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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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    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.

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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!!!

  5. #5

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    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.

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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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    Quote Originally Posted by TRPLXL2 View Post
    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..

    Almost finshed with timing chain replacmement, just to confirm the tech's comment it is indeed a roller motor. But now i got to go back to auto parts store the crank sensro they gave me is about 3-4 inches long, I could make two fo mine out of the one they gave me. old chain was deflecting about 1.2-5/8" new on more like 3/8" i dont think its a smoking gun. Here is another thought the metal tap that holds the crnak sensor in is it required to be a good ground ?? or just mounting tab, my block is very rusty, almost zero oil leaks anywhere, just a seep around engine oil cooler. but alot of flaky rust under and around crank sensor.

  8. #8

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    Generally they act more like a switch sending digital signals so i dont think it needs a ground. In some very rare cases the reluctor wheel that is pressed onto the crank can move causing probs but it is very seldom seen and i would check it as a very last option. Im still in the camp of wiring/ ground issue.
    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.


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    Well I learned something new today!!! I wish mine would have been a roller to begin with, It could have saved me some money. Good luck with your truck, I am out of advice now lol!

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    When is the last time you changed your O2 sensors?

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