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07-01-19 New Month Monday Workchat

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07-01-19 New Month Monday Workchat

Old 07-01-2019, 06:59 AM
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07-01-19 New Month Monday Workchat

Back at it gain.
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Old 07-01-2019, 07:02 AM
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So excited for this week....

Not
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Old 07-01-2019, 07:32 AM
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its a short week tho
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Old 07-01-2019, 08:21 AM
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Anybody know exactly how the stock EVAP canister back by the fuel tank functions? Is there a solenoid controlled by the ECU that is responsible for venting the gas tank that if the ECU does not command it to open the fuel tank is essentially sealed off? My current theory for why my fuel pump flow drops off after extended run intervals is that since my ECU has minimal functionality with only a few components connected that it is not commanding the vent valve in the rear EVAP canister to open. Over time this causes a pressure drop in the fuel tank from displaced fuel and ultimately causes my fuel pump to lose flow trying to pump against a vacuum. This would also explain why the fuel pump works perfectly fine again later. People familiar with the EVAP canister, could this be what is happening?
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Old 07-01-2019, 09:47 AM
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In, amazing start to the week. Technical assistance closed one of my cases AGAIN for the third time before coming to a solution to the turbo noises on a 14 Malibu. This time really pissed me off bc they had me send in data logs and left me with "Once the session logs have been reviewed and a direction can be determined you will be contacted."

Originally Posted by jdbaugh1 View Post
Anybody know exactly how the stock EVAP canister back by the fuel tank functions? Is there a solenoid controlled by the ECU that is responsible for venting the gas tank that if the ECU does not command it to open the fuel tank is essentially sealed off? My current theory for why my fuel pump flow drops off after extended run intervals is that since my ECU has minimal functionality with only a few components connected that it is not commanding the vent valve in the rear EVAP canister to open. Over time this causes a pressure drop in the fuel tank from displaced fuel and ultimately causes my fuel pump to lose flow trying to pump against a vacuum. This would also explain why the fuel pump works perfectly fine again later. People familiar with the EVAP canister, could this be what is happening?
The vent valve on the canister is open at rest. The ecm turns it on and seals it when its purging or testing. If its not venting when disconnected then its either stuck or your canister is stopped up. If liquid fuel gets into the canister it can cause the charcoal beads to stick together and become a solid block. The canister is "serviceable", you can open it and check the charcoal and replace it if you can find a gas resistant mesh bag to hold it in. Ive yet to find a bag that was affordable so I have reused the old one for family vehicles, just used staples to close it back up. Pure activated charcoal that is used for fish tanks will work if that's your issue.

Last edited by Kolt; 07-01-2019 at 10:22 AM.
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Old 07-01-2019, 10:15 AM
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In I'm having Thursday and friday off this week so that should be nice. Maybe I can work on my cars
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Old 07-01-2019, 10:23 AM
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Originally Posted by jdbaugh1 View Post
Anybody know exactly how the stock EVAP canister back by the fuel tank functions? Is there a solenoid controlled by the ECU that is responsible for venting the gas tank that if the ECU does not command it to open the fuel tank is essentially sealed off? My current theory for why my fuel pump flow drops off after extended run intervals is that since my ECU has minimal functionality with only a few components connected that it is not commanding the vent valve in the rear EVAP canister to open. Over time this causes a pressure drop in the fuel tank from displaced fuel and ultimately causes my fuel pump to lose flow trying to pump against a vacuum. This would also explain why the fuel pump works perfectly fine again later. People familiar with the EVAP canister, could this be what is happening?
leave your fuel fill cap loose and see if that corrects it. I would put money down that that isn't your issue. Also, why not delete the evap now that it is obsolete?

I'm willing to bet that something with your hydro mat/modified setup is causing issues with the canister. Or the pump isn't seated properly to allow the canister to fill as designed. I have no idea how you set it up/modified it (or really any other details of your issue), but that's where i would start looking first. You might be depleting the canister after whatever runtime, and then once it sits for a while it allows the can fuel level to equalize with the tank level. Just like the canister is supposed to hold/contain fuel when it is pulled from the tank, it will also keep fuel out while its in the tank if the pump isnt drawing fuel in like it is supposed to. Then after it sits for some time, enough fuel works its way back in to start and run for a while.

Is it worse with lower fuel levels?
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Old 07-01-2019, 10:33 AM
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Originally Posted by 07blackg5 View Post
leave your fuel fill cap loose and see if that corrects it. I would put money down that that isn't your issue. Also, why not delete the evap now that it is obsolete?

I'm willing to bet that something with your hydro mat/modified setup is causing issues with the canister. Or the pump isn't seated properly to allow the canister to fill as designed. I have no idea how you set it up/modified it (or really any other details of your issue), but that's where i would start looking first. You might be depleting the canister after whatever runtime, and then once it sits for a while it allows the can fuel level to equalize with the tank level. Just like the canister is supposed to hold/contain fuel when it is pulled from the tank, it will also keep fuel out while its in the tank if the pump isnt drawing fuel in like it is supposed to. Then after it sits for some time, enough fuel works its way back in to start and run for a while.

Is it worse with lower fuel levels?
No it did it with a full tank. The only factor that seems to cause it is extended run intervals. Canister filling/depleting is non-factor because it essentially no longer exists. The hydromat is completely covered in fuel so the only way it would be a fuel depletion issue caused by that would be if the hydromat straight up doesn't work and isn't allowing fuel to pass through suddenly like an on off switch after extended run intervals. I'm not going around corners and wasn't even moving the car when I experienced this issue on the dyno so I can't really imagine a scenario that the hydromat would cause fuel starvation after extended run periods rather suddenly as the fuel tank was full and not sloshing around.

It only happens if I run the car for over an hour continuously and it has only happened twice. Once after I spent a good amount of time messing with the idle tune and the other time at the end of about an hour long dyno session. I shut the car off briefly to unstrap the car and remove from they dyno to drive home and the fuel flow and thus pressure was back to working normally again.

I do plan on deleting the EVAP canister. I just want to pinpoint if that was the cause or not because I don't want to suddenly lose fuel pressure and go lean during a power run if it is being caused by something else.

Last edited by jdbaugh1; 07-01-2019 at 10:41 AM.
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Old 07-01-2019, 11:28 AM
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So I decided to connect my multimeter to see if the valve was energized as Kolt indicated would put the valve in the closed position and it is energized constantly. What my ECU is doing is really unpredictable because it see's a crank signal but it doesn't see really anything else connected to the engine so it's hard to predict because it isn't even close to functioning like it would on a normal working car. The valve is even energized with the car recently turned off like you can see in the picture below but who knows if that times out after a while. At this point I think I can reasonably assume this closed vent valve could be causing me issues.
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Old 07-01-2019, 11:38 AM
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I got to thinking that may have constant 12V power routed with a ground trigger which would explain why it stays on indefinitely with the car turned off and that appears to be the case. However, it is still energized as long as the car is running and about 5-10 seconds after it is turned off.
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Old 07-01-2019, 11:56 AM
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If you're planning on deleting it, why not just delete it instead of spending time troubleshooting something that is coming off anyway? Worst case you still have the issue, but still get something done you planned on doing anyway. VS spending time troubleshooting something that might not even be the issue just to take it all off anyway.
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Old 07-01-2019, 12:06 PM
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Constant 12v power, ecm grounds the solenoid.
evap schematics.pdf
Attached Thumbnails evap-schematics-.bmp  
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Old 07-01-2019, 12:09 PM
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Originally Posted by 07blackg5 View Post
If you're planning on deleting it, why not just delete it instead of spending time troubleshooting something that is coming off anyway? Worst case you still have the issue, but still get something done you planned on doing anyway. VS spending time troubleshooting something that might not even be the issue just to take it all off anyway.
I didn't have time to delete the canister over my lunch hour but I did have time to hook up a multimeter. And like I said above, I'd like to verify the cause before I make a change and hope the issue is fixed without verifying only to have it surprise me in the middle of a pass or autocross run and causing the car to lean out. It only displays symptoms after extended run times and during high fuel demand because when the flow drops off it maintains normal pressure at idle only to drop with demand as I get into the throttle. I don't want to have to stare at the AFR gauge every time a do a pull in the case that the EVAP canister wasn't causing the issue. If I verify the canister is the cause beforehand I can have confidence I will have adequate fuel flow when I need it most.
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Old 07-01-2019, 12:12 PM
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Originally Posted by Kolt View Post
Constant 12v power, ecm grounds the solenoid.
Attachment 62264
Yeah that's what I noticed. Solenoid is grounded any time the car is running which would mean the valve is closed the whole time the car is running. It sounds like with a normally functioning ECU the valve would only close intermittently for short periods of time.
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Old 07-01-2019, 01:16 PM
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Originally Posted by jdbaugh1 View Post
I didn't have time to delete the canister over my lunch hour but I did have time to hook up a multimeter. And like I said above, I'd like to verify the cause before I make a change and hope the issue is fixed without verifying only to have it surprise me in the middle of a pass or autocross run and causing the car to lean out. It only displays symptoms after extended run times and during high fuel demand because when the flow drops off it maintains normal pressure at idle only to drop with demand as I get into the throttle. I don't want to have to stare at the AFR gauge every time a do a pull in the case that the EVAP canister wasn't causing the issue. If I verify the canister is the cause beforehand I can have confidence I will have adequate fuel flow when I need it most.
I mean you can pop the evap hose off the throttle body and temporarily cap the nipple without even having to go under the car. No matter what you do with the evap, you're still going to have to hawk the wideband for a while regardless until you actually verify it was the issue.

I'm not trying to be a dick, just trying to save you some time and effort, but you do you.
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Old 07-01-2019, 01:26 PM
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Originally Posted by 07blackg5 View Post
I mean you can pop the evap hose off the throttle body and temporarily cap the nipple without even having to go under the car. No matter what you do with the evap, you're still going to have to hawk the wideband for a while regardless until you actually verify it was the issue.

I'm not trying to be a dick, just trying to save you some time and effort, but you do you.
Evap line doesn't even exist anymore. No EVAP purge valve connected to TB. TB nipple is capped off. What we are talking about is the charcoal canister located back by the fuel tank. The nipple, on the rear EVAP canister that would normally be routed to the purge valve in the engine bay, is discontinued and now open to atmosphere. The EVAP canister is now essentially just a charcoal filtered gas tank vent as long as the EVAP canister vent solenoid is in its "at-rest" non-energized state. This is the valve we have been referencing, not the purge valve in the engine bay. I now have the evap canister vent solenoid unplugged, so with the vent-valve open, my gas tank should be vented to atmosphere through a charcoal filter. All deleting the EVAP canister should do at this point is remove the charcoal filtration.

Last edited by jdbaugh1; 07-01-2019 at 01:36 PM.
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Old 07-01-2019, 01:48 PM
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To clarify, I do plan on deleting the EVAP charcoal canister altogether and installing a little breather filter in it's place. I just wanted to verify that the EVAP canister could actually prevent the fuel tank from venting if commanded improperly from the ECU. Based on what I have been told today it sounds like the EVAP canister can and was preventing the fuel tank from venting to atmosphere. If my current understanding of the EVAP canister function is correct and there exists no other mechanism to vent the fuel tank it seems plausible that it caused a low pressure situation to develop which prevented the pump from providing adequate flow at high demand.
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Old 07-01-2019, 01:57 PM
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so you are still using the factory ecu alongside the aem?
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Old 07-01-2019, 02:05 PM
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Originally Posted by 07blackg5 View Post
so you are still using the factory ecu alongside the aem?
Factory ECU still runs dash cluster for speed, RPM, fuel gauge, ECT display, electric power steering, AC, starter/ignition and alternator control. Not sure what else BCM-wise relies on stock ECU.
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