Heated O2 Sensor Diliema - Help

**Cartrax** · 10-03-11, 08:10 PM

Just installed a new heated O2 sensor. Issue is it pushes a flat 450 mv with the car ("84 Vette) running hot. No short in O2 ECM connection and I bench tested the O2 sensor it passed. Also bench tested the heater - applied some juice and got heat. On the car I doubled checked the hot wire to the heater - gets 12V on ignition. Sensor is just past the long tube header collector on the driver's side.So - I'm stuck in open loop, can't tune it, and it's getting embarasssingly horrible mileage. Anybody have any trouble shooting suggestions?

**Hib Halverson** · 10-03-11, 08:13 PM

Have you checked the O2S heater ground??

Also, forget the heater for a minute...what happens when the engine is at operating temp and you put a load on the engine for a while, like up a long hill in 3rd gear....does the sensor output change at all?

Lastly, when you're looking at the O2S output while driving, are you looking at a DMM you've got connected direct to the sensor, or are you looking serial data from the DLC?

**Cartrax** · 10-04-11, 08:29 AM

Originally Posted by Hib Halverson

Have you checked the O2S heater ground??

Also, forget the heater for a minute...what happens when the engine is at operating temp and you put a load on the engine for a while, like up a long hill in 3rd gear....does the sensor output change at all?

Lastly, when you're looking at the O2S output while driving, are you looking at a DMM you've got connected direct to the sensor, or are you looking serial data from the DLC?

Thanks for the input will follow through and respond. May have one problem - not a bunch of hills here in Chicagoland will have to search for one.

Output read from EBL WUD display program connected to ECM. After re-install I'll check it with a direct hook-up that is if the grounds check out doesn't resolve the problem.

**Hib Halverson** · 10-04-11, 10:22 AM

Yeah...not many hills in Windy.

What you want to do is get the sensor hot. You also can do that with successive runs accelerating from 50-80. Head out of town for a ways on some highway in a Sunday morning and let fly with several passes. Even with the heater not working, once the sensor gets hot, it ought to start outputting data.

But first, check the heater ground.

**Cartrax** · 10-04-11, 12:24 PM

Think I just found something. Did sort of a bench test with O2S heater wired to the car but not attached to the pipe. I heated the sensor with the ignition off using a propane torch and got the swing in voltage that indicates a good sensor but as soon I turned on the ignition (activating the heater) the reading went flat. Moving the torch on and off the sensor per the bench test procedure showed little to no voltage movement (heater on). Something funky with the O2S heater appears to be preventing correct operation. Gonna try another sensor.

**Cartrax** · 10-04-11, 06:42 PM

Well um, that was not the problem.

So... I checked the grounds -
1. At the ECM connector pin 15, O2S Ground, for continuity to a ground point -it's there.
2. O2S body to ground - yep
3. O2S heater ground - also ok

Alright, let's install the O2S and do a direct hook up to the volt meter engine running hot. Did that and got a constant ~650 mv. What does that mean? Edit - found out this means I'm running rich and the O2S is probably working but not talking to the ECM or the ECM is hosed. That still sound like a bad ground – what other ground is there?

This is starting to wear me down a bit. Oh yeah forgot - EBL WUD still reads 450mv while direct reads 650mv.

Another edit - OK - next test - get engine to op temp, shut off, and quickly take a reading from the ecm female pins (O2S and O2S ground) if I get ~650mv I know the ecm is hosed, if I get 450mv (or no reading) we have a fault, no?- this should work ? Hey, what do I know maybe I'll just keep buying O2 Sensors...

BTW - Have an extra heated O2S if anyone needs one - guaranteed great price.

**Cartrax** · 10-10-11, 07:51 AM

Update - fault found in ECM. Fix in process.

**Cartrax** · 10-19-11, 05:40 PM

ECM back with fix and installed. Still a long way from where I want to be but I'm getting closed loop, the O2S and ECM are dancing, and she's running more civil than ever.

**terry82** · 10-20-11, 07:59 PM

good job .let us know what else you do to make it run right.

**Cartrax** · 10-29-11, 05:41 PM

Originally Posted by terry82

good job .let us know what else you do to make it run right.

Update - Playing with some of the basics right now. (Whew - long post eh?)

Timing finally tweaked after wasting a day looking for the EST connection (the "tan wire" actually has a black stripe on it). Found the timing at ~ 20 BTDC so I adjusted to ~ 10.

Checked FP - at 15 lbs.

Did the feeler gauge test on the throttle plates for a rough sync - they were at a perfect .0015. Assume the guys at the shop did that - maybe DCS set "em they bored "em to 2". Manometer alignment put off for some future time...

Next checked IAC's. They were loose I could untighted "em with my hand. Pulled "em, sprayed the nose and the empty TBI IAC port w/carb clnr. Made sure they were not extended further than 1 1/8", fabbed a washer and reassembled at 13 lbs torque.

Then looked at the TPS, jeez it only had one screw - spent the next two days trying to find a screw that would fit and ended up buying a new TPS. Got an OK buy from Rock Auto <$30 delivered. Fabbed a test connection see pic (hot glue, spine nails, and a hacked O2S connector) and set it at .53 volts.

OK time for a test drive. Results - running a little better, idle down from ~1,100 to a very jumpy 525 to 620 and it's killing at stop in gear about 60% of the time. Also feels flat, engine seems to labor and not know what to do with a quick punch on the pedal. Back home pop the hood - forgot to reconnect the EST - dumb schitck!

Back on the road - no more killing, idles a little rough but much better ~575 to ~ 625+. Handling the pedal punch just a bit better but still seems to labor way too much - it just ain't running efficiently yet. I guess have to do some VE learns - wish I knew how. Also told I need to watch the AFR closely. Don't even know if I can do that with the set up I have. Will keep reading -

If you'd like to jump in and suggest some next things to do – great! (BTW soon ... not a lot of nice test drive days left up here in the arctic. So I'll be shutting down the tuning and working the interior shortly).

Thanks.

BTW this is what I have - 355, 9.72:1, Renegade (of course), CAM (224/224 .450/.460 @.05 114 LSA), TBI's to 2" by DCS, Hammed 8746 w/EBL, True Duals, Hi Flow Muflrs

**terry82** · 10-29-11, 07:51 PM

since you messed with the iac,your computer may have to relearn again.so if its running better now it should run alot better after the computer relearns what it needs to .on the throttle bodys i use paper to drag between the body and the flapper to get me close .it works but it does not sound as good as using a mano meter.i have no idea why the tps screws are such a off size .i all so had trouble finding them.keep up the good work and keep us posted.