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4.3 running badly (S10 Blazer 91 4x4)

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Old 12-13-2005, 09:54 PM   #1
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4.3 running badly (S10 Blazer 91 4x4)

Recently is has been running like crap. I noticed when i jump into it in the morning and take off its fine on idling and cruising. When at operating temperature it starts to run like crap like its missing. It does the same at idle it sits there and feels like its choking to get gas or its the timing im not sure im not mechanic. The motor idles ok but randomly pops the best i can explain it. not loud back fires. Its like when you step on the gas it hesitates while these gaps occur, like runing out of gas. Anyways best as i can explain it. Any help would be appreciated. Not claiming to be a mechanic just need some explanation.

Thanks for time.
Old 12-13-2005, 09:58 PM   #2
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Re: 4.3 running badly (S10 Blazer 91 4x4)

Throttle position sensor perhaps? Could also be an engine temp sensor not reading properly and making the right fuel mix. I'm sure one of the folks here more familier with GM EFI can be of more help than I can. When were the air and fuel filters last replaced?
Old 12-13-2005, 10:04 PM   #3
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Re: 4.3 running badly (S10 Blazer 91 4x4)

Maybe try a backpressure test to see if the cat is cloged?

When was the last time it had a tuneup? It wouldn't hurt to check the timing.
Old 12-13-2005, 10:07 PM   #4
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Re: 4.3 running badly (S10 Blazer 91 4x4)

i have a 89 s10 with the 4.3 and sounds like the symptoms you are describing, i finally figured out it was the fuel pump after i replaced it, it was like a new truck lots more power and runs so good now. sounds like what your describing to me...
Old 12-13-2005, 10:12 PM   #5
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Re: 4.3 running badly (S10 Blazer 91 4x4)

It has 183000 on it not sure if its rebuilt. I havent had a tune up since i have had it. I do regular maitenence on it. Air filter still looks pretty clean and the fuel filter about 1 and a half on that. It smokes on start up guessing its a valve seal. But other than that it runs pretty good besides what recently is happening.
Old 12-13-2005, 10:15 PM   #6
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Re: 4.3 running badly (S10 Blazer 91 4x4)

would replacing spark plug wires, cap and rotor. Help any? Spark could be misdirecting du to wear ?
Old 12-14-2005, 08:03 AM   #7
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Re: 4.3 running badly (S10 Blazer 91 4x4)

I suggest having a muffler shop check the cat. Usually there is no charge to pressure check the system for a clogged cat.
Old 12-14-2005, 04:21 PM   #8
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Re: 4.3 running badly (S10 Blazer 91 4x4)

mine would run fine for a few minutes and then act like it was running out of fuel, so i started by changing the fuel filter. that didn't fix it, so i got my wife to spin it over and i saw the injectors working fine ('89 4.3 tbi). so i put a timing light on it to check the spark and it was good. next, i removed the oxygen sensor and drove it up the road and back. it sounded like shit, but it didn't cut off any more! thus, i knew the catalytic converter was clogged (caused by my engine burning a lot of oil). so i would definitely get the catalytic converter checked out.
Old 12-14-2005, 10:14 PM   #9
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Re: 4.3 running badly (S10 Blazer 91 4x4)

Yeah i have some thought that it could be that. Any way to really tell besides smell ?
Since is smokes on start up eventually the cat would plug up right ? or if it has a EGR valve could that eventually stick open, not sure that year has one though.
Old 12-20-2005, 06:40 PM   #10
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Re: 4.3 running badly (S10 Blazer 91 4x4)

Quote: Originally Posted by blacknight47
Yeah i have some thought that it could be that. Any way to really tell besides smell ?
Since is smokes on start up eventually the cat would plug up right ? or if it has a EGR valve could that eventually stick open, not sure that year has one though.
mine didn't make any smell before it clogged up. that egg or sulfur smell is usually on older cat. converters and usually when they're being overloaded with too much unburned gasoline. the only way to tell for sure is to bypass it. like i said, i removed the oxygen sensor, which is in front of the cat, so that allowed enough exhaust to move out of the engine to run again, but that was done just for testing purposes. once i confirmed the problem, then i just gutted the cat.
Old 12-21-2005, 01:30 AM   #11
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Re: 4.3 running badly (S10 Blazer 91 4x4)

or if you or a friend has a temp gun see if there is a 50 deg rise from before to after the cat then you know if it is working properly if not clogged.
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