Hello! My 2005 MCS has a slight power surge to it under part throttle accel in the mid range. It's done this forever. It may have started when I installed the 15% pulley, but that's been probably 5 years and 80k miles, I've just lived with it as it's quite minor and didn't bother my wife (it's her daily driver). All other parameters are normal - no codes, smooth idle, smooth full throttle power, normal MPG. In that time I've replaced the crank pulley, the belt a couple times, belt tensioner, plugs, had the SC off to change its oil, etc; a lot of maintenance water under the bridge, so to speak. No change to this phenomenon. I tested for vacuum leaks, nuthin'.

I recently tried the VGS mod, which made this symptom slightly more pronounced. (The VGS also increased low rpm power off the line, which is nice when taking off, less clutch slipping required.) Got me thinking about the BPV, which I didn't really know anything about before. I see the DT one and understand the concept. Is it possible my BPV is fluttering for some reason and causing this power surge?

What should I check?

Thanks! Jeremy

 

Bump

 

You could also check your throttle pedal (remember these cars are drive by wire) you can use a ohm meter to check the throttle response, the Throttle pedal is basically a large variable regulator (Potentiometer) should have a smooth transition through the scale as the pedal moves through full range of motion.

Best of luck

Motor On!

 

My 03' JCW sometimes will do the same thing. I can be cruising down the road around 40mph in 4th or 5th gear.....and the motor will just feel like it's starting to surge. The vacuum on my gauge will not move much (so the throttle is not moving).....but my AFR gauge starts bouncing all over the place (fuel mixture is changing). I don't get any check engine lights either, and everything else seems to work great. It's done it for a few years.....maybe after I installed my 17% pulley...but it's been so long I can't really remember.

One thing I have thought about doing is changing out my O2 sensor(s). It could be giving a bad signal to the ECU, causing the fuel mixture to jump around.

IT might do it once or twice a week.....and if I blip the throttle a little, or get on the gas....it goes away. If I don't do anything, it will keep doing it for around 5 seconds, and then goes away. Very odd.

Do you have a boost/vac gauge on your car? Do you have an AFR gauge on your car? Have you tried a new O2 sensor?

 

Thx guys. I do not have these gages on my car. I do have a BT scanner that I use with the Torque app on my phone. Not sure if it has an AFR display. It definitely has an O2 display, and a fuel trim display. I'll have to check.

I did replace the primary O2 sensor somewhere in that time, fixed a code problem but no change to this behavior.

Mine is not really an intermittent behavior like you describe, but pretty much any time I'm accelerating gently to moderately at part throttle in the mid range. I can't remember if it happens under heavy throttle.

 

My 05 does the same thing at part throttle in 3rd gear. It will even show on my boost gauge and you can see it fluctuate within a pound of boost. It drives me nuts and would love to know what’s causing this.

 

Had the same problem on my MC40 and found an air leak around one of the supercharger boots. Might want to remove the intercooler and check those.

 

Resurrecting this old thread just to say that I solved a very similar problem to this after much searching and head scratching.

It turned out that a small vacuum pipe that connects from the supercharger horn on the hot side of the intercooler to the fuel pressure regulator had fallen off. The space underneath the horn is very tight, I had to use some long nose pliers to grab the pipe and push it back on to the nipple on the horn. As far as I can make out this was causing the engine to run rich under the RPM that the supercharger bypass valve kicks in.

 

My issue turned out to be a flaw in my Detroit Tuned bypass valve. Sent it back in and he found the issue made an adjustment and sent it back. Reinstalled and drove. Problem gone.

 

I also had that hose come off, threw a code when on it hard & under boost. It was sitting there out in no-mans land and took a bit to find its home, used long needle nose to get it back in place.

 

Strangley i had no codes come up. Just the surging / bouncing thing up until the SC kicked in. Also if traction control kicked in it would just completely kill all acceleration.

 

I think a zip tie on it is needed... also, I have a bad BPV and have an external spring on it to "help" it along, seeing 13 psi of boost like it is, not quite where it should be but way better than it was w/o it. Seem like its closing at about 2~3" of vacuum... Sure has brought back some nice power... that I didn't know was missing when I bought it.

 

A zip tie was my fix. It was not easy to get on. Even took the intercooler off which was precisely zero help.

 

This. I am the OP, and our car still does this. I had the system apart recently. Checked out the BPV, seems fine. I did that thing where I made sure the butterfly plate was centered and closing all the way. But no change. I've never had a code because of it, and never had the vacuum hose come off. Weird. Still looking for ideas.

Also, is it normal for the TC to completely kill the power for a whole second or so? That's really annoying if I'm trying to get across lanes of traffic and I happen to scratch the tires a little, and the next thing I know, I have NUTHIN for a whole second!

 

It sounds like you are having the exact problem I was having. The TC stall was particularly dangerous.
the attached pictue shows the nipple the fuel pressure regulator line attaches to. It is on the inside of the curve of the left hand supercharger > intercooler horn and is a pain to get to. The actual fuel pressure regulator is located underneath the intercooler. Its possibly the line could have come off of this end instead I guess.

The line itself does not look like regular vacuum line. It looks more like the black plastic shroud around bicycle brake cables and has a small rubber boot over the end that fits over the nipple.

 

This video will show the location better than that photo.

 

Yeah that nipple is not the easiest to find, definitely zip tying mine when I can get the opportunity. Also going to do the VGS(?) setup to the BPV and set it up so I can easily reverse the vacuum source back to the BPV source... have to see what that is all about.