Thread: MPS slipping?

So I noticed a few weeks ago (or how ever long that was) that the 3.6" pulley I had on my car it seemed that the actual pulley snout stuck out about a 1/16". When I went to install the 3.8" I noticed that the pressed on mounting flange was flush with the snout shaft. I also noticed a little wobble in the 3.8".

Could it be the source of my lack of boost is due to the pressed on flange is slipping?

I am going to put some whiteness marks on the shaft and the pulley flange and see if it moves, but have any of you had an issue with a press on slipping?

When I first heard that GM superchargers used press on pulleys I thought that was ridiculous since it takes more than 60hp to run at full boost, I figured they would have keyed them like any other shaft that requires a lot of power to turn.

If it is slipping has anyone keyed one since if it's slipping then there is no reliable way to hold it to the shaft even if I bought new hub I doubt it would hold against the shaft, if this ends up being the case?

Jeff

Yup, it's slipping.

Who knows what happened. I put a mark on the pulley and SC shaft and checked at lunch and found that they are no longer aligned. I only got on it twice and car still doesn't go into boost. Also the hub is now flush with the shaft where before it stuck out about 1/16" and the center of the pulley went through and centered on the shaft. When I put a 3.8" on the hub and shaft were flush. after installing it I noticed that the pulley was not concentric and had about .020" from the high spot to the low spot. Now I don't think it's slipping continuously, but it is moving. Still not the cause of my ZERO boost condition and ruled out the PCM as the sole cause. I am so stumped. The only other time I have seen a no boost situation like this is the supercharger drive shaft stripped out the end of the drive to the coupling. The last Gen V I was in is from a Jag XKR supercharger and it still had an aluminum hub with the 3 drive pins and was splined as well. Hopefully that Gen V is still in the junkyard this weekend when I have a chance to go, but I am out of ideas and theories.

04' GTP computer didn't make much of a change. Car still will not go into boost, but it does go rich when I floor it instead of dead lean.

Jeff

Originally Posted by BillBoost37

Is the end of the mps flat to the end of the snout?

It is flush. I though it was not though. I think at this point I'm over reacting to any little thing. I thought I left the plug out. I ended up marking it not the plug and I'm sure it's just vibrating around. I thought the Intense pulleys fit better than this ZZP, but maybe the ID around the hub is a little tighter on the Intense ones.

Originally Posted by 99GT2dr

Have you tried spinning the SC pulley by hand to make sure the rotors are turning? Can you hear a slight whistle when you give it a spin by hand? Probably a stupid question, but I just don't see how it couldn't make boost if the SC is mechanically in good condition. Unless there's some '04+ dbw witchcraft going on, that I wouldn't know anything about.

I had the SC off last weekend and found one bolt loose and the gasket was kinda messed up. I posted that in another thread asking about wether I should or shouldn't reuse the gasket. I've inserted a wooden dowel in the inlet and tried to turn the pulley. I tried but didn't want to damage the coating on the rotors.

It turns with more resistance than a clean Gen 3 but I think between the abraidable coating and some carbon it felt normal. Last night I logged throttle position and had 99% displayed and the bypass shut (another one from a gen 3). I removed the plug from the manifold and plugged it, unplugged the connection at the valve, and tied the inlet side back on itself with wire ties and still nothing. I'm going to check the SC fluid a little later and see how it looks. That's one thing I haven't looked at and have time to check.

Thanks,

Jeff

I am not real sure. I had it go into limp mode once a few weeks ago after a full throttle run, and it's always after you let off the gas, and I had the valve disconnected electrically and pneumatically. I have also had it go into limp when everything was connected and I wasn't even WOT, but accelerating more aggressively. It always gives a code with P0068 and Lean bank 1. Since I installed the 04' PCM it hasn't gone into limp home mode and it goes dead rich. now when I floor it. It did give me a pending fault code about turbo/supercharger waste gate error, or something to that affect. I have the Tapp set to warn of pending fault codes.

I have changed both the valve and actuator, but they were both from a Gen 3 blower I have. I have come to the conclusion that the pulley is not actually slipping on the shaft, and that the plastic insert is vibrating around. It's a panel fastener, we called them Christmas trees, when I did audio and alarms.

The supercharger was low so I removed the belt. I'll see if I can get some from my storage before they close.

Thanks,

Jeff