Unfixable 1990 Chevy K1500 Idle Surge.
#11
I think suggestion was to look for paths for water to leak into gas tank. I saw a post once where someone said water was leaking somehow to top of tank under bed and getting into tank thru what I don't know - seal or rust pin hole.
#12
i know you said you clean and check the grounds. but this to me all points to poor connection somewhere. i would disconnect the ecm connection and clean then put back together. as far as the engine grounds i might even replace them as they can appear in good connection but be broken internally or have corrosion at the connection.
#14
Yes, it was not replaced, but tested fine. Although when I unplug it, nothing changes at all. I thought it should go into open loop if you unplug the O2, or does that not happen with a one wire O2?
#15
ECM tries to go into closed loop after some start up criteria are met - like some time period & temperature, not sure if anything else. When it goes into closed loop it expects to be able to make the O2 sensor go up and down when it commands the engine to go rich and lean. Something like above 700mv on rich side and below 400mv on lean side. If it can’t do that it drops into open loop. So, yes if you unplug it you stay in open loop. I’m not sure in what conditions or whether it sets a code in these years. New trucks will set code, I believe if it doesn’t see what it expects from O2 sensor. I have a 93 and had a lazy O2 which would not stay in closed loop because it didn’t vary enough but that did not set a code.
How do you know if you are in closed loop or not? Are you scanning data?
I didn’t see problems like your describing from a bad O2 sensor- mine ran fine, I was just failing emissions. I don’t think you’ll get missing, backfiring as a result of a bad O2.
Did you rule rule out possibility of getting water into gas tank after rain storm like Kevinkpk wondered?
How do you know if you are in closed loop or not? Are you scanning data?
I didn’t see problems like your describing from a bad O2 sensor- mine ran fine, I was just failing emissions. I don’t think you’ll get missing, backfiring as a result of a bad O2.
Did you rule rule out possibility of getting water into gas tank after rain storm like Kevinkpk wondered?
#16
ECM tries to go into closed loop after some start up criteria are met - like some time period & temperature, not sure if anything else. When it goes into closed loop it expects to be able to make the O2 sensor go up and down when it commands the engine to go rich and lean. Something like above 700mv on rich side and below 400mv on lean side. If it can’t do that it drops into open loop. So, yes if you unplug it you stay in open loop. I’m not sure in what conditions or whether it sets a code in these years. New trucks will set code, I believe if it doesn’t see what it expects from O2 sensor. I have a 93 and had a lazy O2 which would not stay in closed loop because it didn’t vary enough but that did not set a code.
How do you know if you are in closed loop or not? Are you scanning data?
I didn’t see problems like your describing from a bad O2 sensor- mine ran fine, I was just failing emissions. I don’t think you’ll get missing, backfiring as a result of a bad O2.
Did you rule rule out possibility of getting water into gas tank after rain storm like Kevinkpk wondered?
How do you know if you are in closed loop or not? Are you scanning data?
I didn’t see problems like your describing from a bad O2 sensor- mine ran fine, I was just failing emissions. I don’t think you’ll get missing, backfiring as a result of a bad O2.
Did you rule rule out possibility of getting water into gas tank after rain storm like Kevinkpk wondered?
#17
I'm here for the party
does the "check engine light" come on with the key "on" engine off?
Troubleshooting sensors and how to test
typical Symptoms of a Defective 02
Poor fuel economy
Higher emissions
Stalling-Hesitation
how do the injectors spray look? i know its kind of hard to compare them to good injectors as far as too much fuel but do they at least have a cone shape?
Troubleshooting sensors and how to test
typical Symptoms of a Defective 02
Poor fuel economy
Higher emissions
Stalling-Hesitation
how do the injectors spray look? i know its kind of hard to compare them to good injectors as far as too much fuel but do they at least have a cone shape?
#18
does the "check engine light" come on with the key "on" engine off?
Troubleshooting sensors and how to test
typical Symptoms of a Defective 02
Poor fuel economy
Higher emissions
Stalling-Hesitation
how do the injectors spray look? i know its kind of hard to compare them to good injectors as far as too much fuel but do they at least have a cone shape?
Troubleshooting sensors and how to test
typical Symptoms of a Defective 02
Poor fuel economy
Higher emissions
Stalling-Hesitation
how do the injectors spray look? i know its kind of hard to compare them to good injectors as far as too much fuel but do they at least have a cone shape?
#20
Any updates on the 1990 k1500!?
I was reading through this fourm because I have a 1995 k1500 with 190k miles with the EXACT same problem as the 1990. Rough idle after rain/humidity then when it dries out it's fine. I replaced/checked everything that CChevy did with his truck, with the exception that I had my TBI unit rebuilt. I just bought a ALDL bluetooth scanner for obd1 and I'm going to do a comparison of the readings when the truck is surging vs. when its dry and runs fine. Any updates/advice would be appreciated.