TPI84GMC

What are the citeria that must be met for the ECM to enter closed loop? Engine operates about 185-195. O2 sensor reads about .87v anything else??? O2 not hot enough?

clf93lt1

do you have coated headers ?

BAM92

Might have to go to 3 wire o2 sensor. I am in hot climate and still had to do the heated o2 sensor thing as my car would go open loop at idle.

TPI84GMC

Uncoated full length headers with the O2 sensor in the collector. I think I am going to go to Arizona TPI in the morning and get the heated O2 sensor and try that out.

BrassRing

The FSM says the O2 Sensor will not close the circuit until it heats up to atleast 600F. If this circuit isn't closed, the engine will run in "open Loop" mode. ECM supplies 0.45 V and the O2 sensor has a voltage range from 0.1 V (rich) to ~ 1.1 V.

65Z01

How do you know the ECM is not going into Closed Loop mode??

The ECM's coolant temp sensor must show >135deg F and the O2 sensor must be hot enough and showing voltage swings between .3Vdc and .8Vdc.

If you have a scan tool and monitor engine parameters you must see periodic swings in the O2 sensor readings. If not, go to the heated sensor.

TPI84GMC

I have scanned it with a laptop and WinALDL and the voltage pretty much just stays at .85-.88 all the time. The engine temp was at full operating temp and still didnt go to closed loop. I picked up a heated O2 sensor today I'll let ya know what I find out!

65Z01

The ECM needs:
-a few mintues of time after startup
-coolant temp >135 deg F
-the O2 sensor to oscillate between .3-.8 Vdc

Since you have a scanner I assume the ECM is seeing the correct coolant temp, which leaves the O2 sensor as the problem.

BigLee

could be you just have a bad o2 sensor.

vader86

Even an uncoated header should retain enough heat to let the O2 enter closed loop, especially at those engine temps.

I think its just a bad sensor.

rick lambert

but I'd probably double check the connetions before I just ran out and replaced it, they're not expensive and at least in my experience there very easy to change.

JAKE

You could try raising the RPMs to about 2000 or so and while holding it there, monitor the Loop status. Many times engines with headers at idle won't enter closed loop when using a stock type 02.

If, at 2000 RPM or so, the system goes Closed Loop, you need to go with a heated 02.

Jake

RRT vette

The O2 sensor voltage reading should go all over the place every split second. If the voltage stays in one spot and does not move rapidly, then the sensor is likely bad or the connection/wiring to it. You will probably need a heated sensor with aftermarket headers.

Just another thought.

TPI84GMC

I installed a heated O2 sensor and now it goes into closed loop almost immedately, BUT the 02 sensor voltage stays at 1.087v!!! Now what?

TPI84GMC

Now that I start to think about it... anyone know how to properly wire a heated 3 wire o2 sensor? 3 pins a(white) b(white) c(black)?????? a(12v) b(to ecm) c(ground)?????

JAKE

The two white wires are interchangable: one goes to a switched 12 volt source that's only HOT with ignition key in the 'RUN" position. The other white wire goes to a good GROUND. Doesn't matter which white wire goes where.

The black wire splices into the wire which leads to the ECM.

Jake

JAKE

NO, that's wrong. Read my previous post.

Jake

TPI84GMC

oops... hope I didnt fry anything having it hooked up wrong... thanks alot. I'll post my results after rewiring tomorrow...