99 Pontiac Gtp Fuel Tank Breather?

I just bought a 99 Pontiac GTP and the guy I bought it from said that he has to leave the gas cap loose or the car will start to backfire and run rough. To me that sounds like the breather for the gas tank is plugged? Just wondering where that would be or any other suggestions?

Welcome to AF.

Any SES/CEL (check engine) light with the gas cap removed or have you tried removing the gas cap yourself and see what it does for sure? Sounds like a evaporative emissions problem related to vacuum.

Thanks for reply. There is a check engine light on and I had the codes pulled and there were three. One was related to the gas cap being left loose. One was to do with an evaperator emission switch and the one was a tcc code for the torque converter. So I went to my local gm dealer and asked if they could get me the switch in the fuel tank and they said they could not locate it on the parts screen. What do I do now?

Are you referring to the pressure switch? That one is located on top of the fuel pump assembly and available separately without having to purchase the complete fuel pump assembly. Do you recall the DTCs? If so can you post them.

The codes are P0452, P1887, P0440

P0452 indicates the PCM module has detected a fuel tank pressure sensor short circuit. This is the sensor that sits on top of the fuel pump assembly I mentioned in my prior post. Could be the pressure sensor, wiring or the electrical connector to it.

P0440 is the gas cap code and classified as a large leak. Probably a result of keeping the gas cap loose.

P1887 is torque converter clutch (TCC) release circuit malfunction. Once set it will prevent TCC operation and disables shift adapts. What are your rpms reading around 55-60 mph and is it shifting to 4th - OD?

It is shifting into OD and I will have to drive it again to see what the rpms are? So you can get the pressure sensor by itself? I wonder why the GM dealer couldnt find it? Thanks for all of your help.

:dunno:

Yes it is available by itself. Not that difficult to replace either.

GM PART # 16238399
CATEGORY: Fuel Tank Meter Sender/Connector (Pressure Switch)
GM LIST: $79.49

The sensor is the one in black. See pics.


http://i5.photobucket.com/albums/y186/lizzywiz/fuelpump_top.jpg


http://i5.photobucket.com/albums/y186/lizzywiz/fuelpump_top2.jpg

Wow thanks for the great pics! You have been a great help. What kind of problem to the car does that torque converter code cause? What are some of the fixes?

If that sensor is bad on the fuel pump could it cause the car to run bad when the gas cap is tight? Right now I have been driving around with it loose. Thanks again.

Hard to say for sure. Obviously the sensor has an issue or the DTC would not set so that has to be looked at. The pressure sensor is used to let the PCM module know that the evaporative emissions is working properly. Engine vacuum is used and then the decay checked during the purge and vent cycles and tests, etc. Evaporative emissions troubleshooting or repair can be a real PITA but I'd start with the pressure sensor.

On the TCC issue after it shifts to 4th - OD look for a dip in rpms meaning the torque converter has locked up. Check it around between 50-60 mph. So let us know what your rpms read. TCC operation is controlled electrically by the TCC-PWM solenoid located at the valve body.

I drove the car around tonight and at about 57mph it was running about 1700 rpms. Also after I got done driving it and shut it off I could hear the gas tank pop like it was under pressure?

Then the rpms is normal indicating the TCC is locking up. Next test is to see if it is unlocking which is what the DTC is all about since it is associated with the release circuits. Keeping the speed constant at the same speed as above with left foot tap the brake pedal. Watch the tach to see if the rpms increase a few hundred rpms or you should notice an upswing in rpms.

I went and drove it and when I stepped on the brake pedal and it jumped up to 2100 rpms.

That sounds normal. It may be a fluke DTC. Have you tried resetting the PCM module to see if the DTC goes away or it is not just a prior history DTC.

Thanks for the help. I just ordered the sensor today and I will try to reset the codes and let you know. Thanks Again!

I will have to reset the pcm and see what happens. My pressure switch will be in tomarrow so I will reset it after I install that. Thanks.

I got the new switch and installed it. Then I un hooked the battery to reset the computer. Then I started the car and the service engine light is still on. How do I reset the computer?

How do I reset the computer?

odb-ii scanner or maybe it will clear with a few drive cycles.

Sorry its took so long to get back. I replaced the sensor and the tank and then had the codes cleared by a scanner. Then I started the car up and the light came back on. Then I rechecked the codes and that sensor code was the only one there. It says the voltage is to low. What do I check now?

check for voltage and ground at the sensor.

I finally got to check the plug last nite and I do not have any voltage or a good ground in the plug that hooks to the sensor. Where does that wiring harness come from or what do I need to check next? thanks.