Hello everyone, I have a 97 z28 m6, and i have been having this gas smell come from it, i cant quite pinpoint where its coming from, but if you get near the car, you can definitely smell gas. Also, a new EGR valve was put on it before i bought it, and all was well until a couple of months ago which is when the P0400 code started coming up again. I have been getting just terrible gas mileage (~9 city) compared to what it used to get, so i was wondering if these things could be contributing to my crappy mileage and if I put a new egr valve on it, would it fix the P0400 code?

 

Welcome to CamaroZ28.com!

P0400 is telling you that when the PCM runs it's diagnostic to detect EGR flow, it does not see adequate flow. The PCM cycles the EGR valve on, and looks for a specific change in the manifold absolute pressure (MAP).

The things that could cause inadequate EGR flow:
-faulty EGR valve
-carbon buildup on EGR valve pintle
-cracked/loose vacuum line from the intake manifold to the EGR vacuum solenoid
-cracked/loose vacuum line from the EGR vacuum solenoid to the EGR valve
-plugged EGR solenoid (if the solenoid was electrically faulty, you would get P0403)
-plugged EGR passages in the intake manifold
-broken EGR riser tube from the passenger exhaust manifold to the intake manifold
-low backpressure exhaust system modifications

Test could be thrown off by a faulty MAP sensor. That will set codes if the MAP falls outside certain limits.

Vacuum leaks, EGR valve stuck open, broken riser tube, inaccurate MAP sensor could all contribute to poor fuel mileage.

Courtesy of Shoebox:

http://shbox.com/1/egr1.jpg

Where EXACTLY does the fuel smell seem the strongest?

 

The gas smell is the strongest probably on the drivers side, by the rear tire. Also, i forgot to mention that the P0400 code only comes on while driving on the highway, never during city driving.

 

The PCM can only run the EGR diagnostic under highway cruise conditions. The throttle position and RPM have to be stable for several seconds before it can run the test. The throttle position has to be between 5 - 20%, throttle can change less than 1%, MAP must be between 20 - 60kPa. Conditions must be stable 1.5 seconds before and during the test.

The charcoal EVAP canister that collects fuel vapor from the fuel tank is located in the driver's side rear fender. Heavy fuel smell could indicate rotted hose from the fuel tank to the charcoal canister, leaking pressure/vacuum relief valve, canister saturated with wet fuel due to over-filling the fuel tank, leaking seal on tank fill cap, EVAP purge system not pulling fuel vapor from canister, excessive heat buildup in the tank due to fuel pump problems. Check also for a leak in the fuel tank. I saw a post on another forum recently where a "snow belt" car had a crack in the fuel tank due to salt corrosion, and it was dripping fuel.

This shows the canister location. 97 will be slightly different, but the location will be the same:

http://shbox.com/1/evap_system.jpg

The two problems - EGR and fuel smell - are not related.

 

I've replaced the gas cap, and the solenoid, and still the gas smell. If you drive the car for a while and take the gas cap off, isnt there supposed to be some pressure behind it? Like you should be able to hear some pressure releasing? Because mine never has any pressure.

 

The tank is normally under vacuum not pressure. The smell and the lack of vacuum would indicate as mentioned above. There is most likely a break in the seal somewhere. Your best bet is to check the lines in front of the tank to the vent valve as well as the vapor canister (again as mentioned above). If you don't see anything, check the forward hoses for leaks. If the leak proves to be rearward, then you have no choice but to lower the fuel tank.

 

According to the factory manual, the fuel tank pressure rises until it lifts the EVAP pressure control valve (5kPa or 0.7psi), and allows the pressure to push the fuel vapor into the charcoal canister. A small amount of pressure in the tank is normal, and it would make a slight sound when the cap is removed.

In his case, the lack of pressure it probably due to the line between the vent connection on the fuel sending assembly and the pressure control valve being cracked. When that cracks, the back of the car stinks of fuel.