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Discussion Starter #1
so ever since i bought my car it has always limited the revs to 4500 rpm's, and for the last 3 years i have been trying to figure out why. at first i thought it was because of the dirty cat's so i had the first cat gutted, then i had the oxygen sensor and the injectors replaced and still nothing. when i reach 4500 rpms the car just starts kind of backfiring and wont go past it. When the engine light was off the light would start flashing when i reached 4500 rpms . when a ecu scanner is plugged in it reads that i have bad oxygen sensor's but regardless bad oxygen sensor's shouldn't limit my rpms right?
here is what i think is going on, is there any way that my car was some kind of rental car and they placed a chip in the ecu which limit's my rpms? when they plugged in the scanner to my ecu they said there was a lag in the reading so it might be because i have some kind of chip that limits my rpms? how would i test this out without wasting too much money?
thanks in advance
luis
 

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here is what i think is going on, is there any way that my car was some kind of rental car and they placed a chip in the ecu which limit's my rpms? when they plugged in the scanner to my ecu they said there was a lag in the reading so it might be because i have some kind of chip that limits my rpms?
luis
I won't comment on whether or not this is possible, but it's not plausible.
More likely it's running badly because... it's running badly.

Have you been driving the last 3 years with the check engine light lit? Impossible to diagnose without having the actual codes.
 

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The car could be thinking something is wrong and going into some sort of limp mode causing the limited RPM? Although this is usually a fairly hard limit and doesnt give backfiring from what im used to with other cars at least.

Also the o2 sensor plays a role in the air-fuel ratio if i understand its workings correctly, so it could just be throwing this way out of wack if the sensors are giving bad readings.

Cheapest way to test if the error code is right/wrong would be to borrow some known-working sensors to try out.

Would also be useful if you had the specific error code it was giving to share with us. Some codes make it sound like a bad sensor, but really mean something more like the sensor is getting a reading its not expecting which doesnt always mean its a bad sensor.
 

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When the engine light was off the light would start flashing when i reached 4500 rpms . when a ecu scanner is plugged in it reads that i have bad oxygen sensor's but regardless bad oxygen sensor's shouldn't limit my rpms right?...
when they plugged in the scanner to my ecu they said there was a lag in the reading so it might be because i have some kind of chip that limits my rpms? how would i test this out without wasting too much money?
thanks in advance
luis
Fill your mouth full of gauze and walk around around the house. You can still breathe, right? Now try sprinting with the gauze in your mouth. Kinda hard, right? Yes O2 sensors can limit rpm's, it's starving itself for air. Swap the O2 sensors and see if the bad read moves spots. If it doesn't probably a bad MAF.
 

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The car could be thinking something is wrong and going into some sort of limp mode causing the limited RPM? Although this is usually a fairly hard limit and doesnt give backfiring from what im used to with other cars at least.
Yup, could be many things. Somewhere I've seen a list of the troubles that force the ECU into 'limp' mode - those are useful to check. But it could also be something not limp-mode related (e.g., losing crank sensor synch at high rpm). Impossible to tell without codes, though.
 

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Discussion Starter #9
thanks for all the answers guys,
i dont remmeber the specific codes "/ but the codes were the ones that said i had 2 bad oxygen sensors sorry i know this isnt of much help :(
i guess ill just have to replace my oxygen sensor's again and take it from there. im going to see if i make a video and maybe that can help ill upload it in a couple of minutes
 

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if you already changed the oxygen sensors then I wouldn't worry about doing them again.(I skimed past that part, sorry). I'd start with the MAF
 

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i guess ill just have to replace my oxygen sensor's again and take it from there. im going to see if i make a video and maybe that can help ill upload it in a couple of minutes
The O2 sensors are very delicate. If they are handled roughly or polluted in any way, they will not work correctly. If you do replace them, be gentle.-_-
 

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Discussion Starter #12
the thing is i dont really trust mechanics and i forgot to mark my old oxygen sensors before i gave the car to the mechanic so im not sure if he actually changed them, another thing is maybe my cat was gutted wrong and they are breaking my oxygen sensor's
just made the video waiting to upload it to photobucket so you guys can see it
 

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here is the video guys, tommorow im going to get my codes checked and i will post them up, thanks for all the help
just click on the picture for the video
 

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Discussion Starter #15 (Edited)
Guys my car has not run right ever since I bought it/ That was three years ago and I am just getting around to figuring out why.

I gutted my cats (which no shop would do as it is illegal) yet I do not trust that my mechanic changed my O2 sensors which had I really gutted my cats I would have had to removed in that process.

I still wanted to pay someone to rip me off and just say I changed your O2 sensors :lol:

You have no idea what has happened to your car. You have had 3 years to figure it out. Moreover when you test drove it and it would not go north of 4.5K you had a choice not to buy it.

So what do you want?

- Us to tell you that this is precat failure?
- Us to tell you that it is not precut failure?
- Us to tell you that this is normal for rental cars?
- Us to tell you that all of us would let this serious problem sit for 3 years before we dealt with it?

I know I am all ears for this one.
lol hey t-bone thanks for taking your time for nothing?
the shop gutted my cats and that illegal, because no one has ever done anything illegal before?
i bought the car from my brother for a really cheap price so i figured that the 4.5k's umm can be fixed? and for the last 3 years ive been saving up money and trying to figure out whats wrong with my car as i am 19 and a working student? by the way t-bone i dont want you to tell me anything, i want someone who actually knows something to tell me
but thanks for taking your time i can tell your a really busy guy
 

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unplug your 02 sensors(from the harness) and turn on your car.. Drive it and see how runs.. if it still has the issue it isn't the o2 sensors. if it is, then there is a problem.. next step, pull the o2 sensors and ensure the cats have been gutted.. If not, get them things outta there! Finally, clean your MAF.... If there is still an issue then it could be bigger things/sensors.

Anyways, the car should run no problem with the o2 sensors unplugged. it isn't ideal by any means, but the car will run all the way up to redline(without o2 feedback). If the o2 sensors are bad/going bad it should cause the car to run rich. how does your exhaust smell??

If your MAF is gunked up your car should be running lean.. Both of which can cause misfires and other issues, hesitation, possibly cause the ecu to go into limp mode.

Any more background on the car? Mileage, owners, etc.. you said rental car??
if i remember correctly the redline is limited by a crystal(of sorts) on the board. a way to remove the redline is by removing the crystal(i think). If that's the case, it could have been altered(or broken) to cause a low redline.

Does it just bog down and loose power around 4500rpm, or does it hit 4500 and just stop there?
More details please
 

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lol hey t-bone thanks for taking your time for nothing?
the shop gutted my cats and that illegal, because no one has ever done anything illegal before?
i bought the car from my brother for a really cheap price so i figured that the 4.5k's umm can be fixed? and for the last 3 years ive been saving up money and trying to figure out whats wrong with my car as i am 19 and a working student? by the way t-bone i dont want you to tell me anything, i want someone who actually knows something to tell me
but thanks for taking your time i can tell your a really busy guy
Oh god, you didn't..
Only a matter of time before Mr T Bone unleashes.

Your "Video" doesn't work.
 

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Discussion Starter #20
unplug your 02 sensors(from the harness) and turn on your car.. Drive it and see how runs.. if it still has the issue it isn't the o2 sensors. if it is, then there is a problem.. next step, pull the o2 sensors and ensure the cats have been gutted.. If not, get them things outta there! Finally, clean your MAF.... If there is still an issue then it could be bigger things/sensors.

Anyways, the car should run no problem with the o2 sensors unplugged. it isn't ideal by any means, but the car will run all the way up to redline(without o2 feedback). If the o2 sensors are bad/going bad it should cause the car to run rich. how does your exhaust smell??

If your MAF is gunked up your car should be running lean.. Both of which can cause misfires and other issues, hesitation, possibly cause the ecu to go into limp mode.

Any more background on the car? Mileage, owners, etc.. you said rental car??
if i remember correctly the redline is limited by a crystal(of sorts) on the board. a way to remove the redline is by removing the crystal(i think). If that's the case, it could have been altered(or broken) to cause a low redline.

Does it just bog down and loose power around 4500rpm, or does it hit 4500 and just stop there?
More details please
i just unplugged my oxygen sensors but still the same problem, my exhaust smells fine dosnt seem to be running rich or lean, the car has 130,000 miles and the engine was redone at about 80,000 im not sure about the rental thing it's just a guess. once it reaches 4500 it just stays there back firing but on the way up to 4500 it drives just fine. im going to try and clean my maf sensor. and im not sure i understand about the crystal? where is this crystal located? im going to try and fix the video issue
see if this works
http://s978.photobucket.com/albums/ae262/luisbaja/?action=view&current=DSCI0062.mp4
 
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