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  1. #1

    Default 03 gmc gremlin problems- flashing engine light, reduced power

    Original owner 03 GMC 1500HD 6.0 liter. 4x4 4.10 gears, original everything except normal maint items. at 160k started having flashing check engine light when cresting the top of a hill on the interstate, noticed when rpms were right around 2500 rpm. Scanned random misfire detected, took to gm shop, when I went back to pick up they already had trade value figured out for me or $2k to tear down and inspect camshaft, tech told me that this engine has a roller cam and they wear out lopes before flat tappet. YEH. OK the next morning I took off for a 2k mile trip with my tailer, now at 195k Ive towed my drag car to the strip almost ever weekend with this truck, it is not missing, it is DETECTING a misfire, mileage may have slipped a little over the years , but I didnt buy it for its mileage performance.

    THis truck has had many electrical gremlins, Reduce engine power on start up 3 times in 10 years. Most recent last week, shut it off started it 2-3 times and gone, check engine light went off after a dozen or so succeful starts, Also from time to time if you open gloove ox or turn on interior light the inst cluster will blink bed light indicator. 2-3 times Have had passenger side electrical windows(front and back) stop working, but next day all works ok. ALso have got in truck started truck jumped in and took off with door chime still going, stop turn off truck restart sometimes maye 3- 4 times before going off. always thought maybe starting before shutting the door, causes this one.

  2. #2
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    TRPLXL2's Avatar
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    Welcome to the site!!

    Holy moly, this gives me flashbacks to my engine swap lol!!! Electrical gremlins suck!!! It has been my experience that when you get this many weird things happening at once, It is either a ground problem or your BCM (interior computer) or ecm (powertrain module) is starting to crap out.. The cam comment threw me for a loop though, I was under the impression that the 4.8. 5.3, 5.7, and 6.0 all were flat tappet cam equipped from the factory. I just did a 5.7 LS1 rebuild, and it had a flat tappet cam but we rebuilt it as a full roller motor..
    2004 Chevy Colorado
    LS1 5.7 swap/TBSS rear axle swap

  3. #3

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    Yes tech comment blew me away also, I wasnt sure if it was a roller or not? My sons 5.7 in his 199? firebird was steel block/ alum heads and it was roller lifters But roller lopes dont wear as much as flat tappet, unless failed lifter. second if I had a lope wore off the cam why would that flash random cylind misfire. Thats why i left on my trip the next morning, they wouldnt do a crank sensor relearn.

  4. #4
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    Normally with a crank sensor relearn, they will only do it if the ecm is pulling timing. My s10 was doing this, when I checked it the crank sensor was -10 at idle. I did the crank relearn, and it still only brought it back to -4. I never did find out what the problem was with that truck lol!!!
    2004 Chevy Colorado
    LS1 5.7 swap/TBSS rear axle swap

  5. #5

    Default

    Im thinking about pulling the timing cover tomorrow, replace the chain/gear set. Should I plan to do a cranksaft sensor relearn after that ??? If I am should I replace crankshaft and camshaft sensor first.

  6. #6

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    ok before you jump then gun here, the flashing ses light means "catalyst damaging missfire". possible causes could be non-firing ignition componants (plug, wires, coil), plugged fuel injector (not getting any fuel so a lot of air is being introduced into the exhaust), and even a plugged cat and cause this (because off excessive back pressure). cover the basis befor you go too deap. when was the last time its had a tuneup (plugs wires, fuel filter, air filter)?
    "i dont think you got the picture. i got a beautiful picture. this baby happens to have an extra turn of speed, which is the only thing i care about. you dont understnad what happens do you? they make cars. they make 'em exactly the same way. one or two of 'em turn out to be something special. nobody knows why. i know why. i may be kiddin' myself, but i think i can make somethin' out of that sad little bucket of bolts." ~ Tennessee Steinmetz

  7. #7

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    plugs, wires and all was done at 100k and then right after 160k when light started flashing, new fuel pump and filter right after that, new air filter every six months or so. most of the items you talk about happens when there is an actual misfire. My truck idles like it was new and pulls like a beast when towing, just dont pass to many gas stations, but when I ordered 4.10 gears i knew that. have left gravel plant with trailer at 18k lbs. This I believe is mis-detection of a misfire. I spoke with another gm dealer today checking on parts and he sent me back to talk with service tech. I have no problem changing a timing set on a near 200k motor. While I'm there I will do Oil pump and water pump, crank sensor and a relearn I dont plant to get rid of it in the next 5-6 years, truck is still solid, just damn blinking light at 2400 rpm, i can pull a hill at 3000 or 5000 rpm no problem back off a little when I top it and blink blink, back off more no lite. If I keep the rpm off 2400 rpm no lite. I have read other post about this same rpm and light flash.

  8. #8

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    The bcm has a connection issue somewhere and it could relate to the engine issues. Heres what i would do, first pull a diagram of all powertrain grounds and power then follow all of those to make sure there is no corrosion. Second check the connector at ghe bcm and do an ohm test to ground through the connectors ground wire(s). I strongly believe with all of these things being widespread and relating to everything the bcm controls its something to do with that. If you need help of diagrams ask.

    Aslo while thinking on trailblazers there was a prob of the ground on the frame right under the drivers door corrodeing and causing these same probs so go through the frame griund with a find tooth comb.
    01' 1500 LT Z71 ECSB 5.3L
    line-x'd front brush guard with KC Daylighters, 6000k HID lows and highs, rewired highbeams, Trans-go mild shift kit, custom stainless duals, 3500 dually OEM taillights, K&N CAI. Still have OEM fender flairs and leveling kit in boxes waiting for time.


  9. #9
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    Quote Originally Posted by shibby2oo8 View Post
    The bcm has a connection issue somewhere and it could relate to the engine issues. Heres what i would do, first pull a diagram of all powertrain grounds and power then follow all of those to make sure there is no corrosion. Second check the connector at ghe bcm and do an ohm test to ground through the connectors ground wire(s). I strongly believe with all of these things being widespread and relating to everything the bcm controls its something to do with that. If you need help of diagrams ask.

    Aslo while thinking on trailblazers there was a prob of the ground on the frame right under the drivers door corrodeing and causing these same probs so go through the frame griund with a find tooth comb.
    This! Also a way to test for a misfire our issue with firing is to apply full pressure and your brakes and light pressure on the throttle, no power braking or spinning your tires, you just want to get your engine under a slight load. It should sound smooth, no spitting or ticking. If there is any hesitation under load, that's an actual misfire.

    The ground on the right side of the trailblazers have them a bad electrical reputation....

  10. #10

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    I Agree thats one way to show a misfire, but I without a doubt dont have an actual misfire, idles perfect, starts fine, dosent hestiate, pulls heavy loads fine. Im going thru the ground connections today, if nothing then timing chain, oil pump and crank sensor, crank relearn.

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