Thread: Boost Pressure Fluctuation

And what ? What will be the idea of running withaout MAP , when his idea is to make a translation table for MAP to MAF(employing speed-density to a mass air flow ECU).Why would you suggest to get rid of the MAP in this case? MAF readings won't be affected when he disconnects the MAP and he won't accomplished his goal.

He is running it with MAF and MAP at the same time. The strange thing is MAF readings show no clue why the MAP is fluctuating - e.g air flow is good and there shouldn't be any fluctuations in the MAP reading.

Offtopic: dfddfd2 , are you going to make changes in the ECU's firmware or you will just modify the VQ somehow to work with MAP readings ? Assuming that you have a IAT may be you are tweaking the firmware for IAT compensation , right?

Yes, street (well, actually I40) pull, no fluctuation in acceleration, pulls strong.



Yes, firmware will definitely change. I'm planning to start out using a 3D map, indexed by MAP kPa and RPM, that contains Q values, then modify that with IAT compensation. This way, all of the other maps and tables will work just like they do now with the MAF. I may ultimately rewrite the whole fuel and timing control to work more like a stand-alone (John with JKTuning wants this).

I did some testing this morning and I believe it's a sensor problem. I pressurized the system to 8psi and the MAP reading gitters randomly as much as 10kPa. Does that sound normal? Manipulating the wiring and tapping on the sensor has no effect. I suspect it's actually a 1bar rather than a 3bar as the barometric pressure is 30.09 inHg = 101.885kPa and the sensor is reading only 88kPa. I'm going to get another sensor and try that.

Thanks,
Dave

Absolutely not normal.

Best idea. Test it with the 8 psi before you even try to work with it.

x2.

OEM GM 3bar MAP sensors are so cheap, I don't know why anyone would want to run an eBay MAP sensor.

Fixed! the problem was not with the MAP sensor but with the way the BOV was plumbed. It was connected to a port before the throttle butterfly and tee'd to the waste gate. I reconnected the BOV to a port after the butterfly, connected the waste gate to the port before the butterfly, and it works fine.

Cheers,
Dave

Where was the MAP sensor in relation to all this?

There are 3 ports:
1. PO - pressure only, on throttle body, before butterfly
2. V1 - vacuum/pressure, on manifold, after butterfly
3. V2 - vacuum/pressure, on manifold, after butterfly

Here's how it was:

PO -> Tee -> BOV & WG
V1 -> Tee -> Boost Gauge & FPR
V2 -> MAP

Now:

PO -> WG
V1 -> Tee -> Boost Gauge & BOV
V2 -> Tee -> MAP & FPR

It works fine now, but let me know if you think there is another configuration which will work better.

Dave

That looks good. Any advice would be nit picking. I like that you have the BOV on pressure/vacuum now. That's really how it should be. Also you're right to have that WG on pressure only.

I'm just baffled that the original setup caused the problems you saw. Never would have expected that. Your dedicated MAP signal should have been perfect.

FYI I have mine like this:

PO -> *nonexistent*
V1 -> Tee -> MAP & Tee -> BOV & WG
V2 -> FPR

Not the best setup either for a few reasons, but it works and I'm not about to change it. MAP signal is perfectly acceptable.

I know this thread is old, but I've been meaning to update it with another reason for the pressure fluctuations. The stock code turns off MAF filtering above 6000rpm. This is fixed in TunerCode V5.

Dave

exactly what i was gonna say. BOV for sure or some other kind of boost leak. its the only thing that would show a change in the map sensor reading and not everything else. If it was a wastegate or exhaust leak between either the head and manifold or manifold and turbo you would also see fluctation in that as well.

Especially if it was using a crappy aftermarket bov it would definitely cause that fluctuation. Seen it more than once.

Lol, I didnt even notice how old this thread was.

This is exciting stuff for sure.