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.

 

[Fless]

Purge valves can be intermittent. Maybe it's misbehaving when it gets warm.

 

[OffRoadN]

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.

Not really. The engine runs fantastic at all times except just after getting gas. Doesn't need to be a full tank (and often isn't). Happens after adding just a few gallons regardless of the level prior to filling. Tank is NEVER overfilled.

Definitely not plugged with charcoal as I have manually activated the valve and can blow through it with ease and without debris being expelled.

As to the multimeter readings... Voltage was at 14.06 Volts and coil resistance is 21.2 Ohms on my buddies (which was installed on his Suburban but now installed on my Tahoe), and 21.5 Ohms on the one that was originally on my vehicle.

Purge valves can be intermittent. Maybe it's misbehaving when it gets warm.

Good thought, but I still go back to the fact that it passes all the OBD-II test cycles (for both purge valve and vent valve) and when I unplug it, the valve is closed and stays closed. If I keep it unplugged but put a Noid on the unplugged connector I can see it rapidly flash on and off just after I start the vehicle. If I connect the connector I can feel this is happening with the solenoid in addition to seeing it.

 

[Fless]

Wouldn't hurt to swap out the purge valve. Since it seems that it's getting over-fueled just prior to a warm restart, you may want to do an injector balance test. One may be flooding out a cylinder.

What do your short- and long-term fuel trims look like? Both banks.

 

[OffRoadN]

During the swap, I noticed that mine is missing a rubber (maybe silicone?) piece that fits under the solenoid. It only removes play, does not affect performance. Mine seemed too loose so I had previously added a couple of washers. Now I see it's missing a part. Anyone know the part number for this? I can't find any exploded parts diagrams on the web anymore.

I'll post in a separate thread with a pic of it, but thought I would mention it here too.

 

[OffRoadN]

Wouldn't hurt to swap out the purge valve. Since it seems that it's getting over-fueled just prior to a warm restart, you may want to do an injector balance test. One may be flooding out a cylinder.

What do your short- and long-term fuel trims look like? Both banks.

I did the swap and will update below. NOT ALL warm restarts! It warm restarts just fine as long as I haven't just gotten gas.

I loaned out my Tech2 so I can't see fuel trims right now (well unless I go to Autozone and see if they'll do it for me).

UPDATE: I swapped out the purge valve and the EXACT same problem is occurring. Swapped them, warm restarted just fine, drove to gas station just fine, filled up (only added 4 gallons which brought me to almost 3/4 tank), attempted a start and no go. Held pedal to the floor, started, dropped down to 2k RPMs for about 10 seconds, drove away just fine. Exact same experience as I have been having with my purge valve.

The valve that was on my Tahoe is now on my buddy's Suburban. It started and ran just fine so we are going to leave them this way for now. Since mine didn't have the rubber piece, his vehicle is currently lacking it until I swap them back in a couple of weeks or so (want to have him get gas before swapping back).

 

[B-train]

Have you tried filling your truck and just leave it running? I'd be curious to know if it starts stumbling. Also, what happens if you open the gas cap and leave it to atmosphere without putting an fuel in it? I'm just trying to figure out if there is some weird tank pressurization or vacuum condition.

 

[Fless]

Even though we think it's not an emissions issue, a purge and seal procedure would indicate that the fuel tank pressure sensor is working and the fuel system is sealing (and holding) properly. Almost a SWAG but a possibility.

EDIT: could also monitor fuel tank pressure before, during, and after fueling, watching for oddities.

 

[OffRoadN]

Have you tried filling your truck and just leave it running? I'd be curious to know if it starts stumbling. Also, what happens if you open the gas cap and leave it to atmosphere without putting an fuel in it? I'm just trying to figure out if there is some weird tank pressurization or vacuum condition.

Yes, I have. It runs just fine I don't notice it stumbling while filling, but it's been awhile and I can do it again.

Lost me on the second part. Do you want me to remove the gas cap and let it sit overnight, or remove it and do a warm restart, or remove it while driving? I haven't tried any of these so let me know what you would like me to test and I'll make it happen!

Edit: Oh, I have kept the gas cap off the truck when trying to restart right after filling. Same problem, but I can try at other times as well if that would be good...?

Even though we think it's not an emissions issue, a purge and seal procedure would indicate that the fuel tank pressure sensor is working and the fuel system is sealing (and holding) properly. Almost a SWAG but a possibility.

EDIT: could also monitor fuel tank pressure before, during, and after fueling, watching for oddities.

What is a purge and seal procedure? Do you mean the OBDII tests that are run for the purge and vent solenoids? Those complete without error.

I haven't closely monitored tank pressure, but I have pulled the nozzle just about all the way out while filling and pulled back (hard) on the flapper that normally seals and can feel some (very light) fumes escaping. through the filler neck this way. No difference, still stumbles, if I don't floor it when starting (or disconnect the electrical connector on the purge solenoid).

 

[Fless]

Purge and seal can be done with a Tech 2 or other bidirectional scanner.

 

[B-train]

Yes, I have. It runs just fine I don't notice it stumbling while filling, but it's been awhile and I can do it again.

Lost me on the second part. Do you want me to remove the gas cap and let it sit overnight, or remove it and do a warm restart, or remove it while driving? I haven't tried any of these so let me know what you would like me to test and I'll make it happen!

Edit: Oh, I have kept the gas cap off the truck when trying to restart right after filling. Same problem, but I can try at other times as well if that would be good...?

What is a purge and seal procedure? Do you mean the OBDII tests that are run for the purge and vent solenoids? Those complete without error.

I haven't closely monitored tank pressure, but I have pulled the nozzle just about all the way out while filling and pulled back (hard) on the flapper that normally seals and can feel some (very light) fumes escaping. through the filler neck this way. No difference, still stumbles, if I don't floor it when starting (or disconnect the electrical connector on the purge solenoid).

OK. You answered my questions. I was going to have you just open the tank to atmosphere on a hot restart like would happen at the station but it sounds like you've already ruled that out.

One other thing you may want to look at would be the fuel pressure regulator. I've seen them fail and flood out engines. It was common for awhile in the early 2000's on various vehicles.