Supercharger boost spike?
 

I went on a marathon tune session yesterday and while going through my log I noticed that my charger spiked during a red-line pull to over 11psi between 6krpm and just over 7krpm!

It wasn't just a spike as such, it climbed to 11psi much like a turbo would build boost and held.

Here is an image:
Attachment 192651
As you can see, my usual boost level of ~7psi is constant right up until 6krpm where you can see the boost build to just over 11psi. It happens on another pull to 6.5krpm but the boost has built to 9psi at this stage before I backed off.

What could be causing this occurrence? Luckily I have an extra row in my fuel table accommodating 170kpa and my AFRs dipped to a nice and rich 11.2:1 and spark retards further to 18* when I hit 11psi. Injector PW values hit a massive 94% too on 425cc units Usually for 7psi it's around 80%.

When it built to 11psi, the car didn't feel any faster through 6krpm than it would at 7psi.

I've posted in thr MS section instead of 'charger chat' as I've a feeling it could be a setting in MS - possibly relating to VICs?

Any ideas?

Weird. VICS open at 5200rpm, so it shouldn't be related. What gear was that in?

That was third. As I said though, it seems to occur through the log on a few occasions - always starting at 6krpm. It is weird.

Do you have a boost gauge to confirm?

Yes but it's always been a few psi off so not to be trusted really. It shows 5psi when it's actually ~7ish.

Well every gauge is usually off a bit, but does it also show an increase in the upper RPM band? Like, does it go from 5psi to to 8-9psi after 6k RPM?

That's weird!

Could it be the calibration of the internal MAP sensor has become corrupted? might be worth a re-cal the the effort it takes.

Other than that I'd be leaning towards a faulty MAP sensor, your pulley ratio isn't big enough to actually create 11psi!

Well why would a faulty MAP sensor only spike after 6k rpm?

I dunno, why does anything faulty do anything? :P

I really don't think Craig's car is making 11psi, as I said the pulley ratio isn't big enough, if his boost gauge correlates this then it either needs recalibrating or is faulty.

It's also quite a sharp spike, chargers don't do that naturally, it's more of a gradual rise after peak torque.

What else could it be?

This isn't a dig at your build, electrical faults happen, no big deal.

I'm not trying to defend my unit or anything, as a faulty MAP sensor wouldn't be my fault anyway (although I would cover it under warranty if it really is faulty). Just really curious.

Some good tips there guys. I'll do another pull and watch the boost gauge and report back.

What is involved in re-calibration? Is it software or hardware based?

Tools>Sensor Calibration

;)

You'll need to set it to something else first, ie "GM 3bar", hit Burn, then set it back to MPX4250 and hit Burn again. I would also reset the ECU.

I know that! :fawk:
I just didn't know if the procedure for a reset was in a particular sequence :)

Cheers Dimitris.

I'll do a pull, check my gauge. If it's not apparent on the gauge, I'll reset the sensor and check again. As Rich mentioned, my car isn't capable of 11psi so it does point towards the sensor.

have an air compressor you can regulate? I dont see why RPMs would make the sensor sudden shoot up.

I have a spare sensor I can send out if you wanna try swapping, unless Dimitris has one, it would have to wait for my next shipment out to him.

I have several in stock if need be.

Guys that's great, thanks for your generosity.

I'll try and determine if I can replicate the issue and then fix it. If I can't, I'll be in touch.

My Dad owns a compressor for spraying cars but I'll need to check if it can be regulated.

Thanks again,
Craig

I have a sensor - sat in a spare MS1 - if required :)

Thanks Rich, I might take you up on that offer after I've had a quick play with it mate - maybe we could do some spark tuning too? ;)

Okay. I did some more tests on the way to work this morning and it's still spiking. My boost gauge also mirrors similar spikes so it seems like the boost is real! The log shows I git 12.7psi of boost.

I glanced over to my gauge which is plumbed into a separate port on the intake manifold and I saw ~9psi.

WTF!? I'm thinking my engine doesn't like boost after 6krpm or doesn't flow very well after 6krpm hence the build up. What could be causing this?

(mods feel free to bang this in the engine forum)