Hello! Looking for advice on my 2007 LTZ Tahoe. I’ve had it 2 years trouble free. It has never, from what I can tell gone into the 4 cylinder mode, it always stays V8 mode. I’ve read enough about this online to gather that can be considered a good thing. My oil pressure gauge has never worked since the day I bought it either and I’m wondering if someone could of disconnected the oil sending unit so as to trick the computer and make it stay in the V8 mode? I get the worst mileage you can imagine. Especially pulling my enclosed trailer. Yes the engine light is on, so I could have another issue going on as to why the mileage is so bad.
Is it everyone’s else’s opinion that I should leave it in the V8 mode and not try to figure out how to get it to function in 4 cylinder mode as well and hope to get better mileage? 250k
Thanks for the help. I selected for other members to email me as well.
Don

 

I have been using a AFM eliminator in my '11 for almost 100k miles now. 4 cyl. mode doesn't save hardly any gas, it just causes lifter issues so V8 is better.
I lost 3 mpg in my 5.3 and after some intense diagnosis my MAP sensor was bad. Do this check if you have instant mpg on the dash screen. Do a coast down from 55 mph and with out touching the gas pedal does the mpg get into the '90's when coasting down. If not then your MAP sensor is bad. Pick up some MAF sensor cleaner also and clean it. I've got my '11 Tahoe back up into the 18 - 20 mpg highway range again depending on terrain. Towing my 6x6x12 cargo trailer has gone up to 14 mpg from 12 on the same route and load.

 

My guess is that it would be a dirty sensor, such as a MAF sensor. You may also want to look into changing spark plugs if there due. I know these engines love to burn oil and that causes the plugs to age prematurely. At 250k, I'd go over the whole fuel system too such as fuel filter and injectors. Little things here and there can bump your milage up just 1mpg but if you do 3 or 4 things that's 3 or 4mpg you saved.

 

I have checked my truck as you said. I was pulling my 12 ft enclosed trailer and on perfect flat ground at 55 with cruise on and 1500 rpm is was doing 12 mpg. Then I released the cruise and let it coast down to complete stop and it showed up to 99 mpg but acted like thats as high as it would indicate. Just say on 99.

 

In my '11 on the instant fuel economy screen it shows V4 or V8. With my AFM disabler unplugged V4 mode will only engage at very light throttle on flat roads or when coasting at speed.
Very hard to feel it as it doesn't engage in V4 with any load on the engine.
If you bought this truck used it may have been ''tuned'' out.

 

Back to what I was initially trying to ask. Do you think someone disconnected the oil sending unit to trick the computer to staying in the v8 mode? I can’t stand to not be seeing oil pressure so I have a new one to install with screen. Repair shop wants ridiculous price to do it. Also starting to hear what sounds like a light lifter peck. Any recommendations on something I can put in oil to help that? Lucas may have something I can get. Good products.

 

On the coast down test with my bad MAP sensor the instant fuel economy readings would go into the '90's and moved up/down into the '50s and every where in between and not stay steady high in the '80's or '90's. with your foot off the gas coasting. Manifold pressures help determine light throttle not oil pressure for V4 mode and fuel mixture. You probably have 2 issues going on. At your high mileage lots of stuff is getting worn out and AFM lifters / cam are a wear out item.