L28ET Idle Ignition Advance

[Namor]

I have an L28ET and I am having issues dialing in my idle.    

 

I have been running right around 20* of timing at idle per the service manual and my idle is around 850rpm (no IAC, so it varies).  The car idles well if I have it set rich (lambda of ~.9 or less) but if I lean it out, it starts getting random misfires when I get close to lambda of 1, maybe 1 misfire per second or so.  

 

These misfires aren't enough to cause RPMs to noticeably drop, but it causes my AFR to jump around and frankly it just sounds bad.  

 

My ignition map is setup so that I Idle in a "valley" and just testing, I decided to take a bunch of timing out, so I lowered all the blocks around where I idle by 10* and my misfire issue went away.  

 

At this point, I plan to leave my timing down around 10* because I care how my car runs, not what a book says.  I'm just curious if this is something anyone has run into before?  What timing is everyone else running at idle?  I figured everyone just set theirs to 20* +/- 3* per the service manual, but now I am thinking maybe not.  

 

 

MS3x

Fully Sequential Injection

450cc injectors (B450L DSM Blue Tops) w/ resistors

Stock FPR

Wasted Spark Ignition

Trigger Wheel from DiyAutoTune

 

[Chickenman]

Golden rule in engine tuning. Give the engine what it wants. If it's happier with a bit richer idle or a bit less timing. Then give it what it wants.

 

I do seen one error in your methodology though. Idle mixtures are typically richer than Stoich or Lambda 1.0. They have to be because the throttle blade is nearly closed. This reduces mixture density and VE. The decreased density require a slightly richer idle mixture to provide good combustion. Typical idle AFR on petrol are usually around 13.5 or 13.1. Stoich is only an effective baseline under Cruise conditions.

 

I just punched a 13.5 AFR ( gasoline ) into my face engine calculation site and it came up with a Lambda value of .92.  13.0 AFR is Lambda .88 . So your engine is trying to tell you it wants more fuel, just as tuning manuals predict. Thta's why the misfire goes away at .9 Lambda...because you are finally giving it the fuel the engine wants.

 

Here is a very good site with a Lambda to AFR conversion for various types of fuels.

 

http://www.wallaceracing.com/air-fuel-lambda.php

 

Big overlap cams often require around 12.5 or 12.0 AFR  at idle ( gasoline ) . Dilution of mixture due to valve  over-lap requires a richer mixture. EGR also requires a richer mixture than Stoich. There are other modifications that can affect idle Lambda values as well. Tune with a vacuum gauge and and your AFR meter. Adjust the Vacuum gauge until you have the highest reading possible. It should be nice and steady with na stock or mild camshaft.That is Best Idle.

 

Tuning richer or leaner than that point will reduce the Vacuum reading.Tuning slightly ricer gives " Rich best idle " and is sometimes beneficial on cars that have big cam shafts. Tuning leaner than the best Vacuum point is " Lean best idle " and is often used to meet emissions specs. Note that lean idle mixtures require a POWERFUL spark to ignite the falme front properly. CD ignitions like Crane Hi-6 and MSD allow leaner idle mixtures because the high enrgy spark can ignite a diluted and low density mixture. 

Edited January 30, 2017 by Chickenman

[Chickenman]

I just grabbed my EFI tuning manual from DIYAutoTuning, and the exact procedure that I mentioned above is noted on page 106 under " No Load Idle Tuning ". If you don't already have this book , get it. It's by Matt Cramer and Jerry Hoffman of DiyAutoTuning. Awesome technical book that is easy to figure out for the Layman.

 

Performance Fuel Injection Susyems. Publisher HP Books . ISBN: 978-1-55788-557-9

 

You can order it online from Amazon and other Book retailers or order it direct from DiyAutoTuning.

 

https://www.diyautotune.com/shop/apparel-merchandise/books/

[Namor]

Oh I'm definitely a believer in "Give the engine what it wants."

 

The main source of information I have been going from is two books by Greg Banish and he essentially says you want to be around stoich, but some things might prevent you from being able to get a stable idle there (such as an aggressive camshaft or batch fire vs sequential) 

 

Since I am running a stock camshaft and have converted to fully sequential, I'm going to stick with what I have found that allows me to idle around stoich.  I was just curious if anyone else had tuned theirs similarly.    

 

 

As for the book by Matt Cramer, I'd buy it, but...I actually already have it (I honestly forgot I had it, just walked over to the bookshelf to double check before ordering.)  I read it cover to cover a while back but found more in-depth information in the books by Greg Banish.  

[Chickenman]

Greg Banish. What are the Titles of the books he published? I'll have to look around my Library.

 

Edit:  Never mind. Found the info. Have just about everything except his publications.

Edited January 30, 2017 by Chickenman

[Chickenman]

IMHO, I'd give it a bit more fuel. Just make it happy.

 

Running Stoich at idle can be done on Modern engines that are designed for it. Combustion  chamber design with high squish and a prei-ignitor chamber  and a killer powerful ignition system are three things that an old engine design like the L-series lacks.

 

Spark Plug gaps in modern engines are often in the .060 range. I've seen some engines ( Ford's ) running .075" gaps from the factory. Got a CDI Ignition  or COP ignition on your engine? That's part of what it takes to run an engine that lean at idle. May not be worth it. You may be able to do it with .045" plug gaps, but you still need a ton of spark with lots of Current flow.

 

Edit: And of course you're running a Turbo. Probably with increased boost and for that you naturally want to reduce the plug gap to prevent spark blowout. Well that's just not going to work with trying to run Stoich or close to it at idle. You need a big fat spark kernel with a wide gap ( .040" and higher ).

Edited January 30, 2017 by Chickenman