Car feels really flat initially

[Tordne]

On the first start of the day (cold start) the car feels really flat and limp initially.

My initial thoughts were that it was related to the spark being retarded by the B5910 ECT Spark Table and the B5956 Multiplier Table.

I basically set the Multiplier Table to all 0 so that essentially no spark would be pulled. This seemed to make little or no difference :eek:.

So the question is: What else could it be?

Cold start for me these days is about 15*C (60*F) so not really that cold.

Cheers,

[TAQuickness]

On the first start of the day (cold start) the car feels really flat and limp initially.

My initial thoughts were that it was related to the spark being retarded by the B5910 ECT Spark Table and the B5956 Multiplier Table.

I basically set the Multiplier Table to all 0 so that essentially no spark would be pulled. This seemed to make little or no difference :eek:.

So the question is: What else could it be?

Cold start for me these days is about 15*C (60*F) so not really that cold.

Cheers,

Have you tried slipping a Viagra into the gas tank 30 minutes before cranking?

But seriously, at what point does the beast feel plump and erect? And how long has this been going on? If it last more than 4 hours, I think you should call a doctor.

[ringram]

Maybe down to bad atomisation of the charge due to cold intake tract which will tend to condense the charge rather than assist atomisation.
Could be dirty injectors not making a nice spray, just squirting a pool of fuel into the port.

[SSpdDmon]

Maybe because initial, cold start commands OL for a couple of minutes?

[joecar]

Could it be too lean immediately after startup...?

[Tordne]

Maybe the Viagra is the trick :)

I'll let my WB heat up for a long time before startup this morning so that I can accurately get the AFRs from cold start, usually I don't care.

It doesn't last too long which is why I thought it must have been those ECT Spark tables. But those retard timing up to about 70*C odd. And it definitely doesn't last that long. So, I'm not really suspecting spark at this stage.

Will post more lately :)

Cheers,

[dc_justin]

Could it be too lean immediately after startup...?

My thoughts. My truck runs a bit rich when cold and has very good throttle response, even with the light throttle I give it.

[Tordne]

OK so the winner would appear to be REAL LEAN. I marked a couple of points where it felt flat and the AFRs were around the 16.6:1 mark with a commanded AFR of approx. 14.7:1.

I have another question as a result of this logging though. I logged a PID called "IAC - Warmed-up Airflow In Gear" (GM.IAC_WD_DMA). This has a value of approx 8 grams/s and gets decayed out gradually. I'm wondering if this added airflow could be causing the lean condition? And, which tables does this PID relate to (doesn't say in the "More info" pane)?

Cheers,

[TAQuickness]

when did you start having this problem?

[Tordne]

Quite a while... I just thought I go about trying to fix it. Tune is otherwise pretty solid right now so I need something else to mess with :muahaha:

[Kris]

It seems to be a pretty common issue among SD tuned cars... mine runs like complete crap until it is warmed up... AFR at idle sticks at about 17:1 and is crazy lean all over the place if I try to drive it before it is warmed up. I haven't bothered messing with it too much since i'm fixing to make a drastic setup change.

[Tordne]

Anyone know what the PID "IAC - Warmed-up Airflow In Gear" (GM.IAC_WD_DMA) relates to in the Tune Tool table wise? I'm wondering if too mush airflow is being added and leaning the mixture.

There must be a fix :)

[Alvin]

Did you tune this car in SD open loop? If so, I have a good idea on how to fix it.

[Tordne]

Car is OLSD all the time :) Don't intend to go Closed Loop at all.

Hit me with the fix :)

[Tordne]

Ross,

Posted this above - do you know the answer?

I logged a PID called "IAC - Warmed-up Airflow In Gear" (GM.IAC_WD_DMA). This has a value of approx 8 grams/s and gets decayed out gradually. I'm wondering if this added airflow could be causing the lean condition? And, which tables does this PID relate to (doesn't say in the "More info" pane)?

Cheers,

[ringram]

Why not change it dude? Drop it down and see what happens.
My latest tune was too experimental, idled, but coughed on throttle. So had to reflash to get to work.. was late.. hehe..

[Tordne]

That PID is actually just a sum of Desired Airflow + Startup Airflow. So the values are correct as the Desired Airflow table is correct.

[SSbaby]

If its the same flatness as I've recently experienced it may be to do with not running enough spark?

I was having driveability issues, notably flat response after cold-start open loop running and surging b/w 1600-2000rpm and discovered a cure only after loading in an old tune.

Yes, I was a better tuner 4 months ago than I am today! :nixweiss::doh:

[joecar]

If its the same flatness as I've recently experienced it may be to do with not running enough spark?

I was having driveability issues, notably flat response after cold-start open loop running and surging b/w 1600-2000rpm and discovered a cure only after loading in an old tune.

Yes, I was a better tuner 4 months ago than I am today! :nixweiss::doh:
Tony,
Not quite, because you had wits enough to go back to the old tune, so you're a better tuner today! :D

Cheers
Joe
:cheers:

[SSbaby]

Thanks Joe. It's lucky I didn't discard "my best tune to date". :D

I guess it also doesn't hurt to get back to basics (i.e. load in a stock tune) and start again... making changes in small increments.

PS The difference between respective tunes is like night and day as far as driveability is concerned.

[Tordne]

In my case I'm convinced it is solely the initial leanness issue. I have tried 0'ing out the ECT Spark Table multiplier etc and it made no difference. The spark tables are fine after the initial flat period. In my logs some of these flat points (where I marked the log) we in the 16-17:1 AFR range from memory.

My current workaround is to use the A0008 table in the Custom OS to command a richer mixture up to 50*C. Seems to have made a difference :)

[Black02SS]

I would look at see about a new tuner. J/K

[Tordne]

I would look at see about a new tuner. J/K

I'd get you to do it but you're to far away and far to expensive :) J/K