I have a 88t2, fresh Atkins Steet Port. Swaped O2 sensors. It seems I am not going into open loop, judging by my AutoMeter AFM Gauge. When in cruise mode, the gauge reads rich by two to three led's. I am reading a few posts on it, but a fresh thread would be helpful for me.

Could the engine not warming up to temp be the cause?
I read about a sensor on the bottom of the rad on the drivers side?

Engine stays high in idle 1500 for a very long period. I shut the car down, restart it, the idle drops to 750. Then it fluxuates here and there.

Anyhow, thank you ahead of time for your input!
Chris

 

You mean CLOSED loop

 

ohhhh, my bad!

 

Closed loop will look unique on the A/F gauge- the needle (or LEDs) should bounce back & forth precisely at the stoich point about 4 to 5 times a second.

Open loop bounces will not move nearly as fast...

 

Sorry to alter subject slightly, but what exactly is open/closed loop? I was running my car with no thermostat for about 5 days and the repair manual mentioned that it might get stuck in open loop. If anyone knows where I can read about this, or if there is a short answer please direct me. =)

 

Closed loop is when the ECU uses the O2 sensor's voltage input to precisely schedule fuel at the "perfect" air/fuel ratio for optimum fuel economy. Only happens in cruise, a couple of seconds after the throttle has been stabilized.

Open loop is everything else- the ECU schedules fuel using the sensor inputs (AFM, TPS, temp sensors, etc). During this time the ECU will attempt to schedule around stoich (or so it appears to me), but the fuel flow changes are not accurate, and the ratio "bounces" wildly around stoich...

 

If this was happening to you, whats steps would you take to diagnose it?

 

Hm... I have yet to see the stock ECU do anything but insanely rich in open loop mode. It pegs the O2 sensor full rich and doesn't go anywhere unless you're in closed throttle fuel cut.

-=Russ=-

 

Verify whether or not it's a guage problem by connecting a voltmeter to the O2 sensor pin at the ECU. Stoichiometric is ~0.5V, above that is rich, below is lean.

Yes, the ECU won't go into closed-loop when the engine's cold. If your engine isn't reaching normal temps, get a new thermostat from Mazda.

That temp swtich won't have anything to do with this (it's emissions related), but the ECU thermosensor on the back of the water pump might. Check it as per the instructions in the FSM.

Then something is very wrong with either your car or your A/F gauge, because that is not normal.

 

Hrm. Well, I just have a narrowband, so "insanely rich" doesn't really mean much other than "richer than stoich", but I've never seen it go lean in open loop mode unless I'm totally off the throttle.

I'm also just testing with a voltmeter, so it's not the most precise thing (I can't constantly watch it while driving). I'm planning to get a wideband here at some point, so I'll know better then.

-=Russ=-

 

Hook up a good meter with a 1-volt scale to the ECU's O2 sensor pin, Russ. NOT a digital one- that'll just drive you crazy trying to interpret all the flashing digits, lol...

Keep it connected, sit the meter in the pass seat, and go for a drive. I've spent DAYS with it hooked up back when I was troubleshooting my "intermittent hesitation on bumps" thingy.

The only "insanely rich" outputs I ever got were at idle...

The ECU TRIES to run at stoich throughout throttle transitions- you can tell if you watch it long enough. It never quite gets anywhere near the beautiful precision of the closed loop, though. That's a truly amazing thing to watch- a meter bouncing between .4 and .5v several times a second as you're toting down the freeway.

 

I actually had the same problem. It turned out that my tailpipe section of my exhaust was hitting the subframe causing it to (overground?) i adjusted the hangers so the pipe would clear and now my a/f guage reads stoich almost all of the time unless im under moderate to high boost.

 

^^^^^^^^^^^^^^^ Very interesting.