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Thread: backfire through tbi, no hair left, need help

  1. #1
    Full Member brutis's Avatar
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    backfire through tbi, no hair left, need help

    hello everyone, good to be back
    88 c3500 454
    I did a rebuild in 2009, Name:  454 343.jpg
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    pic is to just show what I'm working with, this is a everyday driver, well until about 2 weeks ago, driving my spare truck,
    anyway a month ago I got a small pop through tbi under load acceleration, then it go progressively worst, until one day driving to work about 60 miles,
    it starts popping though tbi and backfireing through exhaust , really bad ,
    so having recently doing a tune up plugs rotor cap. I figure it jumped time, it only had 75,000 since rebuild, i'm old school and they used to stock chains last about 75.000 however searching this forum ( till my eyes hurt ) have found now they can last 250 or more

    here's what I've done so far. ( it doesn't back fire through exhaust anymore but through tbi, only under load normal acceleration, and only when completely worm it takes about 10 miles runs fine

    check timing chain , I mean pulled cover , double roller , right on
    checked cam pulled valve covers and watched rockers move , all move fine
    replaced tbi gasket , was bad ,
    set timing
    replaced whole distributor ( under warrantee ) auto zone
    cap rotor dis. came with module and pickup
    found two bad wires, burnt by my headers, happens all the time, ( probably why it's not backfiring through exhaust anymore

    vacuum runs at about 19 to 20 lbs , small jumping a lb maybe ?
    sprayed around new tbi gasket with wd 40 and tbi riser , no change in idle ,
    I can't duplicate the tbi backfire at idle only under load
    it gives a big pop then runs fine when up to speed I can cruse at 60 70 just fine it's pulling out at red lights it backfires
    yes pulled codes,
    had 32 , 42, 44, all o2 and egr related witch is normal since I've all way had the egr unhooked ,
    oh cleared them , and just got 13 , I may have pulled around on wire for o2 ,

    I never set timing with light , before , just went out and bought a new light , allway did it by ear
    I didn't do cam could there be a rv cam or something on here .
    do different cams have different than stock timing ? 4 % tdc

    fuel steam is cone shaped ( seams a little heavy )
    since the 4 years I've been driving this , I have replaced everything except ecm

    temp sender
    tps
    map - twice
    coil , just now and before
    wires several times
    temp censer
    fuel filter , before and just now
    fuel pump
    from reading on here , I havn't done the voltage test on on temps censer , however the original was bad once and not even hooked up and it didn't back fire

    could it be the ecm ? 100.00 I didn't want to through that at it , with no results.


    any input ? would help thanks

  2. #2
    Senior Moderator chevychase's Avatar
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    First thing check the sensors for 5 volts reference from ecm if they have ecm is good...most times ecm will give a code for failed diagnostics,,if bad.
    Seems it is fuel related though. You timed with timing wire disconnected? Need to also check the 02 sensor if not working will have your issues ..i have to get to work ..will give more info if you need..should be able to search on the voltages here .

    CODE 13
    Trouble Code 13 indicates that the exhaust stream oxygen-content sensor (O2 sensor) is not responding as expected. When cold, the sensor is 'biased' by the ECM to about 450 millivolts. Before it warms to at least 600 deg F (315 deg C) it acts as an open circuit and when the ECM reads it, it reads the 450 mV bias. The ECM expects the sensor to warm in a short period of time and begin sending its own voltages. The general conditions for this code getting set are:
    ? engine running at least 2 minutes
    ? coolant temperature at least 50 deg C (122 deg F)
    ? O2 voltage not fluctuating (i.e steady between 350 and 550 mV)
    ? TPS signal above idle
    ? all above conditions met for 60 seconds

    Typical causes may include:
    1. Defective or degraded O2 sensor
    2. Deposit-contaminated O2 sensor (running leaded fuel, RTV silicone deposits etc)
    3. Corroded/defective O2 sensor connection
    4. Defective sensor ground circuit

    Gitter done have fun. Running on empty...running blind...running behind.....

  3. #3
    Senior Moderator chevychase's Avatar
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    Oh check the grounds at the thermostat housing.

    Gitter done have fun. Running on empty...running blind...running behind.....

  4. #4
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    It sounds to me like a timing issue. Maybe a tad to low. You can experiment with it by adjusting it and see if you can get the backfire out of it. Also make sure the ign wires have a good connection at the coil. A timing light is good to use but not a real necessity. I've set timing on many vehicles by ear and performance. I understand it is a must on some of the later models but the tbi's are fairly simple.
    MrMarty51 likes this.

  5. #5
    Senior Member Sodell's Avatar
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    Are you remembering to unhook the wire to the dizzy before setting timing?

  6. #6
    Senior Member batty1214's Avatar
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    My 95 did something similar, ended up being a worn out distributor.

  7. #7
    Full Member brutis's Avatar
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    thank you for all the replies, I got home from work, today and went right at it, seams to run fine now, I'll know tomorrow when pulling my work trailer.
    this is what I did, I tapped on the o2 with a small hammer small taps
    set timing at 14 before tdc ( tried it by sound but after advancing a certain point it sounded all the same
    i think i set it at 14 before just didn't remember it was 4 yrs. ago, on the pointer it's about 1 inch from 4% where it should be
    no back fire through tbi, lots of power ,
    it's a new balancer and rebuilt crank and the same cover i think was stock ,
    the only thing i didn't change on the rebuild was the cam

    any reason the pointer would be off that much ? or would a custom cam make it do that ?

  8. #8
    Forum Moderator Boudin's Avatar
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    Like GP said....need to disconnect the tan wire to set timing. On TBI....I'm pretty sure that 2-4 degrees advanced is supposed to be the "prime" spot. If you didn't disconnect the tan wire and set the timing....go back and do it correctly. The ECM needs to be taken out of the equation to get an accurate ignition timing set.
    MrMarty51 and wirelessrat like this.

  9. #9
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    When rebuilding an engine it's always good to know where the crank is in relation to the cam. This it done by degreeing the camshaft. Here is an explanation of how it's done.
    How to Degree A Cam - Lunati Power
    MrMarty51 likes this.

  10. #10
    Senior Member MrMarty51's Avatar
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    Here is how I tell if the Harmonic Balancers mark is spot on or if the balancer has slipped.
    Bring no.1 to TDC then back up the crank just a little but, say an inch or two, set up a dial indicator, with a LONG stem so it touches the no.1 piston, now, rotate the cranking shft forwards just to the point where the indicators needle stops moving, make a mark on the balancer, rotate the indicators dial to 0, rotate the crank shaft forwards bringing it back to zero again, make another mark on the balancer, half way between the marks is the exact TDC for number one. Be carefull to NOT over extend the indicators allowable range of motion or it could damage the dial indicators components, possibly busting off the extension and having that piece to try and pick out of the cylinder.
    Set timing off of new mark.
    This procedure can also be performed using a spark plug with the porcelean knocked off, the electrode removed and a length of shaft or a bolt welded on in place of the electrode to make a piston stop, just be carefull that the crankshaft is`nt forced any more than the stop will allow.
    Rotate the crankshaft one direction, make the mark on the balancer then rotate it the other direction and make another mark, then, 1/2 way between is TDC.

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