Air in my fuel system?? - PeachParts Mercedes-Benz Forum

tinypanzer · #1 04-20-2009, 05:07 PM

Okay, so I had to pull off my fuel distributor in order to get to a well hidden idle air hose.

Since doing that, and replacing my EHA valve O-rings, my car has had nasty cold start issues. It will start right up and idle, but as soon as you give it any gas it dies. You have to sit there and pump the gas pedal and let it stutter and cough for a few minutes before it finally starts running correctly. After that, it runs great with plenty of power and will rev all the way up to redline.

It is acting VERY much a like a fuel delivery problem, and I assume that since I just had the thing open that I've gotten air in there. I am thinking that if it were pump or filter problems, it would not resolve so well once warmed up.

Two questions:

1) Is my assumption grounded in reality?
2) How do I bleed it out, or will it just go away eventually?

1990 300SE w126

Thanks!!

porkface · #2 04-20-2009, 08:43 PM

bleeding isn't an issue. if you've seen how much fuel is passed when the key is on, you'd understand. it sounds like too much fuel. open the afm and the throttle body and look into the bottom of the intake, the belly. if it's black and shiny, it's wet with fuel. clean it out good with lotsa compressed air. close the afm and throttle body. turn the key on, then pull the 3 pin connector next to brake booster-VERY FAST---CONNECTOR OFF-BACK ON. then look into the belly again. if it gets wet from the intake runners, then the injectors are leaking. if it runs down the side from the fuel dist, then the oring for the plunger is leaking. it might even be both, quite typical. good luck, chuck.

Ivanerrol · #3 04-20-2009, 08:54 PM

Of course you did replace that very delicate small O ring between the fuel distributor and AFM body. And if you did replace it, it must be held in exact position otherwise it risks getting crushed.

tinypanzer · #4 04-20-2009, 09:13 PM

Hi guys, and thanks for the response.

No, I didn't replace that O-ring between the fuel dist. and AFM body. I never took them apart....... I just pulled the whole assembly out as one unit.

I'll have to give that test a try. What exactly does pulling the 3 pin connector do?

Thanks!!

My symptoms seem to be a little better today..... Not really sure. Had no issues starting up, but a had a little bit of surging/lagging after a hot restart. Neither are problems I've seen before with this car.

God, I hope that Techron treatment I did a couple weeks back hasn't eaten up all my O-rings..... Seems like I'm getting a lot of leaks all at once, all after the Techron treatment......

Ugh.

cliffmac · #5 04-20-2009, 09:47 PM

no, it's not any of those things....

tinypanzer · #6 04-20-2009, 09:52 PM

Well that really clears things up..... Any idea what it *might* be?

tinypanzer · #7 04-22-2009, 08:41 PM

I guess I shouldn't have started patting myself on the back because the problem came back this morning.

Started right up, held idle fine, as soon as you step on the accelerator - it would try to die. Sputtering, backfiring, running like crap...... 3 minutes later - runs like a new motor.

WTF????

tinypanzer · #8 04-23-2009, 12:37 AM

Could this be a cloggy fuel filter? Got one, gonna try to put it on tonight....

slk230red · #9 04-23-2009, 12:57 AM

Quote:

Originally Posted by tinypanzer

Could this be a cloggy fuel filter? Got one, gonna try to put it on tonight....

I've been following your post. Have you checked or tested the Fuel Accumulator? I suspect that mine is going bad on my W201. Sometimes on hot starts the engine will miss and not idle on its own for a few seconds, then everything is fine after that. During those few seconds there is a strange gargling sound at the Fuel Pumps and it sounds like fuel going back into the gas tank.

From another site: "Often times the noise you hear can be a droan or a moan which is caused by a faulty fuel accumulator. It's a component that maintains constant pressure in the lines. It can either be leaking fuel or the inner diaphragm spring could be broken."

Fuel accumulator:
The fuel accumulator maintains the pressure in the fuel system for a certain time after the engine has been switched off. When the engine is running it serves to deaden the noise of the electric fuel pump. After the engine has been switched off, the fuel accumulator maintains the pressure in the fuel system in order to facilitate re-starting, particularly when the engine is hot. The design of the accumulator housing is such that it deadens the noise from the fuel pump when the engine is running. The interior of the fuel accumulator is divided into two chambers by means of a diaphragm. One chamber serves as the accumulator volume for the fuel, the other chamber contains a spring. During operation the accumulator chamber is filled with fuel. This causes the diaphragm to bend back against the force of the spring until it is halted by the stops in the spring chamber. The diaphragm remains in this position, which corresponds to the maximum accumulator volume, as long as the engine is running.

tinypanzer · #10 04-24-2009, 07:16 PM

Thanks for the tip. I really think my issue is the fuel pump at this point. I have already purchased a new one (BIG thanks to Phil for getting it overnighted!!).

My symptoms have been getting progressively worse in the past few days, in fact I have stopped driving it. In the last couple days, it was having not just the problem I initially described, but also general lack of power, and surging of power under load.

The whole thing smacks of fuel starvation at this point, and since the fuel pump has 125K miles on it, no big surprise if it's shot. I don't feel bad about just throwing a part at it without a pressure test because the thing is old enough to be replaced on general principle.

Man, whoever came up with that goofy banjo bolt setup on that fuel system should have their head examined. What an unnecessary pain in the arse. Then again, at least they didn't put it in the gas tank.......

porkface · #11 04-25-2009, 06:04 PM

from my previous post on this thread---then look into the belly again. if it gets wet from the intake runners, then the injectors are leaking. if it runs down the side from the fuel dist, then the oring for the plunger is leaking. it might even be both, quite typical.

you said you have fuel in the airflow meter bowl. this means either the injectors and /or the fuel distributor is leaking fuel. there never should be any visible fuel ANYWHERE outside of the injection system. the intake is only for air. these are not carbs on these cars. ANY excess fuel is going to affect the starting and running until that fuel is burned off. and yes, they will leak while running and every shut off until you replace the injectors and/or fuel dist.

the 3 pin connector is a fuel pump run circuit. allows for testing. pity they didn't always do that. good luck, chuck.