9T3VETTE

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?

DanielRicany

With a scan tool or laptop. You can see if the computer is operating in open loop or closed loop. It will tell you.

ezobens

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

9T3VETTE

Thanks, this is my understanding as well. The previous long tube setup on the car didn't have cats, so it always smelled. Now that cats are installed and it still smells like fuel, im thinking it has always needed heated o2's.

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.

DanielRicany

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.

9T3VETTE

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.

9T3VETTE

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.

9T3VETTE

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.

FrankieD

Left O2 BLM of 145 is too lean. You want it to be as close to 128 as possible.
Your Right O2 BLM of 127 is perfect.

9T3VETTE

Thanks, That whats I've gathered from some research. So that's saying it's seeing to lean and compensating by commanding rich correct?
I thought an exhaust leak but everything is tightened down good..maybe a bad O2..

DanielRicany

A sensor that is not warmed up will read lean.

9T3VETTE

Ok, interesting...

How about when cruising...I want to say both sensors were reading the same but in the 130-140 range. Would this be normal operation for low rpm, light load?

Cliff Harris

Can you display O2 sensor readings with that scanner? That would be useful to know.

FrankieD

My suggestion is to buy a cable and use Datamaster for free to capture a datalog. We can analyze the datalog afterwards and it would provide a more detailed analysis

DanielRicany

Check for vacuum leaks.

9T3VETTE

I believe I saw o2 sensor readings when going through the list. Unfortunately, I borrowed it from a co-worker and returned it already.

This is the next step. Now that i've figured out something is going on it's time to invest in an ALDL cable. Is this what you would recommend?

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.

1993C4LT1

Hope you get it figured out. My zo7 ruby smells rich on cold starts also.

1993C4LT1

Read post number 2 and 3

https://www.corvetteforum.com/forums...op-93-lt1.html

9T3VETTE

Based on the scanner reading I was not going into CL at idle. So I ordered some 3 wire heated o2 sensors off rock auto. That should fix the OL at idle issue and may have an effect on the split BLM's im seeing.

Hopefully this thread will help your issue too!

9T3VETTE

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