P0442 2001 grand am 3.4L small leak

[autojoe]

Not too familiar with this scan tool functional tests snap on solus pro.....getting purge at idle that increases when gas is given.ftp sensor around 1.5 volts.no vacuum through purge solenoid when tested off car.should there be purge at idle?could the purge solenoid be sticking?i wouldnt think.someone told me to smoke system that it has a plastic gas tank and the seals on top leak.any ideas or tests to run with this scan tool to point me in the right direction.thanks in advance.Joe

[sbreland73]

Not too familiar with this scan tool functional tests snap on solus pro.....getting purge at idle that increases when gas is given.ftp sensor around 1.5 volts.no vacuum through purge solenoid when tested off car.should there be purge at idle?could the purge solenoid be sticking?i wouldnt think.someone told me to smoke system that it has a plastic gas tank and the seals on top leak.any ideas or tests to run with this scan tool to point me in the right direction.thanks in advance.Joe

Yes, purge at idle is common for most makes after the engine is warm. No, there should be no flow (or vacuum) with the purge solenoid off, as it is a normally closed valve that is PWM operated to open. Try the other functions of the bi-directionals such as purge and seal while observing the FTP pid, and see the rate of decay. GM vehicle are notorious for their vent valves getting dirty and not sealing all the way, so you could command a vent valve close test, and then smoke the system. HTH

[autojoe]

thanks for reply

[autojoe]

how fast should vacuum decay when sealed?

[Orevin]

how fast should vacuum decay when sealed?

That depends on fuel level, fuel temperature, ambient temperature and other factors. A pretty good rule of thumb: FTP voltage should not drop more than 0.4 V in 30 seconds. I usually wait 45 to 60 seconds.

[sbreland73]

That depends on fuel level, fuel temperature, ambient temperature and other factors. A pretty good rule of thumb: FTP voltage should not drop more than 0.4 V in 30 seconds. I usually wait 45 to 60 seconds.

Thanks Kai, I was waiting for you to jump in and say that.

[autojoe]

thanks guys.

[autojoe]

P0442 2001 grand am 3.4L small leak

hello again......pressure dropping with vent closed.tested purge and vent solenoids for sticking and tested good.smoked at evap schrader and showed no leaks but no smoke when removed gas cap.there is a fuel limiter valve in gas tank.i looked at alldata for a fuel spitback valve in filler neck but did not show one.could I take hose from gas tank off fuel filler neck and smoke filler neck for leaks?or is there a spitback valve in the filler neck to prevent smoke from doing this?in that case do I have to drill a hole in a fuel cap like seen on this site and pinch the hose from filler neck to gas tank closed and smoke from cap down?if no spitback valve in filler neck then could I smoke from bottom of filler neck up to cap?I hope this makes sense.thanks in advance.

[Bob's Garage]

It dawned on me the other day, that we have done a lot of fuel filler necks on GM products for P0440 General Evap Problem & P0455 Evap Large Leaks and possible P0442 small leaks.


The first one I did several years ago kicked my a$$, until I smoked the evap system from the gas cap forward. That is when I found the fuel filler neck leaking. I use a Redline adapter that uses two sides tape on a round adapter.It sticks directly to the top surface on the filler neck. This will not seal well on a rusty surface. I also use the Blue Point adapter that goes around the top of the neck, these can also be problematic when thhere is flake rust on the outside of the neck and the rubber cannot get a smooth enough surface to seal.

There is a check valve in the fuel tank that blocks pressurized smoke from getting to the filler neck. A normal smoke test from the Evap service port or Purge hose will not reveal this problem. The smoke pressure will close the check valve.

The PCM knows that there is a leak because it uses vacuum to find Evap leaks and vacuum actually pulls the check valve away from it's seat whereas pressurized smoke tends to isolate the filler neck leak by holding the check valve closed and blocking the filler neck from smoke pressure.

This is a huge problem in the "rust belt" where salt causes filler neck corrosion around a plastic "no spark" filler hole. Eventually, the plastic loses its bond with the metal filler neck causing a small, to large evap leak:

1998 Intrigue filler neck.jpg


I have seen this on GM vehicles from the late 1990's such as Grand Ams, Malibus, Grand Prixs and Impalas

Some filler necks are already obsoleted by GM but aftermarket replacements are available through Dorman and Spectra, the last one we did was a poor fit though...

[greasybob]

No need to start drilling holes. This filler neck adapter from Blue Point will stretch over most openings, just hook up your smoke machine and you can test the fuel system for leaks from both ends.

[autojoe]

thanks for replys....i have the rubber universal filler neck adapter but it does not stay on neck and leaks smoke due to rust buidup on back of neck.If check valve in the tank then i can remove the rubber hose that attaches to the filler neck and blow smoke up the filler neck?correct?

[Bob's Garage]

thanks for replys....i have the rubber universal filler neck adapter but it does not stay on neck and leaks smoke due to rust buidup on back of neck.If check valve in the tank then i can remove the rubber hose that attaches to the filler neck and blow smoke up the filler neck?correct?

Yes, if can adapt from the filler neck diameter to your smoke machine.

Or, you can get the Redline adapter:

Photo 2012-11-24 092702.jpg

Photo 2012-11-24 092729.jpg

[Orevin]

I have both adapters and prefer the Redline. Fit's on every vehicle I worked on, while the other one is hit and miss.

[eddiesverus]

thanks for replys....i have the rubber universal filler neck adapter but it does not stay on neck and leaks smoke due to rust buidup on back of neck.If check valve in the tank then i can remove the rubber hose that attaches to the filler neck and blow smoke up the filler neck?correct?

Just curious if you did a purge and seal test? Also monitor the FTP sensor in H2O for better resolution. With the engine off close the vent and look at the readings. If you remove the fuel cap it should read 0"ih2o. Then if you apply the gas cap pressure should start to increase. Using a graphing scanner is the best way to monitor changes. This will help you confirm if their is an actual leak. If you do and can't find it using smoke. Use a nitrigen based tester to appy more pressure but not to exceed 1psi then use a soapy water solution to locate the leak. This works very good. I've been able to locate many leaks when smoke doesn't.

[autojoe]

yes did purge and seal test....ftp voltage dropping off to quickly.no graphing meter....just have solus pro and a pico 4000 scope and a smoke wizzard.going to smoke filler neck monday.thanks