Need advice on injection

[bahnstormer109]

My 450SEL is K-jet injected and it starts fine when cold but when i start it hot it always takes 2 goes and when it starts it runs chunky for a few seconds and is then fine.

my mechanic said its my "accumulator" thats leaking and to just put up with it because its expensive to replace.

does anyone know where i can find the accumulator and whether its easy to swap in a new one myself??

and second, the benzes ive had that are D-jet injected both left black sooty marks on the ground and the K-jet and carby cars ive had dont.

what causes this black soot to be blown out of the exhaust, mainly when the motors cold?? i assume its the injection running too rich? my 109 does this but the motor doesnt use oil, though is very thirsty.

any advice much appreciated!

cheers,
Paolo,

[CraigS]

I have just replaced the accumulator and yes, they are expensive. Mine was $175 and I believe the MB price is over $200 plus GST.

It is an easy job, albeit fiddly as you have the fuel pump and filter to work around. At the same time, replace all of the connecting hoses. Saves having to do it later and unless you know the last time they were changed, it is best to do it while you are at it. Shouldn't need to be said, but don't use heater hose !

The accumulator keeps fuel up to the fuel distributor, and if it is not, then it will take more to crank it, but it should also then do it cold.

[Grant V]

Paolo,

I think that the problem might be leaky injectors.

My accumulator on my 6.9 was buggered and the car battled to start when both cold and hot.

If the injectors leak, then the car sort of floods, which is fine when cold, because the mixture is rich (like pulling the choke) and therefore starts easily.

When hot, the car floods and it's difficult to start.

Leaking injectors are not a good idea. The leaking fuel can thin out the oil lining the bores and can result in excessive wear. Rather get them checked out.

Hard starting when hot used to be a common problem when I worked for Mercedes and we used to check the injetcors on a special jig. The injector would be screwed into a pipe and then via a plunger, fuel would be sprayed through the injector. If the injector is right, then a small amount of pressure would result in the injector puffing out intermittant sprays of mist.
If the injector is stuffed, then any small amount of pressure would cause the injector to leak, with only large amounts of pressure creating a spray of mist. Sometimes used injectors don't even spray a mist, but a stream of fuel.

I have no idea where you could take the injectors to be tested - maybe MB Spares?

[Nutz]

It only takes 45 psi to make a continous mechanical injector spray,any less and it won't open.

If you have black smoke after fighting it to hot start,your injectors are dribbling into the combustion chamber and losing rest pressure as a result.

[Andrew280SEL]

Hey Bahnstormer,

Mate you just described the problem my car has to a tee.

The funny thing is, if I pump the throttle a couple of times quickly as I turn the ignition key it nearly starts immediately. Still runs a little rough when it starts off course, which is only made worse by a vacuum leak at the manifold.

Not sure why pumping works better than just holding the throttle down though...

[Nutz]

Not sure why pumping works better than just holding the throttle down though...

Because if you hold the throttle body butterfly plate open partially below the venturi/plate,you allow the air/fuel ratio to be crudely corrected more closely because of the increase of all the fuel pooled in the intake manifold.

[Andrew280SEL]

Not sure why pumping works better than just holding the throttle down though...

Because if you hold the throttle body butterfly plate open partially below the venturi/plate,you allow the air/fuel ratio to be crudely corrected more closely because of the increase of all the fuel pooled in the intake manifold.

So.....basicly it just helps to hit the "sweet spot"....instead of just holding down the throttle and opening up all the air and hoping all the best?

Sorry, I'm just trying to get my head around it, hope I make sense....I probably don't 

[Nutz]

Holding the throttle part way open will sometimes help but pumping is futile unless you have a carburetor. Regardless you need to address the problem and correct it for the sake of you exhaust system,muffler mostly due to the negative effects unburnt fuel has on them i.e. clogging.

[Andrew280SEL]

Yes I need to get it fixed certainly, it's just a matter of getting to it.

That's the funny thing though, my problem is pretty much the same as Bahnstormers, it's obviously over-fueling, but pumping actually works for me.

I've always held the throttle down a little ways in the hope of an almost instant fire, and sometimes successful, but sometimes It would just not quite do it and flood even more.

Now, recently I just pumped it instead quickly and seems to fire pretty reliably every time. Any ideas why this is?

You might have already answered my question, but I'm just making sure.

[bahnstormer109]

ok, so its a bit more complex than i was hoping!!

ill try and describe the symptoms in more detail:

to start it cold it does crank for a few seconds before catching. maybe 4 seconds. runs fine. being winter at the moment when i start it stone cold on a cold morning it idles low and unevenly. i hold the revs at about 1500 for a minute to warm it a bit and its fine. but starting it cold in summer it idles fine.

after i turn it off hot, if i go back and start it again within about 15-20 mins it starts fine. but if its sitting longer than that the start procedure is always exactly the same: i turn the key and it catches straight away then dies straight away. i turn the key again and it cranks for a couple of seconds and then catches to a really lumpy low idle that smooths out in a few seconds, faster if i rev it.

dunno if this helps narrow down the problem??

thanks guys,
Paolo.

[Andrew280SEL]

That makes it more complex for us more like! 

I'm not really sure what to say there, it's a tad bit different to my problem after all. All I can think of is maybe its a tiny leak in the injectors. Mines fine if I turn it back on the first couple of mins, but after that things get a little bit tricky. I suspect my leak is reasonably bad.

Nutz??

[bahnstormer109]

I decided that the accumulator on my car would most probably be stuffed as i checked it out and it looked original. if the injectors were leaking too, i thought the accumulator would need to be replaced as well anyway. it was either the accumulator by itself, or both, it and the injectors. i went ahead and got a new one and put it in tonight and it seems to have cured the problem.
i drove the car to warm it up and left it sit for a while a couple of times and it started perfectly.

i figured that if it continued to be hard to start then the injectors would be leaking too, but at least the new accumulator would be ruled out as the only cause.

but the new accumulator has sorted the problem. my injectors seem to be ok so im happy!

[Andrew280SEL]

Well that's very good to hear! 

[SELfor50]

I decided that the accumulator on my car would most probably be stuffed as i checked it out and it looked original. if the injectors were leaking too, i thought the accumulator would need to be replaced as well anyway. it was either the accumulator by itself, or both, it and the injectors. i went ahead and got a new one and put it in tonight and it seems to have cured the problem.
i drove the car to warm it up and left it sit for a while a couple of times and it started perfectly.

i figured that if it continued to be hard to start then the injectors would be leaking too, but at least the new accumulator would be ruled out as the only cause.

but the new accumulator has sorted the problem. my injectors seem to be ok so im happy!

Where did you get your accumulator mate, and how much was it??
Can i rip the old one off my parts car and re-condition it???
I'm thinking of doing this performance friendly piece of maintenance on my beast.  It runs a little rough when warm as well.  I will be checking the injectors as well though.

Cam.

[alabbasi]

Injects run for about $30 / each on the K-Jet cars so it's hardly worth testing. Pull the spark plugs out and find the black plugs and replace the injectors.

WRT to the black soot, it's probably worn valve seals. I have that on my 280SEL 4.5 and it's an expensive job to change out so your better of living with it if the engine runs well.