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don't run like it used to

This is a discussion on don't run like it used to within the General Help forums, part of the LSx Technical Help Section category; Originally Posted by Too Fast Yes it would, however our fuel pumps operate "on demand", so it doesn't run full ...

  1. #21
    Quote Originally Posted by Too Fast View Post
    Yes it would, however our fuel pumps operate "on demand", so it doesn't run full delivery unless the PCM tells it to. So, it could be ok under full throttle and at low throttle it may be weak. You need to hook it up so you can watch it while driving. It would need a long hose, then try carefully to shut the hood and have the gage on the windshield, held in place by a wiper maybe, and go for a drive. If you think a fuel pressure checker is too much money, it really isn't. How much is a diagnostic at the local garage? Prolly more than this gage costs, and then you have one that fits most GMs and a lot of Chryslers too.

    It could be a TPS sensor, they can go bad and not set a code. You would need a scanner to watch the signal to check that, tho. TPS is Throttle Position Sensor, it tells the PCM how hard you have your foot into it. Since most driving is done at part throttle, they wear out in that highly used section sometimes, causing a hesitation.
    Not true...the fuel pump runs full on at all times.

  2. #22
    my ws6 eats rice gokillyourself's Avatar
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    1999 trans am ws6

    today i rechecked my wires and plugs, they are good and tight, had my fuel pressure checked and it is a steady 57 psi. my maf, tb, and intake are still spotless. what else could i check?

  3. #23
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    navy blue metalic
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    flat spot in power curve

    I have same issue, but clutch is pretty new, wires were done 20K ago, TCS is disabled, and problem happens on flat or up hills and only under moderate acceleration, foot to floor,

    A fuel filter seems like a quick fix, where is it located? Not in the tank

    My MAF was just cleaned, problem arose a couple of months after I cleaned it. The air filter is K&N and is clean.

    How do you test the MAF?

  4. #24
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    Quote Originally Posted by bcorwin View Post
    I have same issue, but clutch is pretty new, wires were done 20K ago, TCS is disabled, and problem happens on flat or up hills and only under moderate acceleration, foot to floor,

    A fuel filter seems like a quick fix, where is it located? Not in the tank

    My MAF was just cleaned, problem arose a couple of months after I cleaned it. The air filter is K&N and is clean.

    How do you test the MAF?
    With GM Delco MAF sensors, attach a digital voltmeter to the appropriate MAF sensor output terminal. With the engine idling, the sensor should output a steady 2.5 volts. Tap lightly on the sensor and note the meter reading. A good sensor should show no change. If the meter reading jumps and/or
    the engine momentarily misfires, the sensor is bad and needs to be replaced.

    I would think a faulty MAF would throw a SES light.

  5. #25
    Senior Member Too Fast's Avatar
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    Quote Originally Posted by 35th-ANV-SS View Post
    With GM Delco MAF sensors, attach a digital voltmeter to the appropriate MAF sensor output terminal. With the engine idling, the sensor should output a steady 2.5 volts. Tap lightly on the sensor and note the meter reading. A good sensor should show no change. If the meter reading jumps and/or
    the engine momentarily misfires, the sensor is bad and needs to be replaced.

    I would think a faulty MAF would throw a SES light.
    You'd think so, but they don't always do that.

    To to OP, I am out of ideas without driving the car. Good luck, and let us know what fixed it.

  6. #26
    my ws6 eats rice gokillyourself's Avatar
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    1999 trans am ws6

    i am thinking about unplugging the tps and drive it down the road to see if it still horse power drops still, well it sounds like an idea, i'll try it and let ya know

  7. #27
    my ws6 eats rice gokillyourself's Avatar
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    1999 trans am ws6

    well i replaced the tps, it doesn't drop the hp as much but it still has the hesitation when accel. at normal driving. anything else i can try? its idles a little rough, i wonder if that can have anything to do with it. maybe a new iac?

  8. #28
    Senior Member Too Fast's Avatar
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    I have never seen an IAC cause a rough idle in my 25 years working on cars. Maybe an unsteady idle, but not a rough, misfiring idle. It's hard to diagnose stuff without being there. Hell, sometimes it's hard when you have the car! Just drive to Indy this weekend, I'll help you look at it. I'm off Sunday....the US Nationals are in town thru Monday.

  9. #29
    my ws6 eats rice gokillyourself's Avatar
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    Quote Originally Posted by Too Fast View Post
    I have never seen an IAC cause a rough idle in my 25 years working on cars. Maybe an unsteady idle, but not a rough, misfiring idle. It's hard to diagnose stuff without being there. Hell, sometimes it's hard when you have the car! Just drive to Indy this weekend, I'll help you look at it. I'm off Sunday....the US Nationals are in town thru Monday.
    i replaced the iac, but it was idling funny before and after

  10. #30
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    1999 trans am ws6

    I wonder if an o2 sensor would cause this. Someone said to tap the maf to see if the engine changed, so i did and nothing changed, so i guess the maf is good. I took it to a garage to ask some ?'s, they don't have a clue. I don't know either.

  11. #31
    Senior Member Too Fast's Avatar
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    It's possible, but not probable (O2 sensor) in my experience. Could have a ground issue. And yes, sounds like your MAF is ok. You've done a lot of basic checking, maybe you should take it to a GM dealer (or whoever has a good reputation for driveability) and pay some money.

  12. #32
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    I don't really have the money to spend, but i have been to several garages and explained to them whats happening and all i seem to get is "i don't know", i am thinking "and you call yourself a mechanic". I wonder if it is possible that the cats are getting stopped up, but i doubt it since the power picks back after i get out of the 2000-3000 rpm range.

  13. #33
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    Quote Originally Posted by bcorwin View Post
    i have same issue, but clutch is pretty new, wires were done 20k ago, tcs is disabled, and problem happens on flat or up hills and only under moderate acceleration, foot to floor,

    a fuel filter seems like a quick fix, where is it located? Not in the tank

    My maf was just cleaned, problem arose a couple of months after i cleaned it. The air filter is k&n and is clean.

    How do you test the maf?
    i have no problems on hills or w.o.t., its just during the 2000-3000 rpm range

  14. #34
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    I am having the same problems

    Did you ever find out what was causing your problem? did you change the MAF or check what the voltage output back to the PCM was? did you have the 2-2.5 volts like someone said? i checked mine and I have 4 volts so I'm wondering if I am not getting the right fuel/air mixture due to this????

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