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Old 04-08-2011, 09:46 PM   #1
compression
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Default Normal readings for OBD2 live data?

Attempting to troubleshoot a surging idle, I am now monitoring the engine parameters with an OBD2 scanner that shows real time readings from all the sensors.
I am looking for someone to tell me if any of these reading look off.

With the engine idling (with its periodic surging and stumbling),
Here is my data:




2002 WRX
Hybrid engine (2.5 block, 2.0 heads)
Good compression in all 4
PRE billet MAF housing
PRE reflash tune
750cc injectors



Any feedback much appreciated!!!
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Old 04-08-2011, 09:52 PM   #2
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ya got a vac leak
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Old 04-08-2011, 11:42 PM   #3
compression
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I have been told that before! so good eye.
What tipped you off?

I will double-triple check. I already pressurized the complete intake system and didnt find one, But I will try again! Any other suggestions?
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Old 04-09-2011, 12:56 AM   #4
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Quote:
Originally Posted by compression View Post
I have been told that before! so good eye.
What tipped you off?

I will double-triple check. I already pressurized the complete intake system and didnt find one, But I will try again! Any other suggestions?
http://img585.imageshack.us/img585/9384/img1587cf.jpg

MAP inHg should be at LEAST -17.72inHg


you should take that with ALL accessories turned off....even the radio


and the STFT is over 5%....that aint right
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Old 04-09-2011, 02:04 AM   #5
compression
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OK. thanks a lot. that is great info.
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Old 04-09-2011, 01:05 PM   #6
compression
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that is weird, my boost gauge says at least -20 inHG when idling, but the MAP value is around -9 inHG....I need to look into this....
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Old 04-09-2011, 08:13 PM   #7
compression
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anyone know why my MAP reading is so low, but my boost gauge is showing normal?
I searched all day for a vacuum leak and there is nothing. I have replaced all hoses, pressurized the intake manifold with air, inspected everything.
Bad MAP sensor?
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Old 04-09-2011, 08:55 PM   #8
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so you have a hybrid with 750's and the stock tune? id start with that, atleast find a base map on romraider.
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Old 04-09-2011, 11:34 PM   #9
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Quote:
Originally Posted by compression View Post
anyone know why my MAP reading is so low, but my boost gauge is showing normal?
I searched all day for a vacuum leak and there is nothing. I have replaced all hoses, pressurized the intake manifold with air, inspected everything.
Bad MAP sensor?

Because that's entirely normal... You don't have a vacuum issue...


Quote:
Originally Posted by Uncle Scotty View Post
ya got a vac leak
Quote:
Originally Posted by Uncle Scotty View Post
MAP inHg should be at LEAST -17.72inHg


That is MAP gauge, so zero on that is equivalent to -30 in/hg relative pressure. Most common boost gauges read relative pressure. 9.7 in/hg absolute means your manifold relative pressure is -20.3 in/hg (30 - 9.7). No vacuum leak detected...

Last edited by rkramer; 04-09-2011 at 11:43 PM.
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Old 04-10-2011, 12:38 AM   #10
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.............

Last edited by Uncle Scotty; 04-10-2011 at 02:46 PM. Reason: i guess not, then
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Old 04-10-2011, 01:54 PM   #11
compression
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The boost gauge (DEFI brand) says 20 inHG.
So I know I am pulling enough vacuum.

I plugged all the ports on the intake manifold (except the line to the boost gauge) and the problem did not change.
I just swapped in a known-good MAP sensor from another car and it gave me the exact same readings.

The car has a billet MAF housing, 750 injectors, hybrid engine, VF39, samco turbo inlet hose, and a custom tune.

I guess my main problem is = Why is my short-term fuel trim so damn high at idle? usually 9% up to 24%?
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Old 04-10-2011, 02:45 PM   #12
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Quote:
Originally Posted by compression View Post
The boost gauge (DEFI brand) says 20 inHG.
So I know I am pulling enough vacuum.

I plugged all the ports on the intake manifold (except the line to the boost gauge) and the problem did not change.
I just swapped in a known-good MAP sensor from another car and it gave me the exact same readings.

The car has a billet MAF housing, 750 injectors, hybrid engine, VF39, samco turbo inlet hose, and a custom tune.

I guess my main problem is = Why is my short-term fuel trim so damn high at idle? usually 9% up to 24%?
well then...I guess that's that, then
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Old 04-11-2011, 12:53 AM   #13
compression
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wait a second, whats what?

Is anyone else's MAP reading differently than their boost gauge? You would a OBDII reader with live data to check, so I am guessing not many people have monitored this stuff.

I was monitoring the MAP readings while driving. I would hold partial throttle for a long period of time(like cruising on the freeway), and the boost gauge and MAP reading were very rarely the same. The MAP jumped around a lot.
Is that normal?

As usual, any input welcome. You guys have been helpful so far.

My plan of attack is a new front O2 sensor, then a trip to the shop that originally tuned it for a fresh re-tune. Unless there are any other ideas...?
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Old 04-11-2011, 01:12 PM   #14
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i have a normal boost gauge and AP. the ECU always reports negative pressure as far less than the gauge, usually registers -9 while the gauge shows -20. they stay pretty close in positive pressure. i've had no issues, think its normal.

for the more savvy on the issue, i'm pretty close to sea level down here in TX
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Old 04-11-2011, 02:28 PM   #15
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Did you notice in the first picture the short term fuel trim is 0% and in the second it is 12%

Edit: nevermind STFT B1 S2 is the enrichment to test the cat. (i think)

Edit again: according to SAEJ1979 PID $15 data word B is the short term fuel trim associated with the output of the second O2S.
I wonder what that means. Is it to test the CAT or does it actually use this for overall fuel trim

Last edited by rick-l; 04-11-2011 at 04:07 PM.
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Old 04-11-2011, 02:37 PM   #16
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9.7 inches of mercury = 32 844.2 pascals

0.10197 Mega Pascals is atmospheric pressure

That would read 0.10197 - 0.03 Mega Pascals or about -0.07 on my boost guage so it dosen't seem terrible.
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Old 04-11-2011, 09:21 PM   #17
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Quote:
Originally Posted by compression View Post
wait a second, whats what?

Is anyone else's MAP reading differently than their boost gauge? You would a OBDII reader with live data to check, so I am guessing not many people have monitored this stuff.
I actually turned on the MAP display on my scangauge and watched it... The absolute lowest I could get it was 3.0, and that was downshifting from 3rd to 2nd, and probably spinning about 4k rpm. Idle was around 8-9.5.
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Old 04-11-2011, 11:34 PM   #18
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i noticed when logging on my laptop via romraider the MAP was around -10psi an dmy gauge was much lower near -18-(-20) psi so its just a vacum setup that causes this im guessing.

as far as ur idle surging. do u mean it idles up and down fairly rapidly? i am having this and its because i took the iacv off to clean it and the o ring type of gasket is crap once u take it off from expansion. so slapped it back on as good as i could and it leaked.

we could see this from the maf learning table %. it fluctuated about 20% from -5% to almost 20% fuel trim changes at idle because it was leaking air and the valve couldnt control it because of the leak.
-Basically not saying this is your problem but if it has never been changed or the IACV is super diry from never being cleaned it could be causing some issues for you. keep in mind order the o ring rubber gasket before u take it off because once u do its way to large to get back on correctly and seal.

In the past i have had a leak through the throttle plate shaft on the opposite side of the throttle/cruise cables. it blew out toward the throttle posistion sensor and was just chilling in there so i had to get a new one and push it in.

If you want to do a fairly easy mod you could ditch the evap system and eliminate alot of potential evap leak problems. PM if u want instructions on this. basically just has a slight gas smell on startup and after than nothing else. plus it cleans up the engine bay next to the intake and steering pump.
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Old 04-12-2011, 12:41 AM   #19
compression
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excellent info everyone. thanks!
So the MAP reading seems relatively normal.

Yes, my problem is surging idle and occasional stalling at idle. It idles about 750 and just stumbles up and down right around there. It is showing all the signs of a vacuum leak, but I have searched and tested all the vac lines and pressurized the system with air and watched for leaks(while spraying with soapy water). The high fuel trims seems to hint that it is trying to account for extra air with all the high trims.

The new front O2 sensor and ECU reset did not solve the problem.

It has a billet MAF housing, maybe that was added after the tune...since it seems larger diameter than the factory MAF housing. I am not too sure about this though, since the shop that installed it also did the tune...

I will see if there is any leak by the TPS.
I did take the IACV off to check and clean it. It was not too dirty. I put a new gasket on, the old one was stretched out.
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Old 04-12-2011, 06:37 AM   #20
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Thanks to this thread I have been doing some heavy duty reading. I have an Innovate OT2 smartphone device and I was wondering what all of the metrics it can monitor were all about. Does someone have a link that summarizes all of the acronyms nice and neatly. For example STFT and MAP?

http://www.motor.com/magazine/pdfs/092007_09.pdf

http://groups.engin.umd.umich.edu/vi...ganesan_w2.pdf
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Old 04-12-2011, 07:34 AM   #21
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guys... also check for a pre front o2 sensor exhaust leak. those will PULL IN ambient air especially at idle and that will skew reading lean, leading to +ve fuel trims.

quick way is to run a can of seafoam and watch under the car.
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Old 04-12-2011, 07:35 AM   #22
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are the 750cc modded stockers?
maf table needs some attention even if they are
modded stock injectors..
please check all hoses around intake & throttle body..
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Old 04-12-2011, 09:53 AM   #23
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well if u didnt find any leaks go thru. zip tie all vacum lines to ensure they are secure. if the maf was added after the tune then the whole tune would be bad unless its the same exact size maf housing which from what you said doesnt sound like it.

i would take it to the shop and see what they say about the problem.

heres what i do to ensure no leaks. i went to menards or home depot. anyways i measured the silicone coulper onthe throttle body and got a fitting that goes over the end of a pvc pipe that would fit into the silicone coupler snug with a hose clamp. i drilled a hole and added a air compressor fitting.
Now with the air compressor next to the car and the hose connected i isolated the manifold itself and added pressure slowly. the leak will be easy to hear since the fuel trims seem to be so large.

i did the same thing for my tmic. use the pvc end with the aircompressor fitting and got a diff piece to plug the silicone y pipe off the turbo and isolated the tmic and bov for leaks of any kind.

lastly i got a small piece of silicone to use the same plug as above to close off the turbo outlet and then pressurized the silicone inlet after the maf. just make sure u undo the crank case vent lines and plug then with objects. i use large drill bit ends and my extensions from my socket/racket sets. to plug off the bov return line u will need to remove the black hose from the bov and get something that fits in it and use a hose clamp on it.

I know it seems a little over the top for boost leak tests but at the end of the day I isolated every area and picked out every little problem plus with ur tmic or fmic off u can work easier on the manifold area. Then only places it will leak after reassembly is the tmic to throttle body the maf housing to silicone inlet and turbo to y pipe/fmic pipe.

if ur good after all that then i would head to the shop with the new o2 sensor. a cleaned maf sensor, and a list of everything u have done so u can explain to them the car has been check over and this is the result.
good luck to you.
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Old 04-15-2011, 11:42 PM   #24
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Update:
According to records/receipts from the previous owner, he paid for a tune that included a set of new 750cc injectors.
I pulled them out, had them flow tested and they are 898cc/min when tested at the standard pressure of 3 Bar.
The spray pattern was descent, and they were all consistent.

After looking on the internet, these injectors look A LOT like decapped stock injectors.
Did the shop just de-cap his stock injectors and charge him for a new set of 750cc ones? or was there a screw up at the shop and they accidentally put these in? who knows...

The point is, 900cc is WAY TO BIG for this car (hybrid engine/VF39). And is probably the reason it is idling bad, very poor atomization from such a large flow rate.
SO I am going to get a set of 650's or somewhere in there and have it re-tuned with them. Then hopefully this problem is fixed!
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Old 04-15-2011, 11:53 PM   #25
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take a picture or find one online and show us. that flow rate being so far off would cause the idle to be crappy i would agree. I got 850's and with just a 2L td04 idle is kinda off sometimes. It will be better with e85 but let us know how it turns out. 650's should be plenty for your setup as well unless u go e85. those injectors might support up to a small 16g but dont take my word for it.
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