Injector timing vs ECT -- why is stock EOIT so early for cold ECT?

[JasonS5555]

Hey guys,

After my tip in bog thread, and all the help I received there, I'm starting to look more at the injector timing. VERY interesting stuff. After reading this excellent thread:

http://www.hptuners.com/forum/showth...ereencing-what

My question really is, why did GM change the injector timing SO much when the engine is cold?

For example, the EOIT for cold temps is 2.55, and for warm temps its 5.55. With the stock boundary of 6.5, this implies that the EOIT is 300.5 for warm temps but only 30.5 for cold / startup temps. Why on earth would you want the EOIT to be SO early? I'm just trying to get a handle on this so I can make the appropriate adjustments to my tables based on cam and injectors.

Thanks!
Jason

[mowton]

It's that early when cold to allow sufficient time for the cold fuel on a cold intake valve to evaporate as needed.

Ed M

[JasonS5555]

But isn't the exh valve open if EIOT is that early? That puts it more than the -29 deg of stock "overlap". Right?

Thanks,
Jason

[C5 2000]

http://www.hptuners.com/forum/showth...ereencing-what

[mowton]

Hey guys,


For example, the EOIT for cold temps is 2.55, and for warm temps its 5.55. With the stock boundary of 6.5, this implies that the EOIT is 300.5 for warm temps but only 30.5 for cold / startup temps. Why on earth would you want the EOIT to be SO early? I'm just trying to get a handle on this so I can make the appropriate adjustments to my tables based on cam and injectors.

Thanks!
Jason

Jason,

Actually you add the Boundary and the Injection timing which defines the EOIT at like 95 degrees. I gueess that still pretty early but there is a trade off between fuel evap, idle quality and emissions at cold temps.....

Ed M

[JasonS5555]

Thanks Ed. After doing the math it still seems crazy early.

C5 2000, did you read my original post? I reference and have read the post you list. I wasn't asking about EOIT in general, but specifically why it was SO early at cold ECT.

Thanks,
Jason

[GHuggins]

It's like Ed stated in his first post and on top of that it's supposed to allow raw fuel to better be sucked into the exhaust stream to help quicken the lighting off of the cats or atleast that's what I've been told. Not sure how much you could believe that though. I still don't have the OE understandings of injection timing.

Just know the lower the number on the newer ECM's the more retarded the timing is and the higher the number on the older ones the more retarded it is with all numbers being needed to be added together to get your final timing value - Again as Ed stated earlier...

[JasonS5555]

Thanks for chiming in GH. So I'm not alone in thinking that the EOIT cold timing seems a little crazy.

I may see if tuning the cold ECT EOIT values in the normal table gets rid of some of the cold start fuel smell.

Jason