does a downpipe cause a check engine light?
 

Just picked up a new to me FD. The check engine light comes on and goes off suddenly, seems like there's no pattern. It's not with every drive either. I know that the car does not have a precat...could this be the cause?

I'd like to add that the car seems to drive perfectly...good boost, smooth transmission, very quiet, no rattling or shaking

No it wont cause one by itself.
Could have screwed something up with the o2 sensor.
Pull the code per the manual and see what it comes up with.

another CA car and you say it comes on randomly? Once again my money is on thats its the egr.

As the previous poster said check the engine codes. Its real simple and it will take 5 minutes, just do a search on how to do it.

some downpipes don't have an O2 sensor bung. which can cause a check engine light if the knucklehead who installed it didn't place the O2 sensor anywhere.

Information on Stored Fault Codes
 

Thank you for this guide. It has been the most clear so far.

I got a 15 and 16

15 Oxygen Sensor - <0.55 volts for 25 secs in closed loop zone
16 EGR Function Sensor - open or short circuit

Would one just go about changing these? Should I change the O2 sensor on both the downpipe and the main cat?

Same with EGR? Or does it represent another problem?

There is only one o2 sensor that mounted on the precat or in your case should be on the downpipe or somewhere. The egr can be replaced but I had the same issue with it so I just made up a circuit to defeat it.

Fortunately our o2 sensors are inexpensive. Can't remember who for sure, but IIRC there was a recent post by a veteran owner and Cali resident who was adamant you didn't need the egr to pass emissions and it could be deleted.

yea, just need to put in a small circuit to make sure the light doesnt come on if you diconnect the egr

yeah the EGR valve doesn't do anything except keep the CEL off....

the EGR was only put on the car to keep the tree hugging california hippies off their asses so they would be compliant with the necessary equipment regulations that the state required in order to put the cars on the market.

of course mazda did, and made the system virtually non-functional to spite the tree huggers.

teheehee

man I am liking this car more and more every day!

here was my post on one possible solution

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/egr-code-16-repair-experience-857507/

that sounds like the best solution but I do not have much experience in that kind of thing...but willing to try!! any illustrations?

I got the integrated circuit from mouser and the small pc board and case from radio shack. If you can solder wires its easy. There are 4 wires on the stock ECU plug that you need to tap into.
1B and 40 for the coil/4D and 3J for the contact. They wire directly to the 4 pins on the IC chip, no other parts are needed.

I will see if someone locally can help me with that. I would hate to fry my ECU on accident

Where is a good source for o2 sensors, fuel filters, and the like?

mazdatrix or ray crowe

hmm seems a little pricy still at around $75. can any aftermarket one be used? I do have an aftermarket downpipe after all...

you can go aftermarket with a generic type, but you will need to change out the connector and splice the wires. A rx7 specific aftermarket or Mazda part will be plug and play.

check here: universal denso $16, rx7 specific $44

http://www.densoproducts.com/resultsApp.asp

thank you for the link, bill. you've been really helpful.

Here is a circuit diagram for the "EGR delete" which keeps the CEL light off after the EGR valve is deleted (i.e. after EGR sensor connector is disconnected). Mine is mounted next to the PCME (ECU) behind the right-side cabin panel. This circuit is just a phase inverter, i.e. when PCME terminal 4O is "high," terminal 3J is "low." The same function can be provided with a switching transistor if you like.