GM Active Fuel Mgmt/Flex fuel

[Gillis]

New member here, excuse errors beforehand, I’m an “ole schoolboy” My son is very interested in the 96-03 era GM/Chevy trucks, Tahoe, etc. He’s very anxious to get one. I’m learning these various engines (327, 350) 5.3, 5.7 !! I’m also just finding out about this flex fuel /active fuel mgt ? Also after test driving an 03 Tahoe, it seemed to have a “roar” in 4Hi, when I engaged and drove it. Thanks in advance for advice, suggestions, etc.

 

[Fless]

Welcome to the forum. Moved you here from the 2021+ thread.

AFM was initially implemented in the 2007 models, if I have that right. Other members will correct me if I'm wrong. Flex Fuel allows the use of fuel with a high ethanol content (e85), and that's not related to AFM.

Is your question about the "roar" in the '03? If so, can you describe it more, did it sound like tire noise, or more mechanical in nature?

 

[Micahsd]

Related to the flex fuel, I had a ‘07 Tahoe that supported it and when gas prices creeped up there I did some testing with mileage. Bottom line with flex fuel…don’t use E85.

While it’s cheaper you get terrible gas mileage…in the end the cheaper E85 cost equals what you’d put in for regular fuel if you factor in the poor mileage. FuelEconomy.gov is a good website to compare fuel costs/savings for different vehicles.

I do believe the other person is correct that the ‘07 and up have the AFM. I’d avoid those if at all possible or get a disabler for them.

I also had a ‘99 Tahoe. Loved it as that style was a lot more truck-like.

 

[89Suburban]

Worn front drivetrain? How many miles?

 

[rockola1971]

1996-2003 era? Thats actually a mix of 2 eras (Bodystyle/Generation). The 5.7L Vin R ended around 2000 in the old bodystyle (Pickups had 3 doors) and 5.7L is a Gen 1 SBC. In 2000 you could get the "newer" bodystyle (the pickups had 4 doors) for the extended cab and 4.8L,5.3L,6.0L all Gen 3 SBC V8's. GM stopped making the 5.7L (350 Chevy) Vortec engine in 2000. SBC Gen1 are history now. So generally you want a 2000-2006(with a Gen3 engine) to get the newer bodystyle(compared to the 1996 style).
The roaring in 4Hi Sounds like you may have a bad bearing in the front diff. The front diff is not locked to the Tcase in 2wd via the front driveshaft. Its not going to be cheap if you cant repair yourself or atleast have a friend that can do it. Setting the pinion to ring gear engagement is an art that you just dont learn yourself by trial and error in your driveway.

 

[B-train]

Agreed with @rockola1971

Those years have no AFM crap to deal with. Either is a good vehicle. The LS motors will be less problematic vs the 5.7L vortec. I like the 5.7, but rhe spider injector can cause issues - but fairly easy to fix.

The growling in 4 hi could be bad bearings, but it also could be that you drove it on pavement, or had tires worn weird, or 2 different brands or sizes of tires that caused driveline binding.

If it goes down the road quiet, then find a gravel road and try 4-HI. My guess is it will sound almost the same except for a small amount of extra gear noise from t-case and front axle. They weren't the quietest 4wd units out there. My 2000 silverado had just a hint of extra noise in 4wd, but no adverse effects for 100k.