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  1. #11

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    Quote Originally Posted by Blazer454 View Post
    So when you say "low power" what does it feel like? Missfire, engine tries to die, or engine seems to be struggling to move along? You say it is more noticable in higher gears, is this an auto tranny?
    Imagine what it might feel like if the power wire to the ignition coil were dirty and not making a good connection. Imagine the voltage dropping off under load. I cant exactly say that it feels like a misfire. It feels like a weak spark condition in that it fires, but not with all of the "oomph" that it should. I have advanced the base timing to about 4*, which has helped a bit but has cut some of my take off power.

    It is a 5 speed manual gearbox.
    "It went together didn't it? Well then there has to be a way to take it apart!" - Me.

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  2. #12

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    So the motor struggles a lot almost as if you were towing a HUGE load? I see you have changed almost everything related to fuel and spark. Have you watched the fuel injectors in the tbi unit spray fuel while it is running? I would make sure that they arent gummed up. If you have access to an exhaust backpressure gauge you can take out the upstream O2 and check your back pressure before the cat to see if it is too high. Or just cut out the cat. Since its a 95 with tbi this exhaust only has the upstream O2's that are before the cat right? If so then you dont actually need a cat

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  3. #13

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    I took the downpipes and cat off today to see if that was a problem. Turns out that the cat has already been hollowed out by a previous owner. I can see from the rear of the pipe all the way to the o2 sensor.

    All was not lost, though; I needed to replace the donut seals at the manifold anyway. The injectors seem to be spraying fine, although I know that you really can't tell by looking at them. I am going to disconnect them one at a time to see if the truck acts differently using one of them or the other.

    Yes, it feels like there is a big load I am trying to pull along. A friend of mine says "Dude... It's not a 350. I understand that it is not a 350, and I realistically don't expect V8 power... So this isn't a case of unrealistic expectations...

    Computer maybe?!

    Also, the inside of the exhaust pipe is heavily blackened and sooty. The truck runs rich (or has incomplete combustion maybe). I know this already because I can smell it. I just confirmed it today. Maybe another clue.
    Last edited by moogvo; 08-27-2012 at 11:13 AM.

  4. #14

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    Yeah buddy, no problem man! Hope you can get something figured out. It's a bummer having vehicle trouble... Diagnosis can often prove to be difficult. Best of luck man.

  5. #15

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    Have you considered that it might be something later on in your drivetrain? Perhaps you're having transmission issues or something that's putting excess load on the engine.
    Christopher

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
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  6. #16

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    Quote Originally Posted by Crawdaddy View Post
    Have you considered that it might be something later on in your drivetrain? Perhaps you're having transmission issues or something that's putting excess load on the engine.
    No... I will have to sit on this one and scratch my head... I have considered that it misses Craigslist and wants to be on there again...

  7. #17
    Sr. Engineer
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    Oct 2010
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    487

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    Is the air intake unobstructed and a fresh filter in place? If it was carbureted I'd say look for a stuck choke.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  8. #18

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    Quote Originally Posted by dpeter View Post
    Is the air intake unobstructed and a fresh filter in place? If it was carbureted I'd say look for a stuck choke.
    Clean filter and no obstructions.

    Thanks for chiming in.

  9. #19

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    If the cats were hollowed out did the previous owner re tune ? Exhaust changes such as a hollowed out cat can change your a/f mapping. Could be running to rich in certain areas of the power band.
    2001 Burban 4x 5.3L

  10. #20

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    Quote Originally Posted by My4xburbanrocks View Post
    If the cats were hollowed out did the previous owner re tune ? Exhaust changes such as a hollowed out cat can change your a/f mapping. Could be running to rich in certain areas of the power band.
    Well... it would have been doing that when I bought it if that was the case. This popped up a few months later. I have now replaced the distributor with a brand new unit. It didn't fix anything really, but when I move the timing around a bit, it seems to have an effect on the problem. If I turn it up to where it spark knocks and then turn it back until it quits, the mid range power and the hesitation feel goes away but I then lose take off power and have to ride the clutch to get going.

    I have found a happy middle point with the base timing that seems to give me good take off power and minimizes the low power issue in the mid range, although I can still feel it bucking a bit. First and second gear, it runs like a raped ape. 3rd and 4th it does accelerate fine, but that's when the bucking begins. I can hold my speed up and even accelerate in some cases on small inclines without shifting out of 5th gear.

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