R129 Lack of power when warmed up./

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Biglee

Active Member
Joined
Oct 6, 2013
Messages
70
Location
West Yorks
Car
500 SL & Lexus IS F Sport, Land Rover Ser 2a & Saab Conv
Any ideas. I have R129 1990 500SL. Always had a poor (ish) idle. But now nearly un-driveable when warmed up. Stutters and as though on few cylinders. Plugs changed (Correct non resistor champions from Green Plug company), Rotors, Dizzy caps, Dizzy insulation disks (ouch), HT Leads, New dielectric paste on EZL and second hand OVP. Its been in to Merc who "thought" it might me mixture. Tweaked t a bit and wanted 8 hours to perform more diagnostics. PS no fault code from blink reader.

I have removed coils and was going to replace them as reasonable. Fuel filter also fairly new.

I also had an issue with sporadic instrument cluster Where rev counter and some other gauges would sometimes falter. Now I understand rev counter is fed revs from MAS so I was looking to swap this out too.

Anyone got a spare MAS.. 008 545 87 32 is part number. Yorkshire ish ideally but anywhere. Buy or borrow.

The only other thing I have researched is CPS. If they crack they can cause an issue when they heat up. Anyone experienced this and are they hard to change. ? Or EHA could be playing up. Anyone know how to test ?

Any other suggestions gratefully received.

Cheers Lee
 
Plug colour should give an indication if its mixture related. Guess it might be a fuel supply pressure problem. Choked fuel filter/s tank outlet fuel strainer--- poor tank ventilation leading to partial tank vacuum---- under performing fuel pump/s- some models may have two in series . Best test would be to monitor fuel line pressure to see if it's within spec cold and hot?
 
Thanks Graeme. Plugs are a perfect colour. So I don't think mixture. I don't suspect fuel pressure as when cold it's great. Loads of performance across rev range. Just stumbles when up to 80 plus. Keep suggestions coming as will be trying everything.
 
I fitted a new crankshaft sensor to my SL500. Not a difficult job. In my experience, when one fails it makes the engine difficult to start when hot.
When I removed mine there was an oil-like substance on the end; this could have been causing problems. It might be worth taking your sensor out and making sure it is clean.
 
Thanks Graeme again I had seen the pin out but not the other two. PS I meant 80 degrees not MPH :)

Yes I thought I would get an Ebay MAS. But alas not unless I want to remortgage my house or order from across the world.

Will keep on it. Thanks again.
 
Any ideas. I have R129 1990 500SL. Always had a poor (ish) idle. But now nearly un-driveable when warmed up. Stutters and as though on few cylinders. Plugs changed (Correct non resistor champions from Green Plug company), Rotors, Dizzy caps, Dizzy insulation disks (ouch), HT Leads, New dielectric paste on EZL and second hand OVP. Its been in to Merc who "thought" it might me mixture. Tweaked t a bit and wanted 8 hours to perform more diagnostics. PS no fault code from blink reader.

I have removed coils and was going to replace them as reasonable. Fuel filter also fairly new.

I also had an issue with sporadic instrument cluster Where rev counter and some other gauges would sometimes falter. Now I understand rev counter is fed revs from MAS so I was looking to swap this out too.

Anyone got a spare MAS.. 008 545 87 32 is part number. Yorkshire ish ideally but anywhere. Buy or borrow.

The only other thing I have researched is CPS. If they crack they can cause an issue when they heat up. Anyone experienced this and are they hard to change. ? Or EHA could be playing up. Anyone know how to test ?

Any other suggestions gratefully received.

Cheers Lee

Since you say it happens after warm up , and were told mixture is suspect , I wonder if you have a vacuum leak somewhere which is opening up with temperature ?

You could try spraying something like carb cleaner around manifolds etc with engine idling and see if any change can be noted ?
 
Does your car have a secondary air pump [ smog pump] system. If these are faulty they can lead to problems. Should I beleive only run during the warm up phase
 
No air pump Graeme. 2175mm or 2176mm poly belt.

No visible intake leaks ( Did have one in rocker cover to air filter pipe at rear on Drivers side) but that is now fixed. Will try some carb cleaner when I track down some Bosch coils and replace the CPS if not fixed.

Thanks for suggestions so far.
 

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