97Z-M6

when i scan the car with datamaster it shows the short term counts all just all over the place. one may say 120 and the other will say 136 and constinaly changing back and forth. there are know exhaust leaks before the o2s, and the o2s sensors are going crazy as well. the only time the are still is at wot. and also the duty cycle on the injectors sometime spike over 85%. (stock engine) shouldnt the duty cycle straighten out when i go wot sence the o2s are ingnored (if the 02s are the problem) . im sure this has to do with o2s sensors somehow. the o2s sensor have never been touch they are factory 148k. should i change them.

can someone help out here anything i can try before i put new o2s in, and also will the rear o2s swap and work in the same place as the front o2s. or are the plugs different or something. maybe that can help me rule out o2 sensors. i dont know just looking for some help.

97Z-M6

ttt for thevening crowd.

im at a loss here, can some give me some ideas at where to look now.

97Z-M6

last TTT

please help

anaik

Your short term counts and 02's are acting normally. The 02's make like ten corrections a second. You cannot put the rear 02's in the front. Did you ever read "Injuneers" paper on the Scanmaster? It"ll explain what what you are seeing. I'll see if I can find it.Can't comment on the injector duty cycle.


edit; here it is

http://members.aol.com/InjuneerZZ/ScanMast.htm

Injuneer

As Anaik said, read my ScanMaster writeup.

ScanMaster Writeup

The "short term" corrections are exactly that... "short term". The PCM reads the O2 sensors, makes the correction to the next calculation, then throws the short term correction away, and starts all over again, looking at the O2's. It does this almost 10 times per second.... 128 = no correction.... the readings vary to either side of 128. And each bank will respond independantly... they do not work together.


I don't think you understand "duty cycle". This is the % of the available time in two revolutions of the crank that the injectors are "on". At WOT you have the greatest fuel need, so pulse width (the number of milliseconds the injectors are "on") is a larger number. Therefore duty cycle becomes larger.

If you are getting 85% on a relatively stock engine 85% seems too high. But I have noticed that DataMaster seems to have a "bug" in this area, calculating duty cycles that seem way too high.

But the key concept - duty cycle is a function of injector pulse width and engine RPM.... it has nothing to do with the O2 sensors and whether they are "in the loop".

97Z-M6

im not questioning you guys, but this is whats throughing me off. the o2s i understand will change 10 times every second but my concern is that they are changing so drasticly, one time it will regester 7mv and the next it will regester 850 or so. and my gas mileage is very bad.

im going to read the write up right now. thanks.

Injuneer

The extremes aren't all that unusual. The PCM is trying to maintain EXACTLY 14.7:1. The O2 sensors are EXTREMELY sensitive at this value.... maybe showing 200mV at 14.75:1 and 700mV at 14.65:1. That's why they aren't very good for attempting to measure the 12.8-13.2:1 you want for max power and torque.

To find your gas mileage problems, you need to look at the LONG TERM fuel corrections, often referred to as "block learn multipliers" (BLM). Those are the PCM's response to the variations in the short term corrections. You may find that many of them are approaching 160 because misfires or exhaust problems are causing a "false lean".

If you can do a DataMaster log for "normal" driving and a couple WOT passes, I'll be glad to look at it for you. You just need to make sure you export it as a ".csv" file, or I can't open it with Excel.

97Z-M6

ok ill do that tonight and i appreciate it.