Interpolation

Hi Andre,

When and what is the main reason/ time for using interpolation in a fuel or ignition map? I have been tuning for a few years and never really used the function. Is it helpful in the tuning process? Also not sure if you remember me but I have a ford escort mk1 with a 4age 20v built engine that I was having problems with. The problems have been solved I think because the car is quite a bit quicker. When I get it back on the dyno I will let you know the outcome. Previously the hp was 138 at 8500 rpm. I believe the issue was I had the missing tooth 30 degrees before tdc when it passed the sensor, so I think it was not getting sufficient ignition timing which is why it felt lazy going up in rpm. I have now changed the pulley to a fixed trigger wheel pulley and adjusted the offset to suit. Needless to say it felt a hell of a lot better, but I also put higher lift cams in it, but I don't think that made a huge difference, only for lift at tdc. Let me know what your thoughts are on this.

Thanks

Kurt

Hi Kurt,

Yes i remember your 20V project. I'm happy to hear you have potentially resolved your issues and look forward to hearing what it puts out when you hit the dyno next.

There are two ways I would reference the term interpolation. The first happens in the background and we don't really need to worry about it. Any time the ECU is operating between sites in the fuel or ignition map, the value the ECU uses will be interpolated between the surrounding cells. This ensures smooth operation rather than the fuel and ignition numbers simply 'stepping'.

The other reference to interpolation would be the manual 'interpolate' function where you cans elect a row or a block of numbers in the fuel/ignition map and interpolate between them. I find this function extremely useful when you're tuning an engine for the first time and the current or base map may be a long way off. Let's say for example the efficiency at 3000 rpm and 20% TPS is 45% and at 100% at the same rpm its 92%. We can perform a straight line interpolation between 20% and 100% TPS to get the rest of the efficiency table close. It won't be perfect and will still need to be optimised but the AFR will likely be close when you visit a new site rather than tuning from scratch.

Hi Andre,

Thanks for the reply. That was very helpful. Would you happen to have a 20v ignition map for a built engine that I could use to try or at least compare to mine, I still have not optimised mine yet. the guy who owns the dyno is overseas at the moment. Also do you know mike Marshall. He is coming to Barbados for our International rally in May. Just thought that was cool someone coming from your neck of the woods for our rally. Sorry I have not been on this site in a while, My wife and I are moving to Canada in a week, hopefully that will bring me a little closer to coming to meet you some day. Again what you have done here on this website is really great, I am learning a lot. Thanks. I attached a pic of my car so you can finally see what it looks like.

Kurt

Hi Kurt. The car looks great, good work!

Sorry I don't have an ignition map for a modified 20V engine. I'd still be a little apprehensive about using another map anyway. You should always optimise it to suit your own engine although I understand with no dyno access right now that can be tough.

Sorry no I don't know Mike Marshall? Good luck with the move to Canada - The temperature change may be a bit of a shock i would imagine!

Hi Andre,

Thanks for the kind words. Hearing the car looks great from you really makes me happy. So I had a rally on the weekend, I finished first in class, but coming close to the end the car would not idle, it was misfiring. I would run fine once I kept it above 3000 rpm. I had this problem once before and it was the cam sensor. What I did when I got back to the service area was I put the laptop on it and deactivated the cam sensor and it ran great after, my question is why does my cam sensor keep going bad. I am using a reluctor sensor, the same exact sensor used on a 2zz engine. My adjustable cam sprocket has 4 bolts to adjust the gear, how I have it setup is I put a longer bolt in with spacers to bring the bolt closer to the sensor. Could it be that the width of the bolt is too wide to be used with a reluctor type sensor so it keeps messing with the signal at high rpm and causing the sensor to go faulty? Also what is the best way to setup the cam sensor relationship of where the trigger passes it in comparison with the missing tooth on the crank trigger wheel? I read in another post where you said that the cam trigger should be 180 degrees from the sensor when the missing tooth on the crank is inline with the crank sensor, at present my cam trigger is 90 degrees before the cam sensor.

Thanks

Kurt

Congrats on the win!

A reluctor pickup 'should' be very reliable and that's one of the reasons they are popular. Vibration can cause the sensors to fail, as can the pickup hitting the sensor. It's surprising sometimes how much the pickup will flex and move at high rpm and all that is required sometimes is a light touch and that's enough to cause damage.

With a multi-tooth missing trigger system you wan't to make sure the sync tooth is occurring away from the missing tooth. The only way the ECU can get confused is if the sync occurs in close proximity to the gap. For this reason 180 deg opposite the gap gives the best protection and least chance of trouble although it isn't essential to go this far. As long as your sync pickup is more than about 20-30 degrees away from the gap you should be fine.

As with any triggering issues, a scope is the best way to find out what's going wrong.