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Chevy Silverado and GMC Sierra Fuel Pump/Fuel System



  • fixed mine this weekend. I changed out the pressure regulator and it seems to be working right. $45 at autozone would have fixed my 6 month problem. It seems fine now.

    Changing your fuel filters regularly will save your fuel pump.
  • ksr3ksr3 Posts: 2
    I am hoping to get some feedback from those of you who have driven one of the new 2007 models with the new Active Fuel Management. This is where 4 of the 8 cylinders are deactivated when not needed, and per the articles is supposed to be "seamless".

    The Active Fuel Management is supposed to give you better gas mileage. Is there a tradeoff in performance? Is it really "seamless"? Any comments would be appreciated.

  • They are using a faster CPU with more RAM and a ECMw/TCM instead of just a PCM. They use special lifters which are a lifter within a lifter and special cam lobes on the 4 cylinders that get deactivated when AFM is enabled. The special lifters keep the valves on those 4 cylinders closed when AFM is enabled by having the center portion of the lifter(part that pushes against the pushrod) bleed down when AFM is active. It is used on engines which have the drive by wire throttle body so the ECM is able to push the "gas pedal" down for you without your even knowing it to make AFM "appear" seamless. Of course there is no such thing as a "gas pedal" anymore, but for anyone unfamiliar with electronically controlled fuel injection and drive by wire it can still be called a "gas pedal" since those people don't know the difference anyway.
  • I am also wondering about this 5.3ltr motor with A.F.M. If it was just electronically con-trolled, I might not be so worried. But apparently, there are mechanics involved as well.
    For some reason, I am just worried this motor may develope more problems because of more moving parts/new tech. etc. I am not a gearhead, just looking to buy a new truck.
    ( Currently drive 1994 Silverado Ext. Cab 4.3 V6) I am thinking more about the 4.8ltr
    for the new one???? Any thoughts. Anyone? Anybody driving a 5.3ltr with A.F.M.??

  • The 4.8 doesn't have AFM. The 5.3 does and it is electrically controlled and mechanically activated. It is controlled by solenoids and pneumatically enables and disables the special lifters. That stuff can fail and if it does it will require a top end tear down which is costly and time consuming. The 6.0L V8 also has VVT which phases the camshaft timing. This is also done by the ECM so you're not supposed to know it is even happening. Another thing to break. I'm starting to like the Coates spherical rotary valves more and more.
  • Wikipedia has a pretty good explanantion of AFM. Because AFM shuts off valve lifters to deactivate 4 cylinders it is extremely important to use the factory-recommended oil viscosity. If I recall correctly, the recommended viscosity for the 6.0L engine in the new Silverado is 5W-30 (you should verify this for yourself). I usually run 10W-40 in all my vehicles, but it looks like I'm going to have to make an exception to that rule.
  • I have also read this Wikipedia explanation of A.F.M. It does seem to me that it is possible for more problems down the road, hence my preference for the 4.8ltr engine.
    Also, I will be using my truck for light towing(boat) and loading gear. Thus, I think the
    time the 4 cyl. A.F.M. useage would be minimal. I doubt the truck would be using only 4 cyl. when towing anything.?? So I dont see what the real advantage would be in gas mileage when towing. If you drove it like a car unloaded,.....OK, maybe. Any thoughts??

  • I think the 4.8L is a bit light for towing. AFM doesn't sound that complex to me, and of course things of any sort can go wrong "in the future". If that is the only consideration we'd never try anything new. But, overall, for me the potential benefits outweigh the potential risks.

    When towing, my guess is that AFM would only kick in when coasting downhill. Unloaded, it probably would work a little more often - when coasting downhill certainly and possibly when cruising on a flat hwy.

    Re: the previous comment about VVT, I disagree. It is a proven technology and is being used on most engines nowadays. It's nothing to be afraid of. In fact, VVT is responsible for the great power and mileage numbers we are now beginning to take for granted.
  • My 93 gmc had been sitting for 6 mo.the tank was drained by gas theives.added fuel,now gauge shows way past full & truck will only idle.can make it move by feathering throttle.adding carb clnr will make it run right.replaced fuel fiter,looking at pump.?gauge sit bothers me.any suggs?
  • Is that what that is when My truck wont start? the engine cranks for a few seconds I wait and moment and the it fires up.? Also when I fill up my fuel needle goes wack. I know my tanks full but the needle shoots to empty and goes up slowly and back to empty. *SHRUGS* any ideas?
  • seannooseannoo Posts: 15
    I have been lagging on getting my truck fixed of this problem. Although I am not having the same issues as the other guys (using excessive fuel, etc.) since the fuel pressure regulator fixed their problem, I am going to change mine out too to see if that corrects it. I was at Pep Boys and they wanted a little over $90 for the regulator, so I am going to get it from Auto Zone where one of the guys said it was only $45. I will put it on my to do list for this weekend (for sure this time) and let you know if that fixes things.
    It sounds like you and I have the same issue, in that it won't start the first time unless you crank it for a long time, but once it is running, it is fine.
  • My fuel pump stays ON after the truck has been shut off... often runs the battery down if I dont disconnect it at night. has new fuel pump in the tank and a new switch thing,(like a timer switch)... we have checked out many electrical scenarios, just cant figure this one out! Please help! thank you
  • seannooseannoo Posts: 15
    It sounds like you have an electrical short somewhere. The fuel pump should only run when the ignition is on and the fact that yours is running when the ignition is off is very strange. Does anything else stay on that should not be when the ignition is turned off? Did the problem start around the same time that you had something added to the electrical system? It could also be a bad fuel pump relay in your electrical panel under the hood. The contacts on it could be internally shorting out and causing it to stay on.
  • Hello Sean,
    do you think that a truck like mine would have a timer on the fuel pump that stays on for 20 seconds after the truck is shut off? thats what my mechanic changed out last time he worked on it... I really have never heard of such a thing, but also, do you think that this timer and the relay might be the same thing? I hate my truck... but we just put a new motor in it, it didnt have this problem before, just the gas guage didnt work, this fuel pump thing started after we got the gas guage fixed.
  • seannooseannoo Posts: 15
    litalow; I don't know what would be the purpose of a timer that would keep the fuel pump on after you turn off the ignition; it just doesn't make sense to me. when they fixed the gas guage, did they replace the sending unit or have to drop the tank for the repair? If so, your problem probably lies in the back of the truck in the area of the tank; at least that would be my guess.
  • Hi Sean,
    It sure was nice of you to help me with my truck dilemma... The truck went back into the shop again last week, and I hope that we will finally get all the bugs worked out eventually. believe it or not your comments really helped me to persuade my mechanic to look at that relay one more time... they told me that the relay was the first thing they changed out, but after I had them check it again they said that when they pulled it out, that it had rattling parts inside it and they were able to get another replacement one at no charge to me. I havent gotten it back yet because the other thing they needed to change out was a bad pilot bearing, (clutch)..... it was ready today but they didn't have time to test drive it yet so I should have it in the afternoon sometime tomarrow. thank you so much for your help, and good luck to you with your projects always! R.R.
  • I have 2,000 miles on a new 07 Silverado 5.3 with Active fuel management. It is incredibly seamless. If I did not have the on board computer showing the instant fuel economy, I would not know when it was activated. The fuel economy, however, is not good. Driving many highway miles in cruise control, no rush hour traffic and not pulling anything, my average fuel economy is 14.5 MPG.
  • Does anyone have a location for the fuel filter on a 04 3500 DRW crew cab, with 8.1L and allison tranny? I traced the lines back to the tank, and the only place i think it could be is either the tank or a box mounted on the underside of the bed. 1 line runs to it.
  • rockyleerockylee Wyoming, MichiganPosts: 13,993
    You will get better. My FIL gets 12 mpg with his cummins diesel. My buddy Cody get's 13.1 in his Toyota with the wind behind him. My FIL also in his Ford F-150 only got 14 mpg. I think it's possible you will see 16-18 mpg in the future.

  • ahoronahoron Posts: 30
    the fuel filter slides out of the bracket after you remove the fuel lines
  • ahoronahoron Posts: 30
    Go to a different dealer
  • seannooseannoo Posts: 15
    Litalow, I have been wondering if you have fixed your fuel problem yet and if it was the regulator? I finally changed out my regulator this past weekend and unfortunately there was no difference. I am going to try the fuel pump relay(s) this weekend, and am just hoping I won't have to drop the fuel tank for the fuel filter.
    I am so bummed though; it seems that changing the regulator was fixing everyone elses issues and was hoping for the same.
  • Hi Sean,
    Well I do think we worked all the bugs out this time...
    it seems that even when the fuel relay had been removed from the truck, they noticed that the fuel pump continued to stay on......? so they began tracking the electrical wiring using a skematics to isolate the fuel components, and found a bundle of wiring that had melted when at some point it had crossed over the exhaust next to the engine block. the wires apparently were enclosed inside the plastic tubing commonly used to protect them, and when the two wires touched and bounced around it sent a current, and could not be seen. I got the truck back on friday, and over the weekend drove from colorado to visit my son in kansas and put 1,500 miles on it without any problems.
    is it your fuel pump stays on thats the problem?... or a no start? fuel injected or carb? I have never heard of a fuel filter being in the gas tank before....(well, maybe?) usually on the front of the carb. or looks like a 2 or 3 inch cylinder attached at both ends within the flow of the fuel line, in the engine compartment, or can also be located just under the driver side door mounted on the frame within the fuel line. if you live in a cold snowy area like I do, we have lots of the no start issues with things freezing.. good luck with that... let me know ok, thanks. R.R.
  • On some GM's the fuel pump power is "maintained" after starting through a set of contacts in the oil pressure sending unit. If no oil pressure, no fuel. Not sure about your model. Do you have a wiring diagram? Hope this helps.
  • seannooseannoo Posts: 15
    I screwed up on the typing in my last response; I actually changed out the fuel filter last week, and you were right in that it just unbolted from the bottom of the truck. I meant to say that I am not looking forward to dropping the fuel tank to replace the fuel pump if that ends up being the problem. I am going to check everything else first, but with my luck...the tank will have to come out once I exhaust all the other options by replacing every other possible component.
  • Hey Sean...
    Have you checked your timing?
    Is your truck an automatic? ..if so ..when you put it in DRIVE, and without your foot on the gas, will the truck move by itself? If it does, turn your timing down.
  • seannooseannoo Posts: 15
    I have not checked the timing, but I don't think that is the problem. It is very strange, but here is what it does. The first time I attempt to start the truck, it won't start, if I continue to crank it, it'll take about 10 seconds to start, but then will run fine. If I turn the truck over for a second, stop and then try again, it will usually start right up without the lengthy cranking. If I have recently ran the truck, it will start right up without any problems and once the truck is started, it run's perfect every time. The fuel pump does not turn on to prime the injection system (for 1-2 seconds when I first turn on the ignition) as it did for the first 100K miles I had the truck. I am assuming that the issue is related back to the fuel pump not working properly, but I am not sure if it is the pump by itself or some other component not doing its job by not telling the pump to turn on. It almost seems like to pump is not working at all, because I can't hear it even when the truck is runnig, but I know that would be near impossible for the gas to siphon into the fuel injection on its own.
    Being that the truck runs fine once it's started, it hasn't been one of those hot issues I have been putting as much effort into as I should be....but we all know that these problems end up leaving you stranded one day. So far though, the truck has been doing this for about a year! I know that what I need to do is check voltage going into the fuel pump to see if it is getting the voltage to prime it and then keep it running when the truck is going. That would tell me if it is the pump that is suspect or the relay/other wiring, but I have just been reluctant to dive into it so far. I was hoping someone would have experienced the same problem at one point and maybe this is somewhat of a common problem.....but that does not seem to be the case.
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