e300d air in diesel pipes
 

Hi,
I have a 95 (W124 model) non turbo E300D with 155k miles. Recently I changed all 6 glow plugs to cure bad starting. Now have rough idle when cold - it kind of misses a beat but no smoke. I can see air bubbles when the motor is running in the diesel lines that run to and from the lift pump assy on the side of the diesel pump and assume this is my rough running problem. When the motor is off there is air in the top half of one of the pipes - like the diesel has run half way back down the pipe. I can't see any diesel leaks though. I have ordered the new pipes - is this likley to cure it or is there some where else that the air is getting into the system?

Thanks for advice

Replace the O-ring in the fuel prefilter when you change the fuel lines. Also replace the O-ring behind the shutoff valve. Lots of old threads can be found using the "Search" mode on the topic.

Spray off the entire set of plastic hoses to see if it is leaking. Use brake cleaner so you can get all the diesel off then you can see where diesel is leaking from.

Thanks I have cleaned the pipes and unions off but no sign of a leak anywhere. I thought that diesel found its way out of any slight crack!

This car has a valve that prevents the fuel from going back into the tank when stopped. The valve may be defective. If you follow the clear fuel line back from the pre-filter you will see that valve. Its under the intake manifold

I may have the same problem.

Phil

You might not see a fuel leak. I didn't when the problem developed on my car. Over time the problem may become more pronounced. Best bet is just to replace all of the lines at once and be done with it. :)

I have experienced similar problems in my 95 and replaced all of the lines which proved to be the cure. From all of the investigations I did, it does not suprise me that you do not see any leaks even though you have an "open" system.....after all, fuel delivery from the tank does not rely on a fuel pump and thus is not presurized.

Thanks a lot guys. I am going to replace the lines and the o ring and if it doesn't cure it check out the non return valve. Will let you know.

I thought I see no air bubbles in my lines when the engine is running but after shutdown if I look at it, I see a bubble or two. No missing a beat tho. Definately no leaks because it was redone professionally and all lines replaced and checked by another professional too.

A question to those who already changed their clear fuel lines on a '95 E300D.

Does the intake manifold need to come off, or can you change them by removing the cross-over pipe only?

You'll need to take off the manifold. It's not that bad of a job - but you'll probably wind up breaking a couple of the plastic crankcase vent "injection" pieces which go into the manifold when you take it off. I broke a couple and just plugged them with silicon.

I had a situation however, still unresolved. I ordered all the plastic lines from Phil, but one line did not match the configuration on the car. Phil looked for a superceded part and thought he found it, sent it no charge - but it still wasn't the right one. So I have one line which does not seem to be according to the book, so to speak. Probably have to go to the dealer and eyeball it with a parts guy.

Rgds,
Chris W.
'95 E300D

How about taking off the manifold and get it cleaned with a machine shop hot tank?

Hi Chris,
That is interesting; I too have one line on my 95 E300D that does not look like the parts listing. One of the lines that goes from the back of the fuel filter to the pump is shown in the parts book with a bolt and washer yet on my car there is a push on clip connector - is this the same one you had problems with?

As I said, my car has similar symptoms that I need to deal with. Strangely though, I did notice however that these symptoms are only there when the Fuel tank is less than full. When full, these symptoms disappear.

If you have a chance to experiment, can you check if a full tank of fuel makes your symptoms disappear as well.

Thanks

pberku,

That's because when the tank is full, the height of the fuel is above the leak so air won't leak into the lines. But fuel might leak out.

Put a slight pressure on a full tank and U should be able to find the leak.

P E H