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3.8 Misfire and won't rev. Pops at high rpm.
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hardtrailz
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PostPosted: Thu Aug 22, 2013 10:04 am    Post subject:  3.8 Misfire and won't rev. Pops at high rpm. Reply with quote

My Impala is acting funny. 2000 3.8L

Loss in MPG, slowly for a bit, but more significant this past tank.

Loss in power.

Miss/pop at over 3500 rpm started yesterday, but to be honest I hardly hit those rpm.

Checked fluids n such. Made sure wires were seated on plugs good.

Today, it will not go over 4000 rpm and I get a flashing CEL.

No active codes, but I pulled a pending P301....random missfire.

Then half way to work it would randomly miss for a few seconds then kick back in and be normal on the highway.

Kinda low power in town and would not rev right.

FYI--My buddy and I changed the fuel filter and plugs and wires a few weeks back and it seemed to run better for bit.

I have an inclination it could be Cat is clogged, but thats just gut feeling. No weird smell or anything.

Wonder if its in ignition or coil, but not sure how to test those.

Any ideas?
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PostPosted: Thu Aug 22, 2013 11:51 am    Post subject:   Reply with quote

An exhaust shop can do a backpressure test to confirm if it's the cat or not. If the misfire is on cylinder 6, that also points to exhaust restriction (cat). When my cat was plugged, the car was restricted to 4000rpm as well.

Never done troubleshooting on ignition or coil myself, either.

Aftermarket cats are cheaper but are hit or miss as to wether they will throw a code (which will make you fail emissions testing)

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hardtrailz
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PostPosted: Thu Aug 22, 2013 12:08 pm    Post subject:   Reply with quote

I got a random code for misfire.

Luckily I do not have emissions or any other testing to worry about. I assume that running non-catted will through a code on these motors, or could i try that?
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PostPosted: Thu Aug 22, 2013 1:13 pm    Post subject:   Reply with quote

Non-catted will throw codes because the rear 02 sensor will not be able to read properly. The workaround for this is an 02 simulator.

The 02 simulator available for some years of the 00-05 generation, but I'm not sure which years are compatible with it. I seem to remember someone on here mentioning they are harder to get now than they used to be, so you might have to do a bit of research if you want to go that route.

Flowmaster high-flow cats are supposed to be pretty good, but again, might throw a code.

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hardtrailz
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PostPosted: Thu Aug 22, 2013 5:42 pm    Post subject:   Reply with quote

Thinking fuel pump is dying. Would barely maintain 60 and would buck like it was out of fuel when the throttle was pushed.

Parked it idle smooth and runs up to 4000 rpm then it bogs out like lack of fuel.
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PostPosted: Thu Aug 22, 2013 5:59 pm    Post subject:   Reply with quote

hardtrailz wrote:
Thinking fuel pump is dying. Would barely maintain 60 and would buck like it was out of fuel when the throttle was pushed.

Parked it idle smooth and runs up to 4000 rpm then it bogs out like lack of fuel.


Only way to proceed IMO is with backpressure test or a trip to the shop for dianostics.

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PostPosted: Thu Aug 22, 2013 6:08 pm    Post subject:   Reply with quote

I cant do a back pressure test, but what good is paying a shop for diagnosis? I NEVER use shops and do not know what they will do other than start me a tab and replace parts til it works. I can run codes and there is none now.
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PostPosted: Thu Aug 22, 2013 11:09 pm    Post subject:   Reply with quote

Well, given your grand total of 20 posts since late last year, I expect you've not seen much of these cars. You read my suggestion and moved onto another idea. I'm just saying you should have it diagnosed because you don't agree with someone who's seen this posted dozens of times here in the last 7 years I've been active. Shops will do this without throwing parts at it, if you tell them not to proceed with work beyond diagnostics. An hour's labor for diagnostics would prevent you from throwing parts at it yourself and would get the car operating the way you want it to be.

Basically everything you've posted so far points to a plugged catalytic converter: normal idling, rpms limited to 4000 when driving, loss of power. The engine bogs at 4000 when driving because there's only so much exhaust that can travel through a plugged cat. The car is protecting itself from further damage because it can tell there is an issue.

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PostPosted: Fri Aug 23, 2013 3:46 am    Post subject:   Reply with quote

the rpm problem seams to be more like the rev limiter kicking in (only in park and Neutral) couple things like Lingenfelter said sound like a cat problem. due to performance and mpgs

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hardtrailz
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PostPosted: Fri Aug 23, 2013 8:34 am    Post subject:   Reply with quote

Lingenfelter wrote:
Well, given your grand total of 20 posts since late last year, I expect you've not seen much of these cars. You read my suggestion and moved onto another idea. I'm just saying you should have it diagnosed because you don't agree with someone who's seen this posted dozens of times here in the last 7 years I've been active. Shops will do this without throwing parts at it, if you tell them not to proceed with work beyond diagnostics. An hour's labor for diagnostics would prevent you from throwing parts at it yourself and would get the car operating the way you want it to be.

Basically everything you've posted so far points to a plugged catalytic converter: normal idling, rpms limited to 4000 when driving, loss of power. The engine bogs at 4000 when driving because there's only so much exhaust that can travel through a plugged cat. The car is protecting itself from further damage because it can tell there is an issue.

I have been wrenching on cars for nearly 2 decades. I have never been on a car enthusiast forum that would advise someone to take a vehicle in for diagnosis. I like to do my own work and use forums as one source of information. I do not post here, because this is just my DD/commuter car and it just runs good. It is a simple stock setup and I generally have no issue with taking care of it and it has already got me 30K this year. I like it, but I have a couple custom lifted trucks that my time and effort are spent on. I frequent forums associated with them and I am a leading poster on them and a mod on a couple. I would offer advice and help with diagnosis if someone(no matter how many posts) came asking for help, but not tell anyone trying to do it themselves to go spend any money at a shop. If they wanted to go to a shop…they most likely would have already.


I am trying to find a place to check the cat, but in a small town in a state that requires no emissions or such it is rather difficult.

I ordered a fuel pump because at 180K it is good preventive maintenance anyway.

I checked the plugs and wires and no arcing nor anything loose.

Some simple research for people with issues similar in future…1. The Engine Sputters at High Speed--The most common early sign of a problem with a fuel pump comes when driving a vehicle at a consistent high speed. While traveling down the road, the car will run well for about 10 miles and then begin to jerk around, or sputter, for a mile or two before returning to normal.
What This Means--Many people will mistakenly diagnose a sputtering vehicle as one with "dirty" gas or some other fuel-related issue. And while that can be the case, it is not uncommon for a fatigued fuel pump to create this same symptom as it struggles to supply a constant stream of fuel to the engine at the proper pressure. The loss of pressure causes the engine to sputter.

2. Vehicle Loses Power While Accelerating--The feelings generated by this second symptom are very similar to the first. However, rather than experience a sputtering sensation while driving, vehicles will experience it upon acceleration from a stop. Generally, the vehicle will initially move before making noises and jerking around as if it will stall. Then, it will continue on its acceleration path smoothly.
What This Means--The process of acceleration creates an increased demand for fuel by the engine. A malfunctioning fuel pump, again, cannot maintain the required pressure to deliver this fuel in a steady manner, thereby causing the engine to improperly mix fuel and air and lose power. Once pressure is restored, the engine is able to run smoothly and the car takes off.

3. Sudden Loss of Power When the Vehicle Is Under Stress--A car or truck is put under stress when the work needed to complete an ordinary task, such as forward movement, is somehow hindered by external forces. Generally, this occurs when climbing a hill or when hauling a load. If, when completing these tasks, the vehicle loses power, cannot accelerate, or begins to sputter, the fuel pump is a possible culprit.
What This Means--Generally, a fuel pump, even an aging one, can maintain a steady stream of fuel and pressure when operating under normal conditions. However, once put under stress, the weakening elements of the pump will begin to take control and the fuel delivery will not be able to keep up with its demands, leading to power loss.

4. Surging--The opposite effect of the above symptoms, surging, can also be a sign of a malfunctioning fuel pump. A car that surges will be moving along normally at a consistent speed. Then, with no driver intervention, will pick up and "surge" forward, as if the gas pedal had been depressed.
What This Means--This is something that many people will mistakenly blame on the fuel filter since it is not "like" any of the other fuel pump malfunction signs. However, this surge is created because, as a result of age and normal wear and tear, the fuel pump now has irregular resistance within its motor. This creates a situation where the pump cannot draw enough electricity to maintain the pressure needed for steady speeds and may "surge" with a sudden ratcheting up in pressure.

-----Also…listen to the pump, if it sounds whining or strained…it may be on its way out. If it takes a bit more cranking when the car is hot after running, it may be getting weak as well.
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PostPosted: Fri Aug 23, 2013 11:54 am    Post subject:   Reply with quote

hardtrailz wrote:
Lingenfelter wrote:
Well, given your grand total of 20 posts since late last year, I expect you've not seen much of these cars. You read my suggestion and moved onto another idea. I'm just saying you should have it diagnosed because you don't agree with someone who's seen this posted dozens of times here in the last 7 years I've been active. Shops will do this without throwing parts at it, if you tell them not to proceed with work beyond diagnostics. An hour's labor for diagnostics would prevent you from throwing parts at it yourself and would get the car operating the way you want it to be.

Basically everything you've posted so far points to a plugged catalytic converter: normal idling, rpms limited to 4000 when driving, loss of power. The engine bogs at 4000 when driving because there's only so much exhaust that can travel through a plugged cat. The car is protecting itself from further damage because it can tell there is an issue.

I have been wrenching on cars for nearly 2 decades. I have never been on a car enthusiast forum that would advise someone to take a vehicle in for diagnosis. I like to do my own work and use forums as one source of information. I do not post here, because this is just my DD/commuter car and it just runs good. It is a simple stock setup and I generally have no issue with taking care of it and it has already got me 30K this year. I like it, but I have a couple custom lifted trucks that my time and effort are spent on. I frequent forums associated with them and I am a leading poster on them and a mod on a couple. I would offer advice and help with diagnosis if someone(no matter how many posts) came asking for help, but not tell anyone trying to do it themselves to go spend any money at a shop. If they wanted to go to a shop…they most likely would have already.


I am trying to find a place to check the cat, but in a small town in a state that requires no emissions or such it is rather difficult.

I ordered a fuel pump because at 180K it is good preventive maintenance anyway.

I checked the plugs and wires and no arcing nor anything loose.

Some simple research for people with issues similar in future…1. The Engine Sputters at High Speed--The most common early sign of a problem with a fuel pump comes when driving a vehicle at a consistent high speed. While traveling down the road, the car will run well for about 10 miles and then begin to jerk around, or sputter, for a mile or two before returning to normal.
What This Means--Many people will mistakenly diagnose a sputtering vehicle as one with "dirty" gas or some other fuel-related issue. And while that can be the case, it is not uncommon for a fatigued fuel pump to create this same symptom as it struggles to supply a constant stream of fuel to the engine at the proper pressure. The loss of pressure causes the engine to sputter.

2. Vehicle Loses Power While Accelerating--The feelings generated by this second symptom are very similar to the first. However, rather than experience a sputtering sensation while driving, vehicles will experience it upon acceleration from a stop. Generally, the vehicle will initially move before making noises and jerking around as if it will stall. Then, it will continue on its acceleration path smoothly.
What This Means--The process of acceleration creates an increased demand for fuel by the engine. A malfunctioning fuel pump, again, cannot maintain the required pressure to deliver this fuel in a steady manner, thereby causing the engine to improperly mix fuel and air and lose power. Once pressure is restored, the engine is able to run smoothly and the car takes off.

3. Sudden Loss of Power When the Vehicle Is Under Stress--A car or truck is put under stress when the work needed to complete an ordinary task, such as forward movement, is somehow hindered by external forces. Generally, this occurs when climbing a hill or when hauling a load. If, when completing these tasks, the vehicle loses power, cannot accelerate, or begins to sputter, the fuel pump is a possible culprit.
What This Means--Generally, a fuel pump, even an aging one, can maintain a steady stream of fuel and pressure when operating under normal conditions. However, once put under stress, the weakening elements of the pump will begin to take control and the fuel delivery will not be able to keep up with its demands, leading to power loss.

4. Surging--The opposite effect of the above symptoms, surging, can also be a sign of a malfunctioning fuel pump. A car that surges will be moving along normally at a consistent speed. Then, with no driver intervention, will pick up and "surge" forward, as if the gas pedal had been depressed.
What This Means--This is something that many people will mistakenly blame on the fuel filter since it is not "like" any of the other fuel pump malfunction signs. However, this surge is created because, as a result of age and normal wear and tear, the fuel pump now has irregular resistance within its motor. This creates a situation where the pump cannot draw enough electricity to maintain the pressure needed for steady speeds and may "surge" with a sudden ratcheting up in pressure.

-----Also…listen to the pump, if it sounds whining or strained…it may be on its way out. If it takes a bit more cranking when the car is hot after running, it may be getting weak as well.


Do you mount, align, and balance your own tires too? Laughing

Also, we are very knowledgable here about these cars. That is for sure your cat, ur having all the symptoms associated with these cars for the cat. Many people have had this problem, even me, and gm had a tsb about it. You asked for advice, you got it. Vehicle repair is all about diagnostics, and what lingefelter suggested is exactly what you would do, or even better yet, unbolt the down pipe or the flange at the down pipe and see how much better your car will perform. Or put a dollar bill on front of the exhaust, do it blow around alot or nothing/hardly at all? Simple tests. Some things you need a shop for, you certainly can't perform every single service by yourself unless your a millionaire and can purchase a backptrssure tester or wheel balancer, ect. Not all mechanics are bad, just some bad apples. Just go to a local garage, talk to them. Create a good relationship. But stop throwing your ban against shop talk. People like you give mechanics like me a bad name.

I'm all for the Catless though, but get rid of the u bend also. I feel like 02 simulators are easy to find. 50 bucks from intense or zzp. But remember, they are illegal and considered for offload use only. I still had one though, as long as your state/city doesn't have inspection.

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PostPosted: Fri Aug 23, 2013 11:58 am    Post subject:   Reply with quote

hardtrailz wrote:
I have been wrenching on cars for nearly 2 decades. I have never been on a car enthusiast forum that would advise someone to take a vehicle in for diagnosis. I like to do my own work and use forums as one source of information. I do not post here, because this is just my DD/commuter car and it just runs good. It is a simple stock setup and I generally have no issue with taking care of it and it has already got me 30K this year. I like it, but I have a couple custom lifted trucks that my time and effort are spent on. I frequent forums associated with them and I am a leading poster on them and a mod on a couple. I would offer advice and help with diagnosis if someone(no matter how many posts) came asking for help, but not tell anyone trying to do it themselves to go spend any money at a shop. If they wanted to go to a shop…they most likely would have already.


I'm aware from your other posts that you're not brand new with the car or cars in general, but I'm 95% sure your problem is the cat. And I've been around long enough (not just with the Impala, but speaking specifically from reading here since 2002, and joining in 2006 with over 9000 posts, and personally experiencing what you are now experiencing), that I don't doubt my diagnosis.

I help people who want the help as well, however I've never done troubleshooting on ignition items on any of my vehicles, and mentioned that above when you suggested a potential ignition issue. I don't provide suggestion or troubleshooting advice without disclaiming it if I don't know what I'm doing.

However, if you prefer to take a little longer self diagnosing the problem to save a few bucks, feel free. I have done the same in the past.

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PostPosted: Sat Aug 24, 2013 1:39 am    Post subject:   Reply with quote

if you take the first o2 sensor out if its the cat it should fix the problem also. but heck you want to talk about preventive maintenance, why not replace the motor now? if it aint broke dont fix it.

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PostPosted: Sun Aug 25, 2013 1:09 am    Post subject:   Reply with quote

I have replaced tons of the catalytic converters at the dealership. This sounds like a bad cat to me as well. But you can remove the upstream O2S.Of course it'll be loud, but it should rid you of this problem. Have you had any issues with the vehicle misfiring in the past? Possibly a leaking fuel injector?

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PostPosted: Sun Aug 25, 2013 1:23 am    Post subject:   Reply with quote

I've had a VERY dirty air filter in combination with a dirty fuel filter cause misfiring issues as well. I have never had a clogged cat so those guys are probably on the right track, but I'll throw in that it wouldn't hurt to replace your air filter if it hasn't been done in a long time. Smile

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