closed loop idle questions


schofell84
04-25-2007, 04:53 PM
hey guys i have a 90 z71 with the TBI 350 and from what i hear these engines dont even go into closed loop at an idle, for whatever poor design reasoning or whatever. is there any way to make it more efficient and get it to go closed loop? maybe a newer computer and some modifications like a port and polish and possibly a tbi spacer? maybe even a better intake manifold? my ultimate goals is to make it run stronger with more power but im just tinkering with some ideas at the moment.

thanks for any ideas in advance.

2000CAYukon
04-25-2007, 06:10 PM
hey guys i have a 90 z71 with the TBI 350 and from what i hear these engines dont even go into closed loop at an idle, for whatever poor design reasoning or whatever. is there any way to make it more efficient and get it to go closed loop? maybe a newer computer and some modifications like a port and polish and possibly a tbi spacer? maybe even a better intake manifold? my ultimate goals is to make it run stronger with more power but im just tinkering with some ideas at the moment.

thanks for any ideas in advance.

I don't know where you heard that about not going into closed loop at idle, but it is completely false.

I use WinALDL on my 90 GMC Z71 K1500 and it goes into closed loop at idle. The only reason that it wont go into closed loop is if it does not reach a certain temp or a sensor has failed (which will set the check engine light).

//2000CAYukon

MT-2500
04-25-2007, 07:30 PM
hey guys i have a 90 z71 with the TBI 350 and from what i hear these engines dont even go into closed loop at an idle, for whatever poor design reasoning or whatever. is there any way to make it more efficient and get it to go closed loop? maybe a newer computer and some modifications like a port and polish and possibly a tbi spacer? maybe even a better intake manifold? my ultimate goals is to make it run stronger with more power but im just tinkering with some ideas at the moment.

thanks for any ideas in advance.

Your best fix is to turn the key on and put it in gear and drive it.
If you start fooling with the TBI or pcm it will make it burn more gas and not run better.
Get a 195 thermostat and make sure the 02 sensor is good and tune up is up to par the pcm will take care of itself.

I have saw a few of them when the weather was way below 0 degrees they would drop back out of closed at a slow idle sitting still.
But no problem. Just put it in gear and drive it and all is well.
MT

abaird
04-27-2007, 08:19 PM
Your best fix is to turn the key on and put it in gear and drive it.
If you start fooling with the TBI or pcm it will make it burn more gas and not run better.
Get a 195 thermostat and make sure the 02 sensor is good and tune up is up to par the pcm will take care of itself.

I have saw a few of them when the weather was way below 0 degrees they would drop back out of closed at a slow idle sitting still.
But no problem. Just put it in gear and drive it and all is well.
MT


hehe..i guess i agree. I have given up on trying to make a truck high performance. The TBIs were nothing special when it came to power but they were very reliable and pretty good running motors. Had it not been for OBD2 they would have probabaly been around longer. Anyway, if you are looking for performance, throw on some vortec heads. They should be good for 20-30 horsepower. Also, try a cam upgrade.

I can't remember the last time I had a scan tool on one of these to determine whether or not it actually goes into open loop or stays in closed. I do know that O2 sensors become fairly inefficient at idle. Diferent scan tools will say different things too. We had an old snap-on red brick on a 2000 Camaro SS and at WOT it stayed in closed loop. We thought maybe there was a problem with the car until we hooked up the tech 2 and saw that it was actually going into open loop at WOT. A little off the subject...

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