stuck in closed loop but runs like its not

[texas tough]

trims are just set to some default mapping unless in closed loop - so can’t really say anything about time in control until in closed loop

I have a 93 5.7 and have messed a bit with this but definitely not an expert like those who tune.

there are several qualifiers for getting into closed loop, time is one, temp is one, the ECM will command a change in fuel and expect to see a certain response in the O2 in a certain time, perhaps some other stuff- hard to get clear specifics but you can google around and find some info on it. If you have a tool like TunerPro you can see closed loop qualifier flags and the like.
Once in closed loop the O2 should vary between something like 0.4v to something like 0.8v As the ECM changes from trim up/down. If O2 changes too slowly, it will not stay in closed loop - google “lazy O2”

yes, the book says coolant temp sensor, time and o2 sensor. the book says to run engine over 1200 rpms for 2 minutes, after it gets to normal operating temp. I think it varies from model year to model year.. some books say the CTS will send its signal at 160f, some say 195f. some trucks have heated 02 sensor, some dont. some use 180f t stat, some 195f stat.. having specific model year tech data is critical but even that isnt always definitive.. in my service manual for instance it shows 2 different wiring diagrams for the 4.3 with the 4l60e trans,, one shows the o2 sensor gets its heater circuit power from the GAUGES fuse, and one show it gets its power from the 4X4 fuse.,. had I not stumbled across the wiring diagram that showed the power to come from the 4X4 fuse, I would still be trying to figure it out.. with the logic being, why in the hell would a two wheel drive truck have a fuse in the 4x4 FUSE SLOT.. GM should have labeled the slot for what it is for that truck, O2 sensor. from what I can see, the o2 sensor is the only circuit on that fuse. Im going to put a sticker over the 4X4 label and write o2 on it so this doesnt trip someone else up.. It had to have a fuse in the 4X4 slot from the factory, but over the years, someone likey robbed the fuse, to replace a blown AC fuse or something, and never put one back in, so the truck ran, but not great. also the truck was not throwing a code, so unless a scanner was hooked up you would never know it . they wont throw a code for the heater circuit in the O2 sensor not working,

 

[texas tough]

also it may not vary as much with the 5.7 engine platforms, but on the 4.3 trucks, there are ALOT of variables. the engines were built at 2 different plants with both plants making changes year to year. some were built at the romulus plant, some Tawanda plant.. the 4.3 gets a bad rep becuause of the many changes made over the years, that trips people up and they cant get them to run right. I knew this going in so I checked everything, by block serial numbers, and model year. it took alot of research and time, but it all worked out.

 

[Sabinoerc]

agree, hard to get exact details for specific models. My 93 5.7 has a 2 wire O2, for example.
sounds like you got it running well, congrats and enjoy!

 

[Casey916]

restoring a 93 chevy c1500 with 4.3 stock tbi engine. engine was completely rebuild as well a trans.
engine starts, idles and revs fine,, hooked my autel obd2 scanner up to check things out, NO DTCs.
measured coolant temp sensor resistance/ temp corellation and within spec.. engine had new 195 F thermostat and new AC DELCO heated o2 sensor,. will not go into closed loop at idle, and havent driven it yet , as it needs tires badly.
I tried grounding the old O2 sensor signal wire to the ecm to ground and the scanner showed it went into closed loop, so I assumed it was the o2 sensor to be the problem. so we installed an new one and it still doesnt go into closed loop.. I have read that some trucks have closed loop timers on them, but cant find what they are.. truck sat at idle, at normal operating temp for abt 5 minutes, so I would think it would go closed loop by then,., but it didnt
the o2 sensor in in the manifold, and there is abt 6 inches of pipe left after the sensor, because the pipe was rusted thru so we chopped it off, to put a new exhaust system on it.,,
whats odd is the fuel trims are in control, short term 128, long around 16. o2 sensor is oscillating at around 450 to 510 MV
Truck doesnt run rich, or lean that I can tell. I unplugged the coolant temp sensor plug to see if the ecm would recognize a fault and throw a code, and it did.. the truck was throwing a knock sensor code, because when we rebuilt the engine, we got the wrong sensor,, out truck takes a 3900 ohm resisitance and they sold us a 100.000 ohm resistance knock sensor,, so we are very close to getting the truck running 100 percent perfect, just have to get it to go into closed loop.. any ideas appreciated.. I can give any scanner data requested.. thanks

How do i know what ohm my knock sensor should be beacuse I replaced mine recently and it was hard to get from on back of the block riggt near the oil temp sensor and getting that thing unplugged was hell but got it plugged rigt back in.. But reading this makes me wonder if the. Parts store messed up to.. Reson being is because I have had issues with my local parts store giving me wrong parts. Left. And right.. How can i know and how do i test.

 

[Schurkey]

How do i know what ohm my knock sensor should be beacuse I replaced mine recently and it was hard to get from on back of the block riggt near the oil temp sensor and getting that thing unplugged was hell but got it plugged rigt back in.. But reading this makes me wonder if the. Parts store messed up to.. Reson being is because I have had issues with my local parts store giving me wrong parts. Left. And right.. How can i know and how do i test.

Will you please STOP tagging onto other people's threads with semi-related or totally non-related questions?

You've got your own stand-alone thread. This question belongs in that thread. Perhaps a moderator will move your post to your existing thread.

Code p1351 & On my second catalytic converter

Hello everyone. My truck for over a year now has been laid up due to a code 1 P1351 and two shops can't find the problem everything on the outside of this engine has been replaced I mean everthing.. So im am completely frustrating and put alot of no. Ey in to get no answers and nothing fixed.. I...

www.gmt400.com

 

[Road Trip]

yes, the book says coolant temp sensor, time and o2 sensor. the book says to run engine over 1200 rpms for 2 minutes, after it gets to normal operating temp. I think it varies from model year to model year.. some books say the CTS will send its signal at 160f, some say 195f. some trucks have heated 02 sensor, some dont. some use 180f t stat, some 195f stat.. having specific model year tech data is critical but even that isnt always definitive.. in my service manual for instance it shows 2 different wiring diagrams for the 4.3 with the 4l60e trans,, one shows the o2 sensor gets its heater circuit power from the GAUGES fuse, and one show it gets its power from the 4X4 fuse.,. had I not stumbled across the wiring diagram that showed the power to come from the 4X4 fuse, I would still be trying to figure it out.. with the logic being, why in the hell would a two wheel drive truck have a fuse in the 4x4 FUSE SLOT.. GM should have labeled the slot for what it is for that truck, O2 sensor. from what I can see, the o2 sensor is the only circuit on that fuse. Im going to put a sticker over the 4X4 label and write o2 on it so this doesnt trip someone else up.. It had to have a fuse in the 4X4 slot from the factory, but over the years, someone likey robbed the fuse, to replace a blown AC fuse or something, and never put one back in, so the truck ran, but not great. also the truck was not throwing a code, so unless a scanner was hooked up you would never know it . they wont throw a code for the heater circuit in the O2 sensor not working,

Hey @texas tough,

Nice job presenting a problem, followed by then coming back and sharing everything you found
during your troubleshooting journey. This is so much more helpful than when people ask for
help...and then after other folks try to assist, they never come back and report yay or nay.

(Insert tip of the troubleshooting hat here.) Thanks!