Disconnected Evap Purge Solenoid = Very Happy LNF
03-23-2010, 01:40 PM
#76
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LTFT's were locked at zero for the 3 days I had the sol unplugged, even with the CEL code disabled. Reconnected it and LTFT's started correcting the -0.8 to +0.8 I see during my commute since dialed in.
Haven't tried plugging the line to the canister yet. Maybe tomorrow.
Haven't tried plugging the line to the canister yet. Maybe tomorrow.
The only problem I see with plugging the line is the ECU possibly using the known solenoid open percentage when calculating the amount of fuel and/or air it's going to command. Basically that it will go rich or lean when it commands the solenoid open, since it's expecting a certain effect from it being open and it doesn't happen. When I disconnected the electrical connection, the ECU listed it as 0 the whole time, so there was no chance of this happening.
Thanks to all of y'all that are looking into it. This has been very interesting so far.
03-23-2010, 06:42 PM
#81
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Is the lack of LTFT functionality going to affect performance only, or can the car run so lean or rich without it that it affects reliability?
And Stamina, thanks so much for finding out about this and keeping us all updated. My car feels better than new thanks to you
And Stamina, thanks so much for finding out about this and keeping us all updated. My car feels better than new thanks to you
03-24-2010, 12:29 PM
#84
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ive been getting the p0496 code for a few weeks now ever since i did the vacuum tank delete. Do you guys think it could be because of that. I have a code eraser and every 2 or 3 days i get the code back and it always says EVAP low purge flow and its really annoying. Ill take it to the dealer and see if its that purge sensor. Does it make that big of a difference in driveability? last resort i will put the vacuum tank back in
03-24-2010, 01:03 PM
#85
II was understanding that this wasn't a vacuum tank per say, and because the gas tank rely's on venting via that tank (or the purge solenoid to vent into the intake manifold) - I would suspect the tank delete was a bad idea...
But that's my guess.
Maybe sourcing a vented cap could null in void the need for this whole setup - but that would directly affect the vehicles original emissions since the vented cap in no way shape or form will prevent gas vapor from entering the atmosphere.
Again, making a guess...
But that's my guess.
Maybe sourcing a vented cap could null in void the need for this whole setup - but that would directly affect the vehicles original emissions since the vented cap in no way shape or form will prevent gas vapor from entering the atmosphere.
Again, making a guess...
03-24-2010, 01:14 PM
#86
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i feel like since the car doesnt have that constant vacuum the tank provided, it could have something to do with the purge solenoid because it is hooked right into the intake manifold and so is the other vacuum line from the vacuum tank.
03-24-2010, 01:31 PM
#87
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I'm not sure that we're not talking about two different things.
There's a vacuum tank connected to the front of the engine. Some people have disconnected this to see if it helps with turbo spool, boost, and/or the bypass valve. This has nothing to do with the evap system, and other LNFs, such as the Sky and Solstice, apparently do not even have the tank.
There is a canister by the fuel tank, usually filled with charcoal, that captures the excess fumes from the gas tank so the engine can suck it into the intake manifold with the vacuum in the manifold. Otherwise the fumes would just vent out of the fuel tank vent.
There's a vacuum tank connected to the front of the engine. Some people have disconnected this to see if it helps with turbo spool, boost, and/or the bypass valve. This has nothing to do with the evap system, and other LNFs, such as the Sky and Solstice, apparently do not even have the tank.
There is a canister by the fuel tank, usually filled with charcoal, that captures the excess fumes from the gas tank so the engine can suck it into the intake manifold with the vacuum in the manifold. Otherwise the fumes would just vent out of the fuel tank vent.
03-24-2010, 07:24 PM
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I'm not sure that we're not talking about two different things.
There's a vacuum tank connected to the front of the engine. Some people have disconnected this to see if it helps with turbo spool, boost, and/or the bypass valve. This has nothing to do with the evap system, and other LNFs, such as the Sky and Solstice, apparently do not even have the tank.
There is a canister by the fuel tank, usually filled with charcoal, that captures the excess fumes from the gas tank so the engine can suck it into the intake manifold with the vacuum in the manifold. Otherwise the fumes would just vent out of the fuel tank vent.
There's a vacuum tank connected to the front of the engine. Some people have disconnected this to see if it helps with turbo spool, boost, and/or the bypass valve. This has nothing to do with the evap system, and other LNFs, such as the Sky and Solstice, apparently do not even have the tank.
There is a canister by the fuel tank, usually filled with charcoal, that captures the excess fumes from the gas tank so the engine can suck it into the intake manifold with the vacuum in the manifold. Otherwise the fumes would just vent out of the fuel tank vent.
03-29-2010, 03:36 PM
#91
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Thread Starter
My service advisor called me today for a follow up and to see how the new purge valve was working out. They said that they had another Cobalt in the shop today with very similar issues, so they were going to look into the evap system on the other car and report back their findings. I wonder if that other guy is on here... his name is Reid (sp?), in the Houston area, and drives a black 'balt.
Anyway, any findings on the HPT front?
Anyway, any findings on the HPT front?
03-29-2010, 03:44 PM
#92
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My service advisor called me today for a follow up and to see how the new purge valve was working out. They said that they had another Cobalt in the shop today with very similar issues, so they were going to look into the evap system on the other car and report back their findings. I wonder if that other guy is on here... his name is Reid (sp?), in the Houston area, and drives a black 'balt.
Anyway, any findings on the HPT front?
Anyway, any findings on the HPT front?
03-29-2010, 08:02 PM
#93
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Thread Starter
Update:
I did the mod this evening. Good news so far... The car has retained all of its good driving/idling characteristics that electrically unplugging it gave. I'll be getting it logged later this week to see what's going on behind the scenes in the ECU.
Just stopped by Autozone and picked up an assorted pack of "vacuum caps". I reset the ECU, plugged in the electrical connection to the purge valve, and capped off the purge valve and evap line. I drove in traffic for a while observing AFRs and then did some WOT pulls (stock tune only) once I was comfortable with what I was seeing and the trims had a while to adjust. No sign of the caps coming out/backing off even without zip ties holding them on. This is probably because of the valve only being open during vacuum.
Last edited by Stamina; 03-29-2010 at 08:07 PM. Reason: Automerged Doublepost
03-29-2010, 08:12 PM
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03-31-2010, 01:48 AM
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I've been running my car with the evap purge solenoid disconnected (and also Trifecta tuned) for about 10 days now, and it still feels great. I'm not crazy about the check engine light and apparent lack of long-term fuel trim adjustment, but it's running so much stronger and smoother than before that I just can't go back!
I'd love to hear if there's a good long-term solution that gets rid of the CEL and enables the LTFTs.
I'd love to hear if there's a good long-term solution that gets rid of the CEL and enables the LTFTs.
03-31-2010, 11:11 AM
#97
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I've been running my car with the evap purge solenoid disconnected (and also Trifecta tuned) for about 10 days now, and it still feels great. I'm not crazy about the check engine light and apparent lack of long-term fuel trim adjustment, but it's running so much stronger and smoother than before that I just can't go back!
I'd love to hear if there's a good long-term solution that gets rid of the CEL and enables the LTFTs.
I'd love to hear if there's a good long-term solution that gets rid of the CEL and enables the LTFTs.
We're doing a "double feature" tonight and looking into the air intake flow straightener and mesh ideas/combos too while we're out logging...
03-31-2010, 11:44 PM
#99
The cap method Stamina posted above seems to work! Preliminary results are that his LTFTs and STFTs both function normally, minus the faulty EVAP system.
We'll see if there are any negative long term effects, but I am tempted to call this problem SOLVED.
We'll see if there are any negative long term effects, but I am tempted to call this problem SOLVED.
04-01-2010, 01:50 AM
#100
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Thread Starter
Findings
Below are the findings:
Original issue: (On page 1)
https://www.cobaltss.net/forums/show...79&postcount=1
New Purge Solenoid:
Dealer replaced Evap Purge Solenoid at my request, with backing from a copy of my correspondence with More_Torque_More_HP (left them with a copy).
This fixed the rough idle, some of the lack of response, and some of the erratic AFRs issues I was having. Erratic AFRs were still present. This is possibly the nature of the beast when unmetered fuel-air mixture is ingested by the engine. Overall it helped and the car seems happier, but didn't completely solve the issue to my liking.
The dealer/service advisor called me about a very similar problem another SS/TC that just came into their shop had, and spoke with me about the improvements, any remaining issues, suggestions, and if I had any further correspondence with More_Torque_More_HP. They are currently troubleshooting the other SS/TC and will be updating me on any additional findings they receive.
Electrically Disconnecting the Evap Purge Solenoid:
This method showed major, immediate improvement over the original conditions and still an improvement over the new purge solenoid. Idle was so smooth that you could hardly tell the engine was on, response (especially in light and moderate throttle) was greatly improved, erratic AFRs completely disappeared, and gas mileage also improved.
The problem with this method was the ECU froze the LTFTs at 0 and operated solely off of STFTs. Since my LTFTs are normally negative (taking out fuel due to a consistent rich condition) it would be safe to remain driving like this on my car. On the second start-up a CEL was thrown and remained lit on subsequent drives. The CEL code can be turned off, but LTFTs remain frozen at 0.
It should also be noted that on a cold start, the car would be at normal operating fuel pressures for the RPM during warm-up and not at the high fuel pressures it would be at normally (300-500psi instead of 1100-1400psi), although its cold start warm-up cycle was still present as far as RPM.
Evap Purge Solenoid Electrically Connected, but Evap Pipe Capped Off:
This method retained the idle, response, and lack of erratic AFR advantages of the method above, while re-enabling LTFT functionality.
This method consists of disconnecting the Evap Purge Pipe going to the solenoid and capping off the solenoid with a vacuum cap. It was found that on cold starts the cap could pop off, so a zip tie to fasten it is advised. Further removal of the then unneeded Evap Purge Piping is optional. I disconnected the section that runs from about where the battery is to the solenoid and inserted another cap into the pipe to seal it. It cleaned up the appearance of the engine bay a bit.
At this time I do not know if the Evap Purge System will state that it passed for inspection purposes, although disconnecting it electrically before it's next "fueling event" (filling up on gas) didn't affect its pass state until possibly the next fueling event.
Overall Conclusion:
It appears that due to LTFTs freezing at 0 during Evap Purge Solenoid electrical disconnection, this shows promise for MAF tuning applications, by simplifying the variables present.
I would suggest for long term use, to use the cap-off method instead for several reasons:
-You have a CEL all the time, which doesn't allow you to see it come on in the case of a real CEL event if it's already on.
-If you have it electrically disconnected after a fueling event, you may not pass an emissions testing criteria as seen on the testing machine used.
-You have LTFT functionality, which safeguards your engine from possibly running too lean and causing damage.
-You get the benefits of the electrical disconnection method, while retaining the safeguards and normal operation, such as LTFT functionality and normal cat warm-up fuel pressures.
Thanks goes out to Pyros777 for the logging and helping make all this possible.
Original issue: (On page 1)
https://www.cobaltss.net/forums/show...79&postcount=1
New Purge Solenoid:
Dealer replaced Evap Purge Solenoid at my request, with backing from a copy of my correspondence with More_Torque_More_HP (left them with a copy).
This fixed the rough idle, some of the lack of response, and some of the erratic AFRs issues I was having. Erratic AFRs were still present. This is possibly the nature of the beast when unmetered fuel-air mixture is ingested by the engine. Overall it helped and the car seems happier, but didn't completely solve the issue to my liking.
The dealer/service advisor called me about a very similar problem another SS/TC that just came into their shop had, and spoke with me about the improvements, any remaining issues, suggestions, and if I had any further correspondence with More_Torque_More_HP. They are currently troubleshooting the other SS/TC and will be updating me on any additional findings they receive.
Electrically Disconnecting the Evap Purge Solenoid:
This method showed major, immediate improvement over the original conditions and still an improvement over the new purge solenoid. Idle was so smooth that you could hardly tell the engine was on, response (especially in light and moderate throttle) was greatly improved, erratic AFRs completely disappeared, and gas mileage also improved.
The problem with this method was the ECU froze the LTFTs at 0 and operated solely off of STFTs. Since my LTFTs are normally negative (taking out fuel due to a consistent rich condition) it would be safe to remain driving like this on my car. On the second start-up a CEL was thrown and remained lit on subsequent drives. The CEL code can be turned off, but LTFTs remain frozen at 0.
It should also be noted that on a cold start, the car would be at normal operating fuel pressures for the RPM during warm-up and not at the high fuel pressures it would be at normally (300-500psi instead of 1100-1400psi), although its cold start warm-up cycle was still present as far as RPM.
Evap Purge Solenoid Electrically Connected, but Evap Pipe Capped Off:
This method retained the idle, response, and lack of erratic AFR advantages of the method above, while re-enabling LTFT functionality.
This method consists of disconnecting the Evap Purge Pipe going to the solenoid and capping off the solenoid with a vacuum cap. It was found that on cold starts the cap could pop off, so a zip tie to fasten it is advised. Further removal of the then unneeded Evap Purge Piping is optional. I disconnected the section that runs from about where the battery is to the solenoid and inserted another cap into the pipe to seal it. It cleaned up the appearance of the engine bay a bit.
At this time I do not know if the Evap Purge System will state that it passed for inspection purposes, although disconnecting it electrically before it's next "fueling event" (filling up on gas) didn't affect its pass state until possibly the next fueling event.
Overall Conclusion:
It appears that due to LTFTs freezing at 0 during Evap Purge Solenoid electrical disconnection, this shows promise for MAF tuning applications, by simplifying the variables present.
I would suggest for long term use, to use the cap-off method instead for several reasons:
-You have a CEL all the time, which doesn't allow you to see it come on in the case of a real CEL event if it's already on.
-If you have it electrically disconnected after a fueling event, you may not pass an emissions testing criteria as seen on the testing machine used.
-You have LTFT functionality, which safeguards your engine from possibly running too lean and causing damage.
-You get the benefits of the electrical disconnection method, while retaining the safeguards and normal operation, such as LTFT functionality and normal cat warm-up fuel pressures.
Thanks goes out to Pyros777 for the logging and helping make all this possible.