2003 Silverado 6.0 tune problem...

[Staton]

I have been running the 87 octane tune in my 2003 Chevy Silverado 2500HD 6.0L for the past 8 months. I did notice some improvement when I initially installed the tune....12mpg increased to 13.5mpg and a little more power overall.....a little. After reading some of the forums on the website, I took another's advice that since I have K&N Intake and true-dual exhuast, that I should change the injector slope to negative 2. After making that adjustment, my mpg increased to 16mpg hwy and I definitely felt more power.

Instead of leaving it alone, I decided to try the premium tune with the modified injector slope. After the installation, I notice little....if anything less power. Yes, I did fill up with premium. I decided to go back to the 87 Octane tune. After reinstalling the tune, my truck idles so low that it dies on me constantly and my mpg is back to 13-14 mpg. Also, because the idle is so low, my A/C does not blow cold air unless I am moving....at an idle it blows hot. i don't understand why this is happening when it was running perfect with the adjusted parameters.

If anybody could help me out.....I would really appreciate it.

2003 Chevrolet Silverado 2500HD 6.0L
Ext Cab / 4X4
Predator 87 Octane tune
adjusted parameters include:
Tire size adjusted to 305 / 70R16
Max MPH adjusted to max
Injector Slope adjusted to -2

Problems Include:
Rough Idle too low / routinely dies
A/C only cold when moving
Decreased fuel economy

[CANUCKPREDATOR]

does it do that with the original tune installed? if it does its not tune related.

[Staton]

I never had those issues until the moment I installed the Predator 87 Octane tune 8 months ago. A soon as I unplugged the tuner....I had the idle / A/C problems. I ran it like that for appx 8 months and it did get somewhat better, but after adjusting the injector slope to negative 2, it ran like a dream. I got greedy and installed the premium tune....wasn't impressed, so I went back to the 87 Octane tune. Now I am having the old issues with the newly adjusted injector slope.

[CANUCKPREDATOR]

Two things

1. Try putting the stock tune back in to see if it continues.

2. Change the size of your signature pic, makes reading hard.

[Staton]

One source told me to re-install the factory tune and then unhook the battery for about 30 minutes. He said by doing that I would completely reset everything back to the way it was prior to the Predator.

Your thoughts on that?

[CANUCKPREDATOR]

that would do it.

[Staton]

Thanks for the informaion Canuck!.....I'll reset everything.....see how it runs, then possibly reload the tune.

Will reply tomorrow on status.....

[Staton]

I reloaded the facotry tune yesterday. Also, after the reload, I disconnected the battery for appx 30 minutes as well. The truck runs fine, but my idle is still erratic....it fluctuates from 300-600. I drove it for about 30-40 miles and still have the issue. I'm not receiving any error codes, but a friend told me that it would more than likely have to do with my fuel. It has died on my numerous times.

Would this have to do with the fuel?

I'm going to load the 87 octane tune in this afternoon and see how is does starting with a clean slate....

Your thoughts?

[marcoengineering]

Just chiming in here, have you changed your checked your fuel pressure? How old is the fuel filter, low or inadequate fuel pressure can cause all sorts of wierd things to happen, also did you check to make sure there are no air leaks after the MAF senser? The AC issue is a case of air flow or AC pressure. Make sure the Engine cooling fan is pulling some air at idle across the condensor or you may get the problem you describe, but this maybe realted to the low idle, the erratic idle says lean condition, so fuel or unmetered air you have to rule out somehow. Possible IAC problems or if it is cableless throttle, maybe the throttle plate is sticking, so check to make sure it will close all the way when the engine if off, I have seen times when this plate sticks and messes up idles, again causing all kinds of trouble. Hope this helps somewhat.

[Staton]

Thanks for tips "Marco"! I can rule out the fuel filter, I changed it less than a week ago. I will check into the MAF sensor and the throttle. I do know that as far as the A/C is concerned, with my truck idling...giving just a little gas (enough to hold a steady 500-600rpm), cold air returns.

Will check the MAF and throttle......then will post status.

[marcoengineering]

How many miles do you have on the truck? It does not hurt to check fuel pressure, just to be sure you don;t have fuel pump problems, but it seems like some kind of idle control problem, The idle is probably too low to pull air through the front end cooling module, so when you get to the root of the idle problem, your AC issue will be solved as well. I'll keep thinking of things I have seem before, but make sure to check for vacuum leaks in the engine compartment, even small ones. 500-600 rpm is target drive idle when hot, so something is up in the system?, The 300rpm is the cause of the AC issue and stalling.

[Staton]

The truck has 110K miles.

Though I know a little about the mechanics of my truck....I'm not a complete "motorhead". So, how would I go about checking the fuel pressure?

[marcoengineering]

Somewhere along the fuel rails there is a cap and scrader valve, like on a tire, you need a fuel pressure gauge and the specs for your truck, which I can look up later tonight. Low fuel pessure might give you long crank times to start and other drivability issues. It worth checking, but it seems much more like a small vacuum, or intake system leak, where unmetered air gets by the MAF sensor where it is really noticble at idle more than off idle conditions. A bad MAF would throw a code. Make to sure to check all the clamps on the intake system and PCV valve lines that none are cracked and leaking air into the system unaccounted for. Are you sure your air filter is clean, and there is the possibility that you got oil on the MAF sensor, you can get some CRC MAF cleaner at a parts store and clean the MAF. GM has a TSB out on oil getting on the MAF from aftermarket filters, I would check to make sure the filter is clean (and not full of mud/dirt, Ive seen that before) and then check to make sure the MAF is not contaminated (cleanig with the MAF cleaner will do the trick, but follow the directions on the can), this will throw off the fuel reading and act like an air leak if it is dirty or contaminated, even if it does not throw a code.

[Staton]

Thanks Marco....I'll pull the MAF sensor offf and clean everything out.....and make sure everything is sealed up.

Will reply after.....

[Staton]

I reinstalled the tune with the altered parameters....

Adjusted axle ration to 3:73
Maxed the MPH
Actual tire size to 305 /70R16
Injector Slope -2

After initiall installing the tune, the truck ran decently enough, but the idle was "bouncy" and would hold steady at 500-600 rpms....then drop to 200-300 rpms When putting the truck in Drive, it would stall out half the time. I've been driving it for nearly a week now with the adjusted tune and it's getting better. I"ll be on the road this weekend for a 6-hour round trip. My thoughts are that whatever tweaks the CPU needs to catch-up with the tune, should be worked out on this drive.

Will post after Monday.....