Lean Cold Start Problem

[swingtan]

Hi All,

I'm hoping someone here can help out with this one. I have a problem very similar to this..... http://forum.efilive.com/showthread....ght=cold+start except that it only occurs for 8 to 9 seconds for me.

The car is an L76 Holden, with the E38 PCM and is currently running a MAF-less tune. When it first went MAF-less, it didn't have the problem, but had a very rich idle when warm. After some auto VE work, the warm idle has been fixed, but I now have this cold start lean out problem.

I've attached a log segment showing how the measured AFR's start off well, but then lean out to 20:1. After 8 seconds from start, the AFR's come down to the 14 range and all is fine, but for the first 8 seconds the car runs very rough and sometimes stalls.

Here's what I've thought about....

• Given is really only cold start, it must be something to do with OL fueling.
• I've looked at B0141 to B0148 and tried altering settings to richen up the fuel on cold starts, but there has been minimal effect.
• The 8 second time had me thinking it may have something to do with B1832, but again this seems to have little effect on the problem.

I guess I could try altering the VE table to richen it back up, but that's not the way it should be done. Any ideas on what to look for here ?

Simon.

[hymey]

I would not alter the VE table.

Have you tried B1205. for ECT. I would stick 20% more fuel in at start up.

Cheers

Joel

[swingtan]

B1205 ? Injection timing vs ECT. I can't see that this adds more fuel, simply alters when the fuel is injected. Happy to be corrected though.

[hymey]

That's correct. Not sure if it works. But it has higher settings when ect is lower. So maybe this could help.

I would have thought that cranking enrichment could help.

Also try reducing idle airflow slightly.

I am having dramas with mine hunting now I have gone mafless.

Cheers

Joel

[swingtan]

I've been playing a fair bit with this over the past weeks and am no closer to fixing the problem. Something I have noticed though, is the following....

• B1832 does have some effect on the start up, but only for the first 1 second. Setting the commanded air flow around 12g/Sec will have the car fire and try and hold an idle speed of about 1700RPM. So it's doing something.
• After 1 second, the idle speed drops dramatically and the car runs very rough. The settings in B1832 do not drop below 11g/Sec so the idle speeds "should" be quite high.
• Logging the start process showed an interesting issue. B1832 maps ECT vs GM.RUN_TIME to command air flow. However, logging GM.RUN_TM in scan tool doesn't seem to work.
• When logging GM.RUN_TIME and SAE.RUNTM, I get vastly different results. SAE.RUNTM counts up in seconds as expected, but GM.RUN_TM counts up by 160 every second. So after 1 second from starting, GM.RUN_TM is 160.
  
  
  
  SAE.RUNTM Vs GM.RUN_TM
  
  0 - 0
  1 - 160
  2 - 320
  3 - 480
  4 - 640
• Given that GM.RUN_TIME jumps from 0 to 160, I can see that B1832 will only be used for the first 1 second from start, as after that GM.RUN_TIME = 160, well over the 8 second limit.

So, What is then PCM musing for idle controll in the 7 seconds after the first second from start? I'm guessing it's not the normal idle tables as after 8 seconds from start, the rough idle disappears and it idles fine. SO the PCM either must be using something else, or the normal idle tables simple don't work until 8 seconds after the start.

Are there any ideas as to why GM.RUN_TIME jumps in steps of 160 every second when it seems it should be counting in seconds?

Simon.

[swingtan]

Bump.....

[swingtan]

Interesting update on this......

It seems that "spark smoothing" has been causing some issues for me on this as well. I removed spark smoothing to help with the TCS problem and now mu cold starts have improved to some degree.

Previously the car would fire and flare a little, then the revs would drop right down and the car ran very rough for 8 seconds before the idle picked up and it ran nice and smooth. Every once in a while it would stall in this first 8 second window after a cold start.

Now that spark smoothing has been turned off, it fires and flares, then the revs drop as before but it idles much smoother and doesn't shake around as much. It did stall this morning after the flare but I think some tweaking of B1832 and B0138 will fix that. Here's hoping......

Simon.

[hymey]

spark smoothing fixed my probelems which were very similiar

[ntae]

My hsv had this off as standed , so i take it thats why i was not having that problem

[swingtan]

Probably, it's a "manual only" thing from what I can see. Auto's don't do spark smoothing so they should be immune, so to speak.

( I should say that Autos have it turned off from the factory... )