[Nessal]

I was wondering if anyone ever ran into this issue or know what might be the problem. So my problem is that in any gear, at any speed, at any RPM, if I go WOT the car would stumble immediately and the AFR would run pig rich at less than 10:1. Then about two seconds later, the power would come on and the AFR would start to climb back up to about 12:1 and feel like it should. This happens every time without fail. Now if I slowly bring the RPM up without going WOT and into boost then the car would not hesitate. So that leads me to believe that it is something to do with the supercharger and not a wiped cam or some other problem.

I thought I might be the belt slipping so I decided to swap in a new Gates belt since my old one was on the fritz anyways. That did not fix the problem. I thought it might have been the air filter so I swapped it for a new one and the problem is still there. I thought it might have been the tune so I reflashed it and it is still there. There are no CEL or any codes.

I was thinking that it might be the bypass valve but I figured that if it really was the BPV then wouldn't it affect boost the entire time? But the problem seems to correct itself if I stay on the throttle at WOT. I was thinking of disconnecting the bypass valve and running with it shut just to test it out. If the hesitation goes away, then I can nail it down to the BPV. Good idea?

What say you?

 

[shay2nak]

did you look for any oil around the pulley system? One of my buddies had an annoying squealing from the belt/pulley and it was found that oil was getting on it.

 

[Nessal]

did you look for any oil around the pulley system? One of my buddies had an annoying squealing from the belt/pulley and it was found that oil was getting on it.

It's not the belt because I changed that today and the problem is still there. Also it's dry and I don't see any oil leaks when I was under there today.

 

[Formulabob]

I was wondering if anyone ever ran into this issue or know what might be the problem. So my problem is that in any gear, at any speed, at any RPM, if I go WOT the car would stumble immediately and the AFR would run pig rich at less than 10:1. Then about two seconds later, the power would come on and the AFR would start to climb back up to about 12:1 and feel like it should. This happens every time without fail. Now if I slowly bring the RPM up without going WOT and into boost then the car would not hesitate. So that leads me to believe that it is something to do with the supercharger and not a wiped cam or some other problem.

There are no CEL or any codes.

I was thinking that it might be the bypass valve but I figured that if it really was the BPV then wouldn't it affect boost the entire time? But the problem seems to correct itself if I stay on the throttle at WOT. I was thinking of disconnecting the bypass valve and running with it shut just to test it out. If the hesitation goes away, then I can nail it down to the BPV. Good idea?

What say you?

I say help this man, especially because my car is exhibiting a similar problem. It will be three weeks before I can start the investigate/resolve process on the car and hopefully a solution surfaces before then.

One possibility might be one or more faulty (leaky) fuel injectors that are still supplying fuel even when they shouldn't -- e.g., decel. I say this because the problem is most noticeable on the track for me when getting back on the throttle at corner exit. There also usually is a pop like traction control cutting the ignition although the TC light does not illuminate that I can see. :shrug:

Edit: old CharlieX tune on my car -- eagerly awaiting Fastworks for black dash.

 

[Nessal]

I just want to let you guys know that this issue is now resolved. Here is what happened. My initial suspicion of the bypass valve actuator appears to be correct. There is a nipple on the actuator that has a tube that runs to the intake manifold. Under partial throttle, there is vacuum in this hose which will cause the actuator to retract and hold the butterfly valve open inside of the supercharger. This will cause the air to bypass the rotors in the supercharger thus not creating boost. This is normal. When you go WOT, there is a loss of vacuum in this line which causes the arm on the actuator to release. This in turn closes the butterfly valve in the supercharger. When this happens, the air is then routed through the rotors thus creating boost. As a test, I unplugged the vacuum hose from the intake manifold and capped it off at the manifold. This should theoretically keep the butterfly valve in the SC closed at all time. Then I took the car around the block. The problem was completely gone. So that leads me to believe that the WOT tip in hesitation has to do with the actuator's reaction time.

What happened in my case was that the actuator was not closing the valve fast enough under WOT conditions. On WOT tip in, the car sees 100% throttle input. It will in turn spray more gas with the assumption that boost will be created. However, since the butterfly valve in the supercharger is still opened when it should be closed, no boost was created. This resulted in more gas than air being pumped in which caused my hesitation and rich condition on WOT tip in.

I initially put a vacuum on the actuator to see if it was faulty. Initial testing verified it when it would not hold a vacuum. So then comes the fun part taking off the clam and taking the entire SC off. On initial disassembly, I discovered that the actuator has a brass restrictor valve attached to the nipple. I took the brass restrictor off and looked through the tiny pin hole opening. No light was coming through so that lead me to believe that it is clogged. I tested the actuator without the nipple and voila, it is working perfectly. I took a sewing needle and pushed it through the brass restrictor orifice. What I found clogging it appears to be VERY thick gunk and oil residue. This oil was from the crank case being sucked into the intake as part of the PCV system.

At this point, I cleaned out the restrictor but came to a fork in the road. Do I reinsert it back into the actuator or run without it? I may have to redo this whole thing in the future if I reuse it because the restrictor orifice is about the size of the head of a needle. Super easy to clog up again. I believe that the restrictor is just to slow down the movement of air going into the actuator so on/off boost transitions are smoother but sacrificed reaction time. I decide to run without it and reassembled everything. I test drove the car and the problem is now entirely gone. Boost comes on fast and hard....no lag at all.

There you have it.

 

[fzust]

Nessal, Great post! We'll pass that along as it comes up. I would say this is a good reason to get our catch can and avoid the PCV nonsense altogether, but we realize for purposes of baby seals and puppies we should not do that.

 

[Nessal]

Fred thanks for your help every step of the way!