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Mazda Premacy 2001 - rough idle/oxygen sensor codes


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Underdog01
New User

Aug 17, 2021, 12:31 AM

Post #1 of 6 (552 views)
Mazda Premacy 2001 - rough idle/oxygen sensor codes Sign In

Hello, I just changed my timing belt and changed the oil pan gasket (needed to remove the exhaust to get the oil pan off). Once I was done I decided to fire it up with the exhaust still off (oxygen sensor was also unplugged) to hear the loud exhaust and see it it was running right. I ran it for about a minute and then turned it off. I started it up again and did the same but the idle was rough and it stalled. I put the exhaust and sensor back in and buttoned everything up and started it again, still rough idle and stalling when put in gear. This car has the old Mazda diagnostic port in the engine bay and no CEL so you need to do the paper clip and led thing to get the codes out. I got 15&23 which are oxygen sensor no activity. Iterated the sensor and it’s fine, but I think the ecu has flipped into ‘safe mode’ and turned off the sensor. I tried disconnecting the battery and draining the ecu of power/ unplugging the ecu but I can’t seem to reset its memory. I went for two drives of about 10km each and the car is fine when the revs are above 2000 but not much power. If I come to a stop it stalls. I thought the ecu would realise the sensor is working again and start working again but no. Any help is appreciated


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 17, 2021, 2:30 AM

Post #2 of 6 (545 views)
Re: Mazda Premacy 2001 - rough idle/oxygen sensor codes Sign In

I don't think this version was sold to the US where this site is based.
Still, with that much invasive work on such an old car IDK how well wires and plugs fared for two jobs at once? 1st would be go back and check your work, wiring especially as it gets brittle or busts plus with oil pan check for pinched wire.
You've unplugged the O2 sensor and run it who know what perhaps flames or junk did what too + did anything get in open exhaust pipe how you did that or possible?
You can't clear codes and it's right back and behaving like a non working O2 sensor so the issue is there in that circuit.
> Should have asked up top what it ran like about timing belt BEFORE you did that or just as a routine by miles and time?


T



Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 17, 2021, 4:22 AM

Post #3 of 6 (530 views)
Re: Mazda Premacy 2001 - rough idle/oxygen sensor codes Sign In

You admitted you ran the engine with the 0/2 disconnected so there is no mystery why the code was set.
This car is a 2001. It should have an OBD2 connector and you will need to use a scan tool to reset the codes.

Running it with open exhaust probably dislodged some large chunks of carbon that may have shorted out a spark plug. You will have to locate the misfiring cylinder and see what is wrong with it.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Underdog01
New User

Aug 17, 2021, 4:32 AM

Post #4 of 6 (526 views)
Re: Mazda Premacy 2001 - rough idle/oxygen sensor codes Sign In

It does not have a 16 pin obd2 it has a mazda 17 pin (google has images) and its in the engine bay. I get the feeling that the ecu might be obd2 but the standard interface was not being put in yet becuase obd1 systems should be easy to clear whereas obd2 require the scan tool to clear codes. Spark plugs are all good, to clarify the exaust manifold was still on its the lower pipe under the car that was removed and the o2 sensor goes into that pipe. I will check the wiring tomorrow and hopefully I fid a fault there. There was nothing wrong before the service, I triple checked the timing before putting the covers. I read on some forums that you have to drive around with the car in its limping state (some say a couple miles others say around 30 engine cycles) before the ecu recognises but i think this is kinda riduculus.
Cheers


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 17, 2021, 4:48 AM

Post #5 of 6 (520 views)
Re: Mazda Premacy 2001 - rough idle/oxygen sensor codes Sign In

The rules may be different where you are but here in the US it was mandated to have that plug from 96 on.

I don't know what having the manifold attached has to do with anything. You had the lower pipe removed. That removed all exhaust backpressure.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 17, 2021, 4:56 AM

Post #6 of 6 (516 views)
Re: Mazda Premacy 2001 - rough idle/oxygen sensor codes Sign In

I can't say on the DLC but Hammer is right - the backpressure removed ran OK but OP said only a minute. Deserves checking excessive backpressure IMO,

T







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