I have a 1990 500SL, 93000 on the clock. There is a slight misfire at tickover and when you try to rev quickly the engine hesitates before revving up. Also, at times there is no throttle response- nothing. I can "cure" this by switching off and on again or sometimes holding the throttle to the floor for a few seconds before the engine fires up. This is worse when cold. Usually this lasts for the journey but sometimes when I stop at a junction the no power thing comes back. I think there is a slight lack of power generally, but I have nothing to compare it with. I have replaced plugs, leads, dizzy caps and rotor arms, one coil, fuel filter (new one swapped to each side- no change) and run the car with jet cleaner. Any suggestions. Don't say clean MAF as I don't think this model has one.
Sp!ke
Administrator
It is usually caused by damp in the dizzy caps on these models. Replacung the caps will only help until the next bit of condensation.
It does sound like you are missing on one or more cylinders.. something that a decent indy will be able to pin down reasonably quickly.
It does sound like you are missing on one or more cylinders.. something that a decent indy will be able to pin down reasonably quickly.
Thanks. I don't think the condensation idea gets past the fact that it happens when the engine is thoroughly warm when I stop at a junction. I have a garage friend who has offered to put it on to a diagnostic so hopefully he will be able to confirm the fix.
Sp!ke
Administrator
The condensation gets trapped in the caps no matter how hot the engine is.
Worth while unclipping and giving them a thorough wipe to see if there is any improvement imho.
If it isnt electrical then you'd be wanting to look at compression ratio's on each cylinder I recon.
Worth while unclipping and giving them a thorough wipe to see if there is any improvement imho.
If it isnt electrical then you'd be wanting to look at compression ratio's on each cylinder I recon.
ray_hennig
MB Enthusiast
Hmmmmm
Mine's a 300-24 but I think the fuel system's the same - Bosch KE Jetronic.
BTW, how many coils do you have? If I'm right, only one.
It seems you've done the right electrics stuff.
Eliminate ALL inlet vacuum leaks, if not, you're shooting in the dark.
Check fuel delivery duty cycle - should be 50%.
Also fuel pressure.
Can't remember if you said you'd replaced the fuel filter - worth doing.
If all my assumptions are correct, you do have a MAF, it's just a mechanical one and it must work correctly. Make sure the flap moves smoothly. Look up KE-Jetronic on Google and study hard. There's loads to think about but at least it's electro-mechanical and not 100% electronic which means there's hope!
Then wait here for the brainy boys like old Telly and Alex Crowe - they are the lads. And there are others.
Er.
That's it for the moment.
RayH
Mine's a 300-24 but I think the fuel system's the same - Bosch KE Jetronic.
BTW, how many coils do you have? If I'm right, only one.
It seems you've done the right electrics stuff.
Eliminate ALL inlet vacuum leaks, if not, you're shooting in the dark.
Check fuel delivery duty cycle - should be 50%.
Also fuel pressure.
Can't remember if you said you'd replaced the fuel filter - worth doing.
If all my assumptions are correct, you do have a MAF, it's just a mechanical one and it must work correctly. Make sure the flap moves smoothly. Look up KE-Jetronic on Google and study hard. There's loads to think about but at least it's electro-mechanical and not 100% electronic which means there's hope!
Then wait here for the brainy boys like old Telly and Alex Crowe - they are the lads. And there are others.
Er.
That's it for the moment.
RayH
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I had similar issues with my 1991 300CE which has some similar features. I had the (1) moisture in the caps, (2) incorrect plugs (use non-R, I used to accept Bosch resistor types the motor factors gave me) and also had some (3) vacuum leaks.
Over time, I got them sorted and the car runs well now. You seem to be well aware of the moisture problem. As mentioned above by Ray, have a look under for any perished vacuum rubbers, cracked vac pipes, or broken connections. And, check your plugs are non-R.
best of luck
Gerard
Over time, I got them sorted and the car runs well now. You seem to be well aware of the moisture problem. As mentioned above by Ray, have a look under for any perished vacuum rubbers, cracked vac pipes, or broken connections. And, check your plugs are non-R.
best of luck
Gerard
carat 3.6
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It dose sound like moisture in the dizzy caps, but as the others have said check for vacumn leaks.
I once a 560sel that was way down on power, wouldnt rev over 3000 ect. It turned out one of the fuel pumps was faulty, second hand pump fitted and full power restored. I know it's not the same engine as yours but it may be worth a look.
I am asuming your engine is the quad cam m119? Some of these have exhaust 02 sensors that can fail over time.
I once a 560sel that was way down on power, wouldnt rev over 3000 ect. It turned out one of the fuel pumps was faulty, second hand pump fitted and full power restored. I know it's not the same engine as yours but it may be worth a look.
I am asuming your engine is the quad cam m119? Some of these have exhaust 02 sensors that can fail over time.
if you change the caps dont forget to change the rotor arms...
Thanks to all. I think I did spray the Dizzys with WD40 when fitted. Has new fuel filter and two coils. I will check for condensation and spray (again), I have not noticed leaking or perished pipes. I have sprayed carb cleaner into the flap on the KTronic and it does seem to be moving freely. The plugs and leads were replaced about 2 years ago following a serious misfire on the motorway- cured that at least! This misfire and lack of power doesn't feel the same- does feel like fuel delivery problem. I will keep on keeping on.
carat 3.6
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Check that both fuel pumps are working.
fallen-angel
New Member
hi wilcer
as the guy's have mention about vac leaks but the miss at idle hmm is each plug firing, also what plugs are they, i have known new plugs to fail, (you have changed cap and rotor), and ign timing is correct, after this check compression, next i would check injectors, working? and spray pattern,,, all this being checked out ok and she should idle cleanly,,,,
reving up?? recheck for vaccum leaks as this will cause a lull in power if there is a leak, also mass air flow unit, as you have the problem of it not reving up at all, (thats gotta be elect) and as its intermittent and resets after a restart, somewhere a signal is being lost so first afm after that check throttle pos sensor (resistance test) should suffice for this, if problem is not found by now i think a computer check up to see what fault codes are being put up,, as you have covered most basic posibilities... (if she was a timing belt engine i would say check it but as its a chain then it should be ok) my final say would be to check the fuel sytem for faults,,, hope this helps a little
as the guy's have mention about vac leaks but the miss at idle hmm is each plug firing, also what plugs are they, i have known new plugs to fail, (you have changed cap and rotor), and ign timing is correct, after this check compression, next i would check injectors, working? and spray pattern,,, all this being checked out ok and she should idle cleanly,,,,
reving up?? recheck for vaccum leaks as this will cause a lull in power if there is a leak, also mass air flow unit, as you have the problem of it not reving up at all, (thats gotta be elect) and as its intermittent and resets after a restart, somewhere a signal is being lost so first afm after that check throttle pos sensor (resistance test) should suffice for this, if problem is not found by now i think a computer check up to see what fault codes are being put up,, as you have covered most basic posibilities... (if she was a timing belt engine i would say check it but as its a chain then it should be ok) my final say would be to check the fuel sytem for faults,,, hope this helps a little
ray_hennig
MB Enthusiast
With a proper MB one, I hope, although other will say that Bosch and Beru are good too and they may be.
I had a Bremi rotor and it failed in less than 18 months.
RayH
Terry_
Auhorised Forum Sponsor
I had a similar problem on a 119 engine. Turned out one of the new dizzy caps had a small crack in it. Also when you changed the rotor arms I trust they fitted snugly on the camshaft mounting plates? These were modified along with the rotor arms years ago
