Air in my fuel system??
 

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!!

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.

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.

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.

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

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

I just ran outside and did the little test -

Fuel IS getting in there when I do it. I can't really tell where it is coming from, though. Do I have to remove the air meter plate to see?

Anyway, I pulled the 3 prong wire and immediately heard some clicks, then I quickly put it back in.

The first time I did this, I noticed fresh fuel smell, but didn't see any. After doing this twice more, I noticed there was a small amount of fuel at the bottom of the air meter bowl.

My car has 122K miles, I'm hoping it's not the injectors, even though they aren't too expensive.

What is the plunger o-ring called and can it be replaced without opening the fuel distributor or some other nasty can of worms?

What exactly does pulling that three prong connector do, anyway?

Thanks!!

it appears to me that you have described several different problems, hard cold start, difficult warm start, surging and so forth. Here's what I would do for whatever it's worth (probably not much). This is why I say this, I started working on a 1990 300TE about 2 years ago, my wife did a favor for a friend and bought it from her. The car ran fine for one winter and then seemed to go to hell the minute the weather came around. This is what I have found out since; the idle was low and stumbling, acceleration was poor, cold start typically good but warm start poor, gas mileage was unacceptable and I could smell the engine was running rich simply by sniffing the tail pipe. I repaced the fuel distributor (KE-5) with no satifactory result ($40 from a junk yard)...replaced all the little vacum hoses ($15 from the dealer), no result. Turns out is was the coolant temp sensor and new spark plugs ($35 for the coolant sensor and $18 for the plugs)...problem solved...thing runs like a top and has since last September.

and even more importantly, air in your fuel system? what does that mean?

From your original post it apperea to me that you removed the fuel distributor from the AFM body. Since you didn't do this I wouldn't worry about the O ring.

The rubber body fitting the AFM onto the manifold is sometimes difficult to put on. Make sure that this is seated correctly with no leaks.

Did you drop it the unit when you pulled it off and crack the EHA?

Did you damage the cold start valve which is adjacent to the fuel distributor?

Are all the fuel lines on the top of the FD tight?

Hi Ivanerrol and Porkface,

I am interested to find out where this fuel is leaking into my air meter bowl from, but I don't think it's my problem, just a waste of fuel.

The cold start valve is suspect to begin with, I've previously always had to give it some gas to get it to start up when cold. The problem I've been having lately was the opposite of that, however...... It would try to stall if I gave it gas while it was idling.

Thanks for checking back.... No, I didn't drop it when I pulled it, and I didn't even disconnect the main fuel lines. I pulled all 7 fuel lines from the injectors, and took off the EHA. I then used bungees to pull the whole assembly including the air meter off to the side while I did surgery on the idle air/cold start injector hose.

I had the whole thing apart for a couple hours, and it was tilted at a funny angle for that time, which is why I think I could have air in it.

Interestingly, the symptoms haven't happened in 2 days. I think I may have in fact gotten some air in some obscure chamber of the fuel meter, because it really acted that way, and it is curing itself. The symptom was definitely a lean one..... The car would idle just fine but die if you tried to open the throttle at all. Then it would take a few minutes of pumping the accelerator before it would finally act like it was getting enough fuel. I mean, when you hit the accelerator and the RPMs drop, you've got a fuel starvation issue, no?

And then it would go away and run great until completely cold. But, as I said, the past 2 days I haven't had the problem at all. Start right up and drive away just like I used to. The problem only showed up after I pulled the fuel system apart, never had this symptom before.

"and even more importantly, air in your fuel system? what does that mean?"

Umm..... Fairly self explanatory, Cliffmac. Weather or not it's possible is another discussion, but I think it was plenty obvious what I meant. I also think that the level of sarcasm you offer me is insulting, as if I had my head up my ass when I asked the question. I think it's a pretty reasonable theory considering that I never had such an issue before taking off the 7 injector lines and the EHA valve, and pulling it off to the side. I also think that I might eventually be proven correct since the problem has abated for the last 2 days.

Here's an hypothesis - my cold start injector doesn't appear to be working. I really need to test it.... If it won't open, then there would be a pocket of air in that line after removing it, and that air would have nowhere to go but back into the fuel distributor. Isn't it possible that the air trapped in that line took forever to go away because it had to backtrack through the fuel distributor? Couldn't that pocket of air make its way back into the the chambers of the fuel distributor overnight and cause havoc with the fuel metering during warm up? I really don't know, but I think it is a perfectly reasonable hypothesis given the symptoms and work history.

Just as a note, I have all new wires, plugs, cap, rotor, etc. on my car, so that isn't the issue. I also have brand new temperature sensors. The fuel computer is rebuilt by Programa, and the only things missing from my setup are a working EGR, a working smog pump, and a new Lambda sensor which is about to happen this weekend.

The important thing to keep in mind is that this problem started immediately after opening the injector lines, and never happened before. Unless I broke something in the process which is magically fixing itself, trapped air is the only thing I can think of.

I still want to get to the bottom of the cold start injector and also why there is fuel leaking into the air meter bowl.

Thanks for your help everyone.....

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????

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.

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.......