2011 did not start last two days at 45 degrees

[wsteele]

I am going to get a fuel tester as my next step. I just don’t get why it will not start in cold but again this morning once it reached 60 it started right up again. I appreciate your advice. I’ve never put anything but 87 or higher in for gas.

I wouldn't worry that the gasoline you are pumping isn't what they say it is. What I was getting at is if your Ethanol sensor calculation was off, it could indicate a weak fuel pump.

If your truck thinks it has like 20 or 25% Ethanol when you have only been pumping gasoline, it would tend to run rich when starting it up, so not starting when cold wouldn't be the symptom, unless your fuel pump was also weak.

I should have not confused you with fuel content discussions, I was just trying to get across that you might have a fuel pump issue.

 

[Alphafoxtrot71]

Ok so here is the update! I went to pressure test the fuel. It stayed at zero didn’t even move with key on no start and even when I tried to crank and start. So my next step was to test the relay to make sure it was good before I spent the money on a fuel pump. Low and behold there was no relay there. you can see the clean spot where it was because of the dust around it. I noticed I never heard the pump kick on when the key was turned on but didn’t think nothing about it at the time. So I took a similar relay in the fuse block from the fog lights and put it in and turned key on and heard the pump kick on and it started right up. without relay how would it even start period when warmer out. Needless to say the $16 part fixed this problem. I’ve had this Tahoe for a little over a month so why the relay was missing I have no idea. Thanks for the advice on troubleshooting to all of y’all.

 

[Joseph Garcia]

Thank you for posting the resolution of your issue.

That is a REALLY strange situation, finding your relay missing. I would be thinking about how and who.....

 

[wsteele]

Ok so here is the update! I went to pressure test the fuel. It stayed at zero didn’t even move with key on no start and even when I tried to crank and start. So my next step was to test the relay to make sure it was good before I spent the money on a fuel pump. Low and behold there was no relay there. you can see the clean spot where it was because of the dust around it. I noticed I never heard the pump kick on when the key was turned on but didn’t think nothing about it at the time. So I took a similar relay in the fuse block from the fog lights and put it in and turned key on and heard the pump kick on and it started right up. without relay how would it even start period when warmer out. Needless to say the $16 part fixed this problem. I’ve had this Tahoe for a little over a month so why the relay was missing I have no idea. Thanks for the advice on troubleshooting to all of y’all.

I have to go do some research but I don’t think your model year came with a relay in that position, I think it is normal to be unpopulated.

It may indicate you have an issue elsewhere, like your FPCM, pressure sensor or again your pump.

I will go see if my supposition is correct and get back.

 

[gooffeyguy]

My 2012 doesn't have a fuel pump relay in the marked spot for it in the fuse box

 

[wsteele]

Your truck didn’t come with a fuel pump relay. The combination of FPCM (aka Fuel Pump Drive Module), Fuel Pressure Sensor and PCM, control power to your fuel pump and regulate fuel pressure to the rail.

I suspect what is happening is by populating that relay, you are turning power on to the pump when the key is on, but you may have no pressure regulation, just on full pump pressure.

 

[Fless]

SWAG Is this one of the model years that gets corrosion under the underhood fusebox? Maybe messing around with the fusebox made the connection good again.

 

[Alphafoxtrot71]

Your truck didn’t come with a fuel pump relay. The combination of FPCM (aka Fuel Pump Drive Module), Fuel Pressure Sensor and PCM, control power to your fuel pump and regulate fuel pressure to the rail.

I suspect what is happening is by populating that relay, you are turning power on to the pump when the key is on, but you may have no pressure regulation, just on full pump pressure.

Yeah not sure. All I know is when I put the relay in I heard the pump kick on unlike before. I have an avalanche and a Silverado and both had relays and can hear the pump when key was turned on. The diagram on fuse cover shows a relay. I had plenty of fuel pressure after it was put in when key was turned on. So if it’s not supposed to then I guess I’ll have to continue to trace it down. I also know that when it started during the day that with key on only I didn’t hear pump and that was without relay but still started.

 

[wsteele]

Yeah not sure. All I know is when I put the relay in I heard the pump kick on unlike before. I have an avalanche and a Silverado and both had relays and can hear the pump when key was turned on. The diagram on fuse cover shows a relay. I had plenty of fuel pressure after it was put in when key was turned on. So if it’s not supposed to then I guess I’ll have to continue to trace it down. I also know that when it started during the day that with key on only I didn’t hear pump and that was without relay but still started.

The 2007 and older vehicles had the relay and no FPCM or Fuel Pressure sensor (I own a 2007 Yukon and mine is like this). In these older models pressure is regulated by a mechanical pressure regulator in the fuel pump assembly (back to like 2005 -2006 and then by a regulator up in the engine compartment on older models than that). On the 2008 and later vehicles, all that changed with the pressure sensor and FPCM, which tell the pump to spool up and down to regulate pressure. I believe they discarded the relay and pump fuse with this design.

For whatever reason it started working by inserting that relay, you didn't fix your problem by adding the relay as the design is to not use one. You may have bypassed the problem, or maybe as @Fless indicated, it may also have been a coincidence.

 

[Doubeleive]

easy to put to rest by removing the relay, then on a cold morning again see what happens