R129 no power/dies from standing start

[jefft]

Hi All,

My 1990 R129 500SL has developed a problem, not sure if it's ignition, fuelling or something else related... any ideas greatly appreciated!

Sometimes when I set off from a standing start - say, from a traffic light, there's no response to the throttle at all and the car just sits there. After about half a second, or if I back off the throttle and re-apply it, she's fine again. Once in a while, the lack of response will turn into the engine dying completely.

I've also noticed that it does this at times if I put the engine under a lot of load suddenly - for example, turning onto a hill at low speed and then putting my foot down to accelerate up the hill.

So far, I've checked the plugs (fairly clean), caps and rotors (ditto, and they were replaced less than 6 months ago) and the air intakes (clear, filters clean). The airflow sensor flap (no MAF here) seems to move freely enough too.

Does anyone have any ideas, please?

Thanks!


Jeff

 

[Pookis Dad]

Missing...

I have a similar fault with my wifes "C" 200.

If you floor it there is a hesitancy, then the car "wakes up" and goes like a bat out of hell, but you can almost hear it missing.

I rather suspect the HT leads, but on this model the HT's are extremely short seeing as how the coils are under cover on top of the engine.

I guess the best way to check is to remove the covers and fire up the engine on a dark (and damp if poss) night. If there are fairy lights dancing about in there then it's the leads as they do eventualy break down over time.

I could be wrong, but at least it's a free check.

 

[jefft]

Not the leads... or the plugs...

Thanks for the idea. Finally got time to check it out - nice and dark, quick misting of water to encourage any sparks, but nothing.

Changed the plugs while I was there, for good measure. Nothing stand-out there either, all tips fairly clean and even brown colouring, bit of carbon around the rims but nothing too offensive.

Anyone got any other ideas? This feels like either missing under load on perhaps one cylinder, or something like over/under-fuelling on acceleration, but I'm short of ideas as to what might be behind it.

Thanks guys

Jeff

 

[jibcl500]

What about your air flow meter below the a filters??????

jib

 

[jefft]

...

The air flow metering flap seems to move freely enough and stops at the right position... Looks like it drives a potentiometer, presumably feeding the ECU. I know potentiometers can wear over time - is that likely here? Will see if I can check it out. Does anyone know what the resistance of that airflow meter pot should be and how it varies with the flap position?

Thanks

 

[jefft]

So far, so good...

Well, after the plug change and another dose of injector cleaner - this time, Wynn's rather than Redex - in a fresh tank of fuel, it's so far so good. No misbehaviour.

Fingers crossed...

J

 

[gfern]

Did you try the fuel distributor, my car had similar problems we undid the connections and what looked like a rusty fluid came out, and then a tankfull of injector cleaner solved the problem.