Megasquirt EFI Lean Cruise Reality Check

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440fury

440fury

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Hey everyone,

I am having a hard time getting my tune dialed in for lean cruise, and I wanted to see if anyone has a reality check on me. WOT performance is fantastic, this is specifically only a problem for highway cruising.

The car is a 340 Duster, 4 speed, 3.91s. The 340 is a pretty vanilla build - XE274 cam, 9.5-1, Edelbrock closed chamber heads with some squish. Pulls about 13-14" of vac at idle. Cruising RPM is 3-3.8k.

The ignition map is pretty close to how a distributor would be dialed in. 12-14 initial, 12 "Vac advance" at 70kPa in the manifold (9" vac), and 22 mechanical advance by 3000 RPM (34-36 total). The timing is accurate, and I have set the timing offset in tunerstudio - I am confident there isn't a mistake there. I don't have decel fuel cut on. I really think it's in the fuel and ignition tables.

Here's my dilemma: My cruise AFR is around 14-14.5, as I like to be on the richer side of things as I do the tuning. But as I add more advance at cruise (any more than 38 or so), the engine hates it. I get light pops out the exhaust, and pops on decel. I have pulled all of the low load advance past 3k, so anything over that is a fixed 36 degrees of advance. I was fully expecting to need 40-50 at light cruise, and the fact that I can't get there is leading me to believe the fuel tune is keeping me from getting there.

Now, I am thinking I may be too rich to run any more advance, so I am planning on going up in AFR, then readjusting timing, and repeating the process until I can get a nice lean cruising AFR and a rational advance. Then again, this is the only car I've ever tuned, so I am missing some reality checks (i.e. that cam doesn't want that much cruise advance, too much rear gear, etc.)

Can anyone with similar experiences getting this all dialed in give me a reality check here?

Thanks!
 
What are you running, COP or distributor? Is it possible you have a simple rotor phasing problem?

While I have a neglected MSII in partial assembly, I know little about tuning them
 
67Dart273 said:
What are you running, COP or distributor? Is it possible you have a simple rotor phasing problem?
Click to expand...

My bad - just an MSD distributor. Pretty basic setup - just using the pickup as a basic trigger. The distributor advance is locked out.
 
If you can, post some of your maps. Fuel, ignition. Screen shots should be sufficient. Are there any active table modifiers running currently?
 
If you’re using an msd distributor then phasing is a real problem you need to look at, as Del mentioned. Msd makes an adjustable rotor for this exact reason.
 
And phasing really becomes an issue when the distributor is locked out and you start to add a bunch of cruise advance. I’ll bet it’s skipping to the next tower.
 
TT5.9mag said:
If you can, post some of your maps. Fuel, ignition. Screen shots should be sufficient. Are there any active table modifiers running currently?
Click to expand...

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.

AFR_Table.png


Ignition_Table.png


VE_Table.png
 
Are your actual AFRs matching your target AFRs? If so I would not mess a whole lot with the ve table at this point. Focus on ignition. If you have big descrepencies between target-actual afr then you need to play with the ve table. How is o2 feedback during cruise? Is it pulling or adding a bunch of fuel?
 
TT5.9mag said:
If you’re using an msd distributor then phasing is a real problem you need to look at, as Del mentioned. Msd makes an adjustable rotor for this exact reason.
Click to expand...

Ah, I see what you and 67dart mean with the phasing.
 
440fury said:
Thank you both for this info - this has been a fantastic help. I've ordered the rotor and I should have it by tomorrow.
Click to expand...
Wait......did you check your phasing to make sure it was off before buying anything?
 
EDIT: Missed the late posts above

440fury said:
My bad - just an MSD distributor. Pretty basic setup - just using the pickup as a basic trigger. The distributor advance is locked out.
Click to expand...
OK but you need to check rotor phasing. Remember the trigger in the distributor IS NOT WHERE THE SPARK IS HAPPENING in time or degrees. It is being determined by the computer, and the rotor could be "anywhere" by then
 
TT5.9mag said:
Wait......did you check your phasing to make sure it was off before buying anything?
Click to expand...

No, haven't checked anything yet. Wanted to make sure I ordered it today, so I could have it by the weekend. Can always return the rotor if that's not it!

I'll update either way.
 
PS one of the real tuners guys just did the tune on (you can’t make this up) a rig for a blind guy to set a land speed record. The tuner partnered up with a Boeing engineer for guidance system he did tune and they set a record. They are all crazy smart. I try and listen to them on occasion but my deer in the head lights look with a little drool is a dead give away.
 
Your also going to need a sacrificial cap to drill a hole in to check/adjust rotor phasing.
 
440fury said:
No, haven't checked anything yet. Wanted to make sure I ordered it today, so I could have it by the weekend. Can always return the rotor if that's not it!

I'll update either way.
Click to expand...
Certainly not a bad idea to have one on hand. I just don’t like to throw parts at problems. Order a cap too so you can drill holes in it. As said above.
 
MoparMike1974 said:
Your also going to need a sacrificial cap to drill a hole in to check/adjust rotor phasing.
Click to expand...
So, if a person does not have a distributor machine handy, he could still drill view ports into a distributor cap and use a timing light to observe the position of the distributor cap conductor and the rotor while the engine is running at minimum and maximum advance? Interesting.
 
You an also get a "am I on the right track" feel for this by doing the following:

Without changing anything in the dist or timing, make sure you know what your full advance MS timing is, and get those figures in mind.

Then simply set up the engine to fire on NO1 with the marks stopped on whatever that figure is, such as 35BTC etc. If you don't have the balancer marked, you can just measure it out mathematically, IE balancer is so big around, so many degrees per inch, etc

Now with balancer stopped at total electronic/ MS advance, remove cap and carefully see where the rotor is stopped in relation to no1 tower
 
my68barracuda said:
So, if a person does not have a distributor machine handy, he could still drill view ports into a distributor cap and use a timing light to observe the position of the distributor cap conductor and the rotor while the engine is running at minimum and maximum advance? Interesting.
Click to expand...
Yup I’ve never done one on a machine. Always on a running engine. Just shoot the timing light at the hole and you’ll see the rotor tip and the spark.
 
I don't think you have a rotor phasing problem, as you say WOT is 'fantastic'.
I know nothing about MS, but it sounds like cruise is simply too rich. Too rich burns slowly & mixture could still be combusting when the exh valve opens...which gives popping in the exh. If the injectors are leaking [ faulty, pressure too high? ], then on decel the higher vacuum will pull fuel from them for an over rich mixture....& you know the rest.
 
Following up -

1.) Rotor Phasing
Pulled the cap this weekend at 30 BTDC and the rotor was quite a ways off from the #1 cylinder.

I installed the new one using a process similar to 67darts' procedure and from the Megasquirt website. I am planning on running a max advance of around 50, and a minimum of around 10, so I split the difference. I moved the crank until it was at 30 BTDC, pulled the cap, installed the adjustable rotor (MSD p/n 84211) directly pointed at the #1 post. Things improved dramatically at high advance, but I am still planning on drilling the cap and watching very closely to get it perfect.

2.) Tuning - mostly for someone reading this in the future.
After getting the rotor phasing mostly squared away, I went back to my original ignition table shown above. I have since brought back total timing to around 40-42 degrees at lean cruise which I have been able to have run nicely at around 14.8-15.0:1. I can go leaner, or with a bit more advance, but I'm not going to push to hard until I can get some miles to really study how the car responds to tiny changes.

As for the popping on decel and highway - adjusting the rotor phasing got me about 80% of the way there. I still have an occasional puff from the exhaust at highway cruise, but I still have more adjustments to make and I want to confirm the rotor phasing is perfect. Decel popping was still there after rotor phasing, but was reduced to about 50% of its original intensity. I started fixing this by tweaking my VE table manually under ~40KPa until I was seeing the AFRs I wanted at cruise. I now stop the Autotune from touching anything under 40KPa, just because it's too hard to tell cruise from hard decel.

After, to get rid of the pops, I added in a fuel cut after 1 sec of MAP readings under 40KPa and a TPS of <10%, which has eliminated 99% of decel popping. I still have some work to do there, but it is dramatically improved.

It is important to note that I am by no means a seasoned tuner, this is my first full year of working this system out. These settings are just what I have found worked for my setup, and has given me a basis to go off of while being drivable.
 
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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