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Really frusterating problem...

Discussion in 'The Garage' started by Paxx, Jun 27, 2005.

  1. Paxx

    Paxx 1/2 ton status

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    Ok here's the deal, my truck keeps backfiring through the carb. Everytime it does it the whole truck lurches and then lugs until you let off the gas and gently reapply it. It especially likes to do it when accelerating or under load ie, hills etc.

    I have already torn into it found a bad lifter and some really rough gaskets, replaced them all, and then figured since I had checked the timing and it was good, it must have been the carb itself. Replaced the carb and nothing, still backfiring. :angry1:

    So this all happened back in penticton and I had to come back to Calgary with the truck backfiring or not. So an 8 hour drive later I'm in Calgary and my oil pressure drops. I checked my oil and it was low, topped it up got it home. Woke up looked under the truck and all the oil was sitting underneath it.

    I figure on maybe a rough backfire it might have blown out a seal somewhere or something I just haven't had time to check yet.

    Does anyone know what could be causing this backfiring? I'm running out of money and patience on this.

    Please help! :crazy:

    Thnx
    ~Max
     
  2. Mad-Dog

    Mad-Dog 1/2 ton status

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    sounds like it jumped time dude...... :thinking:
    Chances are the timing chain is stretched out and slipped a tooth on the gears.
    Backfiring is not the likely cause of your oil leak......ya never know,
    sounds like she needs a little long overdue maintenance.
     
  3. Brocky

    Brocky 1/2 ton status

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    My K5 was back firing thru the carb and it turned out to be a lifter stuck, valve guide gone, and the lobe on the cam under the stuck lifter wore real bad. I messed around with timing and different distbruters and different carbs for about a week until I came up with the deceased parts. Good luck, dont mean to scare you, just a little heads up.
     
  4. pornorob

    pornorob 1/2 ton status

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    you might also want to check for arcing. I had the same problem. I found out ,when installing a remote solenoid, that the wires running to the starter (I have a push button that I use to start the truck) from the button were burnt to a crisp and grounding to the headers. When I re-wired it the hesitation and backfiring stopped. Just an idea. ;)
     
  5. bigcountryk5

    bigcountryk5 1/2 ton status

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    i wish i could help ya out but my mechanical knowledge is well limited i'm still trying to learn i will say this though just on the off chance you haven't thought of it with you leaking oil already and backfiring through the carb i just wanted tomake sure you've got at least one good charged fire exstinguisher within arms reach it would suck to half to watch your rig go up in flames just ask phoenixzorn.... :(
     
  6. Brocky

    Brocky 1/2 ton status

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    errrrr. Wires burning onto manifolds. My main power to the starter decided to burn off in a little stream one wonderful day. I was the only one there so I had to lye down in the little stream to fix it. So make sure all wiring is away from them manifolds or headers. It definetly with hesitate and eventually die if this happens.
     
  7. JEBSR

    JEBSR 1/2 ton status

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    Backfiring

    I See The Major Items Covered, But Have You Checked The Small As Well. For Instance If The Timming Chain Jumped Your Timming Marks Would Be Off As The Cam Runs The Distributer, But If You Have A Cracked Distributer Cap It Will Give You The Same Symptom. Fire It Up At Night Or In A Dark Garage, Take A Spray Bottle With Soap And Water (do Not Use Just Water) And Spray The Wires And Cap. If You Get An Electricly Light Show Then That's Your Problem. Just Don't Wan't You To Make The Common Mistake We Have All Made By Replacing A Lot Of Expensive Parts While Overlooking The Cheap Obvious Ones.
     
  8. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    I would think a backfire through the carb would in fact have something to do with timing and its related compononts
     
  9. LongIslander26

    LongIslander26 1/2 ton status

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    Backfiring

    While I agree that you should check all the simple and obvious stuff first, and without knowing what year this truck is, or how many miles are on the motor, Chevy's are notorious for wiping out cam lobes. A stuck lifter could be your problem. Some Marvel Mystery Oil added to the motor oil and letting it idle for a bit will sometimes free up a stuck lifter, if that is in fact your problem.
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    valve troubles??

    Seeing you found a "bad" lifter,its possible you may have other valve troubles brewing...like a burnt valve,bent valve,weak or broken valve springs(an often overlooked item that causes backfiring and other woes,like hesitation)..a rocker arm might be sticking on the stud(they often cut grooves in the stud,and it can get caught in the grooves and cause a misfire)..other causes are ignition,as already suggested check all plug wires for burnt spots or arcing to ground..any short curcuits in the pink wire to the HEI will cause a backfire,as will low voltage to the HEI ,often caused by someone adding HEI to an older truck and using the OEM coil wire off the old points style coil(its a resistance wire--you need 12V to HEI!)..

    It might be a cam lobe as suggested earlier too...usually on chevy small blocks an exhaust lobe goes flat first...the exhaust cant get out of the cylinder because the valve lost most of its lift and cant open far enough--so the next time the intake valve opens,all that exhaust pressure goes out thru the intake and carb,and it backfires.....if your lifter was "bad" because the bottom of it was worn all concave,its likely that cam lobe is flat as well.(watch the rockers with the engine idling while the valve covers are off--you'll see any valves that are not opening as far as the others pretty easily).When a 454 I had lost a lobe,it would backfire bad enough to set the air filter on fire! :blush: ...A backfire CAN blow out seals and gaskets,especially the "end seals" on the intake manifold..

    ..I've seen an engine that was running poorly for quite some time due to a failing electronic ignition box blow the valve covers and oilpan apart when the mechanic substituted a good used "brain" onto it!!-( it was an old Lincoln Town car)-the motor had died at an intersection,and the owner kept cranking and cranking,and loaded the motor with raw fuel...when it got towed in a few minites later,the mechanic put a used "brain" box in,figuring thats why it lost spark--as soon as he cranked it over ,it made the loudest BOOOM I've heard since the 4th of july--and the valve covers,and the oilpan were ripped wide open,and about 6 qts of oil flew everywhere!....scared the S*** out of us !... :yikes: You WOULD be smart to carry an extinguisher with you!--backfiring is the #1 cause of engine fires,next to a gas leak.. :crazy:
     
  11. Paxx

    Paxx 1/2 ton status

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    Thanks for the pointers guys. I will try the soap and water trick first to make sure its not the distributer but I am thinking that it is probably the valve. I had a mechanic buddy look at it and he held a paper towel over the exhaust and said he could see it sucking in every once and a while which he said indicated the valve.

    The engine was rebuilt 2 years ago when I bought the truck and I haven't put too many miles on it since then. Also when it was rebuilt the PO said he installed a dual roller timming chain (I think thats what its called, been so long since I've talked trucks lol) so would that eliminate the jumping chain theory? seeing as how there is two chains instead of one. (I hope I am understanding this correctly)

    Another strange thing is that I filled up the oil again because I had to drive the truck to our new house we moved to and now it is holding the oil??? I'm not sure how but it hasn't leaked a bit since and that was a few days ago. :dunno:

    So I'm guessing this means its time to pull the heads off. Is there any other special tools I will need besides the one for the springs? Also is there anything else I should take a look at while I'm in that deep?

    Thanks a lot for all the help, it might be a few days before I can reply back due to me being swamped at work in the night club. It's Calgary Stampede right now so we are talking 16 hour shifts.

    Should have lots of cash for the truck by the end of this 10 days though :D

    Thanks again
    ~Max
     
  12. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    While you have the heads off, do yourself a favour and replace the seals :)

    If you find that your cam is toast, I've got a good stock cam (I think, it may be an RV style cam as the engine was hopped up a little bit when it was rebuilt) you can have for 20 plus shipping. Has about 25 000 km on it, and worked extremely well when I pulled it out of my 355 to put a bigger comp cam in. Comes with the labelled lifters as well, they look brand new :) The engine the cam / lifters came from still had crosshatching on the cylinder walls :)
     
  13. mudhound72

    mudhound72 1/2 ton status

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    Have you checked your fuel pressure yet.

    A few years ago I had a prob simmler to yours ended up rebulding the motor, still ran like crap, replaced the carb, still ran crapy, all new ing everthing still the same, after a month of hit and miss and replacing everthing on the motor, it turned out to be a partly cloged fuel line :mad: :mad: :mad: pulled both ends off threw the air hose on it, blew globs of mud out ( I wonder were that came from :doah: ) and ran like a dream.

    It is amazing how a 5 min repair caused so many issues

    The lesson is dubble check all the small stuff befor going into the big things, like are yiou 100% sure the carb you installed is good

    Never assume anything

    Todd
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    Compression test will tell you if you've got a bad valve.
     
  15. Paxx

    Paxx 1/2 ton status

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    Ok this is getting to me now. I did the head job and there was definitly some work that needed to be done in there but its all put back together now and still backfiring. I'm thinking now that the fuel pressure might be the problem as last year someone put dirt in my gas tank. It ran fine for a while after fixing that problem but maybe some of it made it past the tank and is in the lines now.

    How do I test the fuel pressure?
     
  16. mudhound72

    mudhound72 1/2 ton status

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    Not to big of a deal , you just need a fuel pressure gauge and a adapter to hook in line were the line goes into the carb, do not dead head the line, do it so you can run it in different RPM to watch the pressure for a bad drop.

    Look in a manual for a PSI that you should be at , not 100% on this but I think around 6.5-7 PSI is what you need
     
  17. Paxx

    Paxx 1/2 ton status

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    hey thanks I'll go pick one up tomorrow morning.
     

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