Guys, I hooked up my scanner 2 days ago trying to find out at what temperature the ECM goes into Closed Loop and was surprised that it never did. I pulled the fuse for the fans and let the engine warm up and then it got hot (about 223*) and it never went to closed loop. The car wasn't being driven and the RPM's was 650-700 (idle). It would only go into closed loop for a brief moment when I revved the engine for a couple of seconds, but then back to open loop. Is this normal? Isn't the engine supposed to go in closed loop even at idle or am I wrong?
Thank, Rick

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'88 GTA 350 Full of Leprosy (rust)
Full Exhaust, Free mods, Xtreme Energy cam, Intake Pieces and 2100 RPM TQ

13.39@102.50 MPH
1.90 Sec ----- Best 60FT
104.23 MPH -- Best Trap Speed
AIM HIGH!

 

The engine should go into closed loop at idle. What does a graph of your O2 mV look like at idle? How many O2 crosscounts within a given period of time? What headers are you running? How old is your O2?

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Sounds like a typical case of failed O2 sensor and/or failed O2 sensor heater? Check the O2 sensor output with a voltmetre and/or scan tool AND check the continuity of the O2 heater element with an ohmmeter.

 

The O2 sensor is pretty new (less than 3000 miles) and it seems to be working fine. I hooked up my Sunpro scanner, but it won't tell me the crosscounts; just what the O2 is doing like go up and down really fast. That's normal right? I'm using hedman hedders.
Thanks, Rick

 

I have to admitt that after paying like $400 for my damn scanner I feel like I bought the biggest piece of $hit out there. It read all the parameters there are, yes, but only with the 730 ECM. I didn't know about this site back then or else I would have never got it.
I had to get that off my chest before I explode.

 

Hey guys, what are the conditions that need to be met so that the ECM can go into Close Lopp? Maybe I can track the problem this way. It's a 165 ECM, if it makes a difference.
Rick

 

F22,

I know what you mean about not getting into Closed Loop and staying there.

My car has Hooker Super Comps on it, and a standard O² sensor. After hooking up to Diacom, I too noticed that it won't go into Closed Loop at idle, and also not even when driving around for several minutes. But will enter Closed Loop breifly when I start to accelerate somewhat hard, and then just jumb back and forth for a minute or so before finally reverting back to Open Loop

All my CTS temperature and time restraints are met (It hovers at ~190°). My O² crosscounts are continuously moving (except when I punch the throttle hard of course).

With the Temperature, and Time, and Crosscount activity met....I wonder if there is ANOTHER reason it won't stay in Closed Loop.

Does it really need to be above 600°F at the O² sensor to keep the ECM in Closed Loop operation even if all other areas are met?....All the other parameters are being met as I said, even the crosscounts, so this bewilders the hell out of me.

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86 Trans Am WS6 Black with tinted windows, shaved door handles
ZZ4, Mini-ram, true duals
***Too many other mods to mention***

"In the future, cities will become deserts,
roads will become battlefields, and the hope of mankind
will appear as a stranger" The Road Warrior

 

Crosscounts is when the O2 is warm enough and start to oscilate up and down the scale, right?
I thought I've seen in WinBin that you can bring the temperature in which the ECM goes into close loop down. Would this help.
You see, the O2 was hot enough because it was moving up and down, temperature was 223*; what else is needed?

 

I'm also wondering what else is "needed" F22.

You're right on the definition of crosscounts/transitions. It's when the O² sensor transitions between a specified voltage (in my case, 550mV).

The ECM counts each time a transition(oscillation) takes place. It will count from 0-255, and when the 255 number is reached, it will reset to zero and begin counting up again. On a line graph (like the Diacom graph), an O² sensor that is operating throughout it's transition point will show a "sawtooth" style line graph...climbing to 255, then dropping to zero again and again.

As far as the O² sensor needing to be warmed up enough for this to occur, I have not seen answered yet. Mine will transition fine but it will do this even when I'm in Open Loop for a long period of time.

Your coolant temperature (223°) looks to be hot enough to satisfy the coolant temp parameter.

I'd also like to know ALL the parameters which determine Closed Loop.....anybody know??

 

You might want to try a heated O2 and see if that solves your problem. From I've heard in the past the O2 sensor is the biggest contributing factor when going into closed loop.

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87 Iroc 5.7, AFR190, SLP Cam(218/224), SLP 1 5/8 headers & cat back, Random CAT, SLP Runners (matched intake-runners-plenum), 48mm TB, 6E(arap) chip, Vigilante & Probuilt trans.

 

There's coolant temp, a timer (3 different values depending on the start-up coolant temp with break points at 59 and 158 degrees F in ARAP bin), and an O2 hysteresis (O2 must go below 199 mV or above 699 mV). Also, the block learns aren't updated below a certain coolant temp, 122 degF in ARAP. I've watched my car warm up and see that 2 of the variables are met (coolant temp and timer) while the O2 sensor is gradually dropping down below 199 mV. This is with the engine idling and not moving anywhere. As soon as the O2 drops below that value, it goes right into closed loop. Of course, starting up and driving around will get the O2 sensor moving and fluctuating faster, so that's generally not the limiting factor while I'm driving.

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Greg Westphal
'87 IROC 305TPI/A4

 

O2 temp is a critical issue here. With headers, and a Non-heated sensor, you will have problems attaining closed loop at idle, the sensor cools enough to drop to open loop. A heated O2 sensor alleviates some of this.

 

Greg,

Thanks so much, that was the number I was looking for!! (O² hysterisis).

Like you've noticed, I noticed too. The engine will pass the time constraint and meet the CTS criteria, but still no Closed Loop.

I looked at my Diacom info, and sure enough like you said, the oxygen sensor never went above or below the 199mV-699mV that you talked about.

The only time it did was when I got on the throttle somewhat hard, and then It would go over 699mV and enter Closed Loop only to drop out several seconds after I eased back on the throttle.

Thanks guys....Looks like it's definately time for a heated sensor.

[This message has been edited by Steves ZZ5 (edited April 12, 2001).]

 

Here's a question for you: Did you move the O2 sensor from the #7 tube into the collector? It's my understanding (although I -have- been known to be wrong!) that with the sensor in the #7 primary it will get hot enough, but if you move it into the collector you'll need a heated sensor.

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408cid 1985 Corvette
http://www.mojosgarage.com

 

In the F-bodies, the stock O2 sensor position is in the collector, well, the bottom of the exhaust manifold right before it dumps into the Y-pipe. The O2 sensor position in my Hooker header is only an inch or 2 further from the engine than my stock manifolds.

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Greg Westphal
'87 IROC 305TPI/A4

 

Hooker super comps sound like longtubes to me, which puts the collector a lot further from the ports than shorty headers or the factory manifolds, which also keep heat in the system pretty well.

 

Hooker Super Comps are also available in shorty headers. I should know since I have a set. But, they only have 1 5/8" primary tubes instead of the long-tube's 1 3/4" tubes.

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Greg Westphal
'87 IROC 305TPI/A4

 

Ok, my bad Greg. Didn't know *blush*

Regardless, I'm planning on running a heated O2 sensor, even though my Mac shortie headers are even going to be coated. I want consistency... maybe I'm just **** *G*