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Engine misses and surges under load!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigBurban350, Jan 9, 2003.

  1. BigBurban350

    BigBurban350 1/2 ton status

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    I did a search, but I did everything suggested. I have a 90' Burban 350 TBI.

    My engine started to miss and surge about 3 weeks ago. Okay, I just got to work when it started so I sprayed the wires down with some water, no effect.

    Well then I thought it was the hole in my gas tank collecting moisture, so I replaced the tank and threw in a brand new pump. It still misses and surges under load. I replaced the fuel filter about 10-15,000 miles ago, though they should last atleast 30,000.

    Okay then I hooked up a scanner and no codes appeared. I tested the TPS and the MAP sensor is reading fine. The O2 wasn't toggling so I replaced it thinking it was the problem. It still misses and surges under load.

    I was driving it for about 20 minutes one day and bam, it was back to normal power like it was before.

    The next day it started missing and surging under load again, so I cleaned it with some top engine cleaner, no effect.

    So today I tested the EGR with a vacuum tester and it operates smoothly. Okay then I replaced the plugs, still didn't fix the problem.

    I am stumped and confused because it ran perfect that one day like nothing was wrong and then began doing this crap again. Tommorow I am going to try see if the O2 I got is junk with the scanner.

    Another thing I noticed today when my truck was idling was a high pitch noise coming from the fuel pump, my tank is full of gas and its a brand new pump WTF! Is that the pump straining to pump the fuel through a clogged fuel filter?

    I can rev the engine to the redline with no problem, its just under load.

    /forums/images/graemlins/1zhelp.gif Please help me /forums/images/graemlins/1zhelp.gif

    /forums/images/graemlins/usaflag.gif /forums/images/graemlins/burb.gif /forums/images/graemlins/usaflag.gif
     
  2. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    An outside possibility, but easy to check. You may have a cracked valve. Sometimes it seats where the crack doesn't matter, and sometimes it doesn't. Load will usally bring the worst of it. At no load, you'd never know it. You can easily check by doing a compression test on all cylinders, if one's lower than the rest, you have a problem.
    I had this symtom before, replaced of bunch of parts, filters, ignition, pumps...etc...to no avail, did a compression test, 1 cyl. was lower, removed the head and saw that a small chunk of one exhaust valve was missing.
     
  3. Thunder

    Thunder 3/4 ton status

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    Sounds like a bad Distributor module. Or a bad magnetic pick up coil. A bad pick up coil will usually throw a code 42 but not always.. The module usually wont throw any codes
     
  4. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Going along with the ignition thing.... Does it have to be warmed up? Modules usually crapped out when warmed up.
     
  5. BiggerRigger

    BiggerRigger Registered Member

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    not to hijack here but I too am haveing the exact same problems that you are haveing and have done the same things that you have sofar to try and fix this problem....mine will run like a champ untill it warms up then it will do the same as your rig....I did replace the 02 sensor but it did not make a diff....please let me know what you find and I will do the same..
    Aaron
    1989 gmc jimmy
    5.7l tbi
     
  6. cheyenne_77

    cheyenne_77 Registered Member

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    Simple and most probably the dizzy cap, thats all.
     
  7. cheyenne_77

    cheyenne_77 Registered Member

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    Actually one thing to do is to set the truck to drive and get someone to stand on the brakes and raise the RPM, (TAKE CAUTION!!) You will notice the miss. Now it is alittle cramped in there, remove each lead and replace untill you find the one that is missing. If you do find it try chaecking the lead as well. You will find that the truck is not only missing under load but constantly and only noticed under load.
     

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