Which PIDs to scan?

[Garry]

Once I get my car on the road, I will need to figure out the cause of some hesitation in the range of 2550 and 2750 under light load & throttle .. someone on ls1.com already suggested I should be turning off the O2's and then do some scanning - which PIDs should I logg in order to narrow down on the cause of the problem? Same as listed in the VE tuning tutorial?

[emarkay]

Turn off the O2's???

What year, model, mods... ... ...

First eliminate any "old school" issues - air filter, fuel pressure, vacuum leaks, backpressure, bad plugs... ... ...

Hessitation can be fuel or spark, or totally mechanical, in which case you may not see a result directly on the scan. Give the car a good "tune up" and a good mechanical diagnostic check, and get back with results and above needed information. :)

[GMPX]

Well, hesitation or laziness can be either timing or fuel, as we always recommend, get a WBO2 to monitor true mixtures, certainly log timing, and as emarkay suggested, don't forget the mechanical basics.

Cheers,
Ross

[Garry]

LC1 is on the way, guess I should have it by next weekend ... will see how that turns out ...

[ringram]

Log spark timing, commanded afr, o2 mv both banks, Id break spark timing down further and log modifiers like burst knock etc. In fact quite a few guys zero out the burst knock tables as it pulls timing when you tip in throttle often for no reason. Just make sure you log actual KR if you do this and make sure you havnt opened yourself up to real knock.

Now strange as this may seem, I had a similar hesitation, stock PE can cause horrific AFR ratio's of 11:1 or worse. Now if you are driving at stoich, and suddenly trip PE mode into washing out your flame with 11:1 you will notice a slight bogging or hesitation. I changed to OS3 and ran fully commanded B3647 fuel map and it got rid of this issue as AFR was progressively richened rather than suddenly triggering for litte to no reason.


Another way to address this on a stock OS is to change/check the stock PE mode MAP trigger. Its normally 15kpa, so basically PE can be triggered at idle! Id change this to 80 or even 85kpa, so PE is only really triggered under load.

But yeah, as the other guys suggest a wideband will help you "see" the problem.

[Garry]

OK, here's the PID list I'm going to run some time this week ... can't find the spark timing PID you mentioned, though ...

[ringram]

burst knock is est_krb_dma total spark after all mods is est_run_dma and knock retard is plain old KR.

[Garry]

Thanks ... I removed the second bank of some of the values to get back into the 24 channel limit ...

[Garry]

just came back from the weekend at the track ... apart from realizing the clutch is starting to head south, I recon my problem with the hesitation might indeed be caused by SOMETHING with the O2 sensors - under load, especially WOT, HO2S11 is almost flatlining, while HO2S21 stays pretty active. Together with this, the motor goes to Open Loop, with AFR dropping to 11.70 ... Under small to no load, both O2 sensors are rather close to each other ...
I will be putting the car up on the lift and swap sensors - see if it's either a cable, or a sensor that causes the problem ... also got my LC1 today, so that is going in some time soon...
Btw, which side is the HO2S11 sensor?

[ringram]

Yep both should flatline at WOT, if only one is, something is wrong with the other one.
At part throttle they should flip from 0 to 1V all the time. Looks like something up with H02S21 might be where your KR comes from. Could be bad injector too. Definately swap sides with the sensor and see what you find. Do you have any DTC codes?

When you start tuning your ve in open loop you can forget about the O2 sensors for a while. Hell many never go back to using them.

If one is bad how about wiring your LC1 in that side and setting it up as NB for a replacement. Mind you it could also indicate an exhaust leak, dodgy injector or something on the side that stays active during WOT.

[joecar]

Looks like you're way too lean (at WOT the LTFT's should be zero or slightly negative, and HO2SV's should peg above 930mV to be at a safe AFR);

you're getting a lot of real knock [sawtooth pattern], probably from being too lean.

[joecar]

As soon as you get a wideband O2, do the Auto VE Tune procedure, and then just run around in OLSD or try on eof the COS's (either way toss the MAF [install a large rubber hose] and the O2's [install bung plugs], you'll never have to worry about those items ever failing, you'll be happier :D).

[ringram]

Yep, how did you know you were at 11.7? Was that just your commanded? As joecar says, go openloop and follow the autotune, it will start you down the path to sort out the issues.

[Garry]

So, from the logg, apart from the O2 Sensor #2, is there anything else that looks fishy?

Yes, I had trouble codes, same as I posted before (did I here?) - O2 sensor not giving out the right voltage ... got it on every quartermile run I did ... on the 200mi trip to the track, it didn't go off ... (didn't do any 100% throttle then, though).

Edit: Oops, missed the three posts on the second page ;) OK, will see that I get the WBO2 installed and find out what happens then ...

[Garry]

Yep, how did you know you were at 11.7? Was that just your commanded?
It's in the diagram of the logg ... I recon as it's pretty constant that the PCM is commanding that AFR for open loop ... !?

[ringram]

Actually as Joecar mentioned there may be no fish about, just that the stock tune sucks. If you start down the autotune route and disable the O2 sensors (with your WB LC1 installed) you should get some more specific data.
However if you get O2 sensor DTC's then that even more reason to start tuning your VE. Might pay to doublecheck exhaust leaks etc though as they will throw autove tune off as well if there are any.

[Garry]

Took a look today - please confirm, the O2-sensors in question are the ones before the cat, right? If so, I can't seem to get either one out ... left side is rusted in pretty badly, the right side is awfully hard to get the wrench on as it's pretty close to the cat ...

[joecar]

Took a look today - please confirm, the O2-sensors in question are the ones before the cat, right? If so, I can't seem to get either one out ... left side is rusted in pretty badly, the right side is awfully hard to get the wrench on as it's pretty close to the cat ...
Yes, the ones upstream of the cats.

Dowse with a liberal spray of WD-40 or Liquid-Wrench or similar and let soak for several hours, and repeat several times.

Are you using an open-end wrench...? I found it easier to use the slotted-socket ($20 at local parts store) with rachet or breaker.

[ringram]

Check on ebay, I got a 22mm o2 special socket for $15 which works brilliant, I still needed a breaker bar on the end of the socket wrench though! Its almost a closed ring, but with a small gap to fit the o2 wires through.

[Garry]

Local car place that I have stuff done at has an open socket, hope it fits in that confined space ... will try tomorrow ...

[joecar]

Local car place that I have stuff done at has an open socket, hope it fits in that confined space ... will try tomorrow ...Garry, what car do you have...?

[Garry]

2k Firehawk ...

Well, used an open socket today - which will of course only fit on the passenger side, as the space is slightly to limited on the driver side ... so I tried to take out the right one first - and stripped the treads on the bung and the sensor while doing so ... going to pick up a tread cutter tomorrow to clean out the bung, I recon I will just put the WBO2 in on the right side, not even mess with the driver side NBO2 and stick to Open Loop ...

[joecar]

Unfortunately, GM spared no expensense to ensure rust gets it's grip. :bawl::frown::mad:

[ringram]

You can enable your LC1 to sim NB anyway, so no need to do anything other than what you have. You still have the option of CL if you wish. Just use the stock 4 wires for power, grnd and nb sim info.

[Garry]

Yeah, that's what I had planned - with my luck, the driver-side O2 is probably the one that's bad ... so, most likely, no use in running with the PCM using the info most likely ... well, will see ...

[Garry]

after re-cutting the treads on the stock bung today, closed it back up (as the stock O2 is stripped, of course) and getting ready to (hopefully finally) installing the WBO2 Saturday. Anyway, though the car is running pretty sh@tty w/o the second O2, I did a scan on it - seems like I lucked out, and the sensor that's messed up is the one that I pulled ... so, with the WBO2 in place, I ought to even be able to run with them activated ... so, for the F-Body folks here, bank 2 seems to be the passenger side ... ;)