Disconnected Evap Purge Solenoid = Very Happy LNF
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From: The Desert
So I just wanted to give everybody an update on the original problem.
In a nutshell: The Evap Vent Solenoid was bad despite it never throwing any codes. That particular solenoid is the one that vents the fuel tank/evap system and is located on the evap canister under the rear of the car.
So my troubleshooting continued now that I've had some freetime over the Break and such. I basically disassembled the whole system, checked all the piping for plugs or leaks, checked the check valves, re-checked the Evap Purge Solenoid, disassembled and cleaned the canister (as much as I could anyway.. it's a sealed container for the most part), and never seemed to fix the problem.
Finally, when coming back home from the Break, I had a 5 hour drive to just think... and naturally the Evap issue came back to mind. I hadn't seen the Evap Vent Solenoid show anything but open on the Dashdaq for a long time. Could it be stuck open? I got to thinking about the symptoms of what something like that stuck open would be, and it seemed to fit what I was having happen.
The purge solenoid would open, and since the vent solenoid was stuck, and the outside air pressure is higher than the intake manifold pressure, it would force evap through the tube and then force fresh air through the tube before the ECU could compensate and/or shut the purge solenoid. Usually the gas fumes are sucked through the evap system/tubes like a straw, with the solenoid opening while in vacuum and the manifold vacuum pulling it, but now it was being force fed.
This was reflected by my random very rich and then very lean swings. Too much evap that threw it rich and then a bunch of fresh air that would then throw it lean. The car would sometimes stumble, sometimes even register knock, and finally forced me to disable the system until I could find out what it was.
I recently received and installed a replacement Evap Vent Solenoid, and it seems to have finally fixed the problem! I'm planning on testing it to see what the point of failure was. Right now, I'm leaning towards a mechanical failure, since the plunger that cuts off the outside airflow seems to get stuck along the edge of the "cage" that is rides up and down within, and the fact that if it was electrical, it may have thrown a code. As you can see, the solenoid itself changed over time too. It looks like it was redesigned.
The new solenoid (left) vs. the old solenoid (right)
The GM part number for the Evap Vent Solenoid is: 25932573
Thanks to all of y'all for your help/support!
In a nutshell: The Evap Vent Solenoid was bad despite it never throwing any codes. That particular solenoid is the one that vents the fuel tank/evap system and is located on the evap canister under the rear of the car.
So my troubleshooting continued now that I've had some freetime over the Break and such. I basically disassembled the whole system, checked all the piping for plugs or leaks, checked the check valves, re-checked the Evap Purge Solenoid, disassembled and cleaned the canister (as much as I could anyway.. it's a sealed container for the most part), and never seemed to fix the problem.
Finally, when coming back home from the Break, I had a 5 hour drive to just think... and naturally the Evap issue came back to mind. I hadn't seen the Evap Vent Solenoid show anything but open on the Dashdaq for a long time. Could it be stuck open? I got to thinking about the symptoms of what something like that stuck open would be, and it seemed to fit what I was having happen.
The purge solenoid would open, and since the vent solenoid was stuck, and the outside air pressure is higher than the intake manifold pressure, it would force evap through the tube and then force fresh air through the tube before the ECU could compensate and/or shut the purge solenoid. Usually the gas fumes are sucked through the evap system/tubes like a straw, with the solenoid opening while in vacuum and the manifold vacuum pulling it, but now it was being force fed.
This was reflected by my random very rich and then very lean swings. Too much evap that threw it rich and then a bunch of fresh air that would then throw it lean. The car would sometimes stumble, sometimes even register knock, and finally forced me to disable the system until I could find out what it was.
I recently received and installed a replacement Evap Vent Solenoid, and it seems to have finally fixed the problem! I'm planning on testing it to see what the point of failure was. Right now, I'm leaning towards a mechanical failure, since the plunger that cuts off the outside airflow seems to get stuck along the edge of the "cage" that is rides up and down within, and the fact that if it was electrical, it may have thrown a code. As you can see, the solenoid itself changed over time too. It looks like it was redesigned.
The new solenoid (left) vs. the old solenoid (right)
The GM part number for the Evap Vent Solenoid is: 25932573
Thanks to all of y'all for your help/support!
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From: Tejas
Dude I unplugged my purge solenoid. That was a HORABLE idea lol! Made my car ran like horse manure. My idle was all over the place. If you dont have a problem with your purge solenoid, DO NOT UNPLUGE YOUR EVAP SILINOIDE! If you all think this made your car run better, then I guess by comparison to a bad purge solenoid it does, but compared to a good purge solenoid it makes it run like garbage lol. When I unplugged it my RMP raced up to 1600rmp then back down to 500rmp then back up to 1000rpm then back to 650rpm and kept sputtering between 1000rpm-650rmp. Like I said, If this is better than a bad purge solenoid I guess you will know if your purge solenoid is messing up lol.
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From: Tejas
Dude I unplugged my purge solenoid. That was a HORABLE idea lol! Made my car ran like horse manure. My idle was all over the place. If you don’t have a problem with your purge solenoid, DO NOT UNPLUGE YOUR EVAP SILINOIDE! If you all think this made your car run better, then I guess by comparison to a bad purge solenoid it does, but compared to a good purge solenoid it makes it run like garbage lol. When I unplugged it my RMP raced up to 1600rmp then back down to 500rmp then back up to 1000rpm then back to 650rpm and kept sputtering between 1000rpm-650rmp. Like I said, If this is better than a bad purge solenoid I guess you will know if your purge solenoid is messing up lol.
You have to either disconnect the electrical part, the electrical part and then the pipe, or cap off the end of the solenoid where the pipe goes. If you did disconnect the electrical part and then the pipe and it did that, then the purge solenoid is stuck open and is therefore a bad solenoid.
Last edited by Stamina; Feb 9, 2011 at 09:55 AM.
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From: Tejas
You push on the ring tab to release it from the solenoid.
Right there it sounds to me like you've got a bad solenoid that isn't closing. It should be closed when electrically disconnected. I haven't heard of anybody having the issues after disconnecting it like what you described.
Are you modded/tuned? The only time a car may run rough after this is if the tune is off a bit and you just reset the ECU. The car needs to go to closed loop mode to correct itself. I used to run with it connected for the LTFTs to adjust a bit if needed, and would then electrically disconnect it. It helped any cold start / open loop issues.
Conversely, the trims may be so off from the potential evap issue that disconnecting the solenoid without resetting the ECU could also cause it to run weird for a while, until the ECU can relearn.
It's hard to say without knowing more.
Right there it sounds to me like you've got a bad solenoid that isn't closing. It should be closed when electrically disconnected. I haven't heard of anybody having the issues after disconnecting it like what you described.
Are you modded/tuned? The only time a car may run rough after this is if the tune is off a bit and you just reset the ECU. The car needs to go to closed loop mode to correct itself. I used to run with it connected for the LTFTs to adjust a bit if needed, and would then electrically disconnect it. It helped any cold start / open loop issues.
Conversely, the trims may be so off from the potential evap issue that disconnecting the solenoid without resetting the ECU could also cause it to run weird for a while, until the ECU can relearn.
It's hard to say without knowing more.
Last edited by Stamina; Feb 9, 2011 at 01:29 PM.
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From: USA
I had disconnected mine when i was messing around with a few other things around the same time this thread came out. And yes, my turbo spooled MUCH faster. Threw a code though everytime, (was still GMS1 at the time).
However I run it connected as I imagine you should. It is a neat discovery though.
However I run it connected as I imagine you should. It is a neat discovery though.
I am completely bolted, and tuned with a GMS1 (hopefully a 27psi trifecta soon). I am having a pain in the rear getting the pipe off. I don't want to brake it. I am pushing on the tab (I think). I will give it one more shot.
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From: Tejas
I'm not able to get to my car right now, otherwise, I'd just tell you which direction. lol
Once you push that tab the correct way, it unhooks it so you can then pop the pipe off the solenoid.
I finally found the ring tab on the pipe. Eh to me its more of a trigger between the electrical connection and the pipe.
Here is my findings. When I disconnected the electrical connection and the pipe, It was almost the same as if they were connected. Cat warm up cycle was almost the same, Idle was almost the same (I could not see any difference on the tac, but I could hear it varying just a little). After the cat warmup and idle if I touched the throttle it responded very similarly, However it would drop just a little below idle at most maybe 50RPM and only for a split second. With everything connected, everything was just a little smoother, and if I touched the throttle at idle, the RMP would not drop below idle. I don't think I have a bad purge solenoid. What do you all think? (again I don't have a RPD or a Dashdaq)
Here is my findings. When I disconnected the electrical connection and the pipe, It was almost the same as if they were connected. Cat warm up cycle was almost the same, Idle was almost the same (I could not see any difference on the tac, but I could hear it varying just a little). After the cat warmup and idle if I touched the throttle it responded very similarly, However it would drop just a little below idle at most maybe 50RPM and only for a split second. With everything connected, everything was just a little smoother, and if I touched the throttle at idle, the RMP would not drop below idle. I don't think I have a bad purge solenoid. What do you all think? (again I don't have a RPD or a Dashdaq)
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From: Tejas
I finally found the ring tab on the pipe. Eh to me its more of a trigger between the electrical connection and the pipe.
Here is my findings. When I disconnected the electrical connection and the pipe, It was almost the same as if they were connected. Cat warm up cycle was almost the same, Idle was almost the same (I could not see any difference on the tac, but I could hear it varying just a little). After the cat warmup and idle if I touched the throttle it responded very similarly, However it would drop just a little below idle at most maybe 50RPM and only for a split second. With everything connected, everything was just a little smoother, and if I touched the throttle at idle, the RMP would not drop below idle. I don't think I have a bad purge solenoid. What do you all think? (again I don't have a RPD or a Dashdaq)
Here is my findings. When I disconnected the electrical connection and the pipe, It was almost the same as if they were connected. Cat warm up cycle was almost the same, Idle was almost the same (I could not see any difference on the tac, but I could hear it varying just a little). After the cat warmup and idle if I touched the throttle it responded very similarly, However it would drop just a little below idle at most maybe 50RPM and only for a split second. With everything connected, everything was just a little smoother, and if I touched the throttle at idle, the RMP would not drop below idle. I don't think I have a bad purge solenoid. What do you all think? (again I don't have a RPD or a Dashdaq)
If you did that and it was still running nasty, then it may be a problem unrelated to the evap system.
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From: Tejas
Is it 110% safe? It depends on your car. If you're having problems that bad, I'd recommend taking it to a shop and having them take a look at it. If it's having idling problems, it could be an air/vacuum leak, such as in the intake after the Mass Airflow sensor, loose charge piping, around boost/Manifold Air Pressure sensors, through a solenoid, or a crack in the intercooler. Additionally, if you're noticing any smoke out the exhaust, a compression test may be in order.
I think its all in my head. It only has a slight idle problem during warm up and only if I touch the throttle. Once its warm, I have no problems. I have no smoke in the exhaust. Again, its probably all in my head, but I will check my charged piping and IC.
I found the caps, but only rubber, I want silicone, do you remember what size? Should I put a cap up the pipe?
I am going to disconnect the pipe and reset the ecu this weekend. I will let you know how it goes. I have never disconnected the ECU. Do I just pull up? Haha I am so going to screw up my car. Oh well how else do you learn.
oh yeah, if I had a leak after the MAS wouldn't that throw a CEL? Just thinking the ECU would recognize the missing air, say WTF and throw a CEL.
I found the caps, but only rubber, I want silicone, do you remember what size? Should I put a cap up the pipe?
I am going to disconnect the pipe and reset the ecu this weekend. I will let you know how it goes. I have never disconnected the ECU. Do I just pull up? Haha I am so going to screw up my car. Oh well how else do you learn.
oh yeah, if I had a leak after the MAS wouldn't that throw a CEL? Just thinking the ECU would recognize the missing air, say WTF and throw a CEL.
I think its all in my head. It only has a slight idle problem during warm up and only if I touch the throttle. Once its warm, I have no problems. I have no smoke in the exhaust. Again, its probably all in my head, but I will check my charged piping and IC.
I found the caps, but only rubber, I want silicone, do you remember what size? Should I put a cap up the pipe?
I am going to disconnect the pipe and reset the ecu this weekend. I will let you know how it goes. I have never disconnected the ECU. Do I just pull up? Haha I am so going to screw up my car. Oh well how else do you learn.
oh yeah, if I had a leak after the MAS wouldn't that throw a CEL? Just thinking the ECU would recognize the missing air, say WTF and throw a CEL.
I found the caps, but only rubber, I want silicone, do you remember what size? Should I put a cap up the pipe?
I am going to disconnect the pipe and reset the ecu this weekend. I will let you know how it goes. I have never disconnected the ECU. Do I just pull up? Haha I am so going to screw up my car. Oh well how else do you learn.
oh yeah, if I had a leak after the MAS wouldn't that throw a CEL? Just thinking the ECU would recognize the missing air, say WTF and throw a CEL.
As for what you are talking about. If you had a massive leak from charge pipes or something, the computer doesn't always throw a CEL
By touching the throttle you are forcing it to not spool the turbo for cat warm up. That is why is bogs and sputters until warm.
#2 Hell if i know
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From: Tejas
I think its all in my head. It only has a slight idle problem during warm up and only if I touch the throttle. Once its warm, I have no problems. I have no smoke in the exhaust. Again, its probably all in my head, but I will check my charged piping and IC.
I found the caps, but only rubber, I want silicone, do you remember what size? Should I put a cap up the pipe?
I am going to disconnect the pipe and reset the ecu this weekend. I will let you know how it goes. I have never disconnected the ECU. Do I just pull up? Haha I am so going to screw up my car. Oh well how else do you learn.
oh yeah, if I had a leak after the MAS wouldn't that throw a CEL? Just thinking the ECU would recognize the missing air, say WTF and throw a CEL.
I found the caps, but only rubber, I want silicone, do you remember what size? Should I put a cap up the pipe?
I am going to disconnect the pipe and reset the ecu this weekend. I will let you know how it goes. I have never disconnected the ECU. Do I just pull up? Haha I am so going to screw up my car. Oh well how else do you learn.
oh yeah, if I had a leak after the MAS wouldn't that throw a CEL? Just thinking the ECU would recognize the missing air, say WTF and throw a CEL.
If you decide to disconnect the ECU vs. disconnecting the battery: There will be a plastic latch on the top of each of the two harnesses/connectors that are on the top of the ECU. You lift up on on the latches and continue rotating until each of the harnesses are free to pull off. Then you just pull off the harnesses and wait. To reinstall, just place the harnesses back on top of where they go on the top of the ECU and then rotate the latch until it stops.
The LTFT is used in conjunction with STFT when the ECU calculates how much fuel to inject. The LTFT is used as a way to "calm" the fueling changes that are based on sensor input that the ECU uses, and therefore allows for more precise fueling. If, for instance, you have an intake that tends to throw off the MAF a lot, then the car would be all over the place as far as fueling. The ECU takes the running average of STFTs over an amount of time to create an LTFT.
Here's something I wrote a while back that may help answer many questions at once:
AFR: Air-Fuel Ratio. This is the ratio of molecules of air to molecules of fuel. At about 14.7, the mixture is said to be stoichiometric ("stoich"), and is the point where all the air molecules will react with all the fuel molecules. If there is more fuel than air (<14.7), then the mixture is said to be "rich". If there is more air than fuel (>14.7), then the mixture is said to be "lean". There are advantages and disadvantages to being rich, stoich, or lean. Typical car engines usually run stoich for normal operation, rich for warm-up and full throttle, and lean for long cruising to save gas. *Note: 14.7 is stoich for gasoline. Other fuels, such as E85, require a different ratio to be stoich due to their different chemical makeup (about 9.76 in the case of E85).
Lambda: This is the Air-Fuel Ratio expressed as a quotient, when stoich is the divisor. For example, if you're running at 13.0 AFR, then that would be about 0.88 (13.0/14.7). Some applications, such as tuning for the LNF, are programmed instead in Lambda.
STFT: Short Term Fuel Trim. This is the amount of fuel that the engine computer adds or subtracts to maintain the desired AFR. It is usually expressed as a positive or negative number representing a percentage. The STFT is updated and tweaked very quickly by the engine computer. Intakes and other factors can cause the Mass AirFlow sensor (MAF) to mis-read the amount of air going past it into the engine. The engine computer also uses STFT to help compensate for this.
LTFT: Long Term Fuel Trim. This is the amount of fuel that the engine computer adds or subtracts over time to maintain the desired AFR.
The engine computer looks at both STFT and LTFT when deciding how much fuel to mix with the air it takes in. It then sees how close it got to what it was wanting and re-adjusts the STFT and later LTFT again. This adjust-feedback-adjust approach the engine computer uses when the engine is in normal operation is called "closed loop".
Lambda: This is the Air-Fuel Ratio expressed as a quotient, when stoich is the divisor. For example, if you're running at 13.0 AFR, then that would be about 0.88 (13.0/14.7). Some applications, such as tuning for the LNF, are programmed instead in Lambda.
STFT: Short Term Fuel Trim. This is the amount of fuel that the engine computer adds or subtracts to maintain the desired AFR. It is usually expressed as a positive or negative number representing a percentage. The STFT is updated and tweaked very quickly by the engine computer. Intakes and other factors can cause the Mass AirFlow sensor (MAF) to mis-read the amount of air going past it into the engine. The engine computer also uses STFT to help compensate for this.
LTFT: Long Term Fuel Trim. This is the amount of fuel that the engine computer adds or subtracts over time to maintain the desired AFR.
The engine computer looks at both STFT and LTFT when deciding how much fuel to mix with the air it takes in. It then sees how close it got to what it was wanting and re-adjusts the STFT and later LTFT again. This adjust-feedback-adjust approach the engine computer uses when the engine is in normal operation is called "closed loop".
Last edited by Stamina; Feb 11, 2011 at 03:54 PM.
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From: Tejas
On that note, I had my system disabled without any issue for more miles than I had it enabled. I had constant monitoring capabilities though. I also let the LTFT settle before disabling.
There's a higher chance at this point that something else is the problem, such as a vacuum leak, intake throwing off fuel trims, engine issue, etc. from what you've described.
At this point I would:
1) Check for codes
2) Check fuel trims (since you've got an intake on your car but a canned tune)
3) Reset the ECU (do this after checking #1 and #2, so they won't be erased)
4) Potentially a compression check