So I just bought myself a 1996 toyota tacoma with the 2.7 liter 3rz a few weeks back and already I'm having some weird issues. My check engine light came on three days after buying the truck I'm assuming the dealer i bought it from was just resetting the computer on the tacoma whenever the check light came on because it happened almost immediately after I bought it. Anyway got the codes read at autozone and its the p0420 code catalytic deffeciency and the p0171 code which is the lean air fuel mixture. Whats real strange about all this is after driving the truck for about three days Il go to fire it up and the engine will not start no matter how long I crank it over for. I either have to reset the computer on the engine by taking off the positive cable on my battery or pull a spark plug crank it over and the replace the plug and it will start up and run fine. Im truly baffled by this I dont have a clue what it could be. Im assuming its probably sensor related because whenever I reset the computer the truck will run great for about three days and then quit on me and will not fire up to save its life. I would think that if this was a mechanical issue then the symptoms would be constant instead of reoccuring after the engines ran long enough to piss off the computer and make it not want to fire up. So far I've replaced both 02 sensors trying to remedy the p0420 code which didnt work, I've replaced all four spark plugs because they were in prett bad shape, replaced my gas cap thinkin maybe my vent wasnt working, I've cleaned my air flow meter and sea foamed the engine while I was at it and still my truck will run great for a few days and then the check engine light comes back on and the vehicle will not start to save its own life until I reset the computer. Truly baffled by this one guys, I definitely need all the advice I can get here. I went ahead and ordered a new catyltic converter from lc engineering so im thinking that will clear up the p0420 code but I just dont understand how these issues would cause my truck not to run period. Even with a bad catylitic converter and a lean air fuel mixture it should it least run and drive right? Sorry about the lengthy post just trying to provide as much info as possible.

 

I could really use some input guys, any thoughts, opinions?

 

You should really spend the money to buy your own OBD II code reader so you know just what codes it is throwing.

Do you install the O2 sensors in the wrong spots were you given the wrong ones.
There are so many things that could cause these issues a step by step trouble shooting of the emission system is the only way to go

You might want to let us know where you live help could be very close

 

i know a bad maf wont let the engine start. but since your resetting the ecu every time and it starts, makes me think the maf is ok. after everything you have done, what are your current codes. also when you crank and crank and crank with nothing. hook up a scanner and see what codes you have before resetting ecu

 

Well, here's my WAG. Engine coolant temp sensor. If it is telling the ECM that motor is warm when it's cold, it will not enrich the mixture so that a cold engine will start. When you reset the ECM, it forces the ECM to start over from start-up mode and thus you get the needed rich mixture. It's like trying to start an old carb car with the choke not pulled.

Then eventually the ECM wants to go into closed loop, it's gets the wrong reading from the ECT sensor, it starts running lean, and sets the P0171--but it still runs. Turn it off, though, and it won't start from cold.

Get a live scanner that can give you coolant temp read-outs and see what you are getting.

I'd wait on the P0420 until the P0171 is resolved, because I doubt the cat efficiency test can be done correctly if the mixture is off due to bad temp readings.

 

Appreciate the input guys, toyotech I actually got my codes rechecked at autozone after I cleaned the mass air flow sensor and the p0171 code went away and the only code thats being thrown right now is the p0420. So at this point im just waiting on my catylitic converter to show up and that should remedy the the p0420 code, I've already tried replacing both 02 sensors before and after the cat and that didnt help at all it would still throw the p0420 code. I still dont know whether or not I've resolved the no engine fire up problem though I've been driving around for the last two days after cleaning the mass air flow sensor and seafoaming my truck and the tacoma hasnt died on me yet. Thats some pretty good advice about checking the coolant temperature sensor. I guess if the computer adjusts the air/fuel mixture based on what that sensor reads for warm engine and cold engine conditions it would make alot of sense that thats whats been screwing up my engine definitely something worth looking into. When you say live scanner do you mean a lazer heat temperature reader to get coolant temperatures? Also where is this coolant temperature sensor located?

 

http://www.ncttora.com/fsm/1996/SIL/.../ects/comp.pdf

http://www.ncttora.com/fsm/1996/SIL/.../ects/insp.pdf

See above for ECT location. A live scanner is one step up from a simple code reader; it plugs into the OBDII plug and does all that a reader does plus it can display and sometimes graph outputs from the various sensors, ECT, O2, RPM, ATF temp, etc. I use an ancient device called a BR-3 that connects to my laptop but there are much newer solutions available.

Here's one that I found with a quick Google, but I haven't actually used it:

http://www.myscantool.com/

I could not survive without mine--it's paid for itself many times over but I would not buy the same one now.

 

i wouldnt worry about the ECT sensor for now. seeing as you fixed the p0171. i see this lot of with dirty mafs. the p0420, i see alot with bad cat. i know the repair manual tells you to check the o2 sensor but i hardly see any issues with them when p0420 pops up. with bad o2, u usually get a o2 sensor code.

live scanner is something that lets you see what the ecu is seeing so you can better diag it without actually going to the part to test, which you usually do anyways if the scanner is showing odd data

ps: if u have anytime of aftermarket filter that needs oiling after cleaning, i see a too many that come in with these and throw a lean code due to over oiling and dirtying up the maf

 

I agree that I would not worry about the ECT now unless the P0171 comes back. I question the second statement. A solo P0420 can definitely be caused by a degraded rear O2 sensor that does not set a sensor fault code. I would always swap the rear O2 with more than 70k before getting a new cat absent physical damage, the sulfur smell, or corroboration by scanner analysis. A new rear O2 cured my P0420--it's been three years and 40K now, and the same is true for several other posters. (Not relevant for the OP since he already changed his.)

I wonder if new cats with a degraded sensor cures the P0420 code because the cat performance is much better--when all that was needed was a better performing rear sensor with the older but acceptable original cat. I'd prefer trying the cheaper solution first.

 

i have access to live data scanner so when dealing with p0420 and i can see if the front and rear o2 sensor are reading the same or different. if they real the same, it a dead cat.
only thing i have really seen go bad with o2 sensors are the heaters in them, the just burn out, a simple ohms test will tell you if its good or bad. most o2 sensor codes are due to the heater circuit of the o2 sensor. from all the codes i have pulled: i have been 1 and 1. see a cat code, replace cat, see a o2 code, replace o2. i dont just do it, i do my test but so far it has been what the code says

 

All I can say is I'm glad I service my truck myself. I hope some others who have had a new rear O2 cure a solo p0420 will chime in here.

Were you able to determine WHY all these cats died? They do not just go bad--there is usually a reason a cat dies and replacing it without finding the cause frequently leads to another dead cat.

 

did you ever figure this problem out about the not starting condition?

 

Replaced a ton of cats since I been working with Toyota. They just suck I guess or that the programming of the ecu isn't that great but if Toyota doesn't release an update to reflash the ecu than all I can do it replace the cat. I haven't had one come back for another yet. Could just be a bad cat or poor gas being used with lack of maintains