Help.
My truck has been running poorly for the last few months and I've already done all the usual (plugs, filters). I purchased the OBD-2 software and ran tests yesterday and this morning.

No CEL, No DTCs

But: I get two EVAP failures.
EVAPG4 Value: -64.0 Min. 2.0
(Evaporative Vapor Generation Maximum Change Phase 4 is -64 in H2O with a minimum limit of 2.0 has FAILED)

EVAPGA4 Value -64 Min 5.0
(Evaporative Vapor Generation Maximum Change Absolute Phase 4 is -64 in H2O with a minimum limit of 5.0 has FAILED)


Any suggestions what to check?

 

More Info:
I just found another "fail" notificatin in my data.

Misfire Monitor Events Tested is 26748 with a max limit of 4000 has failed. Only one cylinder has any misfire data and that is cylinder 1 with a 0.12% with a maximum of 24.1%

Next Day

"Misfire Type A Catalyst Damage Cylinder 6 is .12% with maximum limit 24.61% has PASSED."

Also

Misfire Highest Catalyst Damage Type A is .25% with a maximum limit of 24.61% has PASSED"

And

Misfire Highest Emission Type B is .02% with a max limit of 2.5% has PASSED.

BUT

Misfire Monitor Events Tested is 24536 with a max limit of 4000 has FAILED.

The engine idles low, consistently below 600 rpm in gear and an occasional miss is felt.

Also, feels like it has a significant power "loss" at low rpms, at times almost like a switch goes off after it stumbles out of the gate.

At times, from a slow rolling start, when accelerating onto the free way at 7/8 throttle the engine rpms will rise, dip slightly, then rise again as the truck begins to accelerate.

As I slow to a stop, the rpms sometimes drop to 350 or so before returning to an idle just below 600. Other times, it never dips below 720 or so and idles smoothly.

When I let it idle for an extended period last night in the garage pulling data, the truck became very rough.Next Day

 

Y2k,

I have no idea what EVAPG4 Value: -64.0 Min. 2.0 means. I would like to know. If one of the resident experts would explain I'd appreciate it.

Just going by the symptoms you mention I'd guess EGR system problems. Have you checked for "plugged" EGR passages? If not do a search on EGR you'll find all the info you need. While your there check the PCV system.

Good Luck

 

It actually sounds like you've gat a bad gas cap seal...yeah... as simple as that

 

I'm not trying to step on anyones toes but... the EGR system is a total different system from the EVAP. I agree with Tex that it could be a bad gas cap seal or a plugged return line or a Evap purge valve. Just keep researching and maybe someone with more knowledge will be along soon.

 

y2k,

Wow, I have the same exact senario going on with my truck. I'm real curious what the problem was?? Was it as simple as the cap?


Any help would be appreciated!!

 

anyone get an answer?

 

I have the same problem, I suspect the fuel tank pressure switch. Did you get an answer?

 

pcv system leaks/failure and or a dirty/faulty iac and the gas cap

 

I"ve never gotten a definitive answer. IAC was new when this happened, all ports cleaned. PCV valve was also new.

Have not changed any gas cap.

 

Y2kXLTSport,
First change the gas cap since that is the easiest thing to do.
After I changed the gas cap I still had a problem so I searched further.
What I had was a bad vacuum line to the evac system because of a brake in the vacuum harness just rear of the battery. I fixed the vacuum line and everything is fine. I don't remember the codes but it was an evac code. This can also explain some of the other problems you have if there is just a small vacuum leak. The easiest way to check is pull the vacuum line off the evac valve which is high on the firewall on the drivers side. If there is no vacuum at idle then check further.
Just a thought.

 

There was no pressure or vacuum in the tank when I took the cap off. I am going to look for more vac leaks. What is normal for vacuum at idle? It does sound like a vac leak to me because I also got codes for left and right bank lean. The fuel tank pressure reading of -64 inches of h20 leads me to believe I should hear a loud hiss as I removed the gas cap. There was no hiss and the reading still seems to show a large vacuum in the tank, could the vac loss come from the eec being told that the tank was under extreem vac and was trying to vent?

 

smyles,
It is rare that I hear a hiss when removing the gas cap. If you look at the EVAC vacuum control valve, it has a port to check vacuum to the EVAC system and should not allow more then 1 lb of vacuum. The whole idea is just to vent gas fumes back into the intake and not into the atmosphere.
Vacuum from the line entering the bottom of the EVAC control valve should be normal. Pull the line off and put your finger over the end and it should just about hold itself to your finger. Normal vacuum at idle is 17-20 ".

 

i know this is not related but i have a 72 mustang and when i drive it it will only pick up half a tank of gas and when i stop to fill it back up i get a big swish when i take off the gas cap dose this sound like a cloged vent line or a bad gas cap i have been going crazy trying to figure this out it sucks to fill it up the day before then run out of gas the next day going to work and one last thing will your pvc valve cause this cause mine hasnt been hooked up right thanks 72 mustang