suganuma

im seeing at idle -18 inHg or so of vacuum while the PFC says -500 mmHg.
under boost the guage says 6.5 while PFC says .25 (3.55psi)
and at 9.5# the pfc registers .45kg/cm^2 (6.5#)

what number is everyone else seeing??

the boost gauge is reading from the nipple on the intake manifold.

thanks

spyfish007

I am starting to suspect your MAP sensor . . . did you do the run where you gauge showed 6.5 lbs with the Profec off? If so I think your MAP might be the problem.

suganuma

yes, profec was off
AND when hooking up the profec to the map sensor i had to enlarge the hole through the firewall on the driver's side. while i was doing that my flashlight went out and i tried working by light of the streetlight and accidentally crushed the plastic tubing for the boost gauge. so i ripped all that tubing out and got the idea to try hooking up the boost gauge to where the MAP sensor gets its readings from and got the same 6.5#s on the gauge. i also tried doing the opposite in hooking up the map sensor to the manifold and the boost gauge to the throttle body and still got the same measurements as i posted above.
im ordering a new boost gauge (dont know if im going to stick with the autometer or not - might go with omori)
as well as trying to source a new map sensor.

if anyone has one for sale.....let me know

spyfish007

Sorry to hear about the difficulties. I am probably going to get an Omori too. I think it is a good quality gauge .... but that is only hear say. If your MAP sensor is in fact messed up, then be careful driving. You don't want to blow up that engine.

suganuma

im only allowed to drive on weekends and i only drove it friday night and then for a little on saturday just in between shops getting parts. i will be replacing the boost gauge and MAP sensor before i drive again and hopefully the O2 sensor as well.

suganuma

well i talked to chris at RP and he said that he would trust the PFC over the autometer boost gauge b/c the MAP sensors hardly EVER go bad. sometimes they will burn out from an electical fire or something but he said they dont usually just outright quit or malfunction. he also said to check the grounds for the connections for it.
havent had a chance to do that yet though since my multimeter decided to give out on me a few weeks ago.
i had him send me a map sensor they had in the shop just to be on the safe side.
i also got an awesome deal on an apexi mechanical boost gauge so thats coming as well.

HOWEVER....today i had to move the car and noticed that with the engine OFF and electical ON the PFC shows -180 mmHg (-7inHg)
WTF???
this cant be right can it??

so, yes carson....i think its either the map sensor or its wiring which isnt as much fun as a bad boost gauge and gaining an extra 3psi of boost....heh

i just hope i get it fixed and that also the oxygen sensor job isnt too bad and its just the sensor and not the wiring there either.

any feedback on these pfc boost readings???

or has anyone else had the problems of 0.00V for O2 sensor readings?

thanks

spyfish007

Don't be worried about the MAP sensor with the power off ... if is basically showing you atmospheric pressure .... which is definately lower up ther in CO.

suganuma

well.....i sware i posted this last night.....

but what i basically said was that carson - youre right
i cant believe i didnt think of that

i am at 7,258 ft ASL

standard pressure at 0 ft ASL is 2116.2 lb/ft^2 or 760 mmHg
while at 7,000 ft ASL its 1633 which equals out to 586.5 mmHg

when you subtract that difference in mmHg you get 173.5
and that is pretty damn close to my 180
with the increase of 258ft ASL it is probably dead on, but i didnt get that discretionary with the calculations.

so once again.....im HOPING its NOT the MAP sensor, but instead the boost gauge and ive been missing out on 3 psi of boost all this time.

im trying to find some time tonight before daylight fades to put on the new O2 sensor and see what kind of readings im getting there (hopefully that all goes well and its just the sensor and not the wiring)
and a buddy of mine is giving me a killer deal on a boost gauge (already in the mail).

so cross your fingers.......:p

suganuma

to give an update to anyone who cares......

tried putting on the bosch universal O2 sensor and it wouldnt go on straight. it was too fat at the end and therefore kept hitting my strut tower. i had nothing to dent it with enough to make it fit and so i tried to mash down the end of the sensor to make it a little smaller.
well taht didnt work either. it was only about $20 for the sensor so i just started filing and mashing away at it trying to get it to fit and of course it eventually broke.
i probably could have gotten it on if i took off the downpipe and everything, but i had no jack - i have to park out in the middle of a field for goodness sakes.

so for good fun i start up the engine to see what it all sounds like with the hole in the downpipe exposed and it didnt sound much different actually.....at least not at idle. so i turn it off before it all gets too hot and put the old sensor back in and hook up a line directly to the sensor and run it to a little LED that i have to read O2 sensor voltage. for some reason now.....the thing frikin warms up and starts giving me good readings. so i hook it up back to the stock wiring and all is good.....hook up that LED in parallel (just like a/f ratio gauge).
so all is good.....let it all warm up and take a WOT run in 2nd gear with the profec off (SUPPOSED 6.5#) and get the same .25 kg/cm^2 for boost and .88-.89 for O2 sensor readings.
so at this point im happy on one hand cause now im REALLY thinking the map sensor is fine and the boost gauge was jacked the whole time.

BUT.....that means i have a boost leak somewhere if im only getting 3.5 when i should be getting 6.5-7psi.
i dont even know where to start looking for that if that's the case.

ive been told by several people to disconnect the profec B while using the PFC b/c it just confuses things. so does that mean convert back to stock with the pill and the wastegate solenoid back online???
...might as well try.....anyone got a stock boost pill??

apexi mechanical boost gauge should be here this weekend.....more to come after i hook that up.......

Dr Wankel

Good luck I hope all goes well.

spyfish007

you're making my head hurt!

SARX7

I've got 2 boost guages on the car 3 if you count the PFC.
And the PFC reads different from both.
One gauge is an APEXi Mechanical boost gauge and the other is a Blitz dual turbo timer.

The APEXi gauge and the Blitz TT give very close readings, but the PFC is usually off a bit. I saw .9 bar last night on the Blitz TT and the PFC only registered .78. The APEXi gauge is in PSI and is a little harder to compare as I'm driving but it showed ~13PSI.

I was using the 2nd boost setting on my PFC which hasn't been changed from it's original setting.

suganuma

and guess what.....heh

with the new gauge it says across at the MAP sensor im getting (-) 13-14 inHg of vacuum as well as at the intake manifold nipple while the PFC STILL says -500mmHg (~-20 inHg)
this is all at 750 RPM

under boost with profec off...still seeing .25 (PFC) and on the new gauge i see a solid 7-7.5 psi

SO.....nothing has changed. the gauge is much more responsive, steady, and accurate and looks a whole hell of a lot nicer to boot. if the pfc wasnt giving me crazy readings id be happy with these numbers cause that means im making good, strong boost and apparently have a pretty damn good street port. thanks for the gauge Mr X.

hopefully taht frikin MAP sensor gets here soon so i can compare with a different MAP sensor. its gotta be the map sensor....i dont see how there could be a 3 psi leak that would be so stealthy i couldnt see or hear it.

thanks SARX7.....good to see someone offer up help and advice besides spyfish.

anyone else have comparison numbers for gauge readings vs. PFC boost readings???

matt_ledbetter

I'm in on this a little late, but we've discussed it a couple of times before.

I haven't spoken to anyone who sees identical readings on the PFC any brand of boost gauge.

I have a Autometer boost gauge, Blitz Boost Controller, and Blitz Turbo Timer. All 3 of them read exactly the same... The PFC is always about 2-3 psi low.

I'm not worried about it as long as you tune by air/fuel ratio. At 7500 feet, you will surely be running rich....

By the way, I lived in the Springs and dated a cadet for a couple of years. The Academy is an awesome place.... amazing amount of tax dollars in use there.

-Matt

suganuma

its not a/f ratio that im worried so much about......even thought it is kinda low (id like to see around .89-.9 in third. depending on the night and temps i see lower than that.

what im worried about is the engine running 10# of boost and the PFC reading only 7# and therefore using different ignition timing for that area. cause thatll cause detonation REALLLY fast.

know what i mean?

ANYONE ELSE?????.....cmon guys

matt_ledbetter

Well, personally, I don't worry about it because every Power FC I have seen reads low. So, the system, in my opinion, is tuned in that fashion. Meaning, the base maps were tuned with the readings from the Power FC.

Extreme example: If the Power FC reads 2 psi and you are running 20 psi, it's not a problem if the car is tuned in that state. Of course, if it's a problem with the sensor, that would be a problem. I seriously doubt you have a bad map sensor though.

Really the only way to be sure is to put it on the dyno and monitor the readings.

-Matt

spyfish007

suganuma: I remember the conversation that went on before and I remember 2 lbs was the most people seemed to be off .... I am only off by about 0.5 lbs on the boost side ... on the vacuum side I'm off by about 3.5 inHg because I idle @ 15 inHg vacuum and on the PFC I get about 480 mmHg wich is about 18.5 inHg. Just thought I would post info from my car for you.

suganuma

well chris has supposedly sent me a different map sensor so i can compare things.....so ill try that out.

i REALLY REALLY want to take the car to races here tomorrow night.....but dont want to turn the boost up and pop the motor.

i wish there was a dyno around here with a wide band that i knew of......

who votes i turn it to my high boost profec setting (12.5-13#) and let her rip???

i guess i should find out some timing numbers from y'all for comparison as well.....anyone wanna bite?

SPOautos

Turning the boost up is fine as long as your not getting lean. Just make sure your nice and rich then let it rip. Oh yea, and make sure your not maxing out your injectors. If your running at the track you could ever throw in a little race fuel if they sell it for a little added security.

I say dont worry so much about the numbers themselves but look at the tuning of the car instead.

Thats just my .02 anyway.

Later,

spyfish007

Stephen,

The concern is with the timing. You don't want as much advance in the timing at higher boost levels.

atihun

I first asked this a year ago and no one has found out why there is a difference between the PFC and a boost gauge.

I too see a 2-3 psi difference between the PFC and gauge. Has anyone removed or ran their car without the little filter that is right before the MAP sensor?

By the way, Carson, I just received the blockoff plates. Thanks for setting that up, nice work.

suganuma

i T-d off my line going into the sensor to run the profec Boff of it
i disconnected the profec and hooked up the boost gauge line to it and saw the exact same numbers i see at the manifold.

the filter is a fuel filter. im sure you could try buying a new one or a low mileage one to change out to see what happens.
i dont have the car in front of me right now to look at it.....but i THINK i T-d off the line after the filter. im pretty sure i did so i dont think thats the culprit.
i will look tomorrow.

hopefully the map sensor chris sent me gets here SOON this week.
i'm supposed to drag the car for the first time this weekend.....

cymrex

iTrader: (2)

I believe what you are seeing is related to altitude and the lack of an atmospheric pressure sensor in the PFC. Check page f22 and f34 of the workshop manual and you will notice the stock ecu contains an integral Atmospheric Pressure Sensor. The MAP sensor stands for Manifold Absolute Pressure. The MAP sensor gives the absolute pressure uncorrected for current atmosheric pressure. Thus MAP references zero mmHG. The boost guage references current atmosheric pressure as zero. Thus the boost gauge and the MAP output will differ. Remember atmosheric pressure varies so the correction factor is not a set amount. High and low pressure weather systems directly change the correction factor between absolute pressure and boost referenced to atmospheric pressure. The stock ECU uses the integral Atmosheric Pressure Sensor as another input reference. I could find nothing on how the atmosheric pressure sensor data is used by the ECU, but it was there for a reason. The PFC must be showing the MAP sensor output. This should not harm the engine because absolute pressure and intake temperature are used to calculate how much true oxygen is in the intake charge thus the right amount of fuel will be added to get the desired ratio. The atmoshere is a relatively homogeneous mixture so there are fewer molecules overall in a cubic centimeter of atmoshere at altitude still contaions the same percentage of oxygen. A MAP sensor with the intake temperature is the correct tool to figure out how much oxygen is in the intake charge. So if you get the Air Fuel ratios right then everything will be OK. At altitude you will never reach the higher absolute pressure parts of the PFC settings.

suganuma

i understand that......but that still leaves the problem with the fact that my timing will be way off for the amount of oxygen/fuel in the system. right??

regardless of oxygen content....the air is going into the engine at the pressure shown by the PFC

i just found something tonight that may be of great importance.......the PIM voltage settings.

it seems to me that i need to compensate for altitude with the pressure sensor and that this is the way to do it. my brain is fried right now though and the calcs arent making complete sense. i dont want to make an error that could cost me my engine.......any advice?

anyone messed around with the PIM voltage. IS it to change/compensate for different initial pressure sensor readings (ie altitude differences?)

thanks again

suganuma

CYMREX,

i dont see why the boost gauge should read different from the power FC (getting boost/vacuum readings from the MAP sensor).

i am seeing with the power on, but engine off about -180mmHg which i just realized today equates out to my 3.5 psi difference between the PFC and the boost gauge.
therefore, when under boost the turbos are having to overcome this 3.5# difference in atmosperic pressure, but according to the boost gauge it is still pushing in the right boost #s.

i just dont see why the boost gauge wouldnt also read -180mmHg.....tahts 7.09 inHg......i should be able to see that on the gauge!

the question IS.....
what to do about it......i could:

1. go by and tune from the boost gauge and try to adjust the PFC using the PIM voltage settings to adjust for altitude (absolute pressure will change). this can be seen on page 23 of the commander manual i think it is.

2. tune by the PFC boost readings. this means i can turn the boost up on the PFC settings, but it will make my turbos work to produce 13.5 psi when wanting to run 10 psi.

any ideas????

id like to try this out/get it done tonight or at least by tomorrow.