2011 Avy - Fuel Gauge Accuracy

[wongsol]

Hello all,

My first post here and thank you for the add.

My Avy is a 2011 with a current mileage of 235k KM (Canadian) (146k Miles). I recently replaced the entire fuel pump assembly (aftermarket), At that time, I noticed that the top of the assembly was rusted out and there was a hole drilled for a wire that directly led to the fuel level sensor inside the pump and jumped to the wiring harness outside of the pump. I investigated the wiring and found that there was a connector that was corroded and I replaced it and hooked everything back up and reinstalled the tank.

On my first fill up, the gauge seemed to operate properly by indicating that it was a full tank (I had done the service with less than a quarter tank). As I drove, the tank obviously began to empty. When the low fuel light came on, I went to the gas station and filled up. Upon fill up, I noticed that I only put in 84 litres where the tank has a capacity of 117 litres according to factory specs. 33 litres were still in the tank. I didn't think this was normal as whenever I've had the low fuel light go in, I would have about another 100km left for distance before I call CAA.

I did a calculation and found that my fuel economy was horrible. 19l/100km. I went through another month or so and did some calculations for range on the trip and was very close to coming to within 10 litres left on fill up but still getting about the same economy. On board DIC said that my variable running cylinders were working (going from 4 cyl to 8 cyl). I do get EVAP errors of P0442 and P0455 (small and large EVAP leaks detected resp.). I recently (within the last week), I am now getting P0451 EVAP System Pressure Sensor/Switch Circuit Range Performance error.

I have not replaced the fuel cap as the dealer does not have one and one is on order. Currently have an aftermarket on in from about a year ago and they suck.

On my ODBII reader, the fuel level input was at 14% when there was 33 litres left in the tank and low fuel warning on the dash. At 14%, there should be about 16 litres in the tank which kind of makes sense that the low fuel warning came on. I should also add that EVAP System Vapor Pressure is in the negatives; I believe severe at -400's, there should never be negative pressure, should there?

My question is/are

1. Would the EVAP errors (including the new P0451) have any standing on the incorrect reading?
2. Aftermarket fuel pump assembly a POS and stick with OEM?
3. What would be a logical electrical outlet test on the fuel level sensor (OHM reading) to see if the "new pump" is faulty?
4. Is there a control module fault possible?
5. The negative EVAP pressure fault?

Taking the tank down is a bit of a challenge as I can only get the truck up in the air as far as my ramps and jack stands allow, so I'd rather have a good plan in my hands beforehand.

Any help would be greatly appreciated.

Thank you!!

 

[Rassilon]

I've had the P0455 (Small, becoming large EVAP leaks) detected & reported every summer when the temp hits +7C. According to my now retired Motor Engineer it could be as simple as a blow out of the lines (Which he never got chance to do).

I've done the filler cap & Vapor Canister Purge Valve Solenoid last year & have the Charcoal canister & vapour vent valve to to this spring.

 

[Wpolonavyguy]

I'm getting the same problem now after installing new fuel pump. I'm leaning towards pump itself sending bad signal to PCM.
My Avalanche ran perfectly before replacing pump no evap codes. Afterwards have rich mixture both banks & p451 which had me change evap lines canister and both solenoids without changing a damn thing...
I finally metered electrical wires to both solenoids, vent valve works & open/closes with correct voltage.
The purge solenoid I switched between x3 I have no change so, metered wires.
The wires activated 13.6v at first startup idling which I thought only should open periodically after warming up temperature.
So also odd with mine full tank to 3/4 the codes rectify & no troubles, when fuel gets to 3/4 rich mixture & purge solenoid starts screwing up.

So instead of buying PCM & paying for programming I'm leaning towards the cheaper Amazon fuel pump not working as my 07 5.3flex needs.

Sounds like you're pump is operating the purge solenoid constantly aswell.

 

[wongsol]

Thanks for the replies gentlemen.

Going to start with the OEM fuel cap and wait till I'm down to my last 10 litres (according to mileage/trip) and take some readings on the ohm meter of the fuel level before i go spending money on an OEM fuel pump.

Then I may tackle the EVAP errors.

Thanks again and I'll update my findings here.

 

[wongsol]

This is the resistance test and parameters I was looking for.

Basically most GM vehicles will have a reading of 40ohm empty to 250ohm full.

 

[Wpolonavyguy]

I just replaced my fuel pump again, it is possible the lower cost pump was still ok. Seeing the underside ledges did make me think the seal was leaking.
I couldn't believe it, used a gas resistant non hardening sealant last time & even melted bees wax & poured around to harden against air Leaks.
I'm a bit amazed & waiting to see if the New gasket holds air tight with new pump. Dry seal this time to see if works better.
So far no engine light but could take a few days to set a dtc. Filling gas triggered last time & found the vapor lock seal makes sense now Seeing pump seal was likely not great.

 

[wongsol]

I just replaced my fuel pump again, it is possible the lower cost pump was still ok. Seeing the underside ledges did make me think the seal was leaking.
I couldn't believe it, used a gas resistant non hardening sealant last time & even melted bees wax & poured around to harden against air Leaks.
I'm a bit amazed & waiting to see if the New gasket holds air tight with new pump. Dry seal this time to see if works better.
So far no engine light but could take a few days to set a dtc. Filling gas triggered last time & found the vapor lock seal makes sense now Seeing pump seal was likely not great.

When I replaced my pump, I got a new seal and also replaced the locking ring and sprayed the top down with Fluid Film since I live in a rust belt and the old pump was pretty rusted.

I'm starting to suspect that when I put the pump in, the float rod might have gotten bent? Or the rod was not seated properly. I guess I'll know if I get that far and remove it (again).

I see you also put the trap door in. Brilliant. I'm afraid to do that and or don't trust the measurements I've found. Would you mind giving your dimensions and measurements?

Thanks!

 

[Wpolonavyguy]

If this new pump & seal don't work I'll try to find a thicker/softer pump gasket ring may smash & hold seal better, the lock ring was replaced with prior pump.
Or I can try melting a stronger tensile wax lol , I really thought that would plug any air leaking.

 

[Wpolonavyguy]

Absolutely I wasn't going to drop tank every time something was wrong.

 

[Wpolonavyguy]

I used a wire hole as landmark to measure original cuts in meatal floor, used dremmel at first but slow going & sparked like crazy.
My avalanche has 4in body lift so I had plenty of room to work, tossed a wet towel over the fuel tank & pump.

What worked best was drilling 1/4in hole in each of 4 corners & a jigsaw short meatal blade with teeth pointing upward.
Much less sparks & cut faster than dremmel wheel. I had a neighbor watch underneath while I cut to holler if blade went anywhere shouldn't. Luckily wasn't much to worry about except tank wires & x2 gas lines

 

[wongsol]

Awesome sir. Thank you!

I was going to use a welding blanket over the tank and pump and use a cut off tool. It will spark but at least it won't go as deep as a jigsaw blade. I was also thinking of wedging a 1/4" piece of plywood in between the floor and pump as added protection with the welding blanket.

I have some metal fab tools so I can probably make a proper lid and latch and make it all fancy

 

[redheadedrod]

Cutting a hole in your floor when you have 2 bolts holding the whole tank in place is kinda dicey. Especially when you are likely only going to ever pull the tank down 1 time. It doesn't make sense to do. Once you have it fixed you are done. It is an easy tank to drop. My CTS would sort of make sense to do since it requires dropping the whole rear end to get to but you are looking at starting rust in a location that never normally gets it. So if you are in the rust belt you are especially asking for trouble. But then again if you don't plan on having the truck long, who cares if the whole floor rusts out if you give it to someone else. Depending on how you do it, the access to your fuel pump won't be any easier or quicker with an access door since you still have to get under the seats, pull back carpet etc, not to mention deal with any gas smells you will get into the interior when doing work on the gas tank and spill some in the interior. If you are worried about being full of gas you can pull one of the fill lines and siphon out the fuel if it doesn't just pour right into your cans. Takes longer to cut out the access door and make a decent new one that will seal up than dropping the tank numerous times even if full of gas. Not to mention the danger of catching the truck on fire. I will never understand why you guys decide to cut an access door on these trucks when the gas tanks drop out so easily. Took me about 10 minutes to drop mine with it half full of gas on jack stands and laying on my back. Half excusable if doing in the grass with no other choice but still, the trucks are high enough you don't normally have to jack the truck up to get the gas tank out if standard height. You disconnect the two fill lines which are worm drives, disconnect the 2 or 3 quick disconnect lines at the front of the tank. Put something under the tank to hold it into place, unbolt the two bolts and lower it down. Not sure how much easier it gets.

 

[Wpolonavyguy]

My avalanche doesn't get the mileage use, so makes sense not to drain the gas tank just to lower it. Many of us don't keep more gas storage than 1 or 2 5gal tanks & those usually have lawnmower gas or something already. Then buy a pump or hand siphon to avoid gas in mouth.......
It took maybe 40minutes total, a wet towel drape sealed tank, then measure mark, drill 4 corners & cut under ten minutes.
until you have done the tank drop x4 separate times for junk Chinese made parts, shouldn't throw stones.
I've never gotten gas smells or exaust into cab even b4 I added rubber & sylacone goo when think it'll be shut a while.
There are plenty of easy ways to seal water & elements. Paint is better than most sealants, combination of both id think in east coast.
Eventually I'll design & paint a better door sandwich bolt style or hinged havnt decided. Desert out here so rust barely a worry.

If in a well ventilated area like driveway outside & taking precautions it's not going to explode like guys are picturing. People need to make their own decision if confortable with tools & skills they have to safely do any job.

Plus I'm finding many more chance of leaks every time evap tube unplugged and plugged back. For me was easy decision ill be last owner of mine so junkyard won't care about access door.

I can also check and meter the tank wires without crawling or lieing on creeper.