I'm thinking about replacing my O2 sensor with a heated one to get into closed loop mode quicker, but was told there are 3 conditions to be met to enter closed loop -

1. Coolant temp over about 70 degC
2. oxy sensor producing valid readings (swinging around 450mV, thru 200-700mV range), ie it is hot enough to work properly
3. the engine has been running for xx minutes

So I'm wondering how many minutes this timer is set for ?

I do several short trips each week with 35 minute breaks between and sometimes reckon I spend more time in open than in closed loop mode.

My O2 sensor on my 88 is in the normal place, I don't have long pipes etc that need a heated O2 sensor

S'nut

 

It will depend on the year. Generally I have seen it as x seconds in the code. One that comes off the top of my head for a cold start is 300 seconds, but I can't recall that calibration. I have sigs turned off...if you have one and I don't see it, list the yeah and I will try to find out what your cold/warm/hot timers are set for.

 

My '87s ECM has 3 settings...

Hot Engine O2 Timer: 66 seconds
Warm Engine O2 Timer: 206 seconds
Cold Engine O2 Timer: 300 seconds

Just don't ask me what defines hot/warm/cold. :D

 

HighHopes - I have a 1988. I did put my year (My O2 sensor on my 88 is in the normal place) but I should have put it at the top, sorry

300 seconds - that's 5 minutes, a long time. I really am often in open loop more than closed.

Scorp - what defines hot/warm/cold ? :lolg:

I have the GM Manuals but can never find what I'm looking for, is that where you find the times ? If so, what page?

Is it possible to change the times to suit a heated sensor?

S'nut

 

I doubt that there's many people who can answer this one - I hope one of them is checking the forum this weekend, I'd really like to get moving on this project.

S'nut

 

Possible to change times to suit a heated O2 sensor?
-Yes, but I haven't seen any information on times used in heated-O2 applications...finding out that info might be the way to go.

Since none of the MAF guys have chimed in, this is the best I could find from the BUA_HAC @ diy-efi.org

<BLOCKQUOTE>code:<HR><PRE>
**************************************** ***********
* Closed Loop QUAL'S
*
*
**************************************** ***********
LC551: FCB 107 ; 40.7c, (104.4f) Min Temp for Closed Loop
; CALIB = (deg c + 40) * (256/192)
;
LC552: FCB 147 ; Use Hot C Loop timer If Cool T >= 70.3c, (158.5f)
; CALIB = (deg c + 40) * (256/192)
;
LC553: FCB 73 ; Use Cold C Loop timer if Cool T <= 14.7c, (58.5f)
; CALIB = (deg c + 40) * (256/192)
;
</PRE>[/QUOTE]

Those might be your hot/warm/cold values, but I'd take them with a grain of salt. Maybe it gives you some temps you could log and see how long your car takes to get in CL when startup is at those various temps?

 

Thanks HighHopes, that's a good idea to compare those temps.

I have Win ALDL but it's not communicating with my car yet. It has worked on an 84 so there must be a problem with my ALDL connections.

Also thanks to Doc for emailing me - he has his timer set at 90 seconds for a heated O2 in a 91, so that also gives me some idea .

He also suggested I look in scan and tune.......I forget sometimes how many forums there are.

What is "BUA_HAC @ diy-efi.org ?" sounds like a useful place.

S'nut

 

bua_hac.pdf

It's a file of the factory programming. It is MAF based and looks like it is from an 86 Vette. Basically, if you follow through it, you can geta really basic idea of how the ECM looks at different values and then goes to tables, calculations, etc. Looking at it briefly will let you in on how many things are actually taking place inside the ECM from the programming on the EPROM. Even if you don't understand it (which I don't fully understand these hacks yet), they are handy to have around to see "Why did the ECM just record that change...was spark supposed to jump like that, pulsewidth supposed to increase like that", etc.

 

I don't know the exact times but you can use the diagnostic method on my site (link in my sig below) to see when the ECM goes closed loop.

All you need is a paper clip and to watch the flashes of the SES and record the time till they are of equal duration at about 1Hz.

If you have all the emissions equipment in tact I don't think a heated O2 sensor will help you go closed loop sooner.

 

Ok I just went out for a drive with the scanner hooked up. My car was running for 3:26 (206 seconds) when it went into closed loop. The scanner said the starting coolant temp was 125* (F) so that falls in line with my "Warm" engine start settings above and the temps given in the code.


[Modified by scorp508, 7:20 PM 8/30/2003]

 

Good one Scorp, thanks for taking your vette out to get that info - I have a video here , that I downloaded, of you chasing a ZX.

65Z01 - I have no cats and my AIR pump is gutted.

My SES light came on twice today. Last two times it's been code 13 O2 sensor so I'm sure it's on the way out. My MPG is poor. I want to sort all this out before deciding to go heated or not.

S'nut

 

What is a ZX? :) Wait do you mean like a 300ZX? If its the video I'm thinking of that was a Mark IV Supra TT.

 

Just MHO but I think you're over thinking this timing thing.

It has been my experience that once ANY of the above three requirements are realized the ECM goes into closed loop. Either that or these conditions occur almost simultaneously. I have verified this to my satisfaction with a scanner and found that the ECM went into closed loop as soon as the O2 sensor started producing signals. These tests were made just a few weeks ago during the hot summer. So coolant temp was ambient, not truly cold as it would be during the winter. In every instance the ECM went closed loop in under two(+/-) minutes at idle. I'm sure it would be faster if a load were placed on the engine after started...like driving. The exhaust gets hot RIGHT NOW when you start the engine...try this...hold a header pipe and have a buddy start the car and see how long you can hold on...no really...g'head...try it... :rofl: ... the O2 sensor gets hot fast!

The purpose of a heated O2 sensor is to reduce emissions as quickly as possible after startup...were talking seconds here compared to unheated in any given vehicle. When you factor those seconds with thousands upon thousands of cars built you can see the impetus in TONS of pollutants per any given unit of time. Individually the gain is infantesimal.

I don't think so..unless you're driving to the end of the driveway to check your mail and back 35 minutes later... :smash:

:seeya

 

Thanks MtLSphere, I didn’t know that only one condition had to be met, I was assuming all three had to be triggered.

I’ve got WinALDL but at the moment it is not communicating with my car, (works on another) If I had that working I could see what was happening.

I do drive up to check the mail, I live on the side of a hill with a long driveway so HA !

I received a great link from DOC - http://www.parttrackers.com/library/1/
As he says,”more info than you’ll ever want, about O2 sensors”

So I’m reading through everything and weighing up the pro’s and con’s. If there’s any good reason for me and my car to fit a heated one then I will, otherwise it would be far easier to just stick on a replacement single wire one.

I don’t have cats or AIR pump so there’s no issue there, just want my car to run the most efficient it can.

I was leaning towards getting a heated O2, your comments have straightened out the argument and made me look at it from a different viewpoint, thanks.

Oh, you were right about the exhaust pipe :mad :cry

S'nut

 

I have never tried changing this in a stock ecm but I have a Gen-7 dfi and it uses time to determine when to go into closed loop. Since everything is programable I can set it at whatever I want. I think I could set it for a shorter time but for now it is 120 seconds cold and 55 seconds warm but I can set the temp that determines warm or hot I have that set at 120 degrees above that temp it goes closed loop in 55 seconds.