You can set it to cut fuel when those conditions are met. So if the engine is over 1200rpm the vacuum is high, and the throttle position is lower than 30 (29 is no throttle) and the engine is halfway warm it will cut the fuel. So once it goes under 1200 it starts the fuel back up but it doesn't have enough time to get gas into the cylinders before it dies usually. I could be a normal person and set it to 1300 so it won't die as easy but I would rather just hit the throttle slightly when I am wanting to go to idle to keep it from dying. With it set at 1200 I can basically let off the throttle anytime I want and the injectors will cut. I also don't have any acceleration enrichment for low speed throttle opening so when I give it gas again it just picks up and runs like normal with just a slight stumble without using extra gas.
The ignition table I copied from my kit car to get the rough idea of how it should look I have a knock sensor still hooked to my tape player so when I heard knock I pulled timing from that area. I will do a lot more aggressive timing in a few days when I get the GM Knocksense module in I got off ebay and can wire it in so the ms can detect the knock and log it directly. For now the timing is probably near what the car has stock from what I could tell playing with a timing light on the stock computer. I can probably get a lot more out of the timing once the datalog actually records the knock events but right now hearing the knock on the radio then looking at the display to see where it happened is a stupid way to do it but it worked good enough to get me running.
Once I get the Knocksense hooked up and logging I plan on adding timing on every part of the table till I get knock then backing off a few degrees to set the table to the best I can do without putting the car on a chassis dyno. But for now it is reasonably close and running good on what it has set now. I planned on driving it some today to get a mileage reading but a tree fell and I spent all day playing with a chainsaw cleaning it up so no driving for me today
Can the Megasquirt control the IAC? On my car I turned down the idle speed when the engine is cold, which allowed me to lower the overrun fuel cut temperature. It saves a little more fuel during warmup.
I also have the overrun fuel cut timer set to 1/2 second. The car seems to buck less when driving in stop and go traffic, or at parking lot speeds.
My car also stalls sometimes if I just push in the clutch and let the revs drop. Yes, I have an 'auto-stall' feature, too! I found that having a slightly richer idle setting helped a little. Have you tried adjusting idle mixture to see if it makes a difference? Maybe look at what cell is being used in the fuel table and adjust from there?
The stock metro IAC runs at 12hz and the megasquirt can only get down to 30hz or so. I either burned up the 2n222 transistor on the ms or I killed the IAC when I tried driving it at 30hz. Either way I will get to a junkyard and pick up one that works well with the ms one of these days. Not a big hurry because it idles really well anyway, just the slow down from over 2000 rpm it usually can't catch itself unless I help. Half the time I don't care and just let it die when coasting down a hill or something so it is no big deal to me if I get it fixed or not.
I got MSD 6a and accel supercoil installed today though
It makes the car start and run way better. The stock metro ignition is pretty weak so anything is an improvement. Now I won't have to change the distributor cap and rotor every 5000 miles to keep it running good. The spark is good and strong now. It was missing a lot when I set the idle afr at 15.5:1 with the stock ignition, but I set it to 18:1 and it didn't even seem to notice after I put the MSD on there. I have no idea how lean it can actually go and still run but I guess I will find out sooner or later. I have not set anything any leaner yet though on the tables other than just testing. I should have my knocksense stuff in tomorrow if I am lucky. If it comes in I will get it all working then see how lean I can push the target afr table to see what kind of gain that can give me.
I drove it 50 miles today and the gas gauge barely moved off the full mark. I didn't fill it up yet since I don't think I will need enough gas to get a good number. I will try and drive another 50 miles or so tomorrow so I will use at least one gallon of gas so my average will be more accurate. I want to get a good mileage number before I really push the target afr table into the super lean areas. Over the summer I just don't drive it enough to really even use one full tank of gas so I will have to make do with partial fills for now.
Well either I did really well or my numbers are off
Drove some more today so I went 77 miles total, average speed probably around 50mph. Filled up when I got home using the board like always when I am trying to be accurate and took 0.65 gallons of gas. I thought it seemed low and pulled the handle again and it kicked off instantly and I could hear gas in the fill tube so it was probably full. So if you believe that number, I got 118.46mpg.
Now I don't really think it is accurate I am sure I did something wrong somewhere. I was expecting something good because I have it set to where basically any time i let off the gas pedal it cuts the injectors and any time I lift the pedal up slightly it also cuts the injectors. I have it set to when decelerating it runs at 5% fuel. That and no acceleration enrichment for the most part. All that together should have helped my mileage but I really don't see how it can be that good.
On a side note I can pretty much say that adding a MSD ignition and better coil should be one of the required upgrades to a Metro. It makes the car start and idle much smoother and also takes gas a lot easier. I will also be able to go much longer now without changing the cap and rotor since they are not having to be in perfect condition to help the weak factory coil anymore. The car with the Megasquirt and the MSD ignition is now so smooth that it has no vibrations whatsoever coming from the engine when driving 65mph. I never would have thought a Metro could be so smooth running at that kind of speed.
I've been following your Megasquirt thread as that is a project I would like to tackle at some point. I just wish you were going to be driving some more this summer to see if that 118 was an actual number!
Well I had a weak excuse to go for a drive today so I hit the road
Drove 171 miles, used 3.1 gallons of gas, 55mpg. This was 95% interstate driving at 70-75mph pretty much constant throttle so the computer didn't get to cut the injectors for any reason. Target AFR at that speed/rpm is 15.0:1. I was pretty much expecting about a 1-2mpg improvement in this type of driving and it was around that much of a gain. So the driving I did the other day gets to be put in more perspective I figure. It was following traffic with constant accelerating and decelerating since it is a narrow winding 2 lane road over a mountain. I would estimate less than 5% of it was at constant speed. I think the run the other day had to have a bit of error in the fill but if you consider that probably for 1/3 to 1/2 of the driving I did that day the injectors were off it makes me wonder if I could do that over a longer period of time to try and get a more accurate reading of my mileage for that type of driving.
Either way, add up my totals so far and I am at 66mpg This is before I set the target AFR table to something a bit more aggressive. Now that I am more confident in my numbers I will lean out the tables and see what I can push it to. I have to put a roof on a house starting in the next few days depending on the weather so when that starts I won't be able to tinker with the car till it is done but I am close to having this thing set up the way I want it. Just a bit more time to work on it and drive it and I should have a pretty good setup.
I will also be able to go much longer now without changing the cap and rotor since they are not having to be in perfect condition to help the weak factory coil anymore.
NOT!!! I've been running my MSD for years now and it messes up the cap and button so you'd at least have to clean it sooner than replacing it. Use the brass type or the extra spark from the MSD will eat the aluminum usually found in the cap.
I also got my MegaSquirt running too. Time to work on the cold start and tune for mpg hwy cruise.
1998 Dodge DakotaSport 5.2 auto,
Cam advanced 4 degrees,
MSD Blaster2 Coil,
MSD 8.5mm SuperConductor wires,
Borg-Warner cap & button
and more to come...