Tahoe won't restart after getting gas - Not the usual issue

[OffRoadN]

Posted this elsewhere, but it was suggested I post it here...

2004 Tahoe 5.3L 4wd. Vehicle runs great at all times except after getting gas. When I attempt to restart after filling up, it stumbles, sputters, and dies. Only way to start (without getting under the hood, see below) is to hold the pedal to the floor, start, then quickly drop RPMs to about 2k for 10 seconds.

I know what you are thinking because I thought it too. Canister purge valve stuck open, but not so!

Tested purge valve at the intake and valve tested good (both electrically and the diaphragm). Wiring is fine with +12 volts on the pink with key on and the ECM driver controlling ground via the green/white. When valve is closed I can hold vacuum (external tester) without any leaking for long periods.

No codes/CEL/MIL when driving the vehicle.

If I get gas, then pop the hood and unplug the electrical connector at the purge valve (vent line still attached), vehicle will start and idle perfectly. As soon as I plug it back in, vehicle runs rough, sputters, and dies. I can feel the valve start pulsing on and off as soon as I plug the connector in.

If I follow what I just outlined above but add the step of raising the idle to about 2k, while plugging in the electrical connector, and holding it there for 10 seconds after putting the valve in operation, then all is well again till next time I need to fill up. Sometimes when doing this procedure, CEL will illuminate with a P0443 code, but only when I'm manually unplugging and plugging in the electrical connector, not while I'm driving the vehicle in between fill ups.

Any ideas???

 

[Donal]

Posted this elsewhere, but it was suggested I post it here...

2004 Tahoe 5.3L 4wd. Vehicle runs great at all times except after getting gas. When I attempt to restart after filling up, it stumbles, sputters, and dies. Only way to start (without getting under the hood, see below) is to hold the pedal to the floor, start, then quickly drop RPMs to about 2k for 10 seconds.

I know what you are thinking because I thought it too. Canister purge valve stuck open, but not so!

Tested purge valve at the intake and valve tested good (both electrically and the diaphragm). Wiring is fine with +12 volts on the pink with key on and the ECM driver controlling ground via the green/white. When valve is closed I can hold vacuum (external tester) without any leaking for long periods.

No codes/CEL/MIL when driving the vehicle.

If I get gas, then pop the hood and unplug the electrical connector at the purge valve (vent line still attached), vehicle will start and idle perfectly. As soon as I plug it back in, vehicle runs rough, sputters, and dies. I can feel the valve start pulsing on and off as soon as I plug the connector in.

If I follow what I just outlined above but add the step of raising the idle to about 2k, while plugging in the electrical connector, and holding it there for 10 seconds after putting the valve in operation, then all is well again till next time I need to fill up. Sometimes when doing this procedure, CEL will illuminate with a P0443 code, but only when I'm manually unplugging and plugging in the electrical connector, not while I'm driving the vehicle in between fill ups.

Any ideas???

Sounds like the tank is being overfilled and the engine systems are sensing flooded condition. Maybe the charcoal canister is empty of charcoal as well.

 

[wjburken]

If you’re having to pull power from the purge valve to get it going, something is likely wrong with it and you just haven’t been able to test for the right set of conditions. For less than $50 and a little time, I’d swap out the purge valve.

 

[OR VietVet]

If you’re having to pull power from the purge valve to get it going, something is likely wrong with it and you just haven’t been able to test for the right set of conditions. For less than $50 and a little time, I’d swap out the purge valve.

Yea, I am very surprised you have not replaced the valve yet, with Genuine GM parts by the way. For what you are going thru, it is an inexpensive parts cannon attempt to fix.

Gas: https://www.rockauto.com/en/moreinfo.php?pk=437883&cc=1424247&pt=4936&jsn=1401


Flex: https://www.rockauto.com/en/moreinfo.php?pk=88006&cc=1424247&pt=4936&jsn=1403

Both under $30 at RA.

By the way, welcome to the forum.

 

[OffRoadN]

Sounds like the tank is being overfilled and the engine systems are sensing flooded condition. Maybe the charcoal canister is empty of charcoal as well.

Not overfilled. It happens even if I'm at 1/4 tank and only add 5 gallons.

So, if the charcoal canister is empty, this will happen?

If you’re having to pull power from the purge valve to get it going, something is likely wrong with it and you just haven’t been able to test for the right set of conditions. For less than $50 and a little time, I’d swap out the purge valve.

Thanks, but the purge valve is closed with key off (as it should be). Additional proof can be found by me filling it up with both the vapor line and the electrical connector connected. Then, right before starting, I disconnect the electrical plug (keeping it closed). After it starts and I plug it back in, it opens (I can feel it with my hands cycling at about a 50% duty cycle) and the troubles start.

Yea, I am very surprised you have not replaced the valve yet, with Genuine GM parts by the way. For what you are going thru, it is an inexpensive parts cannon attempt to fix.

Gas: https://www.rockauto.com/en/moreinfo.php?pk=437883&cc=1424247&pt=4936&jsn=1401


Flex: https://www.rockauto.com/en/moreinfo.php?pk=88006&cc=1424247&pt=4936&jsn=1403

Both under $30 at RA.

Appreciate it, and the reason I haven't is that I'm just not the kind of guy who is in the habbit of part swapping in order to locate a problem. I'm convinced the purge valve is good. If not, I wouldn't be able to leave the hose and electrical while getting gas then disconnect only the electrical. Additionally, at one point I connected a Noid light to the wiring and could visually see every time that the ECM commanded it to open/close. The clicking that I can feel was perfectly in sync with the Noid lighting up.

That said, I have a buddy with a Suburban that should have the same purge valve, I'll ask about swapping them to see what happens. I need gas so if he's good with it, I can do both the swap, and get gas, later this afternoon.

 

[wjburken]

I don’t like firing the parts cannon either, but I will sometimes weigh the cost of a part versus the value of my time. If you’re willing to go through the hassle of swapping valves on your friend’s vehicle, you are already committed to installing it at least twice. Once on your vehicle and once back into his and if it does fix it, then you’re installing it for a 3rd time. I’d just set myself up to do it once and be done with it. If it solves it, great. If not, I now have a new valve.

 

[rockola1971]

That purge valve coil could very well still be opening and closing the valve but that doesnt mean that it is still "good". The coil could still be shorted (not to ground). A coil when used as a electromagnetic pull device is just literally a coil of wire. When the wire's insulation which is a shellac breaks down the coil starts to "melt" together and you lose windings. When you lose windings the resistance lowers overall and the power consumption increases. Ohms Law. Get the resistance of Purge Valve Coil with a multimeter and I can do the calculation for you. Will also need a voltage reading taken at the battery while engine is running. Should be somewhere around 13.8v +.

 

[OR VietVet]

Be sure to know if is "gas" or "flex" fuel. You likely will.

 

[OffRoadN]

I don’t like firing the parts cannon either, but I will sometimes weigh the cost of a part versus the value of my time. If you’re willing to go through the hassle of swapping valves on your friend’s vehicle, you are already committed to installing it at least twice. Once on your vehicle and once back into his and if it does fix it, then you’re installing it for a 3rd time. I’d just set myself up to do it once and be done with it. If it solves it, great. If not, I now have a new valve.

Understood, makes sense. Even worse (to your point) I have already removed & replaced mine like three times for testing. The good news is that it is a 1 minute procedure so, thankfully, there isn't much time wasted.

My buddy said I can have at his Suburban so I'll swing by his house on the way to get gas. Thus, we'll have an answer today and I'll report back. Assuming the problem remains, I might just leave them swapped for a couple of weeks for the heck of it (ok with him, I already checked).

That purge valve coil could very well still be opening and closing the valve but that doesnt mean that it is still "good". The coil could still be shorted (not to ground). A coil when used as a electromagnetic pull device is just literally a coil of wire. When the wire's insulation which is a shellac breaks down the coil starts to "melt" together and you lose windings. When you lose windings the resistance lowers overall and the power consumption increases. Ohms Law. Get the resistance of Purge Valve Coil with a multimeter and I can do the calculation for you. Will also need a voltage reading taken at the battery while engine is running. Should be somewhere around 13.8v +.

Understood, BUT the simple fact remains that it's not sticking open! That is what I expected the problem to be, and I think many others too. The valve is NC so without power it shouldn't flow (and doesn't).

Nonetheless, I appreciate the offer to do the calcs and will get you my voltage and both my, and my buddies, coil resistances. We'll see if that yields anything useful.

Be sure to know if is "gas" or "flex" fuel. You likely will.

Gasoline Sir.

 

[rockola1971]

Understood, makes sense. Even worse (to your point) I have already removed & replaced mine like three times for testing. The good news is that it is a 1 minute procedure so, thankfully, there isn't much time wasted.

My buddy said I can have at his Suburban so I'll swing by his house on the way to get gas. Thus, we'll have an answer today and I'll report back. Assuming the problem remains, I might just leave them swapped for a couple of weeks for the heck of it (ok with him, I already checked).


Understood, BUT the simple fact remains that it's not sticking open! That is what I expected the problem to be, and I think many others too. The valve is NC so without power it shouldn't flow (and doesn't).

Nonetheless, I appreciate the offer to do the calcs and will get you my voltage and both my, and my buddies, coil resistances. We'll see if that yields anything useful.


Gasoline Sir.

A huge current draw on the PCM by the purge valve acting like a short to ground can cause the PCM to go haywire and engine to run like crap. Engine works fine with purge valve unplugged but then goes haywire with purge valve plugged in, right? And just because its clicking and opening doesnt rule out the valve being plugged up with charcoal from your canister.