Thanks everyone for the advice and especially the Captain for his exceptional knowledge on these vehicles.

Ok so after I had installed the new pump (AcDelco), CEL popped on after a little driving and it revealed a P0446(eval circuit malfunction at vent valve). Replaced the vent valve with AcDelco, reset the CEL and the code came back. Replaced the purge solenoid, reset the CEL and the code came back. I guess you could call me a parts changer lol. I don't see any leaks and am not sure how to continue to properly diagnose this code.

Any tips or advice would be greatly appreciated.

 

Read the "CIRCUIT DESCRIPTION" in the link below. It explains what is supposed to happen when the PCM runs the EVAP test. Then scroll down to "Check for the following conditions" and read that section. It will give you several things to check. If you don't find the problem, follow the flow chart and it will lead you to the problem.
https://blazerforum.com/forum/diagno...plained-35143/

Just an idea..... on the fuel pump module there are 3 lines: 3/8" line is pressurized fuel to the injectors. 5/16" is the fuel return line from the fuel pressure regulator back to the tank. 1/4" is fuel vapor for the EVAP system. With a little bit of effort, the 1/4" line and the 5/16" line can be transposed during reassembly. When the engine is running, it usually leaks fuel like a big dog on top of the tank, or at the EVAP canister behind the driver side rear tire.

Keep us posted.

 

Thanks Captain for the quick reply. Much appreciation.

Went through the "Check For the Following Conditions" section and here's what I got.

I looked at the fuel lines and the evap line that go to the pump and they are put on correctly. Checked for fuel on top of the tank or at the canister and found no leaks. Never bought an aftermarket gas cap and it secures on tight when tightened so I think I can rule out that. Evap canister has no visual damage. Lines are routed correctly. Vent valve replaced (maybe a POS out of the box, who knows. ACDelco part) Not sure what the fuel tank rollover valve is. All connections appear to be properly secured at vent valve, purge valve, and fuel pump pressure sensor. Not ready yet to start tracing wires to check for damage. No evap lines are pinched. I don't have an appropriate bi directional scan tool to do the diagnosis you sent in the link.

Guess its time to go to the damn shop…

What do ya think?

 

The first five items in the "Check For the Following Conditions" section are all checking for leaks in the EVAP system. The entire fuel system: tank, filler neck & cap, vapor lines, purge canister, vent and purge solenoids are sealed from atmosphere when the vehicle is off. The system captures and contains fuel vapor when the vehicle is off, so you won't see evidence of liquid fuel leaking. With that in mind, if the fuel filler cap doesn't seal tightly, vacuum can not build up in the system when the EVAP monitor runs. The same holds true if there's a rust hole in the fuel filler neck, or a leak in the vapor lines, fuel tank, fuel tank pressure sensor seal, fuel pump module O ring, vapor line connections etc etc. Two door filler necks tend to develop rust holes, some can be .030" or smaller. When the EVAP monitor runs, it will detect the leak, set a DTC in memory, and turn the SES light on. Unfortunately to inspect it, you need to remove it from the vehicle. Without using a smoke machine, locating leaks in the EVAP system is difficult to say the least. If you've checked the obvious stuff, and it all appears good, it might be worth it to have a shop check it out.

 

Thanks Captain

I'm thinking it may be the fuel tank pump module o ring because i had a hell of a time getting it to seal, used a little clean motor oil to get it to go butt it was still a pain and think maybe i didn't use enough oil and its leaking there from not sealing properly. I installed a new snap ring when I replaced the pump and o ring and made sure it was on properly. Might drop the tank next sunday (my next day off) and reinstall it with more oil on the o-ring. Next I would suspect the filler neck because it is somewhat rusted. I think my game plan from here is to drop the tank resea the pump module, check all connections at the module, reset the computer and see what happens, If the code comes back I think I'm going to go have it smoked before I start replacing more parts needlessly.

But is P0446 leak related???? Kinda confused because it says circuit malfunction at vent valve and not a small or large leak code??? Am I looking at a leak issue, a part issue, electrical issue or a combination??? The P0446 is clear its a vent or vent electrical issue but could small or large leaks cause this code???

Thanks for your help these evap codes are really confusing to me.

 

You're right about P0446, it does say EVAP vent control circuit, and it very well could be an electrical issue. The PCM could not pinpoint the problem for one reason or another. The bottom line is that it detected that the vacuum is decaying too rapidly, which could be an electrical issue that is causing a leak, or a physical leak. That's why the flow chart has you check for leaks first.

 

Gotcha, makes sense now. So I would now think it must be a reallllly small leak somewhere which isn't large enough to cause even a small leak code??

 

P0456 is a "very small" leak (.030" or smaller)
P0442 is a "small" leak
P0455 is a "large" leak
P0457 is a "very large" leak, (gas cap loose or off etc)

P0446 is a leak of "undetermined" size.

 

Does the '98 have that little valve at the front of the tank? When taking the tank down it can easily break in its hose connection. If so it wouldn't it give this code?


Jan

 

Possibly, but usually DTC's P0455 or P0457 are set.

4 door fuel tanks are mounted midship, inside the left frame rail. They have one EVAP fitting on the fuel pump module, and one at the front of the tank. 2 door fuel tanks, like the OP has, are mounted behind the rear axle and only have one EVAP fitting, on the fuel pump module.