I have a 2003 Bonneville SSEI with 85K, here'* the story. It just started having issues at high rpm, I will try to describe them as best as I can. At low speeds (20-30), if I give it WOT, it studders. It does not really feel as though it is bogging down, but like something is slipping, which led me to believe the supercharger belt may be slipping. Although at this speed range, I do notice that it looks like I am getting full boost on my scan gauge. At high speeds (70-80) it is more noticeable, at WOT it accelerates much slower and again feels as though it is studdering, although more so than at lower speeds. At this speed range it is does not appear as though I am pushing any boost at all, or not more than 1. This just started happening after I cleaned the engine, sprayed on some degreaser and then washed it off with a garden hose. I had the alternator and coil packs covered, and tried not to hose down anything with wires. I also sprayed it out with an air compressor and let it air dry for a couple hours in the sun before driving it. I have not noticed any other problems, gas mileage is unchanged, still accelerates well other than WOT. The only mods I have done recently were new msd coil packs a couple weeks ago, and just a few days ago a fender well intake. I ran the car and everything checked out after both of those though, this just started after I washed the engine out. I already ordered a new supercharger belt, hopefully that will fix the problem when it arrives, I was just unsure that'* what the problem is because there is no squealing or any other sign to tell me that the belt is slipping and I am looking for a little reassurance. What do you guys think?

When was the last time the plugs and wires were done? Your mention of this happening after it being cleaned makes me think that the wires failing, and it'* not right to change them w/o doing plugs.

Thanks for the quick response!

Wires and plugs were both changed when I bought the car about a year and a half ago. It had 2 bad gaskets and was leaking oil and coolant. Had the dealership fix the one gasket, which then stopped the oil leak. I replaced the plugs and wires after that, and later found it was still leaking coolant. That called for the other gasket being replaced, and I cleaned the front three plugs off with a wire brush since the coolant was running down in that area. It'* got premium bosch plugs and oem replacement acdelco iridium plugs. I'll inspect the wires tonight but I can't imagine anything happened to them during the cleaning unless I got some water in them?

Sounds like a grounding problem. Check out the wires. Run the engine at night in the dark, mist water on the wires and coils and watch for blue flashes. I would pull the plugs and inspect them. I would also change them to autolite copper plugs.

I had an hour and a half to mess around on the highway on my way back from chicago, and noticed this: at WOT I am pushing full boost, 11-12 according to my scan gauge (perhaps not completely accurate), but that throws out my theory of belt slippage. I also noticed that cylinders 3 and 4 were both misfiring at WOT. So when I got home I closed up the garage, popped the hood and misted with some water, didn't see any blue flashes but I'm not convinced it was dark enough so I'll try again when it'* pitch black out. Also inspected and cleaned the front three plugs, noticed a slight orange "dust" or tint, perhaps rust? Cleaned all 3 off with a wire brush and went out for a spin. Now I notice that only cylinder 4 is misfiring. Could be a fluke, but I'm going to try cleaning that plug and see if it makes a difference.

Dan: I had some autolite 604'* in here about a month ago, put them in right before going down to the track and actually thought they were worse than the iridium plugs. Seemed to be 1mpg worse on gas mileage compared to usual at the same speeds, didn't notice a decrease in KR, and actually ran .8 seconds slower in the 1/4 mile than with the iridium plugs last time. This could all be due to temp, different roads, I'm crazy etc. but that'* why I put the iridium plugs back in. I also figured there was a reason they cost 10.94 compared to 80 or whatever the iridium plugs were. I'm willing to give it another go, but with a 3.5" pulley, which plugs would you recommend? I'm going to place an order from zzp, so if you could reference a set from them that would be great! While I'm at it I'll order a set of zzp wires.

Test your coils, what your describing sounds like weak spark. As for plugs, I suggest 1 heat range cooler.

You hit the nail on the head. Brand new MSD coils went bad in two weeks.. Thanks for the suggestions, it was very depressing not being able to pass people on the highway.

Good to hear. Easy fixes are the best.