2007 Mazda RX8 need help with power loss

  • 25 POSTS
  • 2007 MAZDA RX8
  • 43,000 MILES

So while driving the car it stopped running due to the catalyist convertor (I could see it was glowing) waited a little bit and putted home about 10 miles. We gutted the cat out and now it has a major power loss you have to floor it and it will barely get to 2500 rpm but after 2500 or 3000 rpms it starts to pick up speed until you come to a stop it wants to die and also now it has codes po300 random multi misfire po506 idel contorl system lower then expected p2109 tps sensor throttle/pedal senor min stop performance po301cylinder 1 misfire I cleared the codes and need to drive it and see what comes back but I wont be able to do the until saturday but just wondering if you have any ideas that could help me saturday I was going to clean the MAF sensor and srive it to see if that would help

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Thursday, November 14th, 2013 AT 8:29 PM

1 Reply

  • 29,768 POSTS

You're setting yourself up for a pile of problems by not getting a professional involved with this problem. First of all, the glowing converter is proof there's some other problem. You didn't fix that problem by destroying the converter. Code 300 is a random cylinder misfire. You need to determine the cause of that, but as an educated guess, it's spark-related. That results in too much unburned raw fuel AND unburned oxygen going into the exhaust system. It's the catalytic converter's job to burn those hydrocarbons, and too much fuel is what overheats it and causes it to glow. At that point the catalyst will melt and turn into a glob the exhaust gases can't pass through. Before it gets to that point, the Check Engine light should have been flashing. That means stop the engine right away to prevent that damage to the converter.

The next problem you created is on '96 and newer cars, there's a second oxygen sensor after the converter that monitors its efficiency. With no catalyst to change the composition of the exhaust gas, the front and rear O2 sensors will read exactly the same. That's what the Engine Computer looks at to tell if the converter is doing its job. It is going to set a fault code related to the converter's efficiency and it will turn on the Check Engine light. There's two problems related to the light being on. First of all, a totally unrelated problem could occur that is relatively minor, but if ignored, could turn into a very expensive one. You'll never know when that happens because the Check Engine light will already be on and you'll be ignoring it.

The second problem is to set those diagnostic fault codes, the Engine Computer is constantly running a number of self-tests. There is always a long list of conditions that must be met to set a fault code, and one of them is that certain other codes can't already be set. Those relate to things the computer uses for reference or comparison. As an example, the computer knows that after the engine has been off for at least six hours, the coolant temperature sensor and the intake air temperature sensor had better be reading the same temperature. If they are not, there are various strategies it uses to figure out which one is wrong. However, if a code is set for the coolant temperature sensor, that can't be used for comparison to the intake air temperature sensor. That sensor could report it's 80 degrees, (from under-hood temperatures), when it's really 20 degrees, but no additional code will be set. Try and diagnose the cause of hard starting in cold weather or a severe hesitation and stumble in cold weather without that code to give some guidance.

It's good that you recorded the codes already. You didn't say which engine you have so I don't know if you have individual ignition coils, but I'd start with spark plugs, and wires if you have them. If you have a code for a single cylinder misfire and you have coil-on-plug ignition system, switch the coil from the misfiring cylinder with one that isn't misfiring, erase the fault codes, then see if a code sets for the cylinder you moved the suspect coil to.

The first thing you need to do is solve the misfire. Next is to replace the catalytic converter. There was a 10 percent chance it was bad before you destroyed it. There's a 100 percent chance it's bad now.

The mass air flow sensor won't cause a misfire. All it does is measure the weight of the air going into the engine so the computer can use that in its calculations for fuel metering. Dirt on the sensing element will insulate it and cause it to read less air than what's actually going into the engine. The computer will command an insufficient amount of fuel for all of the cylinders for the engine to run properly. You have too much fuel, as evidenced by the overheating converter.

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Friday, November 15th, 2013 AT 12:14 AM

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