LNF - Logging Boost pressure above 22 psi w/ 3 BR MAP's

[Iam Broke]

We've been fooling around in another thread, but I wanted to start a new one so it doesn't get lost.

You can create a custom user defined PID for logging the boost pressure above 255 kPa or approx. 22.4 psi.

After much calculation & trial and error, the LNF 3 BAP GMPP sensors can be logged for boost pressure above 22.3 psi.

You will not see manifold vacuum or pressure with this, but the lower CP pressure from the 3 bar TMAP seems pretty accurate, at least on mine.

Posted in another thread...

Logged it on the way home and did a pull, peaked at 25.4 and as it tapered down the boost at WOT, I saw 22.3 psi @ 254 kPa on the MAP. Looks pretty damn close on mine up top anyway. Still seeing .8 boost with the key on, not running. Pressure depends upon load and rpm while cruising, but that makes sense to me as the turbo spools there will be more pressure in the pipe before the throttle plate.


I'm going to look through the PID's for the 3 bar MAP voltage if it exists, then we will see mani pressure/vac. Edit: None found

To repeat... for the 3 Bar MAPs, the formula

([PID.2339]*9.369)-([PID.2340]/6.895)
(Boost sensor V * 9.369) - (BARO sensor / 6.895)

looks good but only reads positive boost pressure in the lower CP.

EDIT: I had to subtract 0.8 psi from the entire product of the above formula to get my readings to match at 22 psi, might be sensor differences.

If I'm way off base, someone please straighten me out. We couldn't have gotten this close without Gimpsters MAP Voltage tables. Thanks Andy!

Hopefully BYT will repost his 2.5 bar findings.

[shabby]

Still seeing .8 boost with the key on, not running. Pressure depends upon load and rpm while cruising, but that makes sense to me as the turbo spools there will be more pressure in the pipe before the throttle plate.

Im seeing around .5psi with the key on, though i subtracted pid.51.psi rather than [PID.2340]/6.895. Plus im getting the raw voltage from the map sensor on the intake manifold and not from the one on the ic pipe.
I'll do some logging tomorrow as its raining now and see how it differs from the regular map pid using your formula.

[Iam Broke]

Your sensor will also show mani vac in PSI. 1 PSI ~ 2"/hg. I don't have the pro HPT or I'd be using that one also. Sensor accuracy is crap at the low end, I suspect that's where the positive zero is coming from. No PID for MAP voltage in my version of the scanner.

The trouble with using the lower CP sensor is it only matches manifold pressure at WOT.

[shabby]

At idle it hovers around -9psi, i don't have a map voltage pid either, i meant comparing it to the map pid that's limited to 255kpa.

[Iam Broke]

-9 psi is very close to 18-19 " hg vacuum. It's 2.036 " Hg per PSI.

I think you got it!

I saw around that at idle on my old boost pid I had built that capped at 22.3 psi from the MAP sensor.

[shabby]

Alright here's that log, Boost2 is the map pid - baro, Boost3 is the gmpp 3bar voltage reading using your formula. Is yours as erratic too? Maybe i should add a ground to the eio. The regular boost pid was simply map - 14.5, not as accurate without a real baro reading.
Seems pretty much dead on.

[Iam Broke]

I'll have to look tonight. I don't think it was that erratic. I didn't do a pull this morning, maybe tonight.

[Iam Broke]

Boost spiked to 27.1 @ 4100 rpm, I guess I need to back the DAL's down a bit. Gauge wrapped to ~26 out of the corner of my eye. Seems pretty close.

[Iam Broke]

It read 22.1 psi at 249 kPa on the way down but it is a bit erratic on mine also. I think it lacks resolution.

[shabby]

Boost spiked to 27.1 @ 4100 rpm, I guess I need to back the DAL's down a bit.

Why, whats wrong with 27psi?
I added a ground to the eio just now, we'll see if it makes a difference tomorrow but i guess if its erratic for you too then i doubt it. But yours is a bit smoother off boost, maybe the ecm is smoothing it a bit.

[Iam Broke]

Didn't know I was boosting that high before, that explains the burst of KR I see when IATemps are up. Redid the DAL's to 270 kPa (24.x psi I hope) until the pressure starts to decay, then ramped them up a bit more to try and compensate. Need WG duty cycle control.

[T-Man]

I've tried inputting this formula and unfortunately, it will not work for me? Something I'm doing wrong maybe? Are we to stick to the PID only and not use any sensors?

[shabby]

Do you have the 2339 pid in your list? My older version of the scanner didn't, looks like you need a recent beta.

[Iam Broke]

I've tried inputting this formula and unfortunately, it will not work for me? Something I'm doing wrong maybe? Are we to stick to the PID only and not use any sensors?

Make sure you have the pid's 2339 & 2340 (Boost sensor V & BARO sensor) in your table list first or it will not work. They have to be in the table for the formula to work as a custom PID.

[T-Man]

Do you have the 2339 pid in your list? My older version of the scanner didn't, looks like you need a recent beta.

Yes sir, most recent up to date Beta.Yep have the PID in my list.

Make sure you have the pid's 2339 & 2340 (Boost sensor V & BARO sensor) in your table list first or it will not work. They have to be in the table for the formula to work as a custom PID.

I have both in the table as of now. Wish me luck

Thanks gents.

[T-Man]

Spiking to 25lbs in the mid range...

I love boost but damn does this scare me! Haha.. 91 octane piss water and stock GMPP timing, hand smoothed. Anyone see a problem with pushing this kind of boost in the mid range for long term durability? Boost tapers down to about 17-18 at red line, FYI.

[Iam Broke]

Drop your DAL's a bit in the midrange. I'm around 270 for 24 psi, spikes 25 for a split second than cuts back. Also tapers to 18 psi @6k.

The more you exceed 24psi, the greater the risk of ring land damage on long hard pulls.

[BackyardTurbo_FTW]

I ended up ditching this. The reading is so erratic that I just don't trust it.

[Iam Broke]

Mine looks pretty good, but I think I'll add the original back in to my charts also.

[T-Man]

Thanks for your help Tom.

I've found that this boost PID closely matches my gauge and in most cases as it starts to taper off is almost identical to my other boost PID (courtesy of Tom).