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Discussion Starter #1
Sorry, this post is not about my hot rod, but my work truck. It's a 1999 Chevy 1500 with the 4.3. It runs great as long as I don't give it more than about 1/4 throttle, then it acts like it is not getting enough fuel, and coughs and sputters while making zero power. Some days, I can give it a bit more throttle than others and it runs a bit stronger, but never quite right.

It is not throwing any codes at all - the computer thinks everything is fine. With the cold weather here in Utah, it has been getting worse and worse over the last few days.

So, my theories are as follows:

1, Throttle position sensor could be bad.
2, Fuel injectors are plugged.
3, Fuel filter is plugged.
4, Fuel pump is dying - but not quite dead yet. (It does whine a bit while running.)

Any ideas?
 

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check fuel filter, then, fuel preassure, fuel injector cleaner. then check resistance of the TPS, via DVOM set to ohm, have sombody change throttle position, make shure it's within spec.
 

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if the tps did have a worn spot it would bog, but once you increased throttle position past the worn spot it would pick back up, its really hard to check tps with a dvom you need an oscilloscope and you will need to look for a dip in the waveform. and as far as the noisy pump goes, chevy pumps are naturally noisy. take the filter off and blow through it with your mouth....important blow, not suck. if your cheeks puff up change it, and if you smoke i would suggest waiting a few mins before lighting one up.
 

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njbloodline666 said:
if the tps did have a worn spot it would bog, but once you increased throttle position past the worn spot it would pick back up, its really hard to check tps with a dvom you need an oscilloscope and you will need to look for a dip in the waveform. and as far as the noisy pump goes, chevy pumps are naturally noisy. take the filter off and blow through it with your mouth....important blow, not suck. if your cheeks puff up change it, and if you smoke i would suggest waiting a few mins before lighting one up.
to check TPS, probe both leades with Dvom set to Ohm, move throttle back and forth, this moves the contact across the resistor, it should change smoothly and be within spec, no need for an oscilliscope.
 

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you may also want to check your catalytic converter. I had a similar problem on a 4.3 and thats what it was doing
 

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redhed said:
you may also want to check your catalytic converter. I had a similar problem on a 4.3 and thats what it was doing
My choice also, either the cat or fuel pressure regulator. Sounds like the cat though......
 

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matt167 said:
to check TPS, probe both leades with Dvom set to Ohm, move throttle back and forth, this moves the contact across the resistor, it should change smoothly and be within spec, no need for an oscilliscope.
a dvom has lag you will miss the worn spot
 

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njbloodline666 said:
a dvom has lag you will miss the worn spot
not really, because you just have to move the TPS at a steady slow speed. Many people don't have oscli/ lab scopes assesable, but have good DVOM's, most electrical tests, don't need much more. even testing for A/C output in an alt, just do an A/C ripple test by switching to A/C volts and measuring from the output wire, to the body of the alt, an osciliscope would read the same thing.
 

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Discussion Starter #11
Thanks. It's back on track.

I replaced the fuel filter, which had a bunch of dark junk in it when I let it drain out, and it seems to be running great.

I bought it used, so I have no idea whether it had ever been changed.

Thanks for the ideas.
 
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