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Old 06-20-2013, 11:20 PM   #35
mercedestech
 
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Quote:
Originally Posted by 2SSCAMARO View Post
Fuel trims vary day to day based on temp, humidity, DA, RPMS, etc. If you had done numerous logs at a steady RPM on a flat stretch of road at roughly the same AAT on a fully warmed up engine and knew what your average fuel trims were and now found them to be consistanty shifted more positive, it would be an indication of a vacuum leak introducing unmetered air that would cause the LTFT's to be leaner than before.

The boost would be shown on the log as MAP and could be shown in MB's or PSI depending on what logging device is used. Log the MAP, IAT, and any other PID you want, then post up the log.
ALthough this is true, fuel trims on a normally functioning engine will be close to the middle of the range. If the pcm is adding fuel to the point of being close to the high limit, there is a problem. A leak from the intake seals will show a very high stft, and eventually ltft before it actually flags a fault and turns the check engine light on. This is all I was getting at.

Boost is fixed based on the pulley given the same iat etc.. If he is seing 1.5 lbs less after the repair, something is wrong as long as the driving conditions temps etc are similar. Either the blower is not capeable of mechanically producing boost due to belt slippage, or there is a leak. The main point being the whipple and/or pcm does not control boost based on any of the sensors inputs. It can drastically alter power output based on timing, fuel injector pulse width etc, but the boost value is a measurement of a mechanical event. The only exception would be if the pcm is closing the throttle limiting air flow into the supercharger. Given all things equal, iat temp, mechanical condition of the supercharger and engine, it should make the same boost post repair as it did before.
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Old 06-21-2013, 10:10 AM   #36
2SSCAMARO

 
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Quote:
Originally Posted by SSlim View Post
New belt is coming since the other was a little chewed up from sliping.

What would the fuel trims do that would indicate a leak? I was watching them on the log last night but have no idea what I am looking for.

The logger is getting IAT reading. So either that sensor is there and I can not feel it or they are using the MAF or something for temp.

I have 3.75 pulley.

What would boost look like on the logger? I think I might try another gauge just to be sure the reading is right. It pulls like a rapped ape, but don't know that I would be able to tell the difference with a 1# boost loss.
Quote:
Originally Posted by 2SSCAMARO View Post
Fuel trims vary day to day based on temp, humidity, DA, RPMS, etc. If you had done numerous logs at a steady RPM on a flat stretch of road at roughly the same AAT on a fully warmed up engine and knew what your average fuel trims were and now found them to be consistanty shifted more positive, it would be an indication of a vacuum leak introducing unmetered air that would cause the LTFT's to be leaner than before.

The boost would be shown on the log as MAP and could be shown in MB's or PSI depending on what logging device is used. Log the MAP, IAT, and any other PID you want, then post up the log.
Quote:
Originally Posted by mercedestech View Post
ALthough this is true, fuel trims on a normally functioning engine will be close to the middle of the range. If the pcm is adding fuel to the point of being close to the high limit, there is a problem. A leak from the intake seals will show a very high stft, and eventually ltft before it actually flags a fault and turns the check engine light on. This is all I was getting at.

Boost is fixed based on the pulley given the same iat etc.. If he is seing 1.5 lbs less after the repair, something is wrong as long as the driving conditions temps etc are similar. Either the blower is not capeable of mechanically producing boost due to belt slippage, or there is a leak. The main point being the whipple and/or pcm does not control boost based on any of the sensors inputs. It can drastically alter power output based on timing, fuel injector pulse width etc, but the boost value is a measurement of a mechanical event. The only exception would be if the pcm is closing the throttle limiting air flow into the supercharger. Given all things equal, iat temp, mechanical condition of the supercharger and engine, it should make the same boost post repair as it did before.
SSlim asked two questions. I merely tried to answer his questions. Do you feel my response to his questions is incorrect? It appears he does not currently know for sure that his WOT boost is in fact not what it was before the repair because he has not logged the boost to see if it is the same reading he is seeing on the gage.
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