New problem with my 450

[Niclas]

Then it's defenately a fuel related problem, not the piston rings. If it would be something wrong with the piston rings the compression would leak out there cousing to low compression readings not to high.
Soo relax, it's seems tricky but it's going too bee a lot cheaper than dissamling the whole engine...

Maybe the fuel regulator is broken or mis adjusted cousing the fuel to flow freely in to number 4 cylinder and far to much into the others too?? I guess that you could get too high fuel pressure if the return fuel line is stucked too.
Borrow a fuel pressure gauge is my best guess for the next step in the investigation.

/Niclas
I'll race you some day!

[Bulba]

Thats true! Cant understand why i havent thought of the fuel return yet, i will check that tomorrow. Where on the car can i find the fuel regulator?

[oscar]

hi bulba, they're brilliant   I can't find any other reference to what the compression should be but I got 9's and 10's in the 350 from memory.  I think your's are fine.

However, number 4.  Firstly, you've noticed there's liquid fuel in the cylinder.  That fuel is thicker than air so it virtually blocks any gaps between the rings and cylinder.  The result is that you get a huge jump in compression like the 17bar you measured.  There's either something wrong with that injector or the wiring to it.  Has to be the injector though because the injectors work in pairs 1 & 5, 2 & 6, 3 & 7, 4 & 8.  So you would expect number 8 to be playing up too but it's not.  Try another injector in 4.

This is looking promising

[Bulba]

Thats true, it must be the injector itself considering the others work almost perfectly. hmm, im guessing an injector is very expensive, but still, much cheaper, and much less work then taking out the whole engine and change piston rings. im going to try put another injector in nr 4 just as you tipped me. I have so little time now since school started. I have to agree, it looks promising. I was just about to give up.   But im still stuck at the problem why it only runs on about 4-5 cylinders if the only injector broke is nr.4 .

[oscar]

But im still stuck at the problem why it only runs on about 4-5 cylinders if the only injector broke is nr.4 .

Oh yeah, I forgot about that   I could guess and say that if number 4 injector is stuck open that it robs pressure from the other injectors causing the other cylinders to misfire but I really doubt that a stuck open injector could drop the pressure that much.  Who knows, maybe that is what's happening.  is there any possibiblity of trying a second hand injector perhaps off a wreck if there's a wrecking yard near you. That maybe the cheapest option, grab a few second hand ones if you can.

[Bulba]

Its hard to find for my model, i was promised a good shape engine from a friend, but he gave it away to another friend of his. And in the junkyards they only have injectors for 280SE. So i dont really know where to find a second hand one

[Bulba]

I dont know if im ready for these cars yet, financially. Even though i love them and have many memories from them i think it has to wait until i get a job And im gonna buy a nicer one. So now i dont know if im going to keep my 450 or sell it. Anyways, im not going to put any more money at it for now. whether i like it or not, the gas prices are to high here in sweden, and it only brakes down all the time.

[Niclas]

1, unconnect no 4 injector electrically by just pulling off the contact. Test start.  Price 0kr
2, unconnect no 4 injectors hose and plug it. Test start. Price 0kr.
3, check that the return fuel is not stucked by blowing in it. Test start. Price 0kr.
4, reduce fuel pressure by adjusting the screw un the fuel pressure regulator. Test start. Price 0kr.

/Niclas

[Bulba]

OKey i will check that. I decided too keep it, but take a break from it. Soon winter comes and i have to put it away anyway. But i wont give up!

[Bulba]

Now im ready to get going with this car again. Ive had myself a nice vacation and also worked a bit to get some more money. I was tipped of this guy, living a bit on the country side pretty close to the city i live in. Apparently he is some kind of expert on old mercedes escpecially from the 60s and 70s, and he has helped many people who couldnt get help from workshops and such. Now im going to change the oil again, unplug the fuel pump and run a new compression test. Then im going to go talk to that man, and after that i will see what happens.

[Niclas]

Where do you live? I know a great old man in Trollhättan who probebly is born in a Mercedes...
His shop is just open one day a week unfortionately.

/Niclas

[Bulba]

I live in Örnsköldsvik, so its a pretty long way down there

[Bulba]

Did a new compression test today without the fuel pump. These are the results, its looking positive

1. 8,5 bar
2. 8,5 bar
3. 9,1 bar
4. 9 bar
5. 11,5 bar
6. 11 bar
7. 11 bar
8. 9,7 bar

So i guess that injector nr 4 is broken then Or what do you guys think?

[oscar]

So with fuel pump _________  versus ___________  without fuel pump

cylinder 1: 9 bar                                                           8,5 bar
cylinder 2: 10,7 bar                                                       8,5 bar
cylinder 3: 10,3 bar                                                       9,1 bar
cylinder 4: 17 bar                                                         9 bar
cylinder 5: 11,4 bar                                                       11,5 bar
cylinder 6: 11,2 bar                                                       11 bar
cylinder 7: 11,1 bar                                                       11 bar
cylinder 8: 11,1 bar                                                       9,7 bar


I think you're going about it the right way bulba.   test the injector off the car if possible and check the wiring too but I'd imagine a new injector would be the way to go.........steal one if you have to

[Bulba]

I will check for prices on wednesday, if i buy it from mercedes i think it will be expensive as hell, so im gonna check with the local bosch store first