problem started after you purchased the car.

Basically under certain circumstances people have eliminated the cigar hose. The euro pump equiped cars did not have one. So if the injection pump was replaced with a north american version you should install a cigar hose in the circuit.

What I have mentioned is an extremely rare stuation. The engine does tend to act differently at different fuel levels with out one present on the north american version sometimes.

Also these diesels are pretty straightforward. No computor and no ignition system involved. You have the basic engine and a fuel system. I am lazy I suppose but adding a fuel pressure gauge helps to eliminate possibilities quickly. Since you do not have a gauge installed.

Try closing the return from the injection pump off temporarily to see if there is a differance. No harm is done by this as the fuel or lift pump does not stall rather it just sits at a steady pressure determined by an internal spring. While your there have a look for air coming out the return with the fuel as well. No fuel coming out of the return? Your primary fuel pressure is too low.

Submerging a line in a little fuel and watching for air production as well in the fuel will let you know if the primer pump is good and that there are or are not points where air may be getting into the system. You do not have a stream of bubbles processing up through the small clear filter do you? One large pretty static bubble is normall in the small filter..I like simple tests. I dislike changing parts on simple speculation.


What can occur with a very very weak or open injection pump return relief valve. The level of fuel in the tank tends to affect the available pressure in the base of the injection pump. This is why closing the return line off is helping to establish if there is a problem there. . If there is no change at all with the return line closed and no air being processed in the jar test. Then the lift pump may be suspect. A permanently installed liquid dampened 0-30 pound gauge is a good way to monitor a fuel system like this.

It tells you many things but is most importantly giving an early warning when something is deteriourating. You are lucky in that the problem is fuel level dependant. That puts the issue squarely into the fuel system area. No subjectivity there.

[Zacharias]

Originally Posted by digieditny

EDIT: Just wanted to add that I still have the old style primer pump. Could that be the issue? Is there a way to test it?

Do yourself a favour and replace that, just to have it updated and out of the equation.

[funola]

Is the rough idle with tank @ 1/2 way mark repeatable? It may be coincidental. Do you have vacuum in the tank? Open the filler cap when 1/2 full, if you hear a swoosh, you have vacuum. Do you have good clear lines on the return to see air bubbles? Are there any?

Replace the primer pump! You spill a lot of expensive fuel using the old primer pumps! I have a barely used new style primer pump from my 240D if you want to put one in. I have new washers also. I'm in Queens.

[Diesel911]

Originally Posted by digieditny

well many of you helped me replace my fuel tank strainer. I really thought that was my issue... I drove the car for the first time today below the halfway mark and the rough idle still occurs. It just has to be fuel related... I can't imagine what else it can be. When I fill the tank, it idles perfectly. No issues. Around the halfway point it starts to give me issues.

Could the lift pump be an issue? Does it start acting up when there's less fuel? What else can be related? Can it be something unrelated to fuel even though it acts up depending on fuel level?

The primary, secondary fuel filters and tank strainer have been changed. One of my injectors was leaking so I thought that was it. I changed the hose and still not fixed.

EDIT: Just wanted to add that I still have the old style primer pump. Could that be the issue? Is there a way to test it?

Find out where the Fuel tank vent is and make sure that is cleand out.

Fastlane sells Fuel Supply Lift Pump kits with new Valves and Springs and a resonable price. Since it may be a Euro Fuel Injection Pump (M Pump???) you will need to take a look at the little tag that is somewhere on the Fuel Supply/Lift Pump or give the Numbers from the Tag on the Fuel Injection Pump itself.

Although it does not sound like you are having the below issue I am going to post it.
Long Fuel Pressure Relief Valve/Overflow Valve Thread
http://www.peachparts.com/shopforum/showthread.php?t=234609

[digieditny]

Barry. Very interesting! This is news to me. My car does have a cigar hose though. The problem has been there since I have acquired the car. I will try everything you've mentioned! Looks like it's going to rain so I'll have to try later.

Funola. Would I need to buy the whole assembly or just the pump?

I would say it only happens when the tank is 1/2 empty or less. Never when it's full. But I would also say that it doesn't always happen. Sometimes The rough idle goes away and sometimes it gets really really bad (have to switch it to neural and accelerate to keep it alive) but ALWAYS happens when the tank is 1/2 empty or less.

There's no vacuum that I can tell. No swoosh. The car came with the style of fuel cap that clicks when you close it (attached). Doesn't feel air tight. Is it suppose to be?

Here something else that might be a clue to the problem or maybe it's a symptom of something else. I completely forgot about this... If you look at the area I circled on picture 2, that's usually filled with diesel slime (not sure what else to call it). It's not there now because I cleaned it yesterday. It's always there after I drive the car about half a tank. I find myself cleaning that area a couple times a month (I don't drive much). Maybe it's related?


I apologize in advance for my rookie questions...

[loneranger]

sounds like your sucking air from some location when the fuel is down so the weight of the fuel is not able to keep fuel in the line. If you replaced/cleaned the tank strainer try replacing the rubber lines from the tank to the lift pump. The lines may not leak fuel out but air is much thinner and the lift pump may suck air in w/o the weight of the fuel in the tank to keep positive outward pressure. sounds crazy but these diesel don't have to suck much air to run rough.

[funola]

Originally Posted by digieditny

Barry. Very interesting! This is news to me. My car does have a cigar hose though. The problem has been there since I have acquired the car. I will try everything you've mentioned! Looks like it's going to rain so I'll have to try later.

Funola. Would I need to buy the whole assembly or just the pump?

I would say it only happens when the tank is 1/2 empty or less. Never when it's full. But I would also say that it doesn't always happen. Sometimes The rough idle goes away and sometimes it gets really really bad (have to switch it to neural and accelerate to keep it alive) but ALWAYS happens when the tank is 1/2 empty or less.

There's no vacuum that I can tell. No swoosh. The car came with the style of fuel cap that clicks when you close it (attached). Doesn't feel air tight. Is it suppose to be?

Here something else that might be a clue to the problem or maybe it's a symptom of something else. I completely forgot about this... If you look at the area I circled on picture 2, that's usually filled with diesel slime (not sure what else to call it). It's not there now because I cleaned it yesterday. It's always there after I drive the car about half a tank. I find myself cleaning that area a couple times a month (I don't drive much). Maybe it's related?


I apologize in advance for my rookie questions...

Your fuel cap is probably leaking? Thus the diesel slime? The OEM cap is steel. Try finding a used one. My guess is this is unrelated to your rough idle.

[barry123400]

Because the fuel level seems to play into this. Plus the problem was there when you purchased the car.

Do the series of tests with the return line. Of course do not do the tests if the engine has enough fuel in the tank to run normally. When it is runing normally you would find nothing signifigant in most cases.

It should turn out to be cheap to fix once you establish some indication of what it might be.

A quick check for the primer pump is to stretch a ballon over it and squeeze out the air. If it is sucking air this denies the access to it. Has this car been used on waste vegatable oil to the best of your knowledge?