Hello All-

I am having an issue with the truck going out of closed loop and into open loop ~10 seconds after letting off the throttle.
I have a snap on Ethos scan tool.
coolant temp is 190
O2 sensor is jumping from .1 to .8 while in closed loop, then a steady .8 when it kick back to open loop
O2 cross counts in closed loop ~200
New 3 wire heated o2 sensor (upgraded from single wire)
tps .54 at idle

What could cause it to jump out of open loop!
All I have to do is barely bump the throttle and it immediately goes back into closed loop, 10 seconds later back into open loop.

Any help appreciated!

New:
spark plugs
spark plug wires
cap and rotor
ignition module
CTS
O2 sensor
New TBI with new IAC, TPS, EGR
TBI set correctly to 650rpm per procedure
New Cat

 

I did reset the IAC as well.

 

Which vehicle and engine are you referring to? You list 4 vehicles in your profile but don’t provide engine or drive train info. Please state year, truck, engine, auto or manual and with or without 4x4.

Are there anti-foulers installed?

Closed loop is based on coolant temp, engine run time and O2 sensor temp. The O2 sensor specifically has to reach and maintain its own operating temperature (generally about 600*F) before it can accurately read the oxygen content in the exhaust which is why heated oxygen sensors are standard for OBD2 systems.

I’m curious how you went about upgrading to a 3 wire sensor if it was originally equipped with a single wire.

 

Vehicle is a 1992 K3500 Dually 7.4L TBI 4l80E 4X4.

No anti-foulers installed.

I installed the 3 wire heated O2 sensor to help keep the O2 sensor above 600F and to make sure O2 sensor cooling at idle was not the the cause of reverting to open loop.

I took the truck out on a 20 mile drive and then come to a stop...~10 seconds later it kicks back to open loop.....I gently tap the pedal and it goes back into closed loop at ~10 seconds......

The snap on tool reads the engine temp at 190-196deg , so I would think the CTS is at closed loop temp requirement.
The O2 sensor is AC Delco AFS74 and it seems to be operating correctly.

What does that leave......The MAP sensor..? Anything else?

What are the correct values/voltage range for the MAP sensor? (MAP sensor is new NAPA echelin).

Thanks for any help!

 

The hot idle is at ~850-900 RPM. The target idle is 750.
Idle is a little rough,but not bad.

 

I took the part number off the new TBI 17087021,
This TBI is for a 1987 7.4L (older style in the image below.

The correct TBI is 17093049.





Does anybody know if this would cause the issue I am having?
I know the older style has a different TPS sensor style, not sure about the IAC.
Would the older style sensors have different values than the new style?



1


17087021

 

Your tool should provide the oxygen sensor voltages. You may have installed a 3 wire sensor , but if the ECM is not designed to consider that O2 temp , I believe you wasted your time.
There is something else going on, you verified all the engine temp requirements, but we don't know what is going on with the O2 sensor.
There are usually 3 requirements to get into close loop, Time from start up, O2 temp, and coolant temp. Some manufacturers even require miles driven.

You seem to have covered the coolant side , but we don't know about the O2 temp and voltages.

 

What I mean is how did you wire in the control circuit for the o2 sensor heater?

You can spend all kinds of time looking at everything else as a reason for this issue, but here’s an excerpt straight out of the GM service manual….




It goes on to say that the 3 wire sensors are only used on the 4.3 engines, so the implication is the other engines would be relying on a calculated o2 sensor temp based on engine run time and coolant temp.

It’s possible the attempt to upgrade to the 3 wire sensor is actually affecting the ECM’s interpretation of the sensor reading, or perhaps you mistakenly wired it incorrectly.

 

***I installed the heated oxygen sensor to keep the O2 sensor above 600F to make sure the O2 sensor cooling at idle is not the cause of the open loop issue.
The O2 heater wires are connected to a relay that provides battery power to the heater and the relay is powered by key in ON position.
This is only for debugging the open loop problem, I am sure the heater would burn out in short order if left continuously on.



I drove the truck into work this morning ~45 miles and over a mountain pass.
Here is the hot Idle data from the snap on scan tool after the drive:

RPM 875
STFT 128
LTFT 131
Base PW 1.3
Spark Advance 20 deg
O2 voltage in closed loop .1-.9V (as soon as it kicks into open loop the O2 V is .08V+
O2 Counts 242 (during driving the cross counts go from 0 and count up to 255 and then repeat, the reading at hot idle was 242)
Map 31 (kPa) (or 9Hg) snap on scanner outputs kPa
Map V 1.1
Barometer 0.99
Barometer V 4.82

The truck will initially be in closed loop at idle after coming to a complete stop or putting it in park for ~10 seconds and then it kicks back into open loop.
During the closed loop 10 second time period the O2 voltage is swinging normally .1-.9V.
Then ~10 second later it kicks into open loop and O2 V stays above .8V.
If I bump the throttle it will immediately go back into closed loop for ~10 seconds, then back to open loop.....

It seems to me that all the sensors are in the correct value range for closed loop, but I cannot figure out why it will consistently go into open loop @ idle after a 10 time interval.

If I slightly bump the gas pedal, then it immediately kicks back into closed loop.
If I am stopped and in Drive gear, wait 10 seconds for it to kick into open loop, and then let off the brake (foot off the gas pedal).....
It will immediately go back to closed loop........

So tapping the throttle or taking the foot of the brake in drive (with NO throttle applied) will kick it back into closed loop.

 

Hello and thanks for the replies!

All the scan tool sensor data is after a ~45 mile drive, which includes going over a over a mountain pass.

When I am in hot idle, the O2 sensor voltage swings from .1-.9V
As soon as ~10 seconds have passed, it kicks into open loop and the O2 V is .8-.9V.
I am watching the scan tool and the O2 operation seems normal, then it kicks into open loop after ~ 10 seconds and the O2 V are .8-.9 V.

It will immediately kick back to closed loop if I gently tap the gas pedal or if I put the truck in gear and let off the brake (no gas pedal applied).
The 10 second revert back to open loop happens every time I come to a complete stop or if I have the truck in Park.

This make no sense to me....

Regarding the three wire O2 sensor, I installed this heated O2 sensor for debug of the open loop problem.
The heater circuit is wired to a relay and receives Battery power with 12 gauge wire, the relay is powered by key On.
The O2 sensor heater circuit wires are both black.
The original ECM O2 wire is connected to the Blue O2 sensor wire.

I am using the AC Delco AFS74 O2 sensor and have tried 2 of the these, along with another brand.

If the O2 heater circuit is working and I am reading normal (.1-.9V) voltage, what could cause it to kick back to open loop?