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I always thought that the ECU uses both target and main fuel table for the final fuel delivery. In the example for turbo-charged ITBs engine, target Lambda table load axis is MAP and main fuel table load axis is TPS. How can the ECU uses 2 different load axes for areas below 100 kPa?
Think of it like this - Forget about the target AFR table to start with and let's assume that we tune the main VE table with TPS as the load axis to achieve 14.7:1 everywhere. The background fuel equation uses the ideal gas law which accounts for air pressure. What this means is that if we're running at a fixed TPS setting and lets say 100 kPa, and then we double the MAP value to 200 kPa, the ECU will double the injector pulse width and if everything works as it should, we will see the same AFR at 200 kPa - 14.7:1.
So the part to understand here is that even when we're using TPS as the load axis, the ECU is still accounting for MAP in the background.
Ok, now let's add the target AFR table back in to the equation. This table tells the ECU what our target AFR is and it performs another background calculation based on this. For example let's say we use MAP as the load axis (as you need to with a turbo engine) and we're once again at 100% TPS, 100 kPa, and our target AFR is 14.7:1. We tune the VE value at 100% TPS to achieve this target AFR. Now we increase the boost to 200 kPa. We're still at the same 100% TPS so the VE value hasn't changed and nor should we need to alter it. Two things are happening:
1. The background fuel calc has taken into account that we just doubled air pressure and hence has doubled the injector pulse width. This should keep our AFR at 14.7:1, but with a turbo engine this isn't probably what we want. Let's say that at 200 kPa the target AFR moves from 14.7:1 to 11.5:1. The ECU makes a further calculation based on this change of target which is no different to how we can calculate a correction factor based on an error between commanded and target AFR
In this case the ECU would take the original AFR of 14.7:1 and divide it by the new target of 11.5:1. This gives a correction of 14.7/11.5 = 1.28. What this means is the ECU needs to add a further 28% fuel at 200 kPa to get from 14.7:1 to 11.5:1.
So using the two different axis (TPS and MAP) allows us to firstly define VE as a function of RPM and TPS, and then command a different AFR based on changing MAP.
I hope the above better explains the situation. Let me know if you have further questions.
That makes sense now.
For my project engine swap, I had to use TPS for load because of the large cam lift duration and overlap. So I pulled a base map for Chevy V8 that had MAP for load and I simply changed the axis from MAP to TP percentages. While tuning the engine, I found out that I had to change many VE values and ignition angles. For example 10% TPS increment does not match 10 kPa increment of MAP
Base map attached
You can't take a MAP-based fuel table and simply change the axis to TPS and hope for good results - You'll still need to make considerable changes to the fuel/VE values to actually get the engine running properly. The reason is that there isn't a direct correlation between map and TPS. For example let's say a stock engine idles at 30-40 kPa and the base map has been tuned to suit this. Now when you change to TPS as your load axis you'll be idling with 0% TPS so it's likely the VE at this point will be too low to supply enough fuel.
Also you need to consider the way the manifold vacuum changes with regard to rpm. For example with a large cam you may see very limited vacuum at idle with a closed throttle, however at higher rpm the manifold vacuum at the same closed throttle will be much greater.
Ultimately the point here is you can't just take your MAP based fuel table, change the load input and call it done. It's going to call for a full retune.
I had to tune all the sites as nothing come even close.
Any suggestion where may I find TPS base maps to start with as templates?
That's what I'd expect if you change from MAP to TPS. The chances of finding a base map that's exactly suited to your requirements are probably pretty close to zero. I'd just recommend going through and calibrating the table. This will ensure that you have a fuel table that's correct for your particular engine.
I have a Nissan Pulsar GTiR which has quad throttle bodies and using an older Motec M4 to run everything. The Motec has data logging enabled but lambda is not enabled(have to pay extra to get this function enabled) I do,however, have a 14point7 Lambda meter using the Bosch LSU4.9 sensor which is plumbed into my downpipe about .5 metre from my dump. My question relates to tuning my engine properly where I don't have the luxury of having a lambda comp table(as my ecu can't support it) so I have no option but to run MAP as my load. Is it possible to run a secondary fuel map (TPS vs RPM) in conjunction with MAP vs RPM? If I can, how do I go about it and how complicated will it make things?
On the old M4 you can still achieve the same affect. You set the MAP comp table as a 1:1 table (should be this by default anyway), which has the same affect as the Link's 'Load = MAP' option. You can then use the second load table with MAP as the load axis to make corrections to your fuel delivery and achieve your desired lambda as the MAP changes.
I deal with this by using the correction formula we learned in the EFI Fundamentals course. If we assume the fuel table is tuned to lambda 1.00 everywhere then we can calculate what the required percentage change needs to be to get to our desired target. For example if you want a target of 0.80 at 200 kPa, we could take 1.00 / 0.80 = 1.25 which means that in the 200 kPa row of the second load table we would add 25% fuel. This should get you very close and then you can fine tune as required.
Thanks for your response. Yes, the MAP comp table is set as recommended in the notes (ie 0kpa = -100% trim, 100kpa =0% trim etc). So if I create a secondary load table using MAP as the load axis, does this mean I will have to change my primary fuel table(currently MAP vs RPM) to TPS vs RPM as you have done in the webinar?
Also is there a theoretical rule of thumb for fuel enrichment in terms of lambda when a turbo starts to come onto boost in order to help create a smooth and strong engine response?
P.S Loving the work you guys put into your webinars and your strong support on the forums. Top notch stuff!
Yes, change the primary map to be TPS for load axis. As far as rules of thumb for lambda targets, check out this webinar for some more in depth information:
So I plan on tuning my Link G4+ using Alpha-N and the modeled multi-fuel calculation. Main VE table will be TPS vs RPM with a 4D overlay table spanned MGP vs RPM. My question is, for the pump tune I tune the first fuel main VE table and 4D overlay table fully then fill up with the second fuel which will be E85. For the second fuel, do I need a second 4D overlay table or would a single 4D overlay be accurate for bot fuels? Thanks for the help.