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DIY Fuel injection thread.


yoeddynz

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2 hours ago, gibbon said:

Fair enough, I'm looking at Speeduino stuff but holding off til I find an option with a suitable case for a start. Some of it is just a bit TOO bare-bones 

I believe there are a few 3d printable options for cases, otherwise I just gutted a standard ECU case and mounted the Speeduino inside that.

DSC09456-2.jpg

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53 minutes ago, ajg193 said:

Stm pro looks like a nice piece of kit. But again, if the firmware isn't great you could be in for a harder than ideal time

Probably the main issue with the firmware is some OEM trigger setups aren't supported yet. Apart from that it's regularly upgraded and evolving quite well. Works well for my N/A street needs, at 1/3 the cost of a Link Atom.:-D

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10 hours ago, Stroker said:

Probably the main issue with the firmware is some OEM trigger setups aren't supported yet. Apart from that it's regularly upgraded and evolving quite well. Works well for my N/A street needs, at 1/3 the cost of a Link Atom.:-D

Its running Speeduino firmware, which means a large amount of triggers are already available, and more can be added.

https://wiki.speeduino.com/en/decoders

If you're looking at early Megasquirts, there is no reason not to look at Speeduino (other than Knock, which is a waste of time anyway).

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I think Speeduino has proven to be pretty fucking robust now! Like any self build ecu though its fully down to how well its assembled and then actually wired into the car. 

I reckon megasquirt is a bit over priced now for what you get compared to Speeduino for most applications.

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  • 2 weeks later...

Hey anyone got any tips how to wire a 12v constant to a relay setup for the fuel pump?

Ive got a relay with a 30amp fuse built in, the trigger I am running off the ecu controlled + single on the MPI setup in the fake evo (gsr) ecu grounds relay, relay sends power to fuel pump. Its 7-10v at most so ive added a dedicated relay to the fuel pump.

I could run a feed direct to the battery but id like to use the MPI constant 12v to power it (mainly due to extra fuse protection and less wiring length), tried a couple of spade/fork crimps into the MPI but not comfortable with how loose they are. Don't want to cut or splice into factory wiring as I want to keep it original, thinking about a spot of hot glue to hold it in (means I can remove it late) don't want to epoxy/pot it either. Have also considered using the 12v switched power to the MPI as well.

I do have a dodgy 12v connection that ive capped off I could possibly also use but would rather not

Thoughts?

Seriously still thinking about just rewiring the whole car :s

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You need to run any ECU controlled relays via ignition switched power.

Or via some wizardry it ends up back feeding voltage into your ECU and it slowly drains your battery, or gives other weird symptoms.

This might vary depending on ECU but it's probably best practice regardless. 

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  • 1 month later...
7 hours ago, Roman said:

New version of a Speeduino, based on Teensy 3.5 

About $500ish NZD? Seems pretty sweet! 

https://speeduino.com/shop/home/38-speeduino-dropbear.html?fbclid=IwAR0dqopVUzknQyALeIIJJt5_v5LfVRGSKOIX097U0L_UkXepTgrmaG2VwEQ

I watched some of the live speeduino update thing and he was saying that the chip shortage has delayed it and some are unobtainable now, so is having to redesign it. Crazy how many things are being effected now.

 

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Due to the location of my IAT (airbox) sensor on my setup I have always had a little bit of difficulty determining the actual temperature of the air when it gets to the cylinder. The engine has long steel intake runners that heat up over time, affecting the heat transfer. I could theoretically rip the manifold out and weld a bung on to put the sensor right near the head but this would not look quite as per how Toyota would have done it, and Toyota made millions of cars with air temperature sensors in the airbox anyway so it's theoretically possible to make it work well.

Symptoms of incorrect air temperature prediction are leaning out as the IAT increases when idling, AFR changing as the engine is heating up to steady state, AFR bouncing all over the place at certain RPM/load conditions etc.

A fix for these issues is to use an IAT/CLT correction factor that blends to two values as a function of air flow rate to predict the actual temperature. The most common approach is to set the correction factor to near 100% at idle conditions and then the rest is just determined through trial and error and just forgotten about when it's determined to be good enough at steady state.

 

One problem with this setup is that the model uses RPM*LOAD to predict airflow and doesn't care about VE at all, which causes large errors at low load conditions where VE can be less than 50%. I don't believe that this can easily be tuned out.

Anywho, what I recently did was pulled out my old thermodynamics book and opened the section on convection heat transfer into fluids flowing in a pipe. I used GNU Octave to develop a simple model of the intake system and engine and generated a surface map of predicted correction factors for all points in the engine tune map. I can adjust intake runner diameter, runner length, engine capacity, runner temperature profiles etc. The model uses the VE table from TunerStudio to calculate actual mass flow rate at each point (technically this model will cause the VE table to change, so some iteration may be required for more improved results).

A collapsed output from the model is shown below, giving the expected shape of the curve for my particular engine (I still need to actually measure the temperature of the runners at various points to confirm). I've put the predicted curve into TunerStudio and the engine no longer hunts when you sit there holding the engine at around 1500 rpm with no/low loads and the AFR seems to stay constant for a wide range of IATs now. I don't know what can really be done to fix the AFRs being somewhat all over the place (ie being 14:1 when the engine first gets to 85C but slowly changing to 14.7:1 as the runners heat up, with constant IAT) as the engine is warming up to steady state apart from adjusting the warmup enrichment curves.

 

 

image.png.2501f05e6a989f549de8841b39a83ac2.png

 

We see the limitations of the megasquirt correction factor when we compare the results of the MAP*RPM model vs if we include VE (x axis is mass flow rate, kg/s - below). At low load conditions there is a broad range of correction values for each MAP*RPM condition, which results in a large uncertainty of what the actual correction should be.

image.png.dee09a5768a02b1f33a62a1902e63a48.png

Perhaps I should look into playing with a MAF sensor one day, but there isn't really any room left for me to fit one in the engine bay without making it look out of place.

 

 

Side effect of the model is the prediction that if I cut the length of my runners from 650 mm to 250 mm I could increase my power by 6% by dropping the temperature of the air getting into the engine from 57C to 38C at the upper RPM range. That could be a good excuse to make a dual runner system with a butterfly valve that swaps them at a certain RPM in the future.

 

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Nice work. I've given this problem a lot of thought in the past.

OEM use IAT and MAP in this way, (or used to...) but then they closed loop trim everything and dont give any shits.
Then later on when it actually mattered for sake of emissions they use MAF and thermally insulated manifolds.
This is a situation where you're dancing around the fact that you're missing a relevant chunk of information which is easily solved with an extra sensor. 
Which is a thermistor stuck to the surface of the inlet manifold. Probably ideally near the plenum end of a runner or in the plenum itself.
OEM doesnt want to do this, because 1x sensor that they can live without saves them $$$$$ across 10 million cars.
They have to have an oxy sensor anyway, so just treat it as a problem solved by closed loop.

Adding a sensor is the only real way you can account for manifold temp varying while those other values stay the same.
The manifold temperature is a result of temperature in (from the head) and temperature out (carried away by airflow) 

If you do a constant run at full throttle you'll slowly cool the manifold even though all of your measurable conditions stay stable.
If you do a constant 100rpm low load on the motorway, you'll slowly heat it.
If you dont have any way of accounting for this change over time, then you havent solved the problem.

But if you've built an IAT/ECT compensation table that gets it ballpark most of the way there, and stops hunting idle etc then thats awesome! 
Good work. 
You could also look at thermally isolating the manifold from the head. 
Another issue is that you can get variations from fuel temperature soak as well, when the fuel rail heat soaks and there's a low fuel volume in the tank, and a hot road reflecting heat back up at your gas tank. 
Streeter Industries in Oamaru can cut phenolic gaskets if you give them a sample.
 

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