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Issue 2003 Gmc Sierra 2500hd 4x4 6 inch Cognito lift issues
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Replace the fuel pump with an OEM AC-Delco. -
Hello, first time posting here. I have an 03 Chevy 1500HD with the 6 liter gas engine. The truck ran fine until the fuel pump died on me and had to get it towed. Replaced the fuel pump with a precision pump from O’rileys and changed the fuel filter while I was there. The truck will run and drive now but it wants to idle around 500 rpm when in drive and it tries to stall if you touch the gas. It drives fine though, just doesn’t want to idle. Put a fuel pressure gauge on the rail and only have 50 psi. I guess these trucks should have 55-62 psi to run right. I thought the regulator might be the issue because when I would unplug the vacuum hose it jumped to 56 psi. Replaced the regulator and no change. The only thing I can think of is that I was sold a faulty fuel pump. Any help would be appreciated because I’d rather not have to take the bed off again if I don’t have too. Thank you!
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I've been wrenching on GM trucks for 17 years. And I need to get something off my chest because it's been weighing on me for a long time. After all that time, all those motors, all those people standing in my bay, I've figured out there are really only two kinds of owners. The ones who already know about this. And the ones who are about to find out the hard way. A guy came into my shop a few weeks back in a 2018 Silverado 5.3. Sharp guy, maybe 35. Knew his truck cold. He'd been on the forums, read the threads, done his homework. He only rolled in so I could double-check a little module he'd already plugged in himself. Wanted a second set of eyes on it. Ten minutes, in and out, drove off happy. Two days later, a completely different story walked through the same door. Older fella this time, in a 2016 Sierra. Gorgeous truck, clearly babied, not a scratch on it. Wedding ring. Looked like a guy who took care of his stuff. He was in because his engine had started knocking on the way to work. And by the time I got the valve cover off, I already knew it was too late. Lifter collapsed. Cylinder 5. Camshaft chewed up. The whole top end shot. Same kind of truck. Same motor. Same roads, probably the same dealer. The only thing separating those two men was information. I've been at this since 2008, and I've worked on everything GM puts out. Silverados. Sierras. Tahoes. Yukons. Suburbans. Escalades. The 5.3 and the 6.2. Doesn't matter which badge is on the tailgate. They all carry the same problem. So here's the information one of those guys had and the other one didn't. It's called Active Fuel Management. AFM. GM started building it into their V6s and V8s back in 2007 to squeeze out a little better mileage on the highway. Maybe a mile or two a gallon. All to hit government fuel economy numbers. The way it works, the motor quietly shuts down half its cylinders when you're just cruising along. And the little lifters that pull that off have a tiny pin inside them that's constantly clicking in and out. Lock, unlock, lock, unlock. Hundreds of times a drive. Thousands of times a week. Eventually one of those pins wears through. The lifter drops. And it starts grinding the camshaft down like a chisel on butter. And what nobody tells you is that the shudder you feel around 40 or 50 mph? That's the system cycling. Every single time. Here's what really gets me. The pre-2007 trucks, the ones without AFM, they're bulletproof. I've got customers still daily driving them with 260,000 miles on the odometer. Not a problem in the world. GM took a perfectly good motor that would have lasted a lifetime and bolted this system onto it. And it is wrecking engines that should have run forever. The guys who hang around the forums already know all of this. So do the techs. They handled this years ago. They didn't sit around waiting for the dealership to mail them a warning letter, because that letter is never coming. It's the guys who figured somebody would've told them who end up on my lift. And I want to be clear, because this part matters. Maintenance has nothing to do with it. I've torn down motors with barely 30,000 miles on the clock. I pulled apart a Tahoe last summer with 24,000 on it. Practically a brand new truck. Owner had it less than a year. Spotless oil. Best synthetic money can buy, changed early every time. Made no difference. I've seen guys with full dealer records, every interval stamped. Made no difference. The oil changes were never the problem. The pin was. And no amount of babying that truck stops that pin from cycling every single time you drive. That's the part that eats at me. These are good motors. Take the AFM out of the equation and a 5.3 or a 6.2 will run 300,000 miles and never blink. So a few years ago I started telling every single owner who comes through my doors the exact same thing the smart guys already knew. Get yourself a FullForce disabler. It plugs right into the port under your dash. Couple of seconds and you're done. It just tells the computer to leave every cylinder running, full time. No more cycling. No more beating those lifters back and forth every time you turn the key. It doesn't reprogram anything. Doesn't touch your tune. And unplug it before a dealer visit and there's absolutely zero trace it was ever installed. I've had customers come back at 40,000, 60,000, 80,000 miles after I put one in. Zero issues. The trucks run smoother. And the lifters aren't getting beaten to death every single drive. I won't sit here and tell you it's magic. A lifter that's already damaged is a lifter that's already damaged, and this won't un-ring that bell. But it takes away the one thing causing all that wear in the first place. That's the whole game. You don't need a five-thousand-dollar delete. You don't need an expensive tune. You don't need to tear anything apart. You just need to stop the cycling. I'm not writing this for any company. I'm writing it because I'm tired of watching the guys who didn't know pay four and five figures for it. I'm tired of being the guy who has to break the news. I'm tired of knowing that the guys who did know fixed the whole thing for the price of a tank of gas, and the only difference was that somebody told them first. If you drive a Silverado, Sierra, Tahoe, Yukon, Suburban, or Escalade from 2007 or newer with a V6 or V8, you've got AFM. You've got those lifters, and they're cycling every single time you drive. So be the guy who already knew. Not the one I'm scraping metal out of next month. EDIT: A bunch of folks asked, so here it is. The one I put my faith in is FullForce. This is where to find it: https://www.tryfullforce.com/products/fullforce™-afm-dfm-disabler They back it with a 60-day guarantee too. I've handed out more than I can count and not one's ever come back to me. Not one. See less -
Thanks for following along. I'm not author material, my tenses are all over the place and an editor would have a heck of a time cleaning up after me. Reading and writing is still a fun pastime though. My new scanner came in yesterday, wow, where the heck has this thing been?! It connects right up to the Blazer, there's all kinds of bidirectional tests like EGR activation and percentage, toggle the fuel pump relay, EVAP purge valve, IAC control, AC relay, reset the transmission's adaptive learning, toggle shift solenoids and TCC lockup, and I can reset fuel trims with the click of a button...all things I could have used over the last 60 days! It's also telling me there is a stored code in the ABS module for front left wheel sensor open and something about the brake switch. The ABS dash light works. It illuminates normally during the self-test at key on/ start and that's it. I cleared the codes and will see if they set when I take it out later. That, and I'm going to get (hopefully) real data on timing and cam ******. The PID's are there. I connected the tool to my truck...holy smokes. Newer vehicles make early OBDII vehicles look like 8-bit, pixelated, early Nintendo stuff. This? This is like wearing 3D virtual reality goggles playing one of those elaborate, cinematic video games with seasons and plots in comparison. There are SO MANY modules and SO MANY tests and SO MUCH data. There's a scanner sequence for filling the coolant... End of the day, it's a tool with way more power than I need, but the versatility to do old and new is there (and I need an adapter to connect it to my OBDI Camaro). It will allow me to do the first pass of diagnosis when out-of-warranty vehicles need help, and it will enable more DIY maintenance like brake system bleeding, ABS bleed, etc. I probably over-bought here, but, mission is accomplished. Enjoy your Sunday...I need to shut this machine down and go get ready for the week ahead. -
Not that I've read, after all the issues they've had in the past I'm pretty sure they learned their lesson.
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