GrepAwk

I took off the supercharger belt and serpentine belt to trying to diagnose a vibration at various frequencies. For any of you at home yelling "don't do it you're crazy!" you are correct but it is OK for 15 seconds to try to diagnose something.

One interesting observation I made when doing this is the supercharger rotates even though there is no belt attached . I am curious if any of you know whether there is enough air flowing naturally aspirated that is still turning the vanes of the supercharger or is there supposed to be a complete bypass of the supercharger when the clutch is not engaged ?

I gave all the pulleys a nice spin and they seem ok for now.

Another question, does a standard OBD -II scanner pick up on engine misfires? The shudder is at only certain RPMs. I see some oil leakage at the valve cover and assume a wee bit might be getting to the coil pack. If one of the plugs in a cylinder doesn't fire, I suspect that could cause some imbalance. Comments?

PillDrive

I actually drove mine without a belt for 2 days before i was able to get one....its NOT an issue as long as you baby the car....spool the engine and the computer will throw an error and reign in the engine....easily reset with a das system though. I drove for 2 days with very little acceleration and it worked fine....when i had the new belt i pushed the engine before i put it on and the computer jumped right in to protect the engine. Reset it ... put the new belt on and its been fine for 50K+

GrepAwk

Just to be clear for those who read your comment, you were referring only the Supercharger belt being removed. That's Ok to drive around without it. But you must NEVER drive around without the serpentine belt (polybelt) because you would have no coolant circulation/alternator power/power steering/ABC/ AC, etc. you motor and battery would be toast in a matter of minutes.

So does anybody have an observation as to whether the supercharge spins during idle when the SC belt is off?

And what about the question if engine misfires would show up on a standard OBD-II scanner? I don't have star DAS.

PillDrive

Ah yes...sorry...should have made that clear in my post....of course you cannot drive around without the main belt.

As to the supercharger spinning....there is no bypass so the tighter the blades the more it will spin as the air gets sucked through the blades which actually shows you if your blades are still slealing good against each other.\

As for the misfire.....i am not sure if a normal obd reader will be able to detect it but i can tell you that the best thing i have done since owning a benz is to get the das system...so if you are going to be working on your car i suggest you get a system of your own or find someone in your area that has one.....good luck

GrepAwk

Thanks. I assumed that might be pull-through air making it turn. You can stop the SC from spinning with your hand when it's idling. Good to know there's a nice tight gap.

I have been reading for 10 years about getting a Star Diag system. So many red herrings out there for systems based on old DELL laptops with WinXP. But in that time, Windows XP disappeared and I don't fancy going back to an old laptop or trying to use some Chinese clone. So I have been winging it.

If anybody had a recommendation for a bullet-proof, reliable Star DAS solution, I will look into it. I do think it would be helpful. I have a phenomenal one for my Audi.

Flydutch

Yes it spins, The engine will naturally suck in air (Normally aspirated engine) that air will have to go passed the compressor vanes (Progressive Worm wheels in a Lysholm supercharger Mercedes uses on the 5.5 V8) so it will drive the compressor instead of the compressor driving the air. There is a clutch which engage's the gear that drives the worm wheels. When disengaged the belt drives the pulley but not the compressor. You "Put foot" the air metering flap opens, the airflow increases, the clutch on the compressor engages and the belt start driving compressed air into the engine. The advantage of the supercharges is the immediate response versus the "Famous" Turbo lag. I am not aware of a bypass valve on a Mercedes but other cars have a constant drive supercharger but the flow regulation is done with that valve.

wfooshee

My car was like that when I bought it, unbeknownst to me. I'd nail it, and I'd get a series of errors on the dash about EBC failure and belt pretensioner failure, and the transmission would not downshift automatically until I stopped. Shutting down and restarting was all I needed to do to reset the condition.

It turned out my supercharger pulley was sheared, which I discovered when my serpentine belt failed, I had to remove the supercharger belt to put on a new serpentine, and found the pulley like this:


The pulley was spinning on the bearing but wasn't actually connected to the supercharger. Sourced one on eBay and it's been fine ever since.

Anyway, I'd been driving for weeks, even months, with no supercharger, although I with all the error codes it showed, I thought something major electronically was going on. After the "new" pulley, there are no errors, no codes, LOTS of *whoosh*!

JohnLane

The Mercedes 5.5 liter has a bypass. It looks and operates same as a throttle body to allow air that would otherwise be pressurizing the intake to blow off back to the compressor inlet when it is clutched on (if failing memory serves) anytime the engine is over 2000rpms but power is not asked for via the driver's foot. The driver asks for it to GO! and it slams shut for instant power.

wfooshee

It actually allows air otherwise going to the compressor inlet to go to the chamber behind the compressor outlet and on the to cylinder head intake, thus never flowing through the compressor at all, unboosted. This bypass serves as boost control, since the compressor is always clutched on once a certain RPM is reached (about 1500, I think,) with intake air flowing from the compressor inlet to the compressor outlet without passing through the compressor.

The blowoff function you describe applies to throttle closing, cutting off intake air flow. The inlet pressure drops sharply to near vacuum, and the outlet pressure could backflow into the compressor before being consumed by the engine. The bypass opens to vent that pressure into the inlet.

So the valve can flow air both directions, depending on circumstances.

maw1124

So does all of this (the last 2 posts from @wfooshee and @JohnLane ) mean that clutchless supercharger pulleys are “better” because they allow boost pressure below 1500rpm or whatever the clutch point happens to be? I’d have to think that low RPM boost would have to be absorbed by the transmission, which being common with the 65 cars (and G55, etc) I’d think can handle it. Thoughts?

@8899

Cheers,

maw

wfooshee

Clutchless pulleys remove the annoying chirp so many get when the clutch engages, and a lot of the clutches actually slip, as well, if they aren't shimmed properly. Mostly the pulleys are replaced to change the size of the pulley, and thus the rotational speed of the supercharger.

maw1124

Understood. Thanks. I’m asking a different question: is a byproduct of clutchless pulleys that the supercharger gives boost at below 1500rpm, i.e., full time?

maw

wfooshee

I don't know if it makes any boost at that low speed. Won't be any boost anyway until the electronics close the bypass valve when the throttle opens, at which point the revs build rather quickly.