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

[OffRoadN]

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

Ahhhh, right. I have a Tech2 but recently loaned it out after not needing it for a long time. I'll have to work on getting it back sooner than later!

These are the same tests that are run automatically and it passes them, but I like the idea of doing them manually too.

 

[Fless]

Ahhhh, right. I have a Tech2 but recently loaned it out after not needing it for a long time. I'll have to work on getting it back sooner than later!

These are the same tests that are run automatically and it passes them, but I like the idea of doing them manually too.

Sort of. The automatic tests obviously don't evaluate the data nearly as much as the Tech 2 test does.

 

[rockola1971]

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.


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.

Around 9.1w-9.3w of power draw for both. Not out of the ordinary.
Formula for power is (E x I) Voltage times Current
Formula for Current is (E/R) Voltage divided by Resistance

I=14.06 / 21.2 = .66A
P=14.06 x .66 =9.27w

 

[rockola1971]

Ahhhh, right. I have a Tech2 but recently loaned it out after not needing it for a long time. I'll have to work on getting it back sooner than later!

These are the same tests that are run automatically and it passes them, but I like the idea of doing them manually too.

Loaned out your Tech 2? Friends dont let Friends loan out their Tech 2's !!!!!

 

[OffRoadN]

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.

Easy enough to check the rail pressure so I will, but keep in mind that if I prevent the purge valve from opening (by removing the electrical connector) this problem disappears.

I could probably keep running like this forever (with a resistor across the wires to simulate a connected solenoid), but it's purpose, to clean out/resfresh the charcoal canister is beneficial so I would prefer to keep the purge valve in the system.

Sort of. The automatic tests obviously don't evaluate the data nearly as much as the Tech 2 test does.

Very true, but it will give a pass/fail for both the purge valve and the vent valve (as well as detect shorts/opens) and valve operations is what's at the heart of the matter.

Loaned out your Tech 2? Friends dont let Friends loan out their Tech 2's !!!!!

Hahaha! Family friend who is like a dad to me. Lost mine very young, he's a great guy, but (now) lives in a different state. I think I have a USB computer solution with Tech2Win but I'll need to dig it up and see about getting the software installed. I've never played with it because I always used the Tech2 handheld.

 

[Donal]

Easy enough to check the rail pressure so I will, but keep in mind that if I prevent the purge valve from opening (by removing the electrical connector) this problem disappears.

I could probably keep running like this forever (with a resistor across the wires to simulate a connected solenoid), but it's purpose, to clean out/resfresh the charcoal canister is beneficial so I would prefer to keep the purge valve in the system.


Very true, but it will give a pass/fail for both the purge valve and the vent valve (as well as detect shorts/opens) and valve operations is what's at the heart of the matter.


Hahaha! Family friend who is like a dad to me. Lost mine very young, he's a great guy, but (now) lives in a different state. I think I have a USB computer solution with Tech2Win but I'll need to dig it up and see about getting the software installed. I've never played with it because I always used the Tech2 handheld.

Thanks for posting a thought provoking situation. I have read and reread the entire thread several times. Your tests and trials seem to eliminate the purge valve, vent valve, and canister. Using a similiar vehicle to certify components is good thing and helpes focus on the solution. I am considering the possiblity of the computer sensing a lean condition and adding fuel on start up after the tank being opened for refueling. A computer malfunction of some sort, or a sensor reading in error.
Live data during the start up is your friend here. Now I got to go and understand more of what the computer sees during a refuelling event and/or a change in fuel tank pressure.

Excerpts from pages 3258-3260.
Fuel pressure regulator compensates for engine load by increasing pressure when LOW Vaccum is experienced.

Internal PCM calibration controls fuel delivery during starting, clearing flood mode, deccelration and heavy accelration modes.
PCM also uses the ECT, TP and MAP sensors to dertermine the proper A/F ratio for starting.
When the TP sensor is at wide open, (WOT or WFOT,) PCM redues the injector pulse width in order to increase the A/F ratio.

Starting

With ignition switch in the ON position, before engaging starter, the PCM energizes the fuel

pump relay for 2seconds allowing fuel pump to build pressure. Speed density is determined by

inputs from the engine RPM, the IAT and MAP sensors. The PCM first tests speed density, then

switches to the MAF sensor. PCM also uses the ECT, TP and MAP sensors to determine the

proper air/fuel ratio for starting. The PCM controls the amount of fuel delivered in the starting

mode by changing the width of the fuel injector pulse.

 

[OffRoadN]

Thanks for posting a thought provoking situation. I have read and reread the entire thread several times. Your tests and trials seem to eliminate the purge valve, vent valve, and canister. Using a similiar vehicle to certify components is good thing and helpes focus on the solution. I am considering the possiblity of the computer sensing a lean condition and adding fuel on start up after the tank being opened for refueling. A computer malfunction of some sort, or a sensor reading in error.
Live data during the start up is your friend here. Now I got to go and understand more of what the computer sees during a refuelling event and/or a change in fuel tank pressure.

...

Your welcome, thanks for taking it so seriously and spending so much time!

I too thought that the purge valve, vent valve, and canister had been eliminated as the problem(s), but, I believe it was you who mentioned the canister possibly being out of charcoal. This got me thinking... what if it is out (of course, where would it go as there aren't any signs of it being in the lines?), then maybe the fumes are passing through to the purge valve in a much greater volume (and pressure) and the line is substantially richer than it would normally be under fill up conditions. Couldn't this cause this issue as the valve would be pulsing on and off a set amount (based on an SD mapping) expecting a much leaner, and less in volume, vent line mixture?

Assuming there isn't a check valve on at the canister, it seems like maybe I would be able to, after refueling, blow through the vent line backward toward the canister (to lean out the mixture in the line), then start it without the problem.

In regard to a change in pressure, could I somehow simulate a refueling event using an air compressor so I can do additional comprehensive tests at my house without having to actually get gasoline?

The pages you mention, where are those from? The factory Helm manual (which I don't have), or something else?

 

[Fless]

I don't recall if the canister has been checked or replaced. If the charcoal pellets inside are gasoline-soaked then there is probably raw fuel, or very strong fumes, being pulled into the intake when starting up. Disconnect the canister lines and see if any gas or pellets come out.

 

[Donal]

Yes factory manual 2006 and earlier. 9979 pages. I am thinking that you have covered the vap system and I not seeing it enabling your situation. I will keep looking. Got to work with garden tools this afternoon. Tak a looks at short term trims open loop and closed loop.

 

[Fless]

To be clear, the charcoal pellets should remain inside the canister. Any migration outside of the canister will cause evap and other issues.