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Discussion Starter #1
I have a 96 Tacoma 5 speed with the 2.4l just over 200,000 miles on it. Most of the time it runs and drives great. Then bam all of a sudden it starts running like crap with this weird misfire. It's like it goes into limp mode or something. It typically only does it after it's up to operating temp but besides that no rhyme or reason to when or why. All last week it didnt do it once now in the past night and a half it's done it three times. Only thing that has changed since that is I got a bunch if stuff behind my seat right now where last week i didn't have but two things maybe. I noticed one time while it was running bad I could smell a ton of gas when I stopped at a stop sign. It also messes with my ecu because I have a code reader that has a tach gauge and a bunch if stuff I use while driving but as soon as this problem starts it disconnects from the ecu. I've tried multiple code readers while it was running bad and not one would connect. the only code that the truck has on it currently is p0304 I believe it is. It's a catalyst converter code because the previous owner cut it out. While driving it when it starts this problem the less gas I give it the faster it accelerates, the more I push the gas it bogs down hard. And in every gear you can only go so far in the rpm range and it's like it hits a wall. The last thing that is consistent with this problem is that my a/c stops blowing cold like its kicked the compressor off. The only thing I have being able to come up with that it could be is the up stream o2 sensor going bad or wires that are cracked/arcing maybe. Because I was told that o2 sensor deals with the fuel tanks on this model tacoma. Thank you for any and all comments in advance. I will be checking this thread multiple times a day. If anyone needs more info feel free to ask but that's about all I can think of right now.
 

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Mambeau / Admin
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(1) Welcome to CT!

(2) P0304 is not a cat-related code. It's a misfire code for Cylinder #4. Here (attached) is the misfire code description with a listing of possible causes. This doesn't really narrow it down, because there are so many things that can cause a misfire.

(3) The ECM disconnecting you described is worrisome. It may be that the ECM itself is the problem. On the other hand, it might be a clue that something in the wiring to / from the ECM has a fault.

(4) If I understand you correctly the cat has been removed or hollowed out. This should be triggering a whole bunch of codes, because the ECM would detect no difference between the upstream and downstream O2 sensor readings. If you're not getting a bunch of codes it suggests something's amiss with the ECM or the circuit to the connection for a code reader (the DLC3). Are you sure the two O2 sensors are even connected?

(5) If it only happens once the engine is warmed up, two possible faults come to mind. First ... The ECM can't adjust the air / fuel trim correctly because the ECT (Engine Coolant Temp) sensor is faulty or the wiring to / from it is bad. Second ... You've got a short or loose wiring connection once something gets warm and expands.

(6) The behavior you describe sounds a lot like the ECM is throwing the engine into fail-safe mode. However, it's so screwed up I'm not sure it's as simple as a fail-safe condition. You should still be getting multiple codes displayed even if the engine is in fail-safe mode.

(7) Without additional clues I have no idea whether or how the A/C might be involved. There's a signal sent to the ECM when the A/C magnetic clutch is engaged (or supposed to be engaged). If the ECM thinks the A/C is engaged when it isn't it may be trying to increase the idle speed to account for a load that isn't there.
 

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Discussion Starter #3
Thank you for the speedy reply as well as the detail you went into. I'm going to try and make sure there's no obvious wires broke or anything like that. But I do know both o2 sensor are connected. How could I check to see if it is the ecm and if it is will any ecm from a first gen 2.4l work? I'm going to try and figure something out and take all the stuff I out in there out to see if that helps
 

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Mambeau / Admin
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My advice is to leave the ECM for last. Check everything else first, before starting to believe it's the ECM itself.
 

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Mambeau / Admin
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Oh, well in that case ... If the sensors and their wiring weren't damaged it's the hollowed-out catalytic converter.

Here (attached) is the relevant code description.
 

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Discussion Starter #7
So that would make it do it randomly?? Because when my CEL is on it doesn't always misfire. Also the CEL will cut on and off, sometimes rapidly almost like its flashing. At times it stays off for a while then other not so long. Could that be a sign of a failing com as well??
 

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Mambeau / Admin
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If the only code being thrown is P0420 it's a matter of cat efficiency. If the cat has been disabled (i.e., it's non-functional) and the sensors are OK, the ECM is going nuts trying to tweak the air / fuel / ignition parameters. If there's also a problem with the sensors or their wiring it would be worse - perhaps to the point of screwing the ECM's operation up to the point of causing misfires.

If there are actually other codes being thrown, it's anybody's guess how many faults you've got to deal with.
 
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