Hi all,

Okay, in an effort to help me figure out what to focus on in solving my '89 Formula 350's drivability problems (which basically amount to some bogging & stumbling at low RPMs, both in and out of gear), I bought an ALDL-to-serial cable and hooked it up to my laptop. Installed the DataMaster 32x32 beta (for '86-'89 MAF TPI cars) and drove the car around the block for about 10 minutes while recording the data stream.

Problem? I'm an idiot, and don't know what to make of most of the data I recorded from DataMaster. I saved the entire test drive to a .uni file, so I've been playing it back at home in slow-motion and observing what happens. The car will drive absolutely BEAUTIFULLY when it's in open loop, but as soon as it hits closed loop, sh** happens and it's never the same. So I started examining the DataMaster log right around when the car hits closed loop.

I noticed one thing right away: My O2 sensor volts skyrocketed from 27 mV to 892 mV in two seconds, the instant the ECM went into closed loop. From that point on, it cycles back and forth between the top and bottom ends of the scale over and over, sometimes hovering around the middle for a second or two at a time. My problem is, I don't know what normal O2 sensor operation looks like, but this sucker looks like it's running the gamut back and forth. Looking at the INT histogram, it keeps toggling back and forth between rich and lean. The BLM value is between 145-152 for pretty much the whole time, which seems pretty far off the 128 norm value. That may be a separate, unrelated issue (I get really poor fuel mileage and often smell gasoline from outside the car after driving it...)

Anyway, I'm guessing that the O2 sensor is acting wacky, and this would make sense because it is ignored when the ECM is in open loop, thus I have no problems at that time. But I'm wondering if anyone here can help me decide for sure. I ought to just go ahead and replace it, but the sucker is seized in the manifold BIG TIME thanks to the previous owner who didn't know what anti-seize was. I've already tried removing it on multiple occasions with no luck. I am going to keep trying until I get it.

So, learned techs, enlighten me: O2 sensor sound bonkers? Or is it normal? What other information from the ECM scan would you like to see, if any?

BTW, I have the DataMaster .uni file if anyone wants to load it up and check it out, but they will probably need the latest beta of DataMaster 32x32 Beta for 86-89 MAF TPI cars to see accurate readings.

Thanks!

 

The O2 sensor voltage should bounce all over the place in closed loop.
The rich/lean changes are normal.
The BLMs are very high. The ECM thinks that it needs to add fuel.
The open loop O2 sensor voltage looks pretty low, but that may be cause it's not hot enough to start working. On the other hand it may be telling you the O2 sensor is defective (but still producing some voltage).

The o2 sensor voltage reads higher when sensing a rich mixture.
If the sensor becomes "lazy", it will still work but produces less voltage across the board. This will make the ECM think the mixture is too lean, and it will start adding fuel until the o2 sensor voltage hits the midpoint at .45v.
The ECM realizes that it's having to add more fuel than it thought it should to make the O2 sensor happy, which causes the high BLMs.

Keep trying with the O2 sensor replacement.

 

Great information, thanks! So the high BLMs would explain why I am getting horrid gas mileage all the time, because the ECM keeps adding fuel. It's funny because the instant the engine starts, BLMS hit 145 immediately and the car wants to bog down and stall unless I give it a bit of throttle on ignition. After that, BLMs hold steady at 145 for a long time. In closed loop they vary between 142-152 on average. A few times it dips into the mid 130s but that's as low as it gets.

The low O2 sensor volts I mentioned in open loop were actually not that low all the time; I also saw some sweeping higher voltage in open loop as well, so I think it may be operating correctly. But I will keep trying to get the sensor outta there and see what happens after I replace it.