Hi Paul, I tried sending you a message but it wouldn't let me, so hope it's ok to ask you a question here.

 

I remember from ages ago that you work with Mercedes' so thought you might have come across this problem before.

 

I've got an SL55 AMG (I bought the one that I started a thread about ages ago, Clarkson's old car) which has an intermittent fault. Most of the time it's perfect, but occasionally the throttle becomes unresponsive, like it's gone in to some sort of safety mode. It happens after a short blast, no warning lights come on, it just won't accelerate from say 70 or what ever speed it's doing, but will still change gears. There's no coughing or chugging, I don't think it's a mechanical fault.

 

It lasts for about a minute then it's fine again. A mechanic friend suggested plugging it in to a laptop and searching for error codes.

 

The car's on 92k miles, full Merc service history, last service 1k ago. Any ideas would be appreciated - Thanks!

hi bud,

 

you really should get it checked for fault codes on a diagnostic tool first - but a common problem on the AMG's is the electric coolant circulation pump for the charge cooler. As the charge cooler temps increase over a certain limit the ECU will switch the supercharger off.

 

will usually store a code with the pump itself or intake temps too high if this is the case

Thanks for that, I've arranged to get it plugged in on Weds.

 

So the charge cooler is cooled with water or some other fluid which has it's own pump? If so is it likely to be a case of fitting a new pump or possibly just low fluid level?

 

Thanks!

yes - the charge cooler is basically a water cooled intercooler - the pump is a common failure & stops the coolant for the charge cooler circulating. The intake temps then soar too high & the ECU switches the charger off.

 

Let me know what codes are stored once you have it plugged in :)

Ok will do, thanks for help :)

no worries bud

Hey Paul, a local diagnostic bloke looked at the car today and found fault P2027. Y31/1 EGR valve Transducer (P0403).

 

He said he's 99% confident that would cause the problem, but to check with you first . He said the EGR valve could probably be cleaned and would be fine, does that sound ok? Also can you describe roughly where it is please, we can't find it!

 

The other thing I wanted to ask you is, when I give it a blip of throttle in say 2nd gear at low speed, it lets out a very short squeal almost as if a belt slips for 1/4 of a second. Is the supercharger belt driven? I don't know anything about the mechanics on these cars as you can guess, can't even find the air filters.

 

Also it had a new power steering pump (950 quid just for the part - jesus) last year and I've noticed that the fluid level is just about touching the bottom of the dipstick, but my mechanic doesn't know what fluid I should top it up with. I guess you know?

 

Thanks for help, it's much needed on a car like this :)

The EGR valve could cause problems - I have been looking on my Mercedes workshop info but strangely there is no EGR valve listed for the AMG engine.

 

on non AMG engines it is located at the rear of the inlet manifold on the drivers side - the transducer is an electrical valve that controls the vacuum to open the EGR valve itself - check the connector is good to this. From memory the valve all comes as one part with the transducer attached.

 

The supercharger is belt driven & has its own belt which is supposed to be replaced every B service (often gets missed if serviced outside of Mercedes!) - quite common for squeeking so would replace this if noisey - also check the tensioner is in good order. I have also known the double idler pulley that both belts run round to break up - I would check this too.

Check the main belt as you may as well replace this if it is looking a bit worn at the same time.

 

The PAS pump is a dual pump & supplies the ABC suspension too, you should see 2 reservoirs on the passenger inner wing, the large one supplies the ABC system & the smaller one is for the power steering - check both of these.

Fluid is best from a dealer - part no A001 989 2403

only compatible fluid approved is Pentosin CHF11S

 

air filters are in the plastic intake on top of the engine ;)

Thanks for that, I'll let you know how we get on with the EGR valve :)

Couldn't find the EGR valve, like you say perhaps there isn't one on the AMG? I think you're suggestion about the coolant pump is most likely.

 

I googled the fault code and found this,

 

http://www.justanswer.com/mercedes/51b88-sl55-amg-p0403-egr-vacuum-transducer-merc-tell-me-egr-valve.html

 

written by a guy with the same fault code, but the advice is to check the charge air temp sensor and wiring, but I can't imagine the snesor would be faulty because the problem isn't intermitent, it's always after a brief hard boost.

 

I'd like to check the charge coolant pump and radiator, could you give me an idea of where it is please? :)

LOL! I also work on that site you linked to! :D

 

The pump is located on the underside of the body behind the bumper on the drivers side - remove the plastic undertrays under the bumper & engine & look up - you should see a pump with 2 hoses going in & out. This is the pump for the charge cooler system.

 

Some aftermarket scan tools give misleading codes when compared to manufacturers diagnostic tools!

 

This is certainly the most common issue as I mentioned earlier ;)

 

There should be a 2 pin connector - power it up directly to see if it runs - if not then replace it. Its also a good idea to replace the relay if this is faulty as often the relay contacts get burnt out if the pump has overloaded the relay

 

:)

Cheers Paul, Will try and do that today/ tomorrow, I expect I'm going to ask you which relay it is later :)

Cheers Paul, Will try and do that today/ tomorrow, I expect I'm going to ask you which relay it is later :)

 

yea, guessed as much - wanted to wait until I was back at work to check!! :D

 

its relay R in the rear fusebox (located under an access panel in the storage compartment behind the drivers seat) position "R" should be shown on the fusebox itself but as you look at it the relay is the last one on the right (next to a 1/2 size relay)

Ok thanks, will check relay tomorrow.

 

I'm lucky that a mate is a mechanic (one man band) so I can use his lift. We had a look for the pump today and found two in that place right next to each other, a tiny one and a bigger one, we think the bigger one is the charge cooler pump. Didn't have time to test it though as the 2 pins were hard to access, so taking o/s/f wheel off tomorrow to get better access. My mate said does it use the same coolant as the engine - I would guess not - in which case is there a resevoir for it do you know? Cheers :)

We checked the pump and it doesn't work, so I've bought a "Johnson CM30P7-1 CM30 Mercedes Pump SL55" from ebay, which is supposed to pump 3x faster than the Bosch standard one.

 

I've been searching for info about the charge cooler set up, and bizarrely the charge cooler is in the V of the engine, can't think of a hotter place to put it lol. The fluid then gets pumped through the middle radiator to cool.

 

My only problem now is how to refill the system after fitting the new pump. I'll clamp the hoses to minimise loss, but don't want an air lock. Any chance you could find out what fluid it is (presumably water + antifreeze?) and how to top up the system? There must be some room for expansion when it gets hot? Thanks if you can! :)

LOL! if you think that where the charge cooler is located is bizzare then you'l love this: the charge cooler system uses the same header tank as the main cooling system LOL!

 

I suppose it just shows how effecient it is using water cooled charge coolers! - the coolant is pumped through a seperate radiator just for the charge cooler system once it comes out of the header tank - from memory I think there is a check valve in the system so it probably just closes at certain temps to isolate it from the main system.

 

Anyway - as you say, clamp off the hoses - you wont lose much coolant anyway doing this - to bleed the system we would usually use Mercedes STAR to run the pump - just power it up again to circulate the coolant around to get all of the air out.

 

job done :)

Yeah that's weird lol, you would think it would act like an interheater rather than an intercooler! Apparently it's all to do with heat exchange from air to water that I don't need to understand, luckily.

 

One last question then I'll leave you in peace (for now), do you know what the smaller pump does that's right next to the one I'm changing? Cheers :)

not 100% sure from memory without seeing it - if its deffo coolant lines again then its probably just the heater circulation pump

Ok thanks, I'll post back when the jobs done.

 

Btw, they make a truly amazing sound don't they, it's nearly 10 years old and the exhaust sytem is totally sound still :)

 

I was thinking about upgrading the power, not sure yet as it goes pretty well as it is, bucket loads of torque :)

yea - they pull endlessly dont they?! :)

 

we have a customer with a collections of mercs (including a CLK Black Edition) - he has a SL55 with the full Carllsson treatment - around 600bhp & it feels like it! Pretty much close to a SL65 Bi Turbo but more useable!

You were spot on Paul, I fitted the new pump yesterday and the car feels awesomely alive now, it was quick before but now it's ferocious - more responsive and sounds glorious like it's really happy lol, 200 quid well spent and I've learnt a fair bit about the car too :)

 

I'm wondering now if it's had any mods done because it just seems too quick to be standard, the traction control seems to struggle to keep it under control, flashes on quite alot, could do with launch control ideally. I wonder if Jeremy Clarkson had any mods done in the three years he had it, the second owner who I bought it from just used to bimble about in it and never used the power. Do you know any easy ways to identify mods? I think the crank pulley may have been changed. :)

Nice one! glad it is all sorted.

 

A pulley upgrade is a common way of getting more power - the kompressor drive is enlarged to give more boost.

 

Check to see if the 2 pulley drives are the same size - if the one for the kompressor belt is bigger then this will increase boost & power - look here for details:

 

http://www.fabspeed.com/Kleemann%20Pulley%20vs.%20Stock.pdf

Hi Paul, checked it out but everything is standard.

 

Had some bad news today - the car developed a misfire (had just exited a roundabout and accelerated up to 70) and it started running on 7. Took it to Mercedes WSM and after some checks today they said there's only 40 psi compression on cylinder 7 (I think) so they're going to start stripping it down on Monday. They want it for upto 3 weeks!

 

Any guesses as to what the problem will be? He said they used an endoscope and the piston looked ok, so I guess it will be a valve?

 

Just wondered if you've had any similar experiences with SL55's?

 

Also, the guy I bought it from used to poodle about under 3000 rpm, but I drive it upto around 5500 rpm and he reckons that's too high! Surely if that was the case Mercedes would stick a red line or rev limiter at 5000rpm? I can't imagine a car like that can't handle high revs, wondered what your opinion is? If it's true, when I get it back I'll have to think about selling it if it can't handle my driving style lol, I don't want something like this to happen again! Cheers...

Hi Bud,

 

compression problems are really rare on these engines. I cant think of one single instance that we have had!! Usually mechanically the AMG engines are pretty bullet proof so would be interested in what has caused low compression on yours

 

not sure of the exact figure but yes - there would be a rev limiter built in.

 

 

keep me posted & hope all goes well

 

Paul

Ok will do. The guesses from my mates so far are head gasket or valve seat, and a mate who's a mechanic has guessed at cam lobe worn.

Ok will do. The guesses from my mates so far are head gasket or valve seat, and a mate who's a mechanic has guessed at cam lobe worn.

 

If the bore is ok then a valve or seat is more likely TBH

 

A worn cam lobe would not cause lack of compression - the valves would just not open or close enough or not at all - they would be closed more than usual rather than remaining open to cause compression loss. I have seen worn valves on some engines (not these though!) - they can wear around the collet causing them to drop. Also valve & seat wear or guide wear causing the valve not to sit flat on the seat.

 

Head gasket failure that drastic would usually have other symptoms too!

 

A leakdown test would prove what the fault is before stripping down