Megasquirt EFI Lean Cruise Reality Check

TT5.9mag said:

Excellent follow up and good news. Glad the rotor phasing helped. Question, why are you waiting one second to pull fuel? Narrow that down a bit and I bet your popping on decel gets even better. I’d say your doin well for only a year of tuning. Nice work.
Edited to add:
Try leaving the afr alone at cruise and just bring more timing in. Add a few degrees at a time in that area of the map and watch the rpm/mph trace. At constant throttle, when the rpm and/or mph drop off it’s all it wants. Then change fueling and do it again.

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Thank you for your help - it would have taken me a while to figure out the rotor phasing/efi problem without that tip.

I'm in a bit of an odd circumstance as far as the highway tuning goes since I've got the 4 speed, 3.91's, and a cruise RPM of >3200. Is there a manual transmission equivalent of your testing method? My method so far is turning on autotune (above 40kPa still..) with the AFR's I'd like as the target, then changing timing, then the autotune brings it back to the same AFR.

I've been going by what timing/AFR requires the least amount of throttle to maintain speed, without misfires. That's the only thing I came up with so far as an objective tuning target, so very open to criticism on that one.

From the original ignition table above, I pulled the WOT/max advance timing to 32 degrees, and pulled the cruise timing down to 40/42. When I was running 46, I was getting a little bit of a miss. Don't really have a good perspective on whether that's reasonable or not given my setup, but I figured 8/10 degrees of highway advance is better than nothing, so I stuck with that for a baseline.

You’ll get no criticism from me. Your tuning method is right on. The least amount of throttle position required to maintain a given speed will accomplish the same result. I just don’t use the auto tune feature, (on anything really) except maybe when the map is dialed pretty well and other factors come in to play, (like altitude). I like the o2 to make small corrections to account for small variations. The reason I said to leave the fuel alone and just bring in timing is to eliminate variables and the ignition advance will lean it out a bit. But if the auto tune will automatically bring the AFR back to target, then get the cruise advance in, and then change the target to as lean as she’ll take without surging. I don’t like cruise afr much leaner than 15:1 or so, so you’re close. I don’t think there is much mileage to be gained going leaner.

GREAT!! Sound like you have made some good progress "I ain't a tuner" either LOL

My progression/ experiments into EFI:

1...Found an old Holley "Pro-jection" system, one of the old ones with 4 or 5 pot adjustments on the box. These are not programmable, they are pot adjusted, 2BBL TBI. Did not even originally have an O2. They are operated in what is called "Alpha N"

2...Found a used complete Holley "Commander 950, a 4bbl TBI unit with an "all manual" but very capable computer---this was the earlier Holley system, adaptable from TBI to multiport, and could run either Alpha-N or Speed density (MAP sensor)

3...I got a third party program for the above from some guy which "autotunes" the fuel map and that helped but in the end I.........

4.....Bought a bare bones Holley HP computer and harness and used the Commander TB with the HP computer. The HP is in most of Holley's higher end stuff except Dominator which is a different computer. The HP also, can be operated either TBI or multiport, and either Alpha-N or Speed Density

This was all at the "end" of the Dart (which is still apart) and "projections" were to adapt it to multiport or even a Hilborn manifold which I scored

TT5.9mag said:

You’ll get no criticism from me. Your tuning method is right on. The least amount of throttle position required to maintain a given speed will accomplish the same result. I just don’t use the auto tune feature, (on anything really) except maybe when the map is dialed pretty well and other factors come in to play, (like altitude). I like the o2 to make small corrections to account for small variations. The reason I said to leave the fuel alone and just bring in timing is to eliminate variables and the ignition advance will lean it out a bit. But if the auto tune will automatically bring the AFR back to target, then get the cruise advance in, and then change the target to as lean as she’ll take without surging. I don’t like cruise afr much leaner than 15:1 or so, so you’re close. I don’t think there is much mileage to be gained going leaner.

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Leaner is not always better LOL

It sounds like you are on the right track. Since I'm a self taught megasquirt tooner, I'm an expert at it....lol. Here's my $.02

Set your timing like a mechanical advance distributor. Get your AFR where you like it across all scenarios. After that's all set, adjust your timing. Timing does not affect AFR. I tried the "vacuum advance" cruise timing at 40-45 degrees and I didn't care for the way it made my car run. I honestly don't see any benefit. I have individual coils for each cylinder so I can pretty much dial in whatever advance I want. My motor like "all in" advance around 3200RPM. I just keep it there based on RPM, not MAP.

I've never tried the auto tune in Tuner Studio. I've read so many posts where it made fuel tables a big mess. Therefore, I've stayed away from it. (Holley auto tune is a different story).

Here's how I tuned the VE tables and it seemed to work pretty good.

• Go for a long drive while data logging. Drive it hard in every gear multiple times, cruise for a while, sit in traffic, etc. (ride the brakes to get into cells that are outside of normal driving)
• Load your log into Megalog viewer and set up the Histogram/Table Generator to have the same X & Y values as your VE table. MAP on Y and RPM on X. Select AFR on the Z axis. It will automatically show your AFR in the cells and you can see where you are rich/lean. Do some math and determine what percentage you are high/low from your desired AFR and adjust your VE table accordingly.
• Repeat this process until you get your desired AFRs when you are out cruising. It only took me a few times to get it really close.

If you run closed loop AFR control, you will notice it runs much better when your VE it close to the target because the software isn't working as hard to make corrections.


What throttle body are you using?

440fury said:

No table modifiers as far as I know.

Here are my tables from when I started the test drive last night. I could not cruise at highway speed, so dropped the max timing down to 46->40. Got better, still popping out exhaust. Needed to get home without drama, so set everything above 3k RPM fixed at 36. Fine drive home, but I find it hard to believe that's all it could take at cruise.

Here is a possible mistake I may have done - I ran the auto tune feature and had the minimum kPa set to 20, so it was doing the bottom of the VE map. It may be possible that it richened that up big time cause it kept seeing decel AFRs in the 17-18s. My next test I am planning on doing is leaning up the VE around cruise until I hit 15:1 or so, then adding back in some advance and see where that takes me.

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I would adjust the RPM on the AFR table to your usable RPM. You aren't going to be controlling AFR at 0 and 200RPM. Adjusting this can give you more resolution in your operation ranges.

racerjoe said:

It sounds like you are on the right track. Since I'm a self taught megasquirt tooner, I'm an expert at it....lol. Here's my $.02

Set your timing like a mechanical advance distributor. Get your AFR where you like it across all scenarios. After that's all set, adjust your timing. Timing does not affect AFR. I tried the "vacuum advance" cruise timing at 40-45 degrees and I didn't care for the way it made my car run. I honestly don't see any benefit. I have individual coils for each cylinder so I can pretty much dial in whatever advance I want. My motor like "all in" advance around 3200RPM. I just keep it there based on RPM, not MAP.

I've never tried the auto tune in Tuner Studio. I've read so many posts where it made fuel tables a big mess. Therefore, I've stayed away from it. (Holley auto tune is a different story).

Here's how I tuned the VE tables and it seemed to work pretty good.

• Go for a long drive while data logging. Drive it hard in every gear multiple times, cruise for a while, sit in traffic, etc. (ride the brakes to get into cells that are outside of normal driving)
• Load your log into Megalog viewer and set up the Histogram/Table Generator to have the same X & Y values as your VE table. MAP on Y and RPM on X. Select AFR on the Z axis. It will automatically show your AFR in the cells and you can see where you are rich/lean. Do some math and determine what percentage you are high/low from your desired AFR and adjust your VE table accordingly.
• Repeat this process until you get your desired AFRs when you are out cruising. It only took me a few times to get it really close.

If you run closed loop AFR control, you will notice it runs much better when your VE it close to the target because the software isn't working as hard to make corrections.


What throttle body are you using?

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One of the first ignition tables I ran was a "mechanical advance only" distributor curve and the car ran well with it. I struggle to leave "good enough" alone which has led me down this path (and on a larger scale, brought me to EFI in the first place). I saw several threads which all were along the lines of "run vac advance, you are throwing away free fuel efficiency without it", which kicked off this whole round of tuning to get more timing at cruise.

For the throttle body, I am running a Holley Terminator TBI with a 1/2" open spacer below it.

I will give that tuning method a try. I haven't done anything with the datalogger yet, except for accidentally turn it on.

racerjoe said:

I would adjust the RPM on the AFR table to your usable RPM. You aren't going to be controlling AFR at 0 and 200RPM. Adjusting this can give you more resolution in your operation ranges.

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Yeah, I see what you mean. I'll spend some time cleaning up these tables a bit.