Throttle closes momentarily??

[DrX]

What's going on here? When I hit the throttle while rolling at a steady speed it goes WOT, then closes, then re-opens. Its like bouncing off the rev limiter. I recall this happening years ago when the MAP got ahead of the RPM too fast, but I haven't touched the associated table in years. Whatever is causing it is not present long enough to trigger a DTC. I haven't noticed this behaviour from a standing start. Tried a tune from last year and it is still there. Only recent changes are a different 4L80E and converter. Just tested the functioning of the trans brake and noticed that the converter did not hold engine RPM at its rated stall speed(2600).

I have attached an edited log showing the throttle behavior. Another edited log shows the t-brake test(RPM climbs to 3700 before I let off the throttle), followed by the 2-step test(RPM holds at 2500).

I'm also seeing non-identical bank to bank injector behavior even though I have been running OLSD.

[DrX]

Seems that this does not happen if I get into the throttle slightly less rapidly. This new converter is definitely loose. Tested it a full throttle with the trans brake today and it was stalling around 3900 rather than the spec'd 2600.

[joecar]

What's going on here? When I hit the throttle while rolling at a steady speed it goes WOT, then closes, then re-opens. Its like bouncing off the rev limiter. I recall this happening years ago when the MAP got ahead of the RPM too fast, but I haven't touched the associated table in years. Whatever is causing it is not present long enough to trigger a DTC. I haven't noticed this behaviour from a standing start. Tried a tune from last year and it is still there. Only recent changes are a different 4L80E and converter. Just tested the functioning of the trans brake and noticed that the converter did not hold engine RPM at its rated stall speed(2600).

...


Seems that this does not happen if I get into the throttle slightly less rapidly.

...

This tells me that possibly you're reaching boundary in the sanity tables, so you maybe have to enlarge the boundary a little more.


As for injector pulsewidth (and duty cycle) differing between banks in SD: hmmm, I have think about it, for some reason PCM thinks conditions are different between banks based on the sensors and calculations it performs...

[DrX]

Hi Joe,

I don't see any tables that I can expand any further. Seems to somehow be related to the rate of RPM increase, possibly exacerbated by the loose converter. The only table I can see that is exceeded is C3906, which should only be active between 55 and 65 kPa. I disabled the MAP rationality test. C6101 is maxed.

I had inadvertently enabled semi-closed loop by changing B3601(stoich value). I just fixed that, but still see some variation between banks in the IBPW and duty cycles. Funny that according to my widebands, the AFR varied a fair amount even when it was in closed loop. Not that I trust the NB O2s after running race fuel by them. The WB sensors are fresh. Not sure why commanded AFR is 14.63 in the log. The value in B3647 is 14.60.

edit: deleted additional comments...seems that the log playback was messed up on my logging computer...large chunk of missing frames. Viewed on my desktop it was all there. Closed and re-opened on the logging machine and the missing frames were back??

[joecar]

Maybe C3904-5 are not related to C3906-7 (their descriptions do not reference those tables)... maybe try playing with C3906.

Weird about the missing frames.

Try swapping injectors across banks to see if the injector variation follows the injectors or stays with the bank/PCM.

[DrX]

HPT offers a somewhat different/opposite description for those parameters. No access to the tables themselves though. Not sure which makes more sense. Seems that everyone would be failing the C3906 test if it were always active because no TPS value greater than 65% is ever allowed.

[DrX]

I have only had a chance for 1 test drive. This does not appear to be related to C3904-5/C3906-7. P0121 is not even a valid DTC for this vehicle and for those where it is, it appears that a fault condition must exist for around 20 seconds in order to trigger P0121. Seems that the tables are setup so that these tests do not run during the vehicle's normal idle MAP range.

Looking at my logs, I have logged both GM.DYNCYLAIR and GM.DYNCYLAIR_DMA. How is GM.DYNCYLAIR ("predicted grams of air per cylinder") derived? I am running SD.

Edit: Found this:

GM.DYNAIR - GM's estimated airflow in grams per second based on the VE table. This value is calculated independantly of the MAF. It is used to test MAF rationality and when the PCM is in speed density mode (i.e. MAF removed or disabled).

CALC.CYLAIR - EFILive's calculated grams/cylinder value. It is calculated as {SAE.MAF.gps}*15/{SAE.RPM}

GM.DYNCYLAIR - GM's estimated airflow in grams per cylinder based on the GM.DYNAIR value.

GM.CYLAIR_DMA - internal (DMA) PID that is used by the PCM as an index to look up various tables that are indexed on grams/second. This values is derived from the MAF signal.

GM.DYNCYLAIR_DMA - internal (DMA) PID that is used by the PCM as an index to look up various tables that are indexed on grams/second(??). This values is derived from the MAP, RPM, IAT and VE tables and is independant of the MAF.

So what I am wondering....is C6102 using GM.DYNCYLAIR/GM.DYNCYLAIR_DMA even though there is no MAF? Haven't had a chance to test this yet. But then C6102 is again exceeded after the throttle re-opens, only difference being RPMs are higher, but the throttle remains open.

[joecar]

...

So what I am wondering....is C6102 using GM.DYNCYLAIR/GM.DYNCYLAIR_DMA even though there is no MAF? Haven't had a chance to test this yet. But then C6102 is again exceeded after the throttle re-opens, only difference being RPMs are higher, but the throttle remains open.
Good question...

[DrX]

I adjusted C6102 so that it stays under those values.....didn't make a difference. Think I have run out of limit tables to modify.

Did a few drives today and strangely this did not occur on the last drive. The only changes to the tune on the last 2 drives were the VE tables. So I am wondering if there was a cell in my Boost VE table that was causing calculated airflow to violate some unseen limit. Are airflow calculations based on the Boost VE table treated in the same manner as those from the stock VE table when it comes to the rationality tests?

Tune is scaled 50%.

[DrX]

Spoke too soon....same issue still present testing with the same tune I used last time. Seems to occur when GM.DYNCYLAIR is greater than GM.DYNCYLAIR_DMA for .3 sec and under 1.0g/s

[DrX]

Tried reducing the transitional part of the Boost VE by 5% ...didn't seem to help at all. It seems to me that I had a similar issue back when I first installed this engine/blower setup. I think it went away after I scaled the tune 50%.

[joecar]

Good idea, try scaling again.

[DrX]

It is still scaled down 50%. So I would have to scale it down further. Don't see where I am hitting any limits though.

[joecar]

Maybe DYNAIR[g/s] is exceeding the 512 g/s limit...

( Hmmm, I just looked in your log and it is not )

[Highlander]

The problem is there are some tables you can't see here.... C6102 will only trigger p1514 and REP which is not your problem.... I would raise "neutral rev limiter to 7000rpms". and start there.

[DrX]

The problem is there are some tables you can't see here.... C6102 will only trigger p1514 and REP which is not your problem.... I would raise "neutral rev limiter to 7000rpms". and start there.

All ETC rev limits were at 7000. Fuel cutoff in P/N was at 6000. Could also test disabling the ETC rev limiter altogether.

[DrX]

Raised fuel cutoff in P/N and disabled the ETC rev limiter altogether. Throttle did not close down.

Looking at frame 5908, it also appears that I will be close to 512 g/s shifting at 6500 RPM, even though the tune is already scaled down by 50%. I will gain a bit more room when Boost VE is adjusted to get the fuel mixture smoothed out.

[joecar]

Raised fuel cutoff in P/N and disabled the ETC rev limiter altogether. Throttle did not close down.

...Tables B3330 and B5401...?

[DrX]

I only changed B3330 to 7100 and set B2201 to "Disable". B3330 had no effect...didn't see how it would. B2201 is the one that makes a difference. But I would rather keep the ETC rev limiter if possible.

Seems that somehow the rev limiter is kicking in before 4000 RPM rather than the set value of 7000 RPM. Maybe it is the rate of RPM increase that triggers it?? Which appears to be around 7,500-10,000 RPM/sec when the issue occurs. The only other times the ETC rev limiter has kicked in was at 7000 on losing a driveshaft or transmission.