Zetec Megasquirt II tuning help

[Automoda]

Hey. I've got the ZX3 with a MSII running it, and its running pretty well in my Birkin. I'm getting 28mpg roughly, and it is quite drivable. I've got the Jenvey TBs, but otherwise it is an internallly stock engine. I'm using a registered Tuner Studio MS, though initially it was set up using Megatune.

 

I'm working on solving the bad backfires I'm getting when I let off the gas and it is being dragged down in RPM-- like when I'm driving some windy roads and I let off the throttle as a way to slow down rather than the brakes. BANG pop pop bang pop. I'm only now beginning to screw around with my settings, and trying to learn the whole engine tuning art. Frankly my ignition chart looked insane, so I'm going to head out and try a new one I made. But until I get some experience with this and go to a dyno, I'm really just experimenting. Plus there are a lot of base settings that are Greek to me.

 

I was wondering if anyone has a similar setup and if so, could I get a look at your tune? I know most people with the ZX3 are using Emeralds, but I figured I'd ask around anyhow.

[slomove]

I do have the Emerald but get the same popping if I do not use the overrun shutoff function, that is to turn off fuel completely when the throttle is in idle position over 1600 rpm. But that is anyway a good idea to save a little gas.

 

I think the accuracy of the air/fuel ratio close to idle position is not that great with only the throttle position sensor and single stage injectors on the Jenveys to get that perfect. And the Jenveys were anyway not really designed for best road cruising behavior.

 

In the transition area, when the fueling just kicks in there is still a tiny bit of pop from the exhaust but that I got used to that as part of the character. With a little more fiddling I can probably make it go away.

[jlumba81]

I have an 04 Caterham SV w/ a zetec svt, stock ecu. It backfires the same way. The previous owner Mike aka Croc tried to get it tuned out but apparently it had to do something w/ emissions. Croc would be able to explain it better if you have any questions. I seem to get around ~25mpg but I drive short distances and my NJ to AK drive had a lot of fuel w/ ethanol in it.

[Kitcat]

You say backfiring like it's a bad thing:)! If my X-flow doesn't backfire when I get off the throttle, I feel like I have failed:). And I do NOT want to hear abt gas mileage over 20 mph. Anything over 15 mpg, and I say you are not trying:)! (And now I have used up all my smiley faces for the week(:-in fact the system here says I have used 5 images and I only get 4 per message-smiling is to be discouraged I guess-hey I am good with that(imagine a forbidden smiley face here).

Edited July 28, 2011 by Kitcat

[Automoda]

I just got back from a little tuning cruise.

 

First of all my ignition table was mostly nonsense (I think). Really I dont know how to make one but I went in and tried to smooth it a bit and increase the advance in the lower load, higher RPM area where the car seems to backfire (2000-3000 RPM with low throttle). It started raining so I had to quit before I could test my final tweaks but here's what I've been up to:

 

Spark table

http://herb.linkrealms.com/lotus/spark%203.gif

The thing with this table is that while the car is running it has a pointer showing where you're sitting in the table. The pointer zips around as you rev it, but I dont see a lot of sense to it. The pointer goes up and sits along the top row when at idle, and the second you give it gas it starts up from the bottom. Confusing.

 

http://herb.linkrealms.com/lotus/afr%201.gif

I havent messed with the air-fuel ratio yet. I'm sure I need to.

 

http://herb.linkrealms.com/lotus/ve%201.gif

VE table -- it hasnt had time to auto-tune since I modified the spark, but here it is.

 

Ok! Opinions welcome on this stuff. Time for me to learn how it all works.

 

BTW my innovative wideband is showing crazy readings much of the time. Popping lean then rich. I've got the smoothing set to 90ms (default was 60) but it must not be enough. I'll experiment, but right now I have no idea how it can auto-tune with the bouncy signal. Its probably caused by the individual TBs or something. I dont think I have any intake leaks or exhaust leaks etc.

[JohnK]

Spend some time staring at your tables and thinking about what the state of things is when youre in a range where there is backfiring. At each cell where theres no load/off throttle and revs are maybe 2500 and below, turn off the fuel - also you can advance spark (the leaner the mix, the longer it takes to burn). As it becomes clear to you, you should eventually have a large patch in your tables like this. The point of "max volumetric efficiency" is where you run the least advance, cause thats where a cylinder has the greatest amount of oxygen in it, and THAT allows you to run the greatest amt of fuel --- and that mixture burns faster than anything leaner, which is why thats where your engine makes its highest torque. Properly done, you can make it so that, when youre off throttle, it feels like the engine has died - yet a touch of the throttle gives you instant response. It erie feeling. Ask S1Steve about this behavior. BUT it takes a while to get all the ducks lined up. Good tuning.