Greetings,


Does the PFC is accurate to mesure the boost???.

I get only .52Kg of boost on my PFC compare to
.70 kg. on my AVCR boost gauge.

Sorry for the double post

?????????????

Serge

 

A seach would have shown that the PFC displays pressure inacurately.

 

Chuck, is that due to a MAP sensor issue, or something inherently borked in the PFC itself?

 

When I got my car, the boost gauge is ran off the same hose as the map, and my readings are identical. So could it just be placement of the hose tap?

Also, if the pfc sees .56 instead of .7, why isn't the .56 more of what we care about? Isn't that what the ecu is managing fuel for? Is the boost gauge merely a way to manage the max boost we are looking for?

Thanks,
Jeff

 

Chuck,
Why is the PFC inaccurate and an aftermarket boost gauge correct? Accurate or not the boost value used by the PFC, as someone mentioned, is what the PFC is using to detemine fuel and timing. And yes the location of the pressure tap makes a HUGE difference in what readings are seen.
Regards,
Crispy

 

You both make valid points, and I've pondered the same thing myself, but I still trust my boost gauge.

When I had my Pettit ECU, my boost gauge was tapped into the nipple on the manifold, and I saw 10 psi. Installed the PFC and realized that it and the boost gauge didn't agree. What basis would I have for doubting the boost gauge? It's still reading the pressure coming out of the turbos at the same location.

Chuck has speculated that boost as displayed by the PFC is affected by a conversion error, i.e. converting MAP sensor voltage to kg/cm^2. If this is the case, then hopefully fuel and timing correction are based on voltages received directly from the MAP and not post-conversion.

I was working on my own theory that was a combination of a conversion error and differences in altitude (search this forum if you want the whole saga), but I've half forgotten my own damn theory cause I've been so busy.

 

Does anyone recall off hand where the map gets it's vac hose from?

 

I would submit that both gauge and PFC are accurate simply that the pressure taps are at different locations. And even if you "T" into the MAP sensor vacuum hose and *still* get differing values, whose to say "your" boost $60 boost gauge is accurate? Unless calibrated by a laboratory grade vacuum/boost gauge I'd lean more toward believing the PFC and OE MAP sensor for boost values under 14psi. As for the location of the OE MAP sensor vacuum line it's in the middle of the underside of the plenum in the rear/near the firewall. Although I'm unclear off which runner the nipple gets it's measurement. It's been a while since I've had my plenum off.
Regards,
Crispy
PS. notwithstanding Chucks speculation of voltage conversion.

 

So what are the reasons why mazda would tap in there over the manifold? I think it would be interesting to see if you moved the map to read from the manifold if they would agree better.

My questions stem from wanting to see what to base my desired 10/8/10 boost limits on for safety. If the ecu was basing 10/8/10 on the plenum, but now I tune the pfc to 12/10/12 based on the manifold using my boost gauge, wouldn't I really be at/near the stock levels of what the ecu was basing its boost management on?

(I'm also not taking into account the possible math problems at this point)

 

From what I understand the 10/8/10 pattern is a service manual test that uses the same nipple that we use to connect an aftermarket boost gauge.
Since this measure is a common undertanding of what a healthy boost pattern should look like when using the factory recommended test procedure, if it were me I'd stick with these numbers and just let the PFC use whatever values it's obtaining to determine fuel and ignition mapping.
The question then becomes what are you trying to use the boost readings for...to see if your turbo control system is healthy or to work with feuel and ignition maps?
Regards,
Crispy

 

Mainly to set the duty cycle for a safe boost level with my mods, and watch to make sure its not going over that and is getting to it, so I guess to tune the boost levels and watch to make sure it stays healthy.

 

Then I'd use the PFC values. The PFC is using the MAP voltages to determine fuel and ignition curves so why wouldn't you? Not to be facetious but the only real way to "tune " is with a wide band. Without stating the obvious, trying to "keep things safe" by keeping boost down isn't really an answer as motors can go lean just as easily at 10 psi as they can at 14 if tuned improperly. As for keeping a safe boost level in general boost is going to vary 1-2 psi depending on atmospheric conditions anyway so it's going to be tough to nail it down, for example, to 10psi *all the time.* It's just not possible. I use the PFC to see peak values and use my boost gauge to monitor real time boost to look for abnormailties. Just my thoughts,
Regards,
Crispy
- far from a boost expert -

 

Yeah, thats what I've been deciding on doing as well.

When I said tune, I meant the actual level, ie not letting it get to 1 bar or something, I don't really want to boost higher then 10-12lbs with my fuel and what not, thats what I meant by safe.

Thats a good point about boost levels changing based on atmoshere, I hadn't considered that.

-Jeff