I was just wondering if an O2 sensor can be bad without the check engine light coming on? Cause my truck is running like a douche bag. and i cant figure it out its also running very rich and is ridiculously bad on gas im only getting around 10 mpg, plugs, wires, rotor and filter are all new took apart the EFI and cleaned it checked my tps and its fine. Dont know where else to look guys any ideas would be awsome.

 

What year and model and engine is the truck?

 

i swapped in an 87 22re in january

 

the only thing is that the wire harness was for an automatic and my truck is manual so i had to jumper the neutral switch

 

Yes it definatly can, I had an 88 in the shop that ran like crap and I replaced the O2 sensor and the problem was gone. Also check your coolant temp sensor on the front of the manifold. Good luck let us know how you make out.

 

Have you tried pulling codes? it could have some stored without setting the light.

 

If the 02 sensor is bad it can greatly effect your gas mileage. The computer uses the 02 sensor to set the air/fuel ratio, and a bad 02 sensor doesn`t always throw a code.

 

yeah i know theres something wrong with the thermostat its brand new but the the valve that opens and closes it is stuck cause the motor is either really hot or wont stay warm

 

i dont know anyone with an obd1 code reader but ill go get an o2 sensor tomorrow hopefully theyll have one if not ill have to wait till next week but illl let you guys know as soon as i change it

 

When you get a new 02 sensor DO NOT get a Bosch 02 sensor, they don`t work well in toyota engines, get a Denso 02 sensor, there an OEM replacement.

 

If you have a bad thermostat replace it with a genuine Toyota one when you replace it, it will save you a lot of headaches.

 

i knew about the sensor but i just put a normal thermostat in i didnt replace it with a genuine one

 

I don't know if you have anything like an Autozone or Advanced auto parts around you but they will read your codes for free.

 

not in new brunswick haha you need to go to a garage and only a select few have one that works haha and they want like 70$

 

If possible get a toyota OEM replacement thermostat, it seen that they just have fewer problems.

 

k sounds good i gotta go there and order a front brake cable anyway

 

You don't need a code reader... Just a paper clip to pull your codes. There is a test port under your hood, its the same port you have to jump in order to set your timing. Jump the port and turn your key to on, counting the blinking lights and refer to the code chart.

Roger brown has some good information on doing this on his website.

 

k ill try that

 

the only sensor i could get other then a bosch was the NGK O2 sensor should come in next week

 

I ordered a 4 wire Denso O2 sensor through amazon, it it didn't take long to arrive in the mail.