2006 Chevy Optra: fuel tank purge issues

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  #1  
Old 08-30-17, 02:39 AM
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2006 Chevy Optra: fuel tank purge issues

Hello,
Below is the tests i have performed on the FTPS problem so far. I am a DIY'er and seem to have hit a block in the road
I have no wiring diagram for this cars FTPS circuit as i cannot find one. I have a service manual for a 2004 Optra and it doesn't list anything for the FTPS circuit.
NOTE: I do not have a Fancy dancy scanner with square waves etc. I only have a simple Actron scanner CP9580a and a DMM.

Here is what i have diagnosed so far:

CONNECTOR UNPLUGGED,

With Key off
-------------------
1.) I have continutity on the ground wire(black)

With Key on Engine off
----------------------------------
2.) 5Volt Reference - tested 4.99V on the reference wire (gray)
3.) Signal Wire - jumped 5Vref to signal and backprobed the signal wire (ecm side of connector). Test showed 4.99v proving no connector fault.

CONNECTOR PLUGGED BACK IN,

4.) FTPS test - removed FTPS from Fuel Tank Pump assembly and applied -10kpa vacuum on the sensor and it ranged from 1.3v - 4.74v
After releasing the vacuum pressure voltage returns to 1.3v ,,,,Did test 2 or 3 times to verify.

5.) Purge Valve - removed from car and applied voltage to test valve open close operation while applying vacuum - Valve opens
Also listened to the purge duty cycle with stethascope and valve was rattling away.

6.) Vent valve - removed from car and applied voltage to test valve open close operation while blowing thru it - Valve closes.

7.) Gas cap is brand new.

8.) The Drive Test Diagnosis - The MIL IS ON !!!......
After resetting MIL and now 93km later the "Evap Drive Cycle Monitor" is complete and "DTC P0454 is confirmed". P0452 hasn't reappeared as yet, but rest assured it will as i have done this a few times already over past year.

With the DMM connected to ground and backprobed to the signal wire on connector (ecm side) i observed the Voltage reading while driving for 15 minutes. At very low load The signal was perfect (1.4V-3.1V).
Went home let car cool and retested. Drove same distance never tromping on throttle. Stopped, waited a few minutes and restarted car and the MIL went off (expected). All the drive time the FTPS signal Voltage was perfect and MIL went off.

SO I APPLIED SOME FORCE TO HER ON THE NEXT TRIP FLOORING THE GAS PEDAL WHILE OBSERVING THE DMM VOLTAGE and sure enough the voltage dropped below threshhold and went haywire at times. This resulted in the MIL coming back on IMMEDIATELY after the second attempt. I am almost sure that the code is being set when there is positive pressure in tank, because freeze frame data indicates PURGE % = 0.

Below .1 Volts i think is the threshhold which has to happen on 2 consecutive trips for the MIL to come back on and my testing confirmed that.

But i have reservations about going out and replacing the sensor (throwing money at parts) until am absolutely sure about the fix.

Commanded the Vent valve closed with my scanner and applied .5 psi shop air from the evap hose before the purge valve. Everthing seemed to hold pressure but i have no way of determining this as I dont have a fancy smoke machine with pressure gage). So i attached a balloon to the Vent Solenoid end of EVAP system and waited 10 minutes. Came back and the balloon was still holding all pressure, so it seems that i have no leaks, thus no leak codes....dah!!

As mentioned I dont want to throw money at parts until 100% sure of fix.
PLEASE ADVISE, AS I AM NOT SURE WHICH FORK IN THE ROAD TO TAKE FOR THE NEXT STEP. I dont have a wiring diagram showing the FTPS circuit nor do i have a pin layout of the ECM to do a short / open testing on the REF & signal wires.

If anyone has the FTPS wiring diagram and ECM pin layout i would be forever grateful as i cannot find them anywhere on the WWW.

Whats really puzzling is that I have a 2004 Optra Service Manual but it doesn't show any information regarding the FTPS
 

Last edited by CANAM58; 08-30-17 at 03:15 AM.
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  #2  
Old 08-30-17, 10:52 AM
PJmax's Avatar
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Welcome to the forums.

The service manuals are available but they aren't free.

Vapor recovery systems can be hard to diagnose with low vacuum involved. Most I've worked on check for stored vacuum when the vehicle is started. No vacuum = lost fumes = code set.

They also require a continuous vacuum on the tank when running. The purge valve should be closed until the vehicle is running.

Normal sensor parameters: 1.3v - 4.74v. You are correct that any positive pressure in the recovery system would drive the 1.3v down below normal. I would think the system is working normally and you need to find why the tank is becoming pressurized.
 
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