I worked in the engine bay this week tightening down some bolts and reconnected a vacuum hose that I found loose between the firewall and the dynamic chamber and my engine has never run smoother, quieter, or at a steady 800 rpms at idle. But, I have a check engine light that comes on and it is indicating codes 15, 17, and 31. I know that the first two are indicating a problem with the O2 sensor and the 31 is for the relief solenoid. My question is why does my engine run so much better now? Can anyone tell me what is going on?

Its never run bad after the rebuild last fall but it is running so much better now. Should I worry about the engine check light or check what it is indicating? Would a street ported engine run rougher because of the ECU's standard programming?

 

I was always tought "dont fix something that isnt broke"

if it runs good then run it and jerk that bulb out (IMO)

 

Bad advice for a CES light.

Replace your O2 sensor with a Bosch single wire generico, they're like 20 bucks, what can it hurt? As for the relief solenoid, take a peek through the FSM/Haynes and see what you can find. I have no idea how to test either of them, so you're on your own there. But remember, your CES light, low coolant light, and low oil pressure lights are the only thing between a nearly blown engine and a completely toasted one.

 

You probably had a vac leak with that hose off, which is why it's running so much better. Fix the issues and be on your merry way. Good luck!

 

^^ Reminds me, you were right about my vac leak. Was on the two big nipples on the intake tube. I had just circled a big hose between them to block them off. I used some clamps on them a couple days ago, perfect 800rpm idle. I was like... NO FLIPPIN WAY!!?

Then my headlight fusible link blew and all hell broke loose and i almost started my car on fire, lol...

Now i have to search for a fried wire harness somewhere.

Oh well, at least she has an idle (awesome!!) just cant drive at ngiht.

 

Haha, it's always vac leaks!

 

I agree that if it ain't broke don't break it. I will check the vacuum hoses and make sure all is good and make sure all the electrical connections for the oxygen sensor and solenoids are good. Anyone have any other ideas?

 

Any other ideas?

 

Reset the codes and see if they come back.

 

I got under the hood Sunday afternoon and checked the O2 sensor. Found that the wire from the sensor to the wiring harness was hanging together by only a couple of strands and this wire contained two connections from past replacements, one of which was very loose.

I replaced the wire and soldered the new wire to the wiring harness connection and crimped a female spade connector to the other end. I crimped a male connector about 8 inches north of the O2 sensor. When I next have to replace the sensor I can disconnect the wire and add a male connector to the new sensor wire.

I purged the codes and drove it for about 30 minutes and NO ENGINE LIGHT ! Car is still running great and idling so smooth.

 

Don't forget that O2 sensor wire is supposed to be shielded, GTUser (that might be that 2nd splice you were talking about)...If you still have the stock connector at the back of the engine, Bosch makes a direct plug-in unit for us...Post-rebuild is like a born-again car, I'm enjoying mine more & more too...

 

You're right. The part of the cable that comes from the wiring harness is shielded but the single wire from the O2 sensor is single coated and is definitely not shielded and it is supposed to be an OEM sensor.

I'll check out the local Mazda dealership to see what they are selling. Thanks for the feedback.

 

My replacement (generic) sensor was not sheilded either :O

 

I've heard from several people that the sheilding isn't needed. I don't know how much truth there is to that. Sheilding is only needed for VERY low level signals...anyone know the level coming off of the O2 sensor?

-Joe