Josh_C7Z

I've been experiencing some strange behavior recently, and trying to figure out the best way to diagnose what's happening. Basically, at part throttle I'm sometimes noticing a cyclic surge/drop of boost (as reported by the analog boost gage) and a corresponding sluggishness in acceleration compared to what I'd expect.

Background: 2016 M7 Z06/Z07 that I've owned since new. No major modifications - a CAGS skip-shift eliminator went in years ago, and I did the GM MagRide upgrade a few years back. Installed a Soler PTB well over a year ago, and a Soler TC installed about 14 months ago, been happy with those and don't suspect they're the cause - I've noticed the behavior independent of the mode I've had the TC in - e.g. either SP.3 or "passthrough" (OE) - and looking at PDR video I don't see the throttle overlay oscillating when I experience the boost surge/drop. Also, despite being in California where 91 is the norm for "premium", I'm running 94 octane fuel from Sunol Super Stop so I don't suspect that either - not that I'd expect the car to struggle with 91 in my conditions here, but thought I'd mention it to rule out low octane as a potential cause.

Observations: Some of the time, when I'm trying to accelerate moderately, rather than the normal acceleration, I see the boost gage bounce between boost and vacuum, with the corresponding lack of "go". I don't see any other signs in the dash - e.g. no limp mode, nor am I activating traction control. Coolant temps are normal, ambient air temp is 80-90 degrees and I'm just loafing on the highway at 75-85mph, pressing the throttle moderately in 6th (M7) expecting a moderate increase in speed, but instead feeling a hesitation and watching the boost gage bounce up and down. I've noticed this in either Tour or Sport mode - I never use Eco mode and have no reason to think the car's becoming a V4.

And yes, I could obviously downshift and/or give it more throttle if I really need to get going, but I'm really just trying to diagnose why it isn't behaving as expected here since I'd appreciate predictability in throttle response - I've also noticed the behavior at lower speeds, and working around the issue with a heavier foot will likely end up with me emulating a Cars-N-Coffee Mustang driver one day

Looking under the hood, I have a sneaking / unfounded suspicion that I need to bleed the air out of the supercharger coolant (pictures attached) but rather than jump to conclusions I thought I'd ask if others have experiences similar behavior and/or have recommendations on how I should figure it out. Or should I just do the obvious thing of bleeding the air out of the SC coolant system and seeing if the problem goes away? Any thoughts/suggestions appreciated, thanks in advance!

CR49341

I can't say if it's the cause of your surging issue but you definitely need to bleed your supercharger coolant, that is a very large air pocket. I bought a Cooler Bleeder and it worked extremely well. Coolerbleeder.com

AltrdPrcptn

I wanted to bring this thread back ttt. I’m having an identical issue as op and don’t know where to start with diagnosis.

I haven’t found any other threads with a similar problem and ultimately a resolution.

Midnight_rider

Boost leak/spike is normally attributed to a leak in a pipe/connector somewhere. Coolant temp being normal means you have a boost leak somewhere - I'd check with the pipes first. intake, all of the pipes connected to the coolers (may have a hole in one of the intercoolers).

Internets_Ninja

Check the bypass solenoid vacuum lines. Are they all connected, connected properly and not cracked or broken. Also, a datalong would help pinpoint what is happening. Could be the throttle body failing and making it act like it losing boost when the throttle blade is actually closing and the ECU is trying to compensate with abrupt timing changes.

AltrdPrcptn

The bypass solenoid seems to be working properly and have all lines connected without cracks.

Coolant temps were reading about 205-210 when the problem began. I am noticing slightly too much air in the intercooler coolant tank. Not sure if it’s possibly causing the manifold temps to be higher and pulling boost?


My only other thought is that I used 91 fuel this time. I would be surprised if 2/3 through the tank it started causing a problem, but it’s the only other idea I have.

Sammons

The issues you are describing sound like a carbon copy of what I was experiencing in my manual Z06. I tried several different methods to remove the air from the super charger coolant system to no avail. I finally purchased a cooler bleeder and the problems are no longer present. If you were in the Houston area I'd say come by and let's pull the air out and see if that cures your problems. If you can find a local with a cooler bleeder that would be my first step.

Internets_Ninja

Is your intercooler pump working? That typically isn't a large enough air pocket to cause the Manifold Temp to exceed 200F. But if you have a large air bubble hitting the coolant pump, it will shut off until the next key cycle. Step 1 would be to bleed your supercharger coolant circuit. You can bypass the fuse and manually enable the coolant pump even with the key off by injecting 12 volts to the pump side of the fuse circuit. This would verify the pump itself is working.

Bill Dearborn

When I was having my intercooler problem 6+ years ago the dealer mechanic was able to reduce the size of the air bubble to this:

After the air bubble in my 15Z was reduced to this size my WOT intermittent high rpm misfire and power loss issues disappeared.

Bill

CraigZ06

Mr. Sammons,
I sent you a PM about the cooler bleeder. I am local in Houston and actually read your prior posts about your purchase and use of the product. If time allows, check my PM please.

Thanks in advance

Sammons

Check PM Craig