Someone stole gas from me and now my engine runs weird?

[Dustin Jackson]

@Just Fishing I don't have one but I can see if I can borrow one, what exactly would I be looking at/for if I got my hands on one?

 

[Doubeleive]

unless they disconnected the filler tube there is no way they got gas out of the tank without drilling a hole in it. I also think if anything was put in the tank you would have seen evidence of it around the filler. I assume you found nothing and that it was clean. In this case I think it is possible your mind is playing tricks on you.
i would perform some simple basic maintenance.
get a new air filter
get a can of maf cleaner $3-4.00 dollars
get a can of throttle body cleaner $3-4.00 dollars
get some soft rags (lint free)
get a bottle of injector cleaner the lucas big bottle is your best buy (add 10 oz per tank full of gas) the lucas big bottle will do 3 tank fulls
replace the air filter
remove the intake housing and maf
spray the maf off real good both sides and set it aside and let it dry. (do not touch any parts of the maf with anything other than with spray from the can)
using the rag spray the rag and throttle body butterfly and clean it real good, you can push the butterfly open with your finger just hold it open with a finger gently while cleaning the surface inside and out do not force it open beyond where it stops. you will see black carbon residue that is normal and is what you need to clean off.

then re-install the intake and maf, make sure the intake is on correctly and bolts are snug.

drive it, you may notice some idle fluctuation at first start after cleaning but it will clear right up.

other than that if the plugs and wires have 100k or more it is time to replace them and all 4 02 sensors

 

[Dustin Jackson]

@Doubeleive I think you're right man. Paranoia and OCD getting the best of me.

 

[Dustin Jackson]

@Doubeleive What is the average life of the cats on these things? I am about 190,000 and think they are original

 

[Doubeleive]

@Doubeleive What is the average life of the cats on these things? I am about 190,000 and think they are original

cat's should last for the life of the vehicle unless you drive like me in which case you would end up with a check engine code for cat inefficiency or you would start to see a noticeable drop in mpg and then get a code eventually. 02 sensors are rated for 100k but should/could last longer also can be dependent on how you drive I suppose. If you replace them it is recommended to do all 4 at the same time. a set of 4 oem runs close to $200 and you need a 02 socket unless you want to fight getting them installed.

 

[Just Fishing]

cats can become plugged, and your tahoe would run like shit if that was the case.
You can check flow by removing the sensor one and sensor 2 to see if there is a flow difference.
there is also a cat further back, it's all part of the same gigantic Y

 

[Just Fishing]

@Just Fishing I don't have one but I can see if I can borrow one, what exactly would I be looking at/for if I got my hands on one?

I would go into fuel system data.
You should see things like fuel pressure commanded, and actual.
they should be close.

Other things in there also, but it has been a while since i fkd around in the fuel system info stuff.

 

[Fless]

Do what @Doubeleive suggested. If something's really wrong with it, I'd say get someone to diagnose it instead of guessing 'could it be this' or 'could it be that.'

 

[gooffeyguy]

unless they disconnected the filler tube there is no way they got gas out of the tank without drilling a hole in it. I also think if anything was put in the tank you would have seen evidence of it around the filler. I assume you found nothing and that it was clean. In this case I think it is possible your mind is playing tricks on you.
i would perform some simple basic maintenance.
get a new air filter
get a can of maf cleaner $3-4.00 dollars
get a can of throttle body cleaner $3-4.00 dollars
get some soft rags (lint free)
get a bottle of injector cleaner the lucas big bottle is your best buy (add 10 oz per tank full of gas) the lucas big bottle will do 3 tank fulls
replace the air filter
remove the intake housing and maf
spray the maf off real good both sides and set it aside and let it dry. (do not touch any parts of the maf with anything other than with spray from the can)
using the rag spray the rag and throttle body butterfly and clean it real good, you can push the butterfly open with your finger just hold it open with a finger gently while cleaning the surface inside and out do not force it open beyond where it stops. you will see black carbon residue that is normal and is what you need to clean off.

then re-install the intake and maf, make sure the intake is on correctly and bolts are snug.

drive it, you may notice some idle fluctuation at first start after cleaning but it will clear right up.

other than that if the plugs and wires have 100k or more it is time to replace them and all 4 02 sensors

Do the tank fill pipes on the 900s have something the 800s don't? I've siphoned gas from my 01 before replacing the fuel pump.

 

[Doubeleive]

Do the tank fill pipes on the 900s have something the 800s don't? I've siphoned gas from my 01 before replacing the fuel pump.

I believe there is something in there, some kind of restrictor, you might be able to fit a very small tube in

 

[swathdiver]

I would go into fuel system data.
You should see things like fuel pressure commanded, and actual.
they should be close.

Other things in there also, but it has been a while since i fkd around in the fuel system info stuff.

2007s can't see fuel system data. They don't have a FPCM, it was still controlled by the ECM. Have to check with a manual gauge off the rail.

 

[Fless]

My '04 has a removable screen that's right where the fill tube hose connects to the tank. Not sure if that's a Flex Fuel thing or something else.

Pic of fill hose disconnected:

 

[Dustin Jackson]

@swathdiver Do 2008 Tahoes have a FPCM?

@Fless Very interesting about the screen between the filler tube and the tank, might be worth taking a peak on mine and see if it has it but I am not sure what that would change anything. I imagine if something went down the filler neck and got caught in the screen that would only affect filling and not the running of the engine.

Curious, I have a black bear tune and live in a climate that has extreme colds and hot seasons. If I had it tuned in winter would the high temps of summer throw the tune off or something?

 

[swathdiver]

@swathdiver Do 2008 Tahoes have a FPCM?

Yes.

You can ask him but I'm sure Justin compensates for the change in seasons when he's tuning an engine.

 

[stevedonato]

I would suggest maybe someone does not like you? Did you have any heated disagreements with someone lately? More than likely someone poured something into your tank wanting to get back at you for something? Especially as noted already, newer vehicles cannot be siphoned. Jog your memory and re-think about any negative encounters you might have had lately. If you can afford it, maybe you can have the tank countenance analyzed to determine the damaging ingredient.

 

[Joeltz]

Hello gentlemen, in the middle of the night on the 4th of July someone stole gas from my Tahoe while it was parked in my driveway. I went to leave for work the next day and discovered my gas cap on my rear tire.

I put the gas cap back on the Tahoe and drove to work. On my way home from work I filled up with 91 at my usual gas station, but ever since then the motor has idled a little rough and on the freeway my Tahoe has a little shimmy like an unbalanced tire or slight misfire.

I just redid my front brakes the day before my gas was stolen so I am going pull my front tires back off and inspect all mating surfaces but I have this paranoid/OCD feeling in the back of my mind that the stealing of the gas caused something to happen with either the EVAP system or they got dirt in my tank. OR the gas station just switched to summer fuel here in California. Either way my motor isn't running as smoothly as it did a few weeks ago.

Today I filled up another tank of gas and the Tahoe had a very notable rough idle immediately after starting it from filling it with gas.

Along with having my property violated! My Tahoe isn't running as well as it used to and I want to see if there is anything I can check on, I am hoping these are just the early stages of a EVAP failure. I have had a history of not being able to fill up the gas tank in one go, the pump always clicks so I have to hold the nozzle at a special angle to get to a full tank.

Lesson learned, locking my Tahoe every night and installing security camera.

Anything you guys can think of or am I just paranoid?

This is how I found my tahoe:
View attachment 404195

One Time at Sebring 12 hour race my friend on my 250 Maico square barrel jumped over a log, that turned out to be a guy in his sleeping bag. He came back from the midway and at Sunup I must have kicked the kickstart lever 100 times. Went home and after checking everything, I saw water in the glass jar I put gas in.
It had not rained we decided that the Guy he Jumped put either a New or Used Beer in the tank. Try replacing the filter bolted to the frame below driver seat

 

[Doubeleive]

One Time at Sebring 12 hour race my friend on my 250 Maico square barrel jumped over a log, that turned out to be a guy in his sleeping bag. He came back from the midway and at Sunup I must have kicked the kickstart lever 100 times. Went home and after checking everything, I saw water in the glass jar I put gas in.
It had not rained we decided that the Guy he Jumped put either a New or Used Beer in the tank. Try replacing the filter bolted to the frame below driver seat

that filter has not been on any gm suv since around 2003/2004, so twenty years ago.......
probably just needs to do what I already suggested....

 

[Joeltz]

that filter has not been on any gm suv since around 2003/2004, so twenty years ago.......
probably just needs to do what I already suggested....

Sorry , my 2002 Avalanche had one, or maybe it was one of my 4 - 2 Door K5s

 

[03catburban]

I think it's all been over thought, he said he already on his 2nd tank of e85, I'd say IF anything was poured in it'll be long gone by now.

 

[Dustin Jackson]

I would suggest maybe someone does not like you? Did you have any heated disagreements with someone lately? More than likely someone poured something into your tank wanting to get back at you for something? Especially as noted already, newer vehicles cannot be siphoned. Jog your memory and re-think about any negative encounters you might have had lately. If you can afford it, maybe you can have the tank countenance analyzed to determine the damaging ingredient.

@stevedonato The thing about someone disliking me is that is can happen without my awareness, maybe I cut someone off on the road and I didn't realize it OR maybe they didn't appreciate me taking my 94 straight piped 350 k1500 to watch the fireworks on the night of the 4th of July but I think it's more likely that someone didn't realize they couldn't siphon gas from this truck. If this was a disgruntled person there were multiple other ways they could have damaged my property but I think it's the tweaker across the street trying to get gas for his motorcycle.

Either way like @03catburban said we are about 3 tanks of gas into the situation so the damage, if there was any, is already done.

I appreciate your concern for me but this isn't something I want to lose sleep over anymore, I am more concerned that I can't get my brakes bled properly