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help diagnosing driveability prob. in 87 350 TBI...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fortcollinsram, Apr 10, 2003.

  1. fortcollinsram

    fortcollinsram 1/2 ton status

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    I must admit that I have pushed some standard maintainance issues aside on my 350 TBI because I will be swapping in a 454 TBI in the VERY near future...

    First thing to note is that I have a hard cold-start condition that is annoying to say the least...it usually has to crank for about 6-7 seconds in the morning to come to life...and sometimes it has all kinds of power and other times it seems like it is only running with the power of a 6 cylinder

    The main problem I have been having occurs when the motor is nice and warm and I have been crusing around for a bit...When I shut it off for any amount of time (less than about 1.5 hours) it will start back up fine but as soon as I put the motor under load, it will stumble VERY BADLY...it doesn't want to dire really, it just wants to keep idleing...even if I floor it can barely get through an intersecting....this conditon will clear up after I run the piss out of it for a few min...then it runs fine..

    I rebuilt the throttle body a couple months ago...My guess is that the fuel pump is starting to show its age...

    Any ideas?


    thanks

    Chris
     
  2. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Fuel filter maybe.
     
  3. fortcollinsram

    fortcollinsram 1/2 ton status

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    I just replace the fuel filter last summer but I will throw a new one in anyhow...any other ideas...

    I would check the fuel pump if it wasn't such an ordeal hooking up a pressure gauge...

    Chris
     
  4. BurbinOR

    BurbinOR 3/4 ton status

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    Get a scanner and check the 'intake air temp' - www.autoxray.com is what I have and cost me about $150. Worth every penny, it is the first thing anyone with FI should buy.
     
  5. YtseJam

    YtseJam 1/2 ton status

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    Start with the basics. Check all of your ignition components. Cap & rotor, Plugs & wires.
     
  6. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    I just replace the fuel filter last summer but I will throw a new one in anyhow...any other ideas...

    [/ QUOTE ]
    I've had them go bad after a few months. It's just like how I like my women, cheap and easy so that would be the place to start. /forums/images/graemlins/thumb.gif
     
  7. fortcollinsram

    fortcollinsram 1/2 ton status

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    okay today she got a new cap, rotor, plugs, wires are only 9 months old, new fuel filter....

    It still does it...I am thinking fuel pump...I will rig up a way to check the FP pressure and see how it is holding up...

    Chris
     
  8. MTBLAZER89

    MTBLAZER89 3/4 ton status GMOTM Winner

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    vacuum leak
     
  9. 90K5

    90K5 1/2 ton status

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    i'll sencond that vacuum leak...check the intake gaskets EGR and TB gaskets
     
  10. RustBuket

    RustBuket 1/2 ton status

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    If it was a vacuum leak wouldn't it run bad all the time? Just a suggestion. I actually don't know what i'm talkin about.
     
  11. RockyRider13

    RockyRider13 1/2 ton status

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    I think that somthing that you need to check out, if you have not already, is the EGR valve. If the valve is sticking, it will give you that crappy perfromance under load when the engine is cold. Take the EGR out and make sure the diaphram easily moves.

    By the way, I can't wait till I go to CSU next year! /forums/images/graemlins/k5.gif
     
  12. Itali83

    Itali83 1/2 ton status

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    Replace your cold start sensor. It's the Temperature sensor right next to the thermostat housing. It is probably bad, telling your computer the wrong temp reading, causing it to start hard, run like [censored] until the motor is fully warm, and causing the loss of power. How do I know this?? I had the exact same problem you are having now and I'm now in school learning to be a mechanic and know why that sensor will do what you are having problems with.
    If you want to check it you will need either a scan tool or a digital volt meter. There are two wires going to the sensor, one is a 5volt reference from the computer, the other is the signal line back to the computer. When you start up your truck after it is fully cold you will have one wire reading 5volts and the other should be close to that, but, as it warms up, one of the wires should decrease it's voltage going back to the computer. If you don't have that happening, your sensor is bad (which I think it is) and you'll buy a new one. But like someone said before, it is worth it to buy a scan tool if you plan to trouble shoot and fix your computer related problems. Hope this helps!
    Ben 87 Jimmy + 89 Blazer
    /forums/images/graemlins/usaflag.gif
     
  13. fortcollinsram

    fortcollinsram 1/2 ton status

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    OKay, a little update...

    So far I have replaced:

    -cap
    -rotor
    -plugs
    -fuel filter
    -rebuilt throttle body with new fuel press. regulator
    -new EGR valve
    -checked for vacuum leaks

    It is running better but there is still MUCH room for improvement...Any more ideas? I found a fitting at work that I can use to check my dynamic fuel pressure so I will get that hooked up and check to see if the pump is stil lup to par...Keep any more ideas flowin'

    Chris
     
  14. Thunder

    Thunder 3/4 ton status

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    You really should think about getting a scanner. It really helps a lot diagnosing engine problems and will pay for its self by saving you from replacing parts needlessly. If you are planning an engine swap a scanner will be a big help too.They dont just tell you the codes they also give a readout of how all the sensors are operating and what they are telling the computer.
    AutoXray makes a good one. Most autoparts stores sell the GM OBD I for around 150 bucks. I have one. Its easy to use and gives a lot of useful info.
    Or if you have a laptop you can download WinALDL for free its a good program too.

    Your problem might be in the fuel pump but it also might be in the Throttle Position Sensor or the Coolant Temp Sensor. A scanner will tell you if those sensors are operating right and will really help narrow dowm the problem.
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    Just thought I'd post this here as I was looking at my camaro manual for a friend having TBI problems, and I stumbled across the hard to start section.

    GM says that if one of the injectors is sticking partly open, hard starts WILL occur, due to loss of pressure. Dieseling may also occur as fuel is bled after the key is turned off.

    Not saying run out and buy new injectors, but I'd imagine on TBI, dripping nozzles are pretty easy to spot.
     
  16. 87sm465np208

    87sm465np208 1/2 ton status

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    just a little hint, if you have a autozone around you, they will scan it for you at not charge /forums/images/graemlins/smile.gif.

    /forums/images/graemlins/usaflag.gif /forums/images/graemlins/truck.gif
     

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