DIY Fuel injection thread.

[ajg193]

10 hours ago, Roman said:

Has anyone here setup an exhaust pressure sensor before? 

Looking at OEM setups for diesel differential pressure sensors, they have a fairly short stainless steel pipe connecting to the exhaust, and then a length of rubber(?) hose going to the sensor mounted remotely. But perhaps these are more resilient to heat than the map sensor I'm going to use.

Or maybe diesel exhaust gas isnt as hot?
I'll be expecting EGTs of maybe 600-800 deg?
So needs to cool the gas quite a bit.
Damn I wish I still had my thermal camera haha.
Have been advised using copper pipe is a good plan for dissipating the heat, but then what after that? Would silicone hose be okay? 

Probably a silly idea, but I guess for doing the pressure measurements it could be worth using two MAP sensors to get a differential reading, then passing the signal through an op-amp to amplify it to a usable value. That's assuming exhaust pressure is generally not much higher than atmospheric.

 

The pressure signals should travel at pretty much the speed of sound so you don't really need to worry too much about the length of pipe you use for sensing the pressure. You might get away with using a U tube of some sort, with water or similar in the lower portion to separate exhaust gas from the air going into the pressure sensor. This would also act to dampen out the fluctuations and reduce signal noise.

[Roman]

I have a dedicated barometer in the ECU already and a MAP sensor on the intake, so I can look at any combination of these three things as well as MAF readings.

Some ECUs, like the latest Adaptronic one. Instead of having an onboard barometer it has inlet MAP and exhaust MAP sensors. 

Then part of the calculation for the load axis is the pressure ratio between intake and exhaust.

Apparently this allows for changes in altitude etc better than any other system. 

I've found that when I advance the inlet cam at low load, to introduce overlap.... MAP pressure goes up for same throttle angle. At one point went up 60% higher because of EGR effect blowing exhaust back into the inlet.
So its hard to tell which cam setting is more economical, because when you advance the cam it pulls all of your ignition timing out. When it should add it instead.
MAF will be a better load axis for setting this up initially.
So this is where exhaust/inlet pressure ratio would be interesting to look at.
It will be interesting to see if there are noticable peaks and troughs in the exhaust manifold pressure from the tuned lengths of the pipes like you do on the intake side.

I think a combination of MAF / MAP / exhaust MAP will tell an interesting story for deciding on cam settings at partial load.

Lately for 4000rpm+ I have had all load cells with the same cam timing as full throttle. Which I think has helped with snappyness of throttle response as the cam doesnt need to "catch up" when you put your foot down... But now I've noticed a lot of fuel or oil in my intake manifold when it's previously never been an issue. So I think when inlet valve first opens with that much overlap at low load, it's blowing fuel back up the intake runner and into the plenum.

[ajg193]

What do you guys do for near-stall recovery? If I let my revs drop below about 800 rpm the engine will lean out and very likely stall. I've managed to get it to bring itself back from about 500 rpm with about 50% chance by really upping the Ve numbers in the 500 rpm column of the table but I can't really see this being the optimal method. I also tried changing from alternating / 2 squirts per cycle to simultaneous / 1 squirt per cycle and this made no difference. 

 

I can't really remember what the carb was like at low rpm but it definitely idled happily at 750. 

 

Changing from the old 145cc low impedance injectors to brand new 210 cc high impedance injectors made no difference either. But it did stop the fuel leak that was coming from one of the injector bodies!

[Yowzer]

Make sure your injector deadtime is correct or you'll constantly have low rpm issues.

Set your idle timing to around 6° and adjust throttle back up to 800rpm, then have the timing ramp up to maybe 10-12° at 500rpm. See how that works.

[ajg193]

Deadtime is set to 0.9 ms and voltage correction to 0.200 ms/V, which seems to be about bang on as the idle AFR stays essentially constant between no electrical load, some electrical load and full electrical load. I had deadtime set to 0.8 ms before and the idle AFR was kind of all over the place with electrical loading.

 

Ignition is controlled entirely by the distributor.

 

I changed my cranking RPM setting to 400 and this has helped a bit with the leaning issue.

 

1 squirt simultaneous injector control was horrible on a cold engine, it was pretty much refusing to idle. I changed back to 2 squirts alternating and it came right straight away.

 

The car seems to usually recover from near stall conditions now, so it will happily recover somewhat well from 600ish rpm.

 

Now I just need to fine tune cold starting.... It's slowly getting there, just been adding fuel left right and centre seems to have helped a lot.

[Yowzer]

Is your deadtime a guess or have you actually measured it? The ecu should have an injector test function to allow you to do this.

Also, wtf are you doing letting the dizzy do the timing?? Give that shit to the ecu ASAP

[ajg193]

Deadtime is just a guess (based off similar injectors). I'll have a go at flow testing the injectors over summer while I'm up in Auckland. I don't have the space down here to work on that stuff nor the time at the moment.

 

Timing seems to be handled nicely by the distributor, plus I like the look of the 5 limbed octopus. Maybe one day I will add the appropriate sensors to the engine to allow for ignition control but for now I am quite happy with how it is working. The car is leagues better than with the carburetor.

[kws]

I did a lot of work under idle to help with stall recovery in my car. I have no idle valve, so can only control it with fuel and advance.

I added a lot to VE and advance below idle, so when the RPM drops below idle it goes into those cells and it pushes the speed back up again. It hasnt failed me so far. I dont think VE would work alone, the ignition advance made the strongest difference.

[Yowzer]

You don't need to ditch the dizzy, just lock it, plug the trigger and coil into the ecu and away you go. You're missing a massive amount of tuneability without it.

[Roman]

Andy Wyatt does a good video on idle control theory.
 

 

[yoeddynz]

He ^ looks so totally nerdy so I shall watch it and trust him.. maybe.

I have an idle control valve but its only used for warmup duties. Considering I have no powersteering, AC or other high draw thingees I feel I shouldnt need to run my ICV to control the idle.  I have set the values in ignition and fuel table slightly higher and it works well.

 

[mjrstar]

Sounds like the discussion a couple of pages back about idle stall resistance, and tricks to make 2200cc injectors idle nicely.

[kws]

To the peeps in the know. This is the first time I have checked my plugs in about 1500km or so of installing my speeduino. 

Do they look normal? They almost have no colour on them, but no spot or petrol etc. 

this is the most pale plug. All the other seven have some colour to the ceramic. 

[kws]

The rest look like this

sorry for super huge photos. Posting from phone. 

[fuel]

it looks like that plug has seen a combination of rich mixtures and lean mixtures. Ideally you want a nice tan uniform light powdery finish. Given that you've been changing your ECU parameters in that 1500km, I would clean up those plugs with a wire brush and put them back in and see what they are like in another 1000km or so.

[Yowzer]

Might also be too hot? What temp range are they?

[ajg193]

What AFR ratios are you running at cruise?

 

 

[kws]

AFR is about 15:1 at cruise. Standard plugs which are a 6 on the temp range

[ajg193]

Here's what mine look like. Cruise afr around 15.8-16 idle afr around 12.5-13.5. 

 

Black on rim rim is probably from recent fiddling with settings and may clear over time. 

 

I should have taken a photo of the inside of my exhaust manifold the other day. It was almost too clean, no carbon at all

 

Also just for reference:

[Yowzer]

Meh those plugs are fine. Add some boost and worry about plugs later.