93 DOHC Normaly Aspirated, Stealth scan data question

[buickwagon]

Update:

1. replaced the O2 sensor. The new one does work -- if the engine is revved up. If when the rpm drops, the O2 sensor drops almost to 0 volts.

2. built the Palm cable and tried out MMCD. Now I can see the fuel trim. Simultaneous with the O2 voltage drop, the O2 fuel trim drops from ~120% to 78% and vice versa when the rpm rises. If I get the throttle just right, it will kick in and out -- O2 operating as expected for a couple of seconds, then nothing for a couple of seconds, over and over ad infinitum. The RPM fluctuates a bit in synch. It seems like the ECU is dropping in and out of closed loop mode. It seems a chicken-and-egg thing: is the O2 circuit dropping out because the system reverts to open loop or is the system reverting to open loop because the new O2 sensor is cutting out? Why would the O2 sensor cut out at low rpm? The heater circuit is drawing a constant 0.7 amps with 14.4v supply at the connector. Adding a second ground path does not change the current.

On the other hand, why would the O2 sensor voltage drop to near-0 if it was functioning? The open loop fuel map should still simulate 14.7:1 at idle. Can the fuel map be re-programmed on these? Is it possible that a PO was fooling around with things and messed them up? speedy25 mentions a known problem with ECU capacitors, could this be a manifestation of that?

3. Found the source of the fuel smell. Someone "fixed" the fuel line on top of the sender by cutting it off, butting a new piece of tube to the old and spot-welded it in place. Then covered the joint with some sort of epoxy. This abortion was spraying a fine mist into the air when the car was running. The whole thing turned into a nightmare of broken studs, but several hours later it's properly rebuilt (new tube silver-soldered into place, new electrical insulators turned, new studs installed into the flange, etc. etc. etc. Would have been easier to buy a new one, but this was Sunday evening...)

[jake stealth]

A few additional thoughts - -

First of all, I know nothing regarding bad caps in the ECU so Speedy and others might be totally correct there.

Is the car being driven when looking at the O2 readings or is it parked with the engine revving a little? You might try running it on the road to load the engine and see what happens.

This taxes my memory a little but if I remember correctly, when the engine controller goes into open loop and ignores the O2 sensor input, then one possibility is the engine might be too cold. Closed loop does not occur if the ECU thinks the engine is below a given operating temperature.

A second open loop mode occurs when the throttle position switch is closed and the car is deceling. Just a thought, but is the Throttle Position Sensor adjusted correctly? Not sure if this applies to this particular platform or not but under closed throttle decel conditions, we used to open the idle speed motor a little as well put the system into open loop and use a programmed fuel/spark map. The O2 sensor reading might still jump around somewhat but the ECU would ignore it. This programmed map reduced the decel bucking and promoted a smoother transition back to open throttle and hence back into closed loop. Is there any chance that when revving the engine and holding the throttle constant, the TPS switch is making intermittent closed/open? You should be able to observe the TPS action on your scan tool. Your scan tool should also be able to determine if the system is in fact going back and forth between closed and open loop. As noted before, not sure if this applies to these cars or not since my Stealth seems to have all the fuel cut off (??) during decel and when it turns back on at about 1200 RPM, there is in fact a noticeable jump from the engine.

Having said all the above, my first thought process would to be read the service manual and adjust everything to factory specs – including the initial timing and TPS switch – at closed idle. You can also see what the coolant temperature is or what the ECU thinks it is.

I would have a lot of confidence in the O2 sensor readings and suspect the fuel delivery is jumping around on you – the O2 readings are merely responding accordingly.

Lastly, are you absolutely sure the O2 sensor output is not reversed? Make sure the polarity of the sensor is correct – negative voltages which are supposed to be positive and vice versa can cause a lot of headaches.

You mention rusted fasteners and a corroded fuel line. Make sure all grounds are clean, free from rust and free from resistance. Battery cables, chassis-to-engine-connections and the grounds for the ECU as well. Check the service manual for their locations.

Just a few thoughts – might not be totally correct since I’ve been out of this stuff for over fifteen years - LOL

As per usual –sorry for the rant.

Good Luck.

Jake

[speedy25]

Originally Posted by buickwagon

Update:
O2 operating as expected for a couple of seconds, then nothing for a couple of seconds, over and over ad infinitum. The RPM fluctuates a bit in synch. It seems like the ECU is dropping in and out of closed loop mode. It seems a chicken-and-egg thing: is the O2 circuit dropping out because the system reverts to open loop or is the system reverting to open loop because the new O2 sensor is cutting out?

I gave you the best answer before- Talk to rymer. He KNOWS these ECU's inside and out.

-SP

[buickwagon]

Originally Posted by speedy25

I gave you the best answer before- Talk to rymer. He KNOWS these ECU's inside and out.

Forgive my ignorance, but how do I contact him? I did a search of users and "rymer" returns "invalid username".

Nevermind. I did a general search for the term "rymer" and found him. Sent him a PM.

[speedy25]

Good! I think hes your guy to figure out if its an ECU thing or not.

-SP

[buickwagon]

Looking at things again yesterday we realized that the exhaust is not stock. A PO pieced it together and welded a bung for the O2 sensor on top of the pipe instead of cutting a proper saddle into the pipe so the sensor was barely entering the airstream. We reworked it so the sensor is now protruding about 3/8 of an inch into the pipe.

It still doesn't do anything at idle, but it works at cruise now.

However, now the ABS light is on. Arrrrrgh. Any chance there's a palm based scanner for the ABS system, similar to MMCD?

We also attempted to set the idle as per the manual, but the BISS screw seems pretty soft and doesn't want to move. We'll let it soak in penetrating oil for a few days before making any further attempts.

[speedy25]

Good job finding the crap install on the O2 sensor. Keep it in mind as you fix other things on the car. Because having it done right was soooo expensive most people made screwy repairs. SUSPECT ANYTHING you see that was worked on previously.

Originally Posted by buickwagon

We also attempted to set the idle as per the manual, but the BISS screw seems pretty soft and doesn't want to move. We'll let it soak in penetrating oil for a few days before making any further attempts.

DONT mess with the BISS screw. The only time it needs any messing with is if the o-ring under it disintegrates. The fact that you cant move it confirms its still there. 99% of idle problems are IAC related. Test it for shorts, clean it and the TB. Make sure the o-ring is OK, and taa daa instant idle. The other 1% is usually another owner induced vacuum leak problem.

-SP

Pssst- Just in case you didnt find it yet- stealth316 has a LOT of maintenance info with a bit more info than the manual.

[buickwagon]

Seems to idle OK, but a touch high ~850 rpm with the timing wire grounded and datalogger installed. We were going to adjust it to spec as per earlier advice in this thread. Other threads suggest it might be plastic? I can make a nice brass one if I can get the old one out.

On the subject of researching other threads, I found someone else had the ABS light on with the datalogger installed. Sure enough, I called my son and had him unplug it and the light is gone now. Weird. According to the manual, the DLC has a completely separate terminal for ABS.

[rymer21280]

Got your PM, I will answer the best I can when I get a bit more time. work sucks :-)

Thanks speedy!

eric