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Thread: VS engine slows down and loses power at 3500-4500rpm

  1. #1
    Fonzie's Avatar
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    Angry VS engine slows down and loses power at 3500-4500rpm

    Let me first mention this isn't me whining that my car doesn't go fast enough...

    95 VS, 3.8 ecotech engine obviously. Only mods are CAI and an LPG duel fuel conversion.
    The car was serviced 10 days ago (By a mechanic, not me), it's been doing this since before the service... I left it because i thought a service might fix it. Stupidly, i forgot to mention it to the mechanic though.

    What is happening: From a standstill, or a slow rolling start, when i accelerate it gets to somewhere between 3500rpm and 4500rpm in first gear and starts to lose power. The engine seems to shudder, drops back a few 100 rpm, then picks up again and keeps going. It doesn't seem to happen in second gear, but i can only run it to around 4500 before i'd be speeding, so i can't do much of a test there (Losing my license once is more than enough to learn my lesson). This is when it's running on LPG... It doesn't seem to do it on petrol.

    At first i thought maybe coil pack... but it doesn't do it in 2nd gear, or while it's running on petrol. Any ideas? Or should i just get the mechanic to look at it.. Maybe disconnect the battery overnight for a computer reset?
    Quote Originally Posted by Philthy View Post
    ....man, I love how white your car is

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    Fonzie's Avatar
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    Bump.
    Anyone? It's beginning to annoy me.
    Quote Originally Posted by Philthy View Post
    ....man, I love how white your car is

  3. #3
    camstatic's Avatar
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    Sounds like you're not getting enough gas to the engine to feed it at high load/rpm, get a gas specialist to adjust the flow / inspect the system for the problem.
    Check out my VP right 'ere!

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    Quote Originally Posted by camstatic View Post
    Sounds like you're not getting enough gas to the engine to feed it at high load/rpm, get a gas specialist to adjust the flow / inspect the system for the problem.
    It 'shudders', then drops back a few rpm, then revs out the way it should... So it can get to the higher rpm, it just... falters in the middle. Also, it doesn't seem to have a problem in second gear OR neutral at the same rpm.
    Quote Originally Posted by Philthy View Post
    ....man, I love how white your car is

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    Quote Originally Posted by stevieVS View Post
    is it injected gas?
    I would assume so... Given that the ecotec's are fuel injected... How can i tell?
    Quote Originally Posted by Philthy View Post
    ....man, I love how white your car is

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    well this just comes from driving gas converted cars, my old man has injected and has experienced no changes loss of power ect, where as my mothers isnt injected and there is a notable loss of power at certain revs during acceleration, this is in comparison to petrol. and i do recall her having the flow being adjusted and a similar problem being resolved.

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    Quote Originally Posted by chrisdoesitbetter View Post
    could be the knock sensor going off try check that....
    that could be right. when the ecu reads a knock in the engine it will switch to limp home mode making it loose power (revs). i think the knock maybe the engine pinging triping the knock sensor etc. id get your gas converter looked at as it might be running too lean. at just a guess i would think that it wont be injected gas system therefor the converter will be only run off vacume. if the converter has rubbish, wax or corotion in it it might just be in need of a clean out.

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    Quote Originally Posted by chrisdoesitbetter View Post
    could be the knock sensor going off try check that....
    What is it, where do i find it, how do i check it, how do i fix it? Sorry, a bit of a mechanical newbie here.
    Quote Originally Posted by Philthy View Post
    ....man, I love how white your car is

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    Quote Originally Posted by tadpol88 View Post
    that could be right. when the ecu reads a knock in the engine it will switch to limp home mode making it loose power (revs). i think the knock maybe the engine pinging triping the knock sensor etc. id get your gas converter looked at as it might be running too lean. at just a guess i would think that it wont be injected gas system therefor the converter will be only run off vacume. if the converter has rubbish, wax or corotion in it it might just be in need of a clean out.
    Alright, looks like it's a trip back to the mechanic for me. I would've thought, given that he's the guy that installed the gas, that's something they'd check when they service it? It was serviced around a fortnight ago... Ah well. I'll just tear a new hole in the wallet.
    Quote Originally Posted by Philthy View Post
    ....man, I love how white your car is

  12. #12
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    i own a vr and the knock sensor is located behind the oil pump on the side of the block. not sure what model you own but it would probably be bolted to the side of the block somewhere with wires coming off heading to the main wiring loom. looks similiar to an oil pressure sender unit...

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