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My wife and I drive a "senior mobile" Mostly short trips and the last three times she has refueled she has complained of rough engine, surging and stalling immediately after refueling.

Mileage is above 17mpg City and 27mpg Hwy

The last time we re-fueled the engine started easily, ran rough, then stalled at the next three red lights. We aborted the trip and headed for home. Within a mile the problem cleared and we resumed the trip with no further problems.

Known"
No MIL, No DTC's No indications from under the hood of a problem.

Car was tuned 18000 miles ago @ 62,000, when we bought it.

Diagnostic plan: Hook it up to the laptop again, check for DTCs

Pick a different gas station: See if the pump could be spiking the car's PCM.

Change the Gas Cap: Should have tripped a DTC if it is bad. Generally doesn't cause a performance issue.

Check fuel pressure at the Regulator: Don't see how refueling could influence that.

Anyone have a plan for this before I...

Send it to the dealer: & BEND OVER!:icon_frow
 

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When refueling, the pressure in the tank is relieved (the evaporative emissions system is a closed system), so the tank is full of freshly kicked up vapors after the tank is filled. So the LTFT's take off negative and it goes rich for a while (5 min or so). Of course the PCM compensates for that and as the car is driven, the vapors are captured in the charcoal canister to be burned later by the engine as the car is driven.

The PCM doesn't pull vapor out of the tank into the charcoal canister at idle, just off idle.

Check for leaks from the engine to the charcoal canister, sounds like you have a leak. Is the green cap on the hose missing or loose?

Or there is raw fuel getting up the pipe. Is it after filling with full tank or partial? Say if you toss in 1 gallon, does it do it? It is only problematic at idle or cruising?

Remember, the evap solenoid MUST BE CLOSED at idle, and IIRC, on decel. So if the solenoid is stuck open, it would be really bad after a fill up.

Look up Evaporative Emissions.



My wife and I drive a "senior mobile" Mostly short trips and the last three times she has refueled she has complained of rough engine, surging and stalling immediately after refueling.

Mileage is above 17mpg City and 27mpg Hwy

The last time we re-fueled the engine started easily, ran rough, then stalled at the next three red lights. We aborted the trip and headed for home. Within a mile the problem cleared and we resumed the trip with no further problems.

Known"
No MIL, No DTC's No indications from under the hood of a problem.

Car was tuned 18000 miles ago @ 62,000, when we bought it.

Diagnostic plan: Hook it up to the laptop again, check for DTCs

Pick a different gas station: See if the pump could be spiking the car's PCM.

Change the Gas Cap: Should have tripped a DTC if it is bad. Generally doesn't cause a performance issue.

Check fuel pressure at the Regulator: Don't see how refueling could influence that.

Anyone have a plan for this before I...

Send it to the dealer: & BEND OVER!:icon_frow
 

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Send it to the dealer: & BEND OVER!:icon_frow
I resent that

AAA did a study a few years back that found the average repair at a dealer was $100 cheaper!

It isn't hard to figure out why. We are trained. We are shipped mandatory tools are the cost to the dealer.

In 2000 GM came out with ORVR on select vehicles.

I will have to look for that info at home for you. The ORVR has a unique way it deals with fillings. I think. I was trained on it in 1999.

ORVR EVAP System Operation
The Evaporative Emission (EVAP) control system limits the fuel vapors from escaping into the atmosphere. The EVAP transfers the fuel vapors from the sealed fuel tank to an activated carbon (charcoal) storage device (EVAP canister). The EVAP canister stores the vapors until the engine is able to use the extra fuel vapor. When the engine is able to use the extra fuel vapor, the intake air flow purges the fuel vapor from the carbon element and then the normal combustion process consumes the fuel vapor. The system is required in order to detect the evaporative fuel system leaks as small as 0.040 inches between the fuel filler cap and the EVAP canister purge valve. The system can test the evaporative system integrity by applying a vacuum signal (ported or manifold) to the fuel tank in order to create a small vacuum.

The PCM then monitors the ability of the system to maintain the vacuum. If the vacuum remains for a specified period of time, then there are no evaporative leaks, and a PASS is reported by the PCM. If there is a leak, the system either will not achieve a vacuum, or a vacuum cannot be maintained. Usually a fault can only be detected after a cold start with a trip of sufficient length and driving conditions to run the needed tests. The enhanced evaporative system diagnostic conducts sub-tests in order to detect the fault conditions. If the diagnostic fails a sub-test, the PCM stores a Diagnostic Trouble Code (DTC) in order to indicate the type of fault detected.

The EVAP diagnostic tests include the following tests:

Weak Vacuum Test: This tests for large leaks and blockages in the EVAP system. The FTP sensor detects low fuel tank pressure resulting from a large vacuum leak or a restriction in the vacuum supply to the fuel tank. The FTP sensor value should increase over a period of time. If the PCM does not detect in increase, a malfunction is indicated by setting DTC P0440.

Weak Vacuum Follow-up Test: This tests the EVAP system after the Weak Vacuum Test has failed. The FTP sensor looks for high tank vacuum over a period of time. If this occurs. the Weak Vacuum Test will Pass. If Weak Vacuum does not pass, the test continues through this ignition cycle.

Vacuum Decay Test: This tests for small leaks in the EVAP system. The decay rate is determined by measuring the change in fuel tank pressure (vacuum) over a period of time. If the decay rate is greater than a calibrated value, than another vacuum decay test will be initiated. If vacuum decay is still greater than a calibrated value, a malfunction is indicated by setting DTC P0442.

Fuel Vapor Build Pressure Test: This test is used to determine the vacuum leak size. When the vacuum has decayed to near zero, the PCM subtracts measured sloap from the vacuum decay to calculate to predict leak size. If the calculation indicates that a leak is present, the small leak test will fail.

Canister Vent Restriction Test: This tests for a restriction in the EVAP vent system. The FTP sensor looks for sufficient vacuum from the engine intake manifold. After a period of time and conditions have been met, then this test will pass. If the vacuum value is to high, a malfunction is indicated by setting a DTC P0446.

Purge Valve Leak Test: This tests for small leaks to the intake manifold. This is accomplished by sealing the EVAP system purge valve and vent valve, and allowing the PCM to monitor the FTP sensor. The FTP sensor value should not increase. If the PCM detects an increase, a mailfunction is indicated by setting DTC P1441.
 

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Guess the first things I would check would be leaky fuel regulator or leaky intake plenum. When the plenums are failing, their first symptoms are slight coolant leak which can duplicate you miss/stall descriptions. While that evap issue is possible, it's sort of uncommon.

Good luck, Jake
 

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Guess the first things I would check would be leaky fuel regulator or leaky intake plenum. When the plenums are failing, their first symptoms are slight coolant leak which can duplicate you miss/stall descriptions. While that evap issue is possible, it's sort of uncommon.

Good luck, Jake
FPR would be my first item to check, but if it is only on filling then I think it has an ORVR malfunction.

Pull the vacuum hose off of the FPR and check for fuel
 

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Discussion Starter #6 (Edited)
Refueling update...

FPR would be my first item to check, but if it is only on filling then I think it has an ORVR malfunction.

Pull the vacuum hose off of the FPR and check for fuel
Thank you all for the Helpful responses.
And my apologies for the critical comment about dealer pricing..

I pulled the Vac hose of the FPR... No fuel or even vapors noticed.

Ran with the computer linked to the car. I use OBDcom.com's software/Hware

1. Drove 2 miles, added 3+ Gal fuel: No problem.

2. Drove 4 miles, Filled the tank. (to first pump shut off)
Again, No problem ...

3. Watchec STFT & LTFT as we drove home.
STFT stayed near 0. LTFT went to about -20 then returned to-0.8 by the time we got home. I recorded the last half mile and include it as a CSV with Graph at the end. Scan rate of the computer was 1.4/sec.
 

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