EVAP troubles

[prophiseer]

looking for some opinions here, someone might know a bit more . . .


anyways, since putting in the aftermarket fuel pump (and pump assembly) I've been fighting intermittent P0452 and P0453 codes (0452 - fuel tank pressure sensor low voltage / 0453 - fuel tank pressure sensor high voltage). Oddly enough, by the time the MIL is thrown, both codes are set, even though they're kinda conflicting. I've still got to diagnose out if it's the tank press. sensor, or a fault in the wiring or a poss fault with the PCM, but from the datastream I pulled this morning, sensor voltage at idle is about 0.02 and can range up to 5.09V (which has me thinking it's the sensor, it shouldn't be able to return more than the 5V reference).

My query, though, could the high flow fuel pump cause that much of a pressure difference? I figure it's partly related, but with a sealed and vented tank EVAP system, I wouldn't figure it'd make that much of a difference. Not all that in the know with EVAP systems, we don't do that much diagnosis and repair in the shop (aside from fixing people fuel filler cap's )

[tractorman]

I just got done dealing with a PO442 code on my 01 lumina. The code indicates a "small leak in the exaporative emissions system". Turns out that the hose clamp where the filler pipe connects to the tank was loose and damn near rusted off (kinda odd for an 01 in Kansas).

Anyway, I wasn't sure at the time that that clamp was the culprit... and I don't have access to a smoke machine. So I dropped the tank and inspected a few things. One thing that I checked was that pressure sensor that you mentioned. It only measures vapor pressure, so the pressure isn't very high at all, and I don't think it would be affected by your fuel pump. I dont know what the resistance of that sensor should be(you could probably find that somewhere), but I hooked up my meter to it, and made sure that the resistance changed when I blew into it.

Considering your conflicting and intermittant codes... I think you've got a wiring problem. My two guesses are this: Either the pins got pulled out partially from the connector that goes into the sensor, or maybe the wires got pinched when you bolted the tank back up in place. I'd probably remove the tank, inspect the wiring, and maybe replace that sensor if you don't see anything obvious.

[prophiseer]

well, the assembly is an aftermarket unit from Advance, so I'm sure the press sensor is some cheap unit. I really don't like the pump assembly compared to the stock one either, but at the time I didn't have much of a choice (dropped the tank and the stock unit broke off the top). Even the wiring harness it came with kinda irked me - so I put the stock harness back in.

Anyways, this morning I followed GM's diagnostic outline for the p0452 and narrowed it down to the press sensor, so I'll swap an OE one in later this week at the shop and see how it goes - or I might just put an OE pump assembly back in, we'll see . . . not worrying about the 0453 yet . . .

I really didn't think it'd be related to the pump, but it was kinda odd that it was shooting these codes after I installed the pump into this assembly, didn't know if anyone else had similar issues.

[prophiseer]

Well, I took care of the EVAP issue I was dealing with; dropped the tank down and sure enough, the tank pressure sensor on the top of the assembly was loose as hell, it popped right out.

Put a GM assembly back in with the [W] pump w/ the t-fitting sold through zz - kinda a tight fit, real pain in the ass, so we'll see how it goes . . .