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Old April 4th, 2007, 11:47 AM   #1
scorpio_vette
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4.3L acting strange

got a 95 s-10 with a 4.3L Z motor. under hard acceleration (like punching the pedal completely from a dead stop) it stumbles and for a second almost sounds like the engine shut off. even while driving if you gun it, it will just stumble. but as long as you apply slow steady throttle, it drives fine.

we did a tuneup (plugs, wires, cap, rotor) and checked the cat for any problems (we temporarily removed it and still have the same problem).

i also noticed something else that's really strange. with the scan tool hooked up and the engine at idle, the computer shows that it's running at between 9,000-9,999 RPM. the engine idles just fine at what i would guess is around 700-800rpm. so how do i explain the 9,999RPM, and could that be related to the stumble on hard acceleration???
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Old April 4th, 2007, 12:00 PM   #2
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i had a similar prob and it was the fuel pump and filter
no idea in the 9000 rpm idle
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Old April 4th, 2007, 12:05 PM   #3
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yeah, I would try the filter first and if it still does it, it is more than likely the pump.
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Old April 4th, 2007, 12:05 PM   #4
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i dont think u would have much of and engine when u hit 10k rpm. but yea fuel filter and fuel pump. mine did the same thing to when i was driven up to petoskey once
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Old April 4th, 2007, 12:18 PM   #5
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Tps?
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Old April 4th, 2007, 12:19 PM   #6
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tps reading seem to be within spec.

i was thinking of doing to filter/checking supply pressure since it seemed to be acting like it's starving. but the 9,999RPM is really throwing me off on what to think.
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Old April 4th, 2007, 03:01 PM   #7
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my first thought was TPS before I read the 9,999 rpm part you sould find out were the pcm gets it's tac input from and search that part out before tossing parts at it. Fuel pumps are very common for failing in the 100,000-140,000 mile range.
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Old April 4th, 2007, 05:03 PM   #8
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if you have a electric shift trans its got a trans rpm sensor that acts like a tach. that could be the problem. it might not be a stumble but the trans hanging up before you accellerate.
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Old April 4th, 2007, 05:05 PM   #9
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i would like to see a 4.3 at 10k. that would be cool!!
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Old April 4th, 2007, 05:08 PM   #10
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Quote:
Originally Posted by kiss my crack scotty!! View Post
i would like to see a 4.3 at 10k. that would be cool!!

...can you say "Grenade!"
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Old April 4th, 2007, 11:31 PM   #11
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Scorpio.... Sounds like the EGR valve is opening up causing a lean miss. It probably has the computer controlled vacuum switch and either vacuum is getting past it or the computer thinks it's cruising down the road (due to the RPM problem and WOT when you punch it) and tells it to open up to lean out tail pipe emissions.

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Old April 5th, 2007, 06:31 AM   #12
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...can you say "Grenade!"
thats something they would do on mythbusters, then hide behind plexiglass. i have blown up alot of stuff, and the best i ever had to hide behind was an igloo cooler.
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Old April 5th, 2007, 07:17 PM   #13
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well i was sick today and had to stay home, but my body shop tech went ahead and put a new fuel filter on since i told him to make sure there were no fuel restrictions. he called me up and said that the truck runs fine now and squeals the tires again and takes of nicely when he stomps it. as far as the 9,999 RPM, i'll have to look into that some more when i get back and see what i can find. that is kinda interesting.
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Old April 5th, 2007, 11:15 PM   #14
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"my body shop tech went ahead and put a new fuel filter on since i told him to make sure there were no fuel restrictions. he called me up and said that the truck runs fine now and squeals the tires again and takes of nicely when he stomps it."

I hope your paying him good cash to beat the crap out of your truck!

Hahaha, just kiddin. Maybe i had too many beers.
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Old April 6th, 2007, 09:48 AM   #15
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it's his truck, so he can do what he wants with it. lol but yes he does beat on my jeeps quite often. i let him drive my XJ very often for parts runs and stuff, and he fell in love with it and has been looking for one for himself. and now i let him drive my 84 grand wagoneer, and now he wants one of those too. lol he's never been in a jeep, and after driving my XJ, TJ and grand waggy, he fell in love with them. lol
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Old April 7th, 2007, 09:21 PM   #16
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Ignition switch is going bad...not enough power going to the coil.

Ignition switch is about $100.00, and at most should take about 1 1/2 hours to replace.

Same thing happened to us, and we have the same model and year. Ours was stumbling, the trans wasn't shifting correctly, and it was all due to low voltage of the computers.

Last edited by blackcat818; April 7th, 2007 at 09:26 PM.
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