..............

 

Vacuum leak.

 

(Not sure what happened to my whole post up above? It shows I edited it, but I didnt. Both of my daughters used my computer over the weekend. Ill check with them and see if they accidentally did it.)

Anyways, ive got it partially figured out. My fuel pressure regulator was shot. I pulled the vacuum line on it, and it shot fuel out at me. I bought a new one and replaced that a few days ago. It is definitely running better. The starts have been normal since and it hasnt stumbled anymore. But it threw a P0420 code, catalyst efficiency below threshold. Now I gotta dig into that one and try to figure it out. I did search for vacuum leaks, but didnt find any at all. So now I guess I need to check my O2 sensors and my cat somehow.

Also noticed this morning when I went in for physical therapy, that it was idling pretty high, and didnt want to idle down til it was completely warmed up. It was idling at around 2200 rpms? What could be causing this. This is new for sure. Unless im missing a vacuum leak somehow?

 

Watched a few videos online trying to diagnose bad cat. Went and bought an OBD2 scanner, which I needed anyways. Checked downstream voltage and it was all over the place. Everything I read and watched said the downstream voltage should remain close to a steady .5v. Mine was reading all over from about .01 to .9v. I know I need to do more checks, but from what I've found so far it's definitely pointing to a bad cat.

 

Good Morning!
Nice job on the fuel pressure regulator.
P0420 is most likely indicating a shot catalytic converter. I advise you not spending money on O2 sensors.
You can try this:


Also use this sticky for the Protege. Your 626 is pretty much the same: https://www.mazdaforum.com/forum/maz...g%C3%A9-31136/

 

I appreciate the response. I watched that video yesterday and was going to give it a shot. Thought about trying the thinner first, but then watched a few other videos of people trying it, and it not doing any good. From the OBD scanner readings, my o2 sensors seem to be working fine, other than the downstream readings oscillating just as much as the upstream when held at about 2000 rpm heated up. I check my wifes Jeep, with a known bad cat and it was reading the same as my 626. Then checked my truck that has given me no issues, and that reading stayed pretty steady with only mild fluctuations. Im guessing that since that regulator was feeding excess fuel into the intake through the vacuum, it probably toasted the cat. This car is new to me, only had it a couple weeks now, so just trying to get it lined out. I might try to go ahead and remove the cat this weekend and look it over. I know the bolts are all going to snap off though when I do.

(Im a wrench turner, havent done much as far as using a scan tool to diagnose things. Where would one find all the factory parameters, like the fuel trim readings, etc, so I can compare to what the scanner is showing me?)

 

Still digging, and looked at a WSM, (for a 1996, should be the same though, right) and it is saying the P0420 is for the upstream cat, the warm up converter? Does that sound correct? I was going to buy the downstream, but ill hold off for now.

 

I am only familiar with the Protege. It only has 1 cat. The second thing that looks like a cat is only a resonator.
The Scotty lacquer thinner (NOT PAINT THINNER!) method only works if there is dirt that can be removed with lacquer thinner. So it is a shot in the dark.
I think you are right that the cat was damaged by excess fuel. It may actually have molten the core. This should have been accompanied with a blinking CEL.

Our Protege had the dreaded P0420. We drove it anyway as our state does not (yet) require emissions testing.

I hope that grim_reaper or another pro help you further in your decision making.

 

I was thinking about trying cataclean. Sitting here on my lunch break reading up on it and it seems to work well. I just dont know how long that regulator was bad and how much damage it may have possibly done to the cat. From what I see on the 626, there is a warm up cat right after the exhaust manifold, then there is a regular 3 way cat just before the muffler. No o2 sensors near the downstream one.

 

Remove the cat, shine a torch in it, it should look like a fine mesh/honey comb.

Photo 1 Cat is good
Photo 2 Cat is bad