Confirming open/closed loop operation
#1
Drifting
Thread Starter
Confirming open/closed loop operation
1993 LT1.
Recently I put long tube headers on my car (coated) and a set of cats. Last night I took it out when it was chilly outside (45deg.) and at idle it seemed to smell like it was running rich.
I'm thinking the car may not be going closed loop at idle due to the location of the o2 sensor. Other than that it seems to be running great.
What is the easiest way to confirm this point and determine if I will have to put heated o2's on?
Recently I put long tube headers on my car (coated) and a set of cats. Last night I took it out when it was chilly outside (45deg.) and at idle it seemed to smell like it was running rich.
I'm thinking the car may not be going closed loop at idle due to the location of the o2 sensor. Other than that it seems to be running great.
What is the easiest way to confirm this point and determine if I will have to put heated o2's on?
#3
Drifting
If you are using the OEM non-heated O2 sensor with long tube headers and the sensor is now down at the collector or even further back, you WILL now need a heated O2 sensor.
Just my .02
Just my .02
#4
Drifting
Thread Starter
I was wondering if there was a quick way to determine closed loop operation without an ALDL cable and software but doenst sound like it.
#5
Still, in open loop it shouldn't be excessively rich. It is only supposed to be slightly richer during hot open loop mode.
If the CTS is faulty and reading colder than normal, you could be injecting too much fuel for the actual engine temp. In this case, depending on how cold the CTS reports, you may never be going into closed loop at all.
If the CTS is faulty and reading colder than normal, you could be injecting too much fuel for the actual engine temp. In this case, depending on how cold the CTS reports, you may never be going into closed loop at all.
#6
Drifting
Thread Starter
Thanks for the help. I got ahold of an old school OTC 4000 scanner, hopefully that will show me for sure what's going on.
#7
Drifting
Thread Starter
Ok, got the scanner hooked up and took it for a quick ride.
At startup and after a few minutes of idling in the driveway it was open loop. As soon as I pulled out of the driveway and took off it went CL and stayed there. At stop lights it also stayed CL.
Came back home let it idle for 2 or 3 minutes and it still stayed CL. However, it was 75deg here today and high humidity which may play a factor in it. I suspect it may go open loop at idle on cold Michigan mornings so i'll wire up heated o2's anyway.
Also, I took a quick look at BLM's. I found that one bank was consistently higher than the other and include some pictures below. I'm no OBD1 expert so any advice would help.
The below is on startup (notice "open" on the scanner)
After cruising for 10 minutes came to a stoplight and this was the split
Cruised some more and this was at idle in the driveway when I got home
ECT on the scanner matched ECT on the digital display so I would think the CTS is ok.
At startup and after a few minutes of idling in the driveway it was open loop. As soon as I pulled out of the driveway and took off it went CL and stayed there. At stop lights it also stayed CL.
Came back home let it idle for 2 or 3 minutes and it still stayed CL. However, it was 75deg here today and high humidity which may play a factor in it. I suspect it may go open loop at idle on cold Michigan mornings so i'll wire up heated o2's anyway.
Also, I took a quick look at BLM's. I found that one bank was consistently higher than the other and include some pictures below. I'm no OBD1 expert so any advice would help.
The below is on startup (notice "open" on the scanner)
After cruising for 10 minutes came to a stoplight and this was the split
Cruised some more and this was at idle in the driveway when I got home
ECT on the scanner matched ECT on the digital display so I would think the CTS is ok.
#8
Drifting
Thread Starter
forgot to mention, the car has a mail order PCMforLess tune on it. Only engine mods are LT headers, 3" exhaust and a cold air intake.
#10
Drifting
Thread Starter
I thought an exhaust leak but everything is tightened down good..maybe a bad O2..
Last edited by 9T3VETTE; 05-25-2015 at 08:28 PM.
#11
#12
Drifting
Thread Starter
#16
Drifting
Thread Starter
http://www.aldlcable.com/products/aldlobd1u.asp
Good thought...I've never had luck finding vacuum leaks but can always try again. This may explain a high initial rev when cold started, followed by a slow rpm drop to idle. Sometimes it idles high as well.
#19
Drifting
Thread Starter
Hopefully this thread will help your issue too!
#20
Drifting
Thread Starter
Update: I finally got around to ordering an ALDL cable with a USB hook-up. Hopefully it will be here in a few days and i'll also be able to get my heated 02's wired up this weekend.
However, I did read on datamasters website that the program doesnt work all the time with the USB cable hookup. Hopefully that's not the case for me as I had already ordered it
However, I did read on datamasters website that the program doesnt work all the time with the USB cable hookup. Hopefully that's not the case for me as I had already ordered it