‘99 Suburban dies at idle after going into closed loop .

[Zorad1000]

My ‘99 Suburban k15000 starts fine and runs great as long as it isn’t idling . But as soon as it goes into closed loop the engine dies . It has always started right back up . This problem started a couple of years ago then it went away on its own . Now it has started doing the same thing. When it first started a couple of years ago , I replaced the idle air control motor. That seemed to help a little but the problem was still there just not as bad , but now it is worse than before...I have a scanner and checked for codes , there are none . I watched the o2 sensors and all 4 seem to be working but the downstream bank 1 o2 sensor seems a little high most of the time . Just before the engine dies maybe 15 seconds before all 4 o2 sensors go to about .900 and the fuel trim goes to -30.5 on both banks . Then the engine dies . It always starts right back up . I forgot to mention that I had replaced the bank 2 catalytic converters last year , but I knew that it was bad and the engine light was on with the code for the converter... just wondering if anyone could help me out with this problem?

 

[zora]

Does your scanner allow you to see what engine temperature the ECM is seeing?

 

[Zorad1000]

Yes , the engine temp is at about 180 to 190 . The scanner can see some data but not all .

 

[zora]

Did you change the 195 thermostat?
You should have a minimum reading of 195 on a warmed up engine and as high as 220.

 

[Zorad1000]

No , I haven’t changed the thermostat. I put a new one in 9 years ago . I guess it is time for a new one . I bought the Suburban with a rod knocking in the engine . I replaced the engine with a new one from the local GMC dealer . I also got the new thermostat from the same dealer . I’ll get a new one and replace it this week and see what happens. Thanks for pointing me in a logical direction. I’ll let you know what happens.

 

[Zorad1000]

No , I haven’t changed the thermostat. I put a new one in 9 years ago . I guess it is time for a new one . I bought the Suburban with a rod knocking in the engine . I replaced the engine with a new one from the local GMC dealer . I also got the new thermostat from the same dealer . I’ll get a new one and replace it this week and see what happens. Thanks for pointing me in a logical direction. I’ll let you know what happens.

So I replaced the thermostat and while I had the coolant low I replaced the coolant temperature sensor. These two things didn’t seem to have any effect on the way the engine runs . It still dies out after it goes into closed loop . This time I was watching the coolant temp when it first died and the temp was 160 degrees. The down stream o2 sensors seem to be doing something odd . The down stream bank one sensor is always above .500 volts while the other down stream sensor is under .100 volt until just before the engine dies . Then about 15 seconds before the engine dies it goes to .900 volts . I’m tempted to swap the down
Stream o2 sensors with each other and see what happens. What do you think about that ? If the readings stay the same I suspect a bad catalytic converter if the readings follow the sensors I suspect a bad sensor.

 

[Zorad1000]

After driving the vehicle for about 10 minutes , the engine began to run much better and hasn’t died since then . I’ll try it tomorrow after it cools down completely.

 

[zora]

After driving the vehicle for about 10 minutes , the engine began to run much better and hasn’t died since then . I’ll try it tomorrow after it cools down completely.

So this is before the O2 sensor swap?
Look up the sensors before you try that, they may not be the same.

 

[Zorad1000]

After driving the vehicle for about 10 minutes , the engine began to run much better and hasn’t died since then . I’ll try it tomorrow after it cools down completely

So this is before the O2 sensor swap?
Look up the sensors before you try that, they may not be the same.

yes before swapping sensors, I’ll make sure they are the same part number before I swap them.

 

[Zorad1000]

After driving the vehicle for about 10 minutes , the engine began to run much better and hasn’t died since then . I’ll try it tomorrow after it cools down completely

yes before swapping sensors, I’ll make sure they are the same part number before I swap them.

So I just drove about 30 miles and the engine performed flawlessly. The downstream O2 sensors still have very different readings but since my problem seems to have been solved , I’ll leave well enough alone...

Judging by the temp reading on the dash gauge, there may have not been anything wrong with the thermostat because the dash reading seems to be the same as before. Best I remember.

The problem may have just been a tired coolant temp sensor.

 

[zora]

That sensor would do it. Glad to hear you solved it.

 

[Zorad1000]

Thanks for your help!