Tune Up Intervals?

nonotme42 · August 14, 2009

Hey fellas, haven't been around recently, but it's been nuts.

Anyways, I keep track of my fuel purchases and economy like a hawk. Not the DIC economy, which tends to be extremely optimistic, but the actual fuel in, calculated numbers. But this isn't about the DIC. What it is about is that last year, I averaged 15.95 mpg. This year, 13.95. Exactly the same conditions, same driving patterns, etc. It also doesn't seem to idle with the same smoothness as when I got it with 31k. It's now got 65,700. It also has a tendency to not start the first time when I hit it my remote start. Once or twice, actually didn't start twice, and it has no effect whether its hot or cold. To the best of my knowledge, GM's recommendation is 100k for plugs and wires, and absolutely everything else on the truck is up to date. I use 0W-30 Amsoil SSO in the engine (Currently at 10k), Dex VI and a WIX filter (Now at 15k) in the transmission with a B&M cooler, Mobil1 75W-90 in both differentials (At 15k), GM AutoTrak II in the transfer case (At 15k), only Shell or Chevron (top tier) fuels, along with Techron concentrate or Seafoam every 5k miles. Air filter is a new Purolator PureONE, PCV is new, obviously can't get to the fuel filter, and all that's really left is the plugs and wires....am I forgetting anything else? I really don't want to do a tuneup yet if that's not going to fix my problem...since I'm going to have to use Delco Iridiums and MSD wires (I have a serious problem with buying cheap replacement fluids and parts). I suppose it could use a tune, and maybe I could squeeze a bit out that way, in combination with the new plugs and wires, but I just want to verify I'm not missing anything.

hcpyro13 · August 14, 2009

Clean the MAF sensor lately?

WilliamBos · August 14, 2009

Try running regular (87) grade gas. You are literally pouring you money down the drain by running higher grade fuel. It will not hurt any. Not sure if that will help the mileage, but why not try.

And how about the MAF?? (like posted above.) Also the throttle plate...

Use the AC Delco wires. There is nothing wrong with them. Sometimes you pay more for the aftermarket name, and get a less quality product. (MSD.)

Hey fellas, haven't been around recently, but it's been nuts.

Anyways, I keep track of my fuel purchases and economy like a hawk. Not the DIC economy, which tends to be extremely optimistic, but the actual fuel in, calculated numbers. But this isn't about the DIC. What it is about is that last year, I averaged 15.95 mpg. This year, 13.95. Exactly the same conditions, same driving patterns, etc. It also doesn't seem to idle with the same smoothness as when I got it with 31k. It's now got 65,700. It also has a tendency to not start the first time when I hit it my remote start. Once or twice, actually didn't start twice, and it has no effect whether its hot or cold. To the best of my knowledge, GM's recommendation is 100k for plugs and wires, and absolutely everything else on the truck is up to date. I use 0W-30 Amsoil SSO in the engine (Currently at 10k), Dex VI and a WIX filter (Now at 15k) in the transmission with a B&M cooler, Mobil1 75W-90 in both differentials (At 15k), GM AutoTrak II in the transfer case (At 15k), only Shell or Chevron (top tier) fuels, along with Techron concentrate or Seafoam every 5k miles. Air filter is a new Purolator PureONE, PCV is new, obviously can't get to the fuel filter, and all that's really left is the plugs and wires....am I forgetting anything else? I really don't want to do a tuneup yet if that's not going to fix my problem...since I'm going to have to use Delco Iridiums and MSD wires (I have a serious problem with buying cheap replacement fluids and parts). I suppose it could use a tune, and maybe I could squeeze a bit out that way, in combination with the new plugs and wires, but I just want to verify I'm not missing anything.

tramz · August 15, 2009

I've had 1.8 MPG drop over the past year. I was talking with the manager of the local fuel depot/distribution station, an acquaintance through a mutual friend and he explained that the ethanol mix in fuels has negatively affected MPG. He said that the gas is 84/85 octane and the added ethanol boosts the octane to 87 in low grade. He recommends running mid-grade as this is simply a blend of low and high grade and will burn better. He explained why and went into a whole rant about the ethanol its ill effects on all engines. He showed me the storage tank where it's stored before they blend it, the tank was covered in this thick black residue, I asked what it was, his reply was, it’s mold, plant/food bi-product and then more ranting. He also said that ethanol was the alternative to high gas prices, and because it has to be trucked everywhere the price per gallon is over $3.00. This is what was told to me, and hope I conveyed it correctly. I don't have anything to validate it, but it sounded good at the time.

nonotme42 · August 15, 2009

thanks for the responses.

Yes, I forgot to mention, I clean the MAF on my vehicles every 20k.

I don't use premium fuel, I only use 87, but have, before, gone with a small stint (5 fillups or so) of premium from one station or another to see if that affects my mileage, as well as stints on non-ethanol fuels (when they still had the handful around here before the mandation went into effect, and I can say for sure that while the ethanol did indeed make a difference, it wasn't contributing significantly, because on a road trip I made up to New York May 2008, I averaged between 16.9 and 22 mpg, and every single station had up to 10% ethanol. Trust me though, I absolutely HATE the idea of ethanol altogether...its not a solution to a damn thing.

However, I have no problem believing that quite possibly, ethanol affected the long duration maintenance intervals that GM called for on this truck, one way or another.

And as far as the ignition wires go, yes, normally, I'd go with Delco, as normally, OE is a superior product, but MSD Super Conductor wires specifically are some of the highest quality aftermarket wires on the market besides Napa Belden. They're the absolute lowest resistance available, and the highest shielded to prevent any and nearly all electronic interferance. And since they're not INSANELY expensive, I can't justify knowing about them and not using them. But that's of course, an entirely separate conversation.

I've been driving like an absolute SAINT on my last tank, and just averaged 14.5 mpg. WTF.

1990ss · August 15, 2009

How do you clean the MAF?

2COR517 · August 15, 2009

How do you clean the MAF?

Here's a little reading on MAF and TB cleanup. I had fantastic results, both power and economy.

http://www.gm-trucks.com/forums/index.php?showtopic=99880

John, I think I would spring for the wires and plugs at this point. Also TB cleanup and Seafoam through the manifold might help.

nonotme42 · August 23, 2009

I think I'll do the TB cleanout at 100k. I'm sure it's a lot easier to remove with the drive by wire motor replacing the TPS, IAC, and throttle cables. I suppose I'll look into that and make sure there will be no surprises with the motor though...if its easy to separate from the TB to clean, etc

As far as Seafoam Goes....its been one of the best wrenches in my toolbox for quite a few vehicles. However...on the 2004 MY Gen III 5300, at least in particular, seems to have been designed with a complete lack of vacuum lines. I guess it's good...removes an entire section of complication from the engine design, so..I can't argue with it too much...but it does hinder one of the most effective ways to get Seafoam into the engine quickly. I might just get a new can of aresol GM Top Engine cleaner, take off the intake tube and go at it right at the throttle plate. I imagine the engine will run a bit strange without the MAF having air go past it, but, we'll see.

Plugs and wires. Well, I've pretty much come to the conclusion...ethanol has probably been the main culprit in lowering the high mileage interval on those...so I'll be doing those sometime soon, but I might just wait and do it all at one interval..say..75k. Right around when I'll be doing my next amsoil change, and next transmission pan drop. I'll make a day of it.

2COR517 · August 23, 2009

Don't you still have a vacuum line for the power brake booster?

nonotme42 · August 24, 2009

nope, I have hydroboost brakes, as i believe for sure, all avalanches got in 04, not sure about others like suburban, etc

2COR517 · August 24, 2009

Hydroboost on the 1500s too. Learn something everyday.

Just pour the Seafoam right in the throttle body.

jblakeney · August 24, 2009

thanks for the responses.

Yes, I forgot to mention, I clean the MAF on my vehicles every 20k.

I don't use premium fuel, I only use 87, but have, before, gone with a small stint (5 fillups or so) of premium from one station or another to see if that affects my mileage, as well as stints on non-ethanol fuels (when they still had the handful around here before the mandation went into effect, and I can say for sure that while the ethanol did indeed make a difference, it wasn't contributing significantly, because on a road trip I made up to New York May 2008, I averaged between 16.9 and 22 mpg, and every single station had up to 10% ethanol. Trust me though, I absolutely HATE the idea of ethanol altogether...its not a solution to a damn thing.

However, I have no problem believing that quite possibly, ethanol affected the long duration maintenance intervals that GM called for on this truck, one way or another.

And as far as the ignition wires go, yes, normally, I'd go with Delco, as normally, OE is a superior product, but MSD Super Conductor wires specifically are some of the highest quality aftermarket wires on the market besides Napa Belden. They're the absolute lowest resistance available, and the highest shielded to prevent any and nearly all electronic interferance. And since they're not INSANELY expensive, I can't justify knowing about them and not using them. But that's of course, an entirely separate conversation.

I've been driving like an absolute SAINT on my last tank, and just averaged 14.5 mpg. WTF.