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88 Suburban with 454 TBI problems - help me troubleshoot - Grim?

Discussion in 'The Garage' started by Mudzer, Jan 15, 2004.

  1. Mudzer

    Mudzer 1/2 ton status Author

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    About a month ago my Burban started running real crappy. At first, I thought I got a tank full of water. The truck would start, immediately go to Fast Idle then it would backfire through the throttle body as well as out the exhaust. I can work the throttle to keep it running, but it pops through the exhaust and through the TB and I am constantly pumping the throttle to maintain some state of the engine running. Well, every once in a while it clears up and goes back to very Fast idle. I finally ran the tank down real low and drove it sputtering all the way to the gas station. I filled it with Premium and about 3 cans of Heet. It still sputtered on the way home, barely pulling itself at times. I sat in the driveway doing my normal pumping of the throttle while it backfired as before and finally it went to "Very Fast Idle" again (probably somewhere around 3000 RPM) and it stayed this way for about a week. Every time I drive it, even when it warms up, it stays at the 3000 RPM idle. Well here I am just below a half tank of gas again and was driving down the interstate and the darned thing went into its popping fit again. I thought I had it cured of that since it drove for a week at fast idle but no popping.

    I've checked the codes with engine shut off but key in run position. All it does is flash a 12 code over and over. No other codes in this mode.

    When I start the truck, with the code reader installed, the Check Engine light blinks at a slow rate and does not flash any codes, it just blinks steady. Sometimes when I rev it up in this mode, it blinks faster.

    So, anyone had this problem? Grim, how was your Burban running when you had that problem, and what was the problem/fix?

    Thanks for the info. I know this is vague, but its the best description I can give.
     
  2. JK5

    JK5 1/2 ton status GMOTM Winner

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    I had a simular problem...on my 91 2500 454TBI

    On start-up...it ran fine...until it warmed up...
    Then it would start popping when giving it gas..
    When I took the air cleaner off...
    I noticed it was dumping gas..

    My problem was...the temp sensor...wasn't working...
    and later I had to replace the computer...

    From what I heard...
    these trucks have alot of computer problems..
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    these trucks have alot of computer problems..

    [/ QUOTE ]

    I don't think thats the case at all. The newest of these trucks are now 13 years old, and most are still running with the original ECM, which is the same basic design as every other one used in every GM vehicle from 1981 until after 1991.

    People like to replace them because they don't understand them, not because they are truly problematic. Whats the saying for carbs? 90% of carb problems, aren't?
     
  4. Mudzer

    Mudzer 1/2 ton status Author

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    [ QUOTE ]
    I had a simular problem...on my 91 2500 454TBI

    On start-up...it ran fine...until it warmed up...
    Then it would start popping when giving it gas..
    When I took the air cleaner off...
    I noticed it was dumping gas..

    My problem was...the temp sensor...wasn't working...
    and later I had to replace the computer...

    From what I heard...
    these trucks have alot of computer problems..

    [/ QUOTE ]

    I wonder what is causing the popping? Is the ECM changing something in the firing order? I mean, go back to theroy of how an internal combustion engine works. Typically if its popping through the intake, then an intake valve has to be open, bent or have a hole in it while the cylinders are firing - in order for it to actually blow flames up through the TBI. Is this right? So, what could the ECM be doing? Firing the cylinders in the wrong order? I didn't think the ECM controlled firing order - the distributor's magnetic pickup does this right? Just rambling now, but its a definate shot to try for sure. Will a bad ECM not show codes?
     
  5. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I am buying an 87' blazer with a TBI 350 and it would fire up for about 20 seconds, sputter and die completely. We found out that the fuel pump is worn out and not pumping enough pressure to the throttle body.
     
  6. HarryH3

    HarryH3 1 ton status Author

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    The order in which you have the plug wires attached to the distributor cap determines the firing order. /forums/images/graemlins/wink.gif
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Neil, sounds like the poster truck for a vacuum leak. Check the gasket under the throttle body.
     
  8. TopOff

    TopOff 1/2 ton status

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    I second a vacuum leak. Could be a bad/leaky EGR. Could also be a vacuum leak to your MAP.

    Good luck.
     
  9. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    I second a vacuum leak. Could be a bad/leaky EGR. Could also be a vacuum leak to your MAP.

    Good luck.

    [/ QUOTE ]

    I'll 2nd that both of those have the potential to make a vehicle run really horrible. Especially the MAP.
     
  10. BurbinOR

    BurbinOR 3/4 ton status

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    I say this every time, so sorry if I sound like a broken record. Get a scanner or winaldl. The only way to see what is going on is to read what the sensors are doing. Codes are not always set, in fact for drivability issues they rarely are from my experience.

    It well could be the temp sensor...........my TPI motor has similar symptoms, scanned it, found the intake air temp sensor was reading 100* on a 40* morning. New sensor, problem fixed. TBI doesn't have an intake air temp sensor but coolant temp sensors can give you this problem too. We're all guessing but a scanner will give you much more info to diagnose this properly. /forums/images/graemlins/tongue.gif
     
  11. JK5

    JK5 1/2 ton status GMOTM Winner

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    [ QUOTE ]
    I wonder what is causing the popping? Is the ECM changing something in the firing order?

    [/ QUOTE ]

    Well...the computer looks for a signal from the temp sensor...
    every time the distributor rotates...
    starting with cylinder 1..
    since it didn't receive a signal..
    Cylinder 1 wouldn't get a spark!!!

    After replacing my temp sensor..
    It ran...but from time to time...
    I'd run into the same problems...
    having to disconnect the battery resetting the computer..

    After messing around I decided to replace the computer...
    It did have over 200,000...

    Since I did that...it's been running without any issues.. /forums/images/graemlins/thinking.gif
     
  12. Mudzer

    Mudzer 1/2 ton status Author

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    Just ordered a WinALDL PC Interface Cable and have downloaded the software. I might have to take it to a shop to diagnose tomorrow because Im leaving town and will not have the cable in time for my trip.

    Temp sensor is cheap as is EGR valve. Time to start looking!
     
  13. Mudzer

    Mudzer 1/2 ton status Author

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    Forgot to ask. Is there a way to test an EGR Valve as well as the Temp Sensor? Anyone have the numbers for testing the temp sensor handy?
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    One of the better tests of the EGR valve I believe is to disconnect vacuum to it, and plug teh vacuum line, then test drive.

    You can also apply vacuum to it, and make sure it holds the vacuum once you plug it. When truck is off, reach your finger underneath the EGR valve, and press up on the diaphram. Should be smooth in movement, and return to same position each time. Sometimes they will be "sticky" which can cause them to stay partially open when it shouldn't.

    Temp sensor needs to match engine temp. The gauge isn't real accurate, but I believe the ECM only cares if the engine temp is over something like 160* or not. I'm not sure that the ECM constantly references the temp sensor or not.

    It's basically common sense, but if the temp sensor scan shows around 195* when completely warmed (if you have stock thermostat) then it should be fine. It should read close to ambient air temp IF the engine is completely cold, such as sitting overnight.
     
  15. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Almost every problem I had including generally poor performance, loaping idle, serging and high idle were all Vacume leaks. The plastic lines to the EGR had cracks, The base plate gaskets where the TBI adapter meets intake was bad. I also found the EGR control doohicky hanging over the front of the passengerside valvecover was hangin. Couple drops of tool oil got it working. I fixed that and the leaks and most of my problems are gone. I do have a cold run issue that I am about conviced is a bad temp sender. It's running way rich about mid way through warm up..

    Sorry just ran accrss the post. They got a new firewall at work and it catches this softwear. Doesn't cat PBB and 67-72 through LOL.

    Check foir the leaks and I'll get with you tomorrow evening AFTER Dakar at 6:30 eastern LOLI gramb my factory shop manual.
     
  16. Mudzer

    Mudzer 1/2 ton status Author

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    Thanks for the help Grim and everyone else. I might have it on a diagnostic scanner today.
     
  17. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Get it on the scanner yet?
     
  18. Mudzer

    Mudzer 1/2 ton status Author

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    I didn't have the time today and the guy will not be around tomorrow (saturday). So, it looks like I'll troubleshoot it tomorrow on my own. Again, thanks for the info.
     
  19. crazykev4x4

    crazykev4x4 1/2 ton status

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    I had a similar problem on my 88K5. I had a bad distributer shaft the ring that runs by the pickup cracks and then it changes the timing . it will spin on the shaft . GM dealers carry the shaft and it is easy to change and check . You would be surprised how many of these actually are bad and how much they can screw up how a vehcle runs

    Kevin /forums/images/graemlins/k5.gif /forums/images/graemlins/truck.gif
     

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