Misfire between 45-55 mph

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_nickjoseph

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1997 k1500 5.7l, misfires between 45-55 mph. No codes it’s done this even after a tune up and changing a bunch of parts
 

indexcow

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1997 k1500 5.7l, misfires between 45-55 mph. No codes it’s done this even after a tune up and changing a bunch of parts
Is it possible that what you think is a missfire is something else? Like a bad u-joint or out of balance tire?
 

_nickjoseph

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Is it possible that what you think is a missfire is something else? Like a bad u-joint or out of balance tire?
The exhaust makes a choppy sound during this speed and the power reduces, when I let off the gas it no longer acts up
 

DerekTheGreat

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Sounds like it's running REALLY lean or trying to. Don't them thar Vortex (pun intended) engines like to have their intake gaskets re done and something about the upgrade kit for the fuel injection stuff?? Sorry, TBI guy here who lurks & reads other threads.
 

PlayingWithTBI

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LOL - on my TBI (and other posters too) the ICM went south and caused surging by sending false pulses to the ECM making it think that the engine was revving up to as high as 4800 RPM (on the data log's tach) when it was really ~2000 - 2400. The ECM then would lengthen the injectors' pulse width momentarily which caused the surging.
 

_nickjoseph

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LOL - on my TBI (and other posters too) the ICM went south and caused surging by sending false pulses to the ECM making it think that the engine was revving up to as high as 4800 RPM (on the data log's tach) when it was really ~2000 - 2400. The ECM then would lengthen the injectors' pulse width momentarily which caused the surging.
You changed the icm and it fixed it? Did You have issues like I’m having?
 

PlayingWithTBI

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Yep, that fixed my surging while cruising, a bad coil and dripping injectors (remember this is in a TBI) helped cause my stumble at idle. I found the bad coil by spraying water on it while idling (just the body of the coil, not the connections), it would stumble worse and try to die.
 

_nickjoseph

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Yep, that fixed my surging while cruising, a bad coil and dripping injectors (remember this is in a TBI) helped cause my stumble at idle. I found the bad coil by spraying water on it while idling (just the body of the coil, not the connections), it would stumble worse and try to die.
Sprayed water on mine and nothing happened
 
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