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Old 01-08-2018, 01:03 PM   #1
bugwrx
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Default Slightly higher boost reading on AP. Shift spike?

I have an 02 wrx with 118000 miles on it and recently went stage 2 from stage 1 with Cobb's ots acn 91 stage 2 map and am currently working on some maintenance n upkeep in preparation for a pro tune. Since I've switched to stage 2, I've noticed on occasion while I'm accelerating and boost is building, I see a slightly higher boost reading on the AP's boost gauge(compared to the OEM lamco gauge when converting mpa to psi) that only shows up as I shift, otherwise the 2 are very close to reading the same as far as I can tell.

Example being, I'm accelerating and both my lamco gauge(mentally converting to psi) and ap could show 1-3ish psi, as soon as I shift the AP's gauge will read, say between 4.60-4.93psi(only between these specific values I've noticed) for literally a split second but my lamco doesn't show this little spike, at least that I can tell. It doesn't seem to matter what throttle % or boost I'm seeing wether it's alot or a little this occasionally happens and is always very slight when it does. I am hitting target boost just fine at 16.5 give or take depending on the weather here in Phoenix. The little spike does not occur at peak boost with wot.

I have a catless tbe(thinking this may be the cause?), catless uppipe, replaced all boost/vacuum lines with correct id and length, also have restrictor pill in with correct orientation. Perrin turbo inlet with their air box hose, a k&n panel filter with box silencer delete.

Everything is otherwise stock. I'm not seeing any knock, anything odd or off. Car runs and feels superb. I checked the turbo and there is very little if any shaft play and it spins freely. I haven't been able to find anything regarding this specifically but some posts across forums saying the AP boost gauge isn't always perfectly accurate and to be taken with some salt. Something to do with the boost table values at certain times? Ive been scratching my head for the last couple months on this, unless it's just different readings from the 2 gauges and I'm thinking too hard about it. Any ideas would be greatly appreciated. Thanks

Update- Over the last couple weeks I've been super anal about eyeballing both ap and oem boost gauge. I've noticed now that this little "spike"if you will, only shows up as soon as I depress the clutch to shift, however it only occasionally pops up. The oem gauge doesn't show this spike either and sometimes it'll show when I'm not in boost, like if I'm accelerating at less than 20% throttle. The spike is a very very quick 4.60-4.93 value, I can't even see it when it shows on the ap either.

Unfortunately I can't log at the moment, I'm in the middle of repairing my computer. But I will as soon as I fix it.
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Last edited by bugwrx; 01-20-2018 at 03:16 PM.
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Old 01-08-2018, 01:07 PM   #2
Aherna00
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Posting a log would greatly help in diagnosis of this. I would trust the AP readings, personally. But, we have to see a log to give any kind of meaningful opinion.
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Old 01-08-2018, 02:04 PM   #3
Charlie-III
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Do the gauges have different sensors? If not, may be just the sampling rate each gauge uses giving different values in a high rate change. So the steady state the lag in readings is not noticed.

Frankly, if a common pressure source, take a chill pill.......nuff said.
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Old 01-08-2018, 02:23 PM   #4
bugwrx
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Quote:
Originally Posted by Aherna00 View Post
Posting a log would greatly help in diagnosis of this. I would trust the AP readings, personally. But, we have to see a log to give any kind of meaningful opinion.
This is my next step. Would a wot log be necessary since this is just something that I can replicate at lower loads? It's also been quite cold here in AZ so I'd prefer to not do a wot pull if I can for worry of overboost.

Last edited by bugwrx; 01-08-2018 at 03:14 PM.
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Old 01-08-2018, 02:29 PM   #5
bugwrx
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Quote:
Originally Posted by Charlie-III View Post
Do the gauges have different sensors? If not, may be just the sampling rate each gauge uses giving different values in a high rate change. So the steady state the lag in readings is not noticed.

Frankly, if a common pressure source, take a chill pill.......nuff said.
I've been telling myself it could just be the different sources the readings come from. I believe the AP gets everything from the ecu. The OEM lamco gauge is ran from the bpv line and t'd off to run through the firewall. Itd make sense that one could have slightly different readings.

Last edited by bugwrx; 01-08-2018 at 03:15 PM.
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Old 01-08-2018, 03:27 PM   #6
rtv900
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Quote:
Originally Posted by bugwrx View Post
I've been telling myself it could just be the different sources the readings come from. I believe the AP gets everything from the ecu.
well it's a certainty the ap is getting it's data from the ECU considering that's it's only source of data
so you know that one for sure
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Old 01-11-2018, 08:46 PM   #7
bugwrx
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Anyone one else have any ideas or experiences with something like this?
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Old 01-12-2018, 12:52 AM   #8
ThinWRX
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From my experience with hooking up an AFR gauge to log through the cobb AP; the cobb ap will say something slightly different than what the log says. I am not sure why it does this, but I do experience it. My boost gauge also shows a different value on occasion than the AP, however If I go back and look at a log it looks just fine.
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Old 01-12-2018, 07:04 PM   #9
hijinks
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I have an aem digital boost gauge and it is way more inconsistent than my Cobb boost readings. In my experience the Cobb is extemely accurate and the aem is usually within a 2-3psi range. Seems normal.
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Old 01-13-2018, 02:51 PM   #10
GDR
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There's no real problem.

The AP is just displaying what the ecu reads off of a electrical pressure sensor on the throttle body.

Your boost gauge is mechanical and not designed to react as fast to see these small fluctuations. With the stock Lamco there is a restrictor in the line somewhere to dampen these out.
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