03 gmc gremlin problems- flashing engine light, reduced power

Discussion in 'GM Electrical Tech' started by 620nova, Jan 27, 2013.

  1. 620nova

    620nova New Member

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    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.
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  2. TRPLXL2

    TRPLXL2 New Member

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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..
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  3. 620nova

    620nova New Member

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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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  4. TRPLXL2

    TRPLXL2 New Member

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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!!!
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  5. 620nova

    620nova New Member

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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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  6. a.graham52

    a.graham52 New Member

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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)?
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  7. 620nova

    620nova New Member

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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.
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  8. shibby2oo8

    shibby2oo8 New Member

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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.
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  9. zigger215

    zigger215 New Member

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    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....
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  10. 620nova

    620nova New Member

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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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  11. zigger215

    zigger215 New Member

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    When is the last time you changed your O2 sensors?
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  12. 620nova

    620nova New Member

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    o2 sensors are orignal. Ok put truck on lift, reworked a couple grounds. removed water pump , broke my puller trying to get balancer off, it was my smaller puller, couldnt get large one in there. I will pick up a larger 3 leg one tomorrow. looking at book the oil pan has to come off to change timing gear set and oil pump. looking at the pan, does the fornt carrier have to come out ? looks like a lot of room around it. might be a good time to put a new fornt actuator in it anyways. plan to change timing set, oil pump, water pump, crank sensor, dealer relearn, new cats and exhaust next monday.
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  13. shibby2oo8

    shibby2oo8 New Member

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    Ouch been there before, you can rent tool from az, advance etc in a pinch. I really feel eventually your gonna find the green monster in a connector or in a wire loom and it will fix all of your problems. The oil pan has a rear pickup tube and even then just take the bolts out of the motor mounts and jack up the motor some. I would take the pan off before the crank pulley.
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  14. TRPLXL2

    TRPLXL2 New Member

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    I'm sure you know this already, but make sure you buy a new balancer bolt. They are one time use bolts, If you reuse it you can end up with the "death wobble" on the balancer. Since your doing the oil pump, look into an LS6 high volume Melling pump. They are ported for better flow, I am running one on my LS1 no problem. Take note of the rubber o-ring on your water pump shaft as well, the new pump will come with 3 different colored o-rings. Red, green, and black, It is very important that you replace with the correct color o-ring.

    I would tell you what we had happen with our balancer, but I don't want to jinx you lol!! We had it on the engine stand too, let's just say the factory puts lots of loctite on that bolt!
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  15. 620nova

    620nova New Member

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    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.
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  16. shibby2oo8

    shibby2oo8 New Member

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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.
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  17. TRPLXL2

    TRPLXL2 New Member

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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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  18. 620nova

    620nova New Member

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    all is back together, below is the list 0f changes

    1). reworked grounds, none appeared bad
    2). cleaned throttle body housing and blade
    3). cleaned mass air flow
    4). also cleaned throttle body anodization where rubber goes around outside. oxidaztion around the bottom was really bad maybe leaking there ?? I took emery cloth and polished up the outside of the trottle body and cleaned rubber boot.
    5). replaced timing chain/gear set
    6). replace oil pump
    7). replace crank shaft sensor
    8). replace temp sensor
    9). new thermostat new water pump new belt tensioner

    Started right up, clean and crisp, before when i would unhook battery thruck wouldnt idle just right until i ran it a little ways, this time it didnt do that. as soon as rpm come off and idle the flashing light, which was expected.
    Tomorrow at 8am new flowmaster cats and duals, then gm dealer for crank relearn at 3pm. wish me luck ???? Thanks for your help guys.

    Yes I bought a new crank bolt 5.70 at gm dealer.

    - - - Updated - - -

    ok new cat and flowmasters, went to dealer they did the crank relearn and amazinly didnt come back with anything on thier 32 point check. tech said all sensor feedbacks looked good. thought it was all good, pulled out, exhaust a little louder than i wanted but a good deep tone, just then blinky , blinky , blinky. ses light blinks from just off idle to 3k. i called the dealer back and its going back wend. put it in the garage for the last 6 hours tonight, going back thru grounds, added grounds to each head,firewall,battery. fuel pressure 48psi at idle, give a little gas and it runs up to 55. put a timing light on each plug wire and watched it fire form idel to 3k. checked computer connectors. also new mass air flow tonight also
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  19. TRPLXL2

    TRPLXL2 New Member

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    I learned from experience, and other peoples problems with grounding off of the heads. Not a good idea. All the engine swaps I have read with LS engines warn of using the heads for a grounding point, I relocated mine to a different location after I had some freaky issues with sensor inputs and outputs. I could take a test light while the motor was running, and hold it on the bolt on the back of the head and you could see it blinking or fading. My heads were brand new too, so you would think they would be a good ground??
    #19
  20. a.graham52

    a.graham52 New Member

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    not to sounds like a jerk but i feel from the beginning you should have gotten your hands on a scan tool that would show you cylinder missfires. that way you could see if it is a single cylinder that its seeing or if you have random, multiple cylinder missfire.


    just to make my idea more concrete... i had an 05 silverado yesterday that came in for as SES light. had a p0420 cat low inefficiency code turning the light on. ALSO had a p0300 that had set but had yet to command the light on. you wouldnt know it was missing but it had skips on cylinders 1,3,4,5,6,8. i found out the customer had been in a other place to have some work done and that place had installed some ngk plugs and most of them were loose and plug wires loose on the plugs themselves. hell cylinder 6 i never even took the wire off, just in screwed it from the block :0. but to be honest i would never had known it was skipping if i hadnt looked that deep with a scan tool.

    all im saying is if you check it with a scan tool and find out the ecm believes only one cylinder is skipping then that drastically reduces your possibliltys of what the problem could be. not only that but when you have problems like this its a lot cheaper to recheck things like ignition componants then it is to throw parts at it.

    3 years ago i refused to recheck spark plugs i had recently installed in my truck when it ran like crap. went as far as putting a brand new carburetor on it and did sure as hell didnt fix my problem. ended up damaging number one plug when i dropped it on the steering shaft when i installed it. a $500 repair when a free check and $6 plug would have fixed it.

    if you check missfires and find them all on one bank you could possibly be looking at plugged cats. seen it happen with my roomates truck. you could have a cylinder balance test done at a dealer or repair shop to verify the ejectors are all flowing properly. jsut some more ideas.
    #20

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