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I have a 03 impala with the 3.8l v6. I've have had basicaly the entire ignition system replaced. I've had the injectors tested and cleaned with one being replaced after testing bad. I've also ran bg 44k through twice. I've replaced the fuel filter as well. It's only misfiring about 50% of the time and only when above 3500 rpm. Just looking to see if anyone knows anything about it. thanks
 

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I have a 03 impala with the 3.8l v6. I've have had basicaly the entire ignition system replaced. I've had the injectors tested and cleaned with one being replaced after testing bad. I've also ran bg 44k through twice. I've replaced the fuel filter as well. It's only misfiring about 50% of the time and only when above 3500 rpm. Just looking to see if anyone knows anything about it. thanks


I would start with pulling any engine trouble codes - then diagnose from there.
 

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If you pull any p0300 series misfire codes, suspect plugs, wires and coil in that order.
ya I'm pretty sure it was one of those but the wires are bandnew we checked the spark plugs and the coil packs have all been replaced. That's kinda why I'm so lost on what it could be.
 

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I have a 03 impala with the 3.8l v6. I've have had basicaly the entire ignition system replaced. I've had the injectors tested and cleaned with one being replaced after testing bad. I've also ran bg 44k through twice. I've replaced the fuel filter as well. It's only misfiring about 50% of the time and only when above 3500 rpm. Just looking to see if anyone knows anything about it. thanks
Hey bro, i think your problem lays with fuel. (mine was headgasket)How many miles are on your impala ? I had the same issue only mine is a 3.4l, had P0300,P0302 so i knew my issue was bad. Looking deeper into it i replaced plugs, and wires and got a temp fix. Misfire came back with same codes, so i replaced my fuel filter which did nothing. I than replaced my fuel injectors thinkings those would fix it. After everything the mis was still present so i finally did a compression test and has anti freeze squirt onto me from cylinder 2. Long story short, run a compression test to verify headgasket is good.
 

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If the head gasket is good id replace all 6 injectors, you could get a set online for $100 or less like i did. Before buying anything if the compression is good do a fuel pressure test using the fuel pressure test gauge found on the fuel rail. Im not sure what a good psi is but google has the answer :) if you got low psi theres your problem, but youll have to find out what causing low psi. Test the psi after the fuel pump but before the fuel filter than again but this time after the fuel filter. Did you check fuses ? If any are blown replace them. If all else fails its most likely ecm. (Very unlikely to be the problem). Sorry for all the info but hope it helps. Btw my impala is a 2004 3.4L so pretty simialar to yours. Ive worked on the 3.8L as well.
 

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If the head gasket is good id replace all 6 injectors, you could get a set online for $100 or less like i did. Before buying anything if the compression is good do a fuel pressure test using the fuel pressure test gauge found on the fuel rail. Im not sure what a good psi is but google has the answer :) if you got low psi theres your problem, but youll have to find out what causing low psi. Test the psi after the fuel pump but before the fuel filter than again but this time after the fuel filter. Did you check fuses ? If any are blown replace them. If all else fails its most likely ecm. (Very unlikely to be the problem). Sorry for all the info but hope it helps. Btw my impala is a 2004 3.4L so pretty simialar to yours. Ive worked on the 3.8L as well.
If your psi is low from the pump to filter your pump needs to be replaced, if youre psi drops after the filter replace the filter.
 

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Let's say I have the same issue, but have not decided to worry about it on a 2000 Impala LS 3.8L. Sitting in neutral and idling at around 3500 RPM it essentially stutters, but does not set any codes. iI's almost as if it's being intentionally being limited.

Some history: A shop did a very bad insurance repair when the mice chewed the MAF sensor wires and the plug wires.
the shop also left exposed wires when they replaced the MAF sensor pigtail and the routing of the plug wires was really bad. After the mice were evicted, the squirrels moved in the following week.

It started out as an intermittant problem with misfires set randomly and rarely, but usually when driving up a long grade or constant acceleration and/or rainy weather. Codes moved to different twin coils and I replaced them. Finally, they went constant for a particular coil (#6) and that's when the wires were all replaced the right way, I had the car in for service for something else and the shop discovered that the air cleaner box wasn't shut all the way, There were no codes initially. It took about 3 months to sort the stuff out. One hard rain and foggy day, the idle got really bad and the car was barely driveable. That coil had to be replaced immediately. So, I do believe that the poor routing took out the coils and the real problem was wires.

Simultaneously, I looked at other things: 1) Replaced air filter (It was due); 2) Cleaned MAP sensor 3) replaced fuel filter and 4) Looked at the TPS signal vs time (Scan tool graphs)

Many years ago when I had MAF problems, the new sensor died a few days after it was replaced, The car would not even go into limp mode. Once stated, the accelerator had to be continually depressed just to keep the car running, The car went into limp mode when the sensor was disconnected.

It's not the first fuel pump for the car and the filter had 70K miles on it. A Toyota dealer said the fuel filter almost always isn't a problem.

The fuel filter is not the easiest repair basically because the filter body needed a 17mm flare nut wrench which is "very expensive" mac and Snap on have them, but it's not $20.00 like a 19mm wrench is. It's like 3x that value. A 5/8 flare nut wrench was required for the fuel line nut. The fuel filter is not the most fun thing in the world to replace,

I sprayed it in penetrating oil and hit the fitting a few times over a couple of days. Then, the aftermarket wrench uses a 19mm nut on the filter. I actually expected something like that, so I checked the size of the nuts when I purchased the filter.

Long ago, I bought a Beck Arnley aftermarket oil filter for a Toyota, The wrench required was SAE.

if I were throwing money at it, I might suspect the catalytic converter, It failed some IR thermometer checks.

So, interested in this thread.
 

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Let's say I have the same issue, but have not decided to worry about it on a 2000 Impala LS 3.8L. Sitting in neutral and idling at around 3500 RPM it essentially stutters, but does not set any codes. iI's almost as if it's being intentionally being limited.

Some history: A shop did a very bad insurance repair when the mice chewed the MAF sensor wires and the plug wires.
the shop also left exposed wires when they replaced the MAF sensor pigtail and the routing of the plug wires was really bad. After the mice were evicted, the squirrels moved in the following week.

It started out as an intermittant problem with misfires set randomly and rarely, but usually when driving up a long grade or constant acceleration and/or rainy weather. Codes moved to different twin coils and I replaced them. Finally, they went constant for a particular coil (#6) and that's when the wires were all replaced the right way, I had the car in for service for something else and the shop discovered that the air cleaner box wasn't shut all the way, There were no codes initially. It took about 3 months to sort the stuff out. One hard rain and foggy day, the idle got really bad and the car was barely driveable. That coil had to be replaced immediately. So, I do believe that the poor routing took out the coils and the real problem was wires.

Simultaneously, I looked at other things: 1) Replaced air filter (It was due); 2) Cleaned MAP sensor 3) replaced fuel filter and 4) Looked at the TPS signal vs time (Scan tool graphs)

Many years ago when I had MAF problems, the new sensor died a few days after it was replaced, The car would not even go into limp mode. Once stated, the accelerator had to be continually depressed just to keep the car running, The car went into limp mode when the sensor was disconnected.

It's not the first fuel pump for the car and the filter had 70K miles on it. A Toyota dealer said the fuel filter almost always isn't a problem.

The fuel filter is not the easiest repair basically because the filter body needed a 17mm flare nut wrench which is "very expensive" mac and Snap on have them, but it's not $20.00 like a 19mm wrench is. It's like 3x that value. A 5/8 flare nut wrench was required for the fuel line nut. The fuel filter is not the most fun thing in the world to replace,

I sprayed it in penetrating oil and hit the fitting a few times over a couple of days. Then, the aftermarket wrench uses a 19mm nut on the filter. I actually expected something like that, so I checked the size of the nuts when I purchased the filter.

Long ago, I bought a Beck Arnley aftermarket oil filter for a Toyota, The wrench required was SAE.

if I were throwing money at it, I might suspect the catalytic converter, It failed some IR thermometer checks.

So, interested in this thread.
I replaced my fuel pump sending unit on my 2000 because the fuel gauge was not working. When I did (great YouTube video on how to do it here
) I saw the bottom of my fuel tank looked like it was full of pretty dirty fuel. For all of the time that I had been driving without a gauge, I had only allowed up to 130 miles on my trip odometer before refilling, just to be safe. After seeing what that fuel looked like on the bottom, I decided not to let my fuel go down below 1/2 tank in hopes of not ending up with a problem. I wonder if that is why it misses sometimes, a problem with dirty fuel? I am not very knowledgeable about cars, so if my theory is all wet, feel free to tell me. I won't be the least bit offended.
 

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... I decided not to let my fuel go down below 1/2 tank in hopes of not ending up with a problem.
Good for you. Maybe let ¼ be your refill threshold - that's plenty safe. But definitely try to stay above ⅛.

The debris floats on the surface, and is only a threat when the level gets down near the pickup. I clogged the filter in my 74 F100 driving on empty all the time.

I doubt you have a dirty fuel issue - the misfire is caused by something else.

Doug

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Double post, mods can delete this one.
 
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Might check the ignition module. Places like autozone can test it for you. Was having random misfires on my daughter's buick a few years back with a 3.8. She was 5 hours away at the time so I did not get a chance to look at it for a few months. Autozone and others had her replace plugs, wires, a coil pack and told her it was her injectors. I was under the hood for less than 30 minutes and after swapping coil packs on the faulty cylinders only to still have the same issue, determined it was likely the module. Autozone tested it and sure enough it was a bad module causing random misfires on 2 cylinders.
 
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