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Thread: 93 Sierra, 1/2 ton, 2w, 5.7, TBI power issues - Please Help!!!

  1. #1
    Full Member Burdett's Avatar
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    93 Sierra, 1/2 ton, 2w, 5.7, TBI power issues - Please Help!!!

    Hello fellow members,
    I have scoured this site to no avail, I must now ask for help.
    I have a 93, 5.7, TBI and I am having problems with low power, hesitation, and stalling issues.
    At first it was low or little power at higher rpmís, it was gradual and eventually couldn't even get up to highway speed, like the throttle had just one spot, and it wasn't a very good spot for gaining speed, upon reading others posts and troubleshooting what I could I have since did the following things
    1, Replaced air filter
    2. Replaced fuel filter
    3. Replaced coil
    4, Replaced TPS
    5. Re-checked spark plugs(4 month old A/C Delco) for gap, and tested wires for continuity back to underside of distributor cap. Cleaned rotor also.
    6. Replaced distributor cap. (chipped the old one trying to re-install after checking plug wires.
    7. Replaced engine coolant sensor on intake near thermostat hose connections.
    8. Wirebrushed all intake ground connections, and two other engine grounds straps I found.
    9. Pulled my fuel tank, cleaned and tested fuel pump, and even sewn back together the strainer basket, wiped and air dried tank to perfect condition and blew out fuel lines on the truck with an air hose. And put in 7 gallons of clean fuel.
    10. Pulled off EGR valve and cleaned, re-installed with new gasket. Itís a little hard to push in, but my truck idles fine.
    11. Pulled off fuel injectors and fuel pressure regulator, cleaned and re-installed with new gasket.
    12. Had ignition module tested at Autozone, tested fine, re-installed with dielectric silicone lubricant as per manual. (Had a code 42 at one time, I checked wiring and after re-installing module, code no longer showed up)
    13. Checked IAC, tested within parameters according to my Chiltons manual (also have a Haynes, and a fast laptop, I cross reference everything).
    I have checked timing, it is dead on and the motor sounds very good at idle.
    Truck ran fine for about 5 miles, but again I have lost power, like not getting enough spark, bogs down when I apply throttle, had to pull over last night because it nearly died, so I turned the key off, and re-started and the truck had some power again. It would last for a mile or two and lose power, so I would turn the key off and then on again to reset, to re-gain power.
    I am also under thinking maybe and electrical short in the dash somewhere near the ecm which is behind the glovebox, because my radio (after market and installed in the center of the console) would sometimes loose power. I have an alarm system that is installed but the remotes were lost long before I became the owner, the light flashes when I slam the door, but never had a problem with it. Not sure if that is helpful, just trying to give what I believe to be all pertinent info.
    I am getting no codes, and my head hurts, just point me in a direction and Iíll handle all the hard labor.
    Thanks

  2. #2
    Senior Moderator chevychase's Avatar
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    Sounds maybe catalyst converter stopping up .

  3. #3
    Senior Member scavanger's Avatar
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    I agree with chevychase, check the exhaust for restrictions. Catalytic converters will get more restricted when they warm up if they are going bad.
    One way to check is hook up a vacuum gauge to manifold vacuum. Run the engine to around 2000 rpm and hold the throttle steady, don't move it.
    If vacuum and engine speed begins to drop you most likely have a restriction in the exhaust.

    Scav

  4. #4
    Full Member Burdett's Avatar
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    Thank you gentlemen for the timely responses!

    I do have exhaust pressure out of my tailpipes, if the catalytic converter were restricted would I be able to tell a difference?

    Never the less, I did ask for advice and I will check that out.

    Is there a special fitting on the intake manifold that I hook my vacuum guage to?

    It just seemed weird that even warmed up, I was able to turn off the motor and immediately restart while I'm coasting, and the problem subsides a bit, but only momentarily, like a minute or two, or the time I would suspect the brain catches up to whats happening and shuts me bogs me down again.

  5. #5
    Senior Member gmctrucks's Avatar
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    I agree with them two smart cats above sounds like your Cat is clogged buy a Manaflow high flow cat. I found one on craigslist and ebay also has them cheap at times.
    http://i961.photobucket.com/albums/ae98/falken86/dadnew-1.jpg

  6. #6
    Full Member Burdett's Avatar
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    O.k. So I hooked up my vacuum guage and I don't believe the catalytic converter is my problem. I followed the instructions of my vacuum pump manual, and I did get a weird reading.


    1.
    Normal engine (Figure 6)

    An engine at idle at sea level
    should show a steady needle, and a
    vacuum of 15 ~ 22 in. (38 ~ 56 cm)
    Hg depending on manufacturer's
    specifications. Quickly opening and
    closing the throttle should cause
    the vacuum to momentarily drop to
    below 5 in. (12 cm) Hg, followed by
    a momentary rebound to approximately
    25 in. (64 cm) Hg, before
    returning to normal 15 ~ 22 in.
    (38 ~ 56 cm) Hg

    Mine held steady at 18 in Hg, but when I gave it gas and let go, instead of dropping down and rebounding up, it increased to 21 and then dropped back to 18 in, where it again held steady. I can't find anything in my manual that explains that. Anyone have any ideas???

  7. #7
    Full Member Burdett's Avatar
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    Update!!!! 04-15-03

    O.K., I bought the gasket kit from kragens for my tbi, It was indeed filthy, and the kit came with the pressure regulator diaghram (bonus). But, unfortunately that wasn't my problem either. It was nice to know that although not curing the problem, I shouldn't have problems with it in the near future (It's spotless).
    So, after noticing some bare wire just outside of the pick-up coil, I tried to unhook the connection and broke the tab. So, I made myself another project, pulling and dismantling the distributor so I can replace the pick-up coil (again, it was filthy, but now it is spotless).
    After a few trial and error attempts to re-time the engine (my markings using permanent marker were not so permanent), I was able to time it spot on. The TBI was sucking alot of air at first but seemed to settled down after a moment, I assume the computer was re-teaching itself. I at first got a code 42, but assumed it was because I started the motor with the IC undone, I cleared the code, and it hasn't shown up again.
    Truck ran great, nice power on the low end, but again at highway speed it seems to lose it balls and start slowing down, Turning the key off and on again made it re-gain power for a few minutes but it would inevitably lose power again.
    Not sure what to do from here, No one is giving me their two cents of advice. I guess I will keep on doing research and keep and open mind!

  8. #8
    Full Member Burdett's Avatar
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    Update!!!! 04-15-11

    O.K., I bought the gasket kit from kragens for my tbi, It was indeed filthy, and the kit came with the pressure regulator diaghram (bonus). But, unfortunately that wasn't my problem either. It was nice to know that although not curing the problem, I shouldn't have problems with it in the near future (It's spotless).
    So, after noticing some bare wire just outside of the pick-up coil, I tried to unhook the connection and broke the tab. So, I made myself another project, pulling and dismantling the distributor so I can replace the pick-up coil (again, it was filthy, but now it is spotless).
    After a few trial and error attempts to re-time the engine (my markings using permanent marker were not so permanent), I was able to time it spot on. The TBI was sucking alot of air at first but seemed to settled down after a moment, I assume the computer was re-teaching itself. I at first got a code 42, but assumed it was because I started the motor with the IC undone, I cleared the code, and it hasn't shown up again.
    Truck ran great, nice power on the low end, but again at highway speed it seems to lose it balls and start slowing down, Turning the key off and on again made it re-gain power for a few minutes but it would inevitably lose power again.
    Not sure what to do from here, No one is giving me their two cents of advice. I guess I will keep on doing research and keep and open mind!

  9. #9
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    Have you ran a fuel pressure test at the lines going to the TBI ? Sounds like you have a fuel pressure problem....

  10. #10
    Full Member pzVS8Oli's Avatar
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    I have had that problem with my 95 Yukon and the problem was a sticky EGR but in your case I would check the EGR solenoid.

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