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#4475249 - 07/31/17 07:05 AM 1999 s10 4.3 miss/lack of power on highway
nwjones18 Offline


Registered: 11/30/09
Posts: 1052
Loc: Warner Robins, GA
I just got a 1999 s10 4.3 automatic that only has 51k miles on it. When I got it the intake manifold gaskets were leaking and I'm just now getting it back on the road. The truck seems to run perfect, idles smooth and has plenty of power if you get on it, but when you are cruising in OD at 55-65 mph and come to a slight hill it just feels like it has no power and seems hesitant to downshift unless you floor it. No codes set. I honestly can't tell if its some sort of misfire, or maybe a torque converter shuddering I just know there is a lack of power and some very light vibration. Truck doesn't have a tac so its sort of hard to tell what its doing. Plugs/wires appear to be original and I assume the atf is as well, although it looks very good on the dipstick. Any thoughts?
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#4475254 - 07/31/17 07:14 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
ltslimjim Offline


Registered: 08/06/10
Posts: 5642
Loc: WatUpDoc
Plugged fuel filter or degraded components since 1999('98 year technically?)?

I'd start with age related/seldom driven type of problem areas for this engine and see if someone can comment on other known performance problems for this app. I believe this one has a MAF in the intake.

It could also use a good Italian tuneup at the very least after verifying fuel filter isn't the original but if say the plugs/wires are original then I doubt it has been replaced... (AC Delco has a professional series filter made in USA sold on Amazon or RockAuto)

drive

Do seldom driven cars develop combustion chamber/piston head related issues that can cause these performance symptoms? Might it be worth running a bottle of Red Line then a bottle of Berryman's B12 for the newer 1,2 punch approach before swapping fuel filters as relatively cheap additions through the gas tank? Has there since been a superseding ATF from what the factory fill would have been for the transmission side of things?

Not driven enough...but hopefully enough oil changes before now.


Edited by ltslimjim (07/31/17 07:20 AM)
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#4475265 - 07/31/17 07:37 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
Lubener Offline


Registered: 01/22/11
Posts: 2577
Loc: N.Ohio
Fuel filter if it hasn't been changed recently. Plugs could have been affected by coolant and the leaking intake gaskets.
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#4475271 - 07/31/17 07:45 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
Chris142 Offline


Registered: 06/05/03
Posts: 16832
Loc: Deplorable in apple valley, ca
Definatly change the plugs, wires cap and rotor...have fun with the front plug on the driver side smile
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#4475276 - 07/31/17 07:52 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
Trav Offline


Registered: 11/20/06
Posts: 18896
Loc: MA, Mittelfranken.de
After plugs, wires, cap, rotor, filters, etc check for a clogged cat.
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#4475286 - 07/31/17 08:06 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
nwjones18 Offline


Registered: 11/30/09
Posts: 1052
Loc: Warner Robins, GA
Thanks everyone I'll start with the fuel filter and then work down the list. I did change the cap/rotor while I had the distributor out for the intake. The truck did have a code set for the cat P0420, and I just put one of those 02 sensor spacers on there and it hasn't come back. But I guess it could be clogged. hard to believe with only 50k on it though. Will report back after fuel filter replacement.
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#4475348 - 07/31/17 09:09 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: Chris142]
thorromig Offline


Registered: 03/22/12
Posts: 804
Loc: BerksCounty/Pa.
Easiest way to address that front plug on the drivers side -- just take the front tire off and access it from the bottom. Had a 96 Blazer 4.3L and learned the hard way!!! Like mentioned earlier -- new plugs/wires/cap & rotor. Would not hurt to run acouple back to back runs of Techron Fuel System cleaner or some other "quality" fuel system cleaner also.
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#4475351 - 07/31/17 09:10 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
thorromig Offline


Registered: 03/22/12
Posts: 804
Loc: BerksCounty/Pa.
After market 02 sensors are junk. My opinion -- OEM 02 sensors are the only way to go.
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#4475386 - 07/31/17 09:46 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: Trav]
c502cid Offline


Registered: 01/17/03
Posts: 1003
Loc: Elizabeth. Colorado
Originally Posted By: Trav
After plugs, wires, cap, rotor, filters, etc check for a clogged cat.


^^^this^^^
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#4475412 - 07/31/17 10:11 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
barkingspider Offline


Registered: 12/22/13
Posts: 2049
Loc: socal
New plugs, wires, dis cap, fuel filter, motor oil/filter, trans fluid/filter, PS fluid, diff fluid, brake fluid, air & cabin filter, coolant / stat, valve cover gaskets, serp & acc drive belts, grease all zerks, clean throttle body and MAF if applicable, should be good to go. Oh, check tires and brakes. The truck should take you to 200k
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#4475416 - 07/31/17 10:13 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: c502cid]
Bgallagher Offline


Registered: 04/17/12
Posts: 3159
Loc: Boston, MA
Originally Posted By: c502cid
Originally Posted By: Trav
After plugs, wires, cap, rotor, filters, etc check for a clogged cat.


^^^this^^^


+1
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#4475426 - 07/31/17 10:19 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: Bgallagher]
Carbon Offline


Registered: 09/04/09
Posts: 554
Loc: near Chicago
On many vehicles, the air filter is easier to change than the fuel filter. The fuel filter in the gas tank is the hardest.

On the highway, if the problem is the fuel filter, downshifting would usually make the problem worse. When the downshift does occur under those conditions, does that make you accelerate more or lug down more?

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#4475447 - 07/31/17 11:01 AM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
Vladiator Offline


Registered: 01/04/16
Posts: 728
Loc: NC
1) Add a bottle of fuel system cleaner (Redline is my favorite), run that tank of gas with the cleaner. Then change the fuel filter and run another bottle of fuel system cleaner.
2) Ignition components as listed above by other posters.
3) Tranny flush. Usually $120ish at the stealership.

If symptoms are still there - I'd consider replacing a fuel pump. Shop I used to work at had an Astro Van with the 4.3L. Over 130k miles the fuel pump had to be replaced 5 times... I met a few more guys with frequent fuel pump failures on those 4.3 GMs. But definitely get a second opinion first from a reputable mechanic before yous start throwing parts at it.
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#4475511 - 07/31/17 12:08 PM Re: 1999 s10 4.3 miss/lack of power on highway [Re: Trav]
Nick1994 Online   content


Registered: 02/19/13
Posts: 10119
Loc: Phoenix, AZ
Originally Posted By: Trav
After plugs, wires, cap, rotor, filters, etc check for a clogged cat.
Yup, clogged or broken cat.
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#4475667 - 07/31/17 02:31 PM Re: 1999 s10 4.3 miss/lack of power on highway [Re: nwjones18]
JimPghPA Offline


Registered: 08/22/09
Posts: 3859
Loc: Pittsburgh,PA U.S.A.
Along with all of the things already mentioned which it very well could be, it also could be an ignition coil going bad.
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