Thinking about enabling highway mode for gas mileage on my car. 6E xdf. Wondering how much spark advance to give it. Currently my SA is limited to 41* total. Whats the max I can go. Going to set AFR to 15.3 to see if I can save a little gas.
I know, too much time on my hands.

 

Nothing wrong with trying out the lean cruise mode. Note that the maximum SA is likely 48* BTDC. With the initial at 6* BTDC, and being able to program 42* into the distributor, 48* at the crank is the limit.

I have a good post on tuning lean cruise mode here someplace. Basically, lean the AFR as much as possible but do not allow lean misfire to occur.

Then add in SA to get some power back. Too much SA and the engine will either ping or get rough.

RBob.

 

Thanks. I set the max advance to 41* a long time ago 6* base timing included. I will search for lean cruise threads.

 

Please post your results as I am attempting the same thing. ;-)

 

I think I will give it 6* advance, 47 total. Take the AFR to 15.3 and datalog. May be a few days before I try it.

 

No, no, no, the maximum SA and the maximum retard values in the calibration are distributor constraints. Not the at-crank timing values.

See the Tuning Guide Book sticky, Chapter 5, 8746/'7747/'8063 section, SA Logic thread.

RBob.

 

My datalogs never show more than 41* total. With the values screen showing it actually says degrees relative to TDC.
I also use Datamaster. the display gives me a choice. SA or SA computed. SA computed will show 35* when SA shows 41*.

 

I set up HF mode and ran a short log. It went to 47*A at 60 mph cruise. It should have went to 15.3 AFR but this did not appear. ????? Max time allowed is 255 seconds in HF mode. I will have to run a longer log to see how this works. If not watching the datalog you dont notice the change.

 

Just ran a long datalog with both Highway spark and fuel allowed. Its all doing what it should. Adds 6* advance and AFR goes to 15.3. Not seeing any issues so far. Now I need a roadtrip to see real results. Next fill up may show something, if it does I'll post it.

 

At the mid-range MAP you can likely command a leaner AFR. I've been able to go into the 16.1 range. At real low MAP the 14.8 - 15.3 AFR works better to prevent misfire. The density of the mix in the chamber is so low it becomes difficult to light off.

It isn't uncommon to get a 10% increase in mileage. Be sure to let the ECM drop out of lean cruise mode for 10 - 12 seconds. This allows the BLM to adjust for a more consistent AFR.

RBob.

 

Thanks R, 10% would be awesome. Every 255 seconds it drops out for 10 seconds. MAF car, by the way. Im sort chickenchit so I went consevative. 15.3 AFR at LV8 32 and 64, 15 at 96 and 128. 6* A at LV8 112 and 3* at 128. I may tweak on it later this week. Thanks for your input on that.

 

i haven't done any tuning in a long time, been having an issue with it going extremely lean only when i use cruise control & using my wideband.
but when i was tuning, i played with hiway mode a lot.

i forget how lean i've gone on my motor, a search should turn it up. but i believe i have gone up around 16.5~16.8 with no problems.
i don't think i ever mentioned it in any of my other posts on running lean cruise,
i have the small cap distributor so i bumped my base timing up, IIRC to 10 degrees. i think the large cap can handle more advance from the ECM.

something i am jealous of is that you guys with 6E have the ability of controlling time in & out of hiway mode separately.
with 8D, time in is the same as time out. i would love to do 2~3 minutes in & 20 seconds out.

 

Last tank, I got a 1 mpg increase. It may be a while before I make a roadtrip. I may lean it to 16 to 1 before that. My normal driving is sort of rural. Not a lot of interstate, not a lot of in town traffic.