What would cause this to happen? If I was too lean? from what I can understand the O2, coolant temp and internal timers all need to hit a certain point before you go to closed loop. but when in closed loop I would guess that the only thing that could cause the ECM to go Back to open loop would be a Lean condition. correct?

This is on my 89 Vette.. 165 ECM Miniram'ed motor. the odd thing about it is that the BLMs and INT seem to be right at 128 +/-3

O2 volts show as .45 which leads me to believe I am running lean.

I have a heated O2 sensor (which may need replacing since the car was running real rich) and the O2 sensor is located at the end of the long tube header in the collector..

I am also using 24# SVO injectors but have the constant set for #26 (which I have heard should be correct for those)

Would bumping the FP help? or should I back down the Injector constant to 25# or am I even looking in the right spot?

Thanks



------------------
-=Jeff=-
89 Corvette Coupe White with Black Grand Sport Stripe
-=ICON Motorsports=-
Check out my mods on My '89 Vette

 

If the o2 voltage doesn't move, that's the reason it doesn't stay in closed loop. Also, .450 is a static o2 voltage so even if the o2 were disconnected it would show .45V. Make sure the o2 moves first.

 

Yes the O2 does move.. when it goes into closed loop it moves.. then at low accel (tps at .8) it goes to .45 and sit..

Once I accelerate again it goes back to closed..

still confused

 

How do you know it's open loop, vs fail soft mode?.
Coolant temp., being too low will do it.
What are the O2 cross counts. There is a gray area from code 13 to poor working O2
.45 is the ecm ref voltage to the O2. Almost sounds like an open wire to O2 if not might try a good O2 sensor (AC)

 

Grumpy,

as far as I can tell by using my Ease software. it has a parameter that states Open or Closed loop. What is Fail Soft Mode? How can I detect that?

WHat are O2 Cross counts? mine has O2 trasitions.. at one point it is 106 another time is 228

If you would like to email me at jdebuhr@home.com I can reply back with an excel spread sheet from my latest scan.

I am slowly learning this stuff and this board is very helpful.

Thanks

Jeff

 

Fail Soft is when the ecm is using a default value for a failed sensor, what is commonly called Limp Home, which it isn't.

You need to go thru you logging and see what's acting up. I don't use excel, not even installed, those spread sheets give me headaches, seriously.

 

You mention that you can see it going into closed loop then open loop. I interpret that to mean that you are in closed loop at some time and then go into open loop. What is the driving situation when this occurs?

It is normal for the ECM to go into open loop under certain driving conditions and return to closed loop later. Prolonged idling and long deceleration down a hill will do this.

Also, as Bruce said, a weak CTS sensor could also be a culprit or a thermostat stuck open. In this situation, your reading at the CTS may be just hovering above the threshold for enabling closed loop. While driving, enough air gets flowing to cause a drop in the coolant temperature (or reading) so that it falls below the threshold. This will toss you into open loop. What are your CTS readings?

 

Glenn,

To answer this.. YES

CTS readings range from 174.7 to 177.7 when it is in Open Loop, but also the same temp ion Closed Loop. Most the time it switches to Open when I am decelerating like you said. There was also a couple of spots when I am just idling too. I just looked at it again, and with what you said it now makes more sense..

Thanks

Jeff


[This message has been edited by -=Jeff=- (edited August 19, 2001).]

 

I came to this thread too late, and I'll be leaving for a week, so hopefully it'll still be an active thread when I get back.

I'm experiencing almost the exact problem as Jeff has.

My car (description in signature) with it's Speed Density Miniram tends to jump in and out of CL/OL much too often. I do have a heated Bosch 3-wire O² that I installed a redundant fourth-wire ground to. The sensor has less than 100 miles on it. My O² transitions are moving beautifully, and the coolant temp is at ~180°-185°F.

I have SVO 33# injectors and have played with the constant between 32 and 35 with the same results.

The odd thing about all this is that the BLM will peg out at 160 indicating lean, and no matter what I do with FP or injector constants, it never comes back around to a viable BLM....Remember, I have great cross-counts with the O² sensor, so this confuses me a bit. This only started happening after about 50 miles on the sensor.

Grim thoughts about a short lifespan for the O² sensor have come to mind, but I wouldn't think it would go bad so soon....I'd hate to dish out another $70 odd dollars and still have the problem.

And Glenn, I'm with you on the cycling of OL/CL. But, if I'm at a steady cruise RPM on a flat plane, or decellerating, it'll often pop into OL. If I give it a quick throttle blip for about two seconds, it will find it's way back to CL, but often not for too long.

I have looked at my Diacom shots quite a bit, and see where all this is happening, but the numbers don't show anything odd as to what might be causing OL/CL jumping and the runaway BLM.

Thanks for the posts so far, and I'll check back with you guys in a week or so when I get home from vacation.

------------------
86 Trans Am WS6 Black with tinted windows, ZZ4, Mini-ram, true duals, LT4 HotCam, AFR 195 heads.
***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