MicroSquirt – Page 3 – Not Your Average Engineer

August 1, 2014June 21, 2020

Trouble with RPM sensing

11am: I’m having some trouble with RPM sensing on my MicroSquirt. Previously I thought that I had fixed the problem but it appears to be back. The bike is otherwise in good health. I would consider taking my RPM data directly from the ignition pulse triggers but the pulse generator plate (shown as #22 here although I haven’t been able to find a part number for it in the microfiche yet.) has an oddly configured set of teeth. There appears to be difference in the spacing and also the thickness of the ring. This page and this page in the shop manual show that the bike actually has dual triggers for spark. The second figure on the second page linked in the last sentence shows what I think indicates that the bike’s ignition control module determines when to fire a spark based upon the absence of material rather than actually counting teeth. I however don’t know if this is true or not. Unfortunately I don’t have a man on the inside at Mother Honda in Japan to tell me the secrets that I need to know.

1pm: It looks like I’ve solved the RPM sensing problem. I discovered that I had the wires reversed for the RPM sense circuit. There is a small note for Pins 30 and 31 here that indicates the OPTION + should be connected to the ground terminal on my bike and the OPTION – should go to a clean 12V source. This is a bit backwards compared to what I’d expect but it seems to work. Now I am reading 800-900 RPM pretty consistently when cranking at the starter.

2pm: LIFE! I just had the bike up and idling!!!

3pm: Tuning is starting in earnest now. I’m having some troubles with a few quirks in the TunerStudio software. Also it appears that the shorter I set the pulse for the injectors, the more fuel is actually delivered. Not sure what that’s about! Also I can’t get the air fuel ratio up high enough even at hot idle. At hot idle, it’s ranging around 10.3-10.5 when it should be more like 14.7-15.2. I can’t figure out what to adjust to lean out the mixture but without reducing the idle speed.

I am looking for help on the MicroSquirt forums now for some of my questions. Hopefully I’ll have more time tomorrow to work on this.

July 30, 2014

Finishing the PC800 Fuel Injection Throttle Body, Wiring, Air Box, and First Start

The last time I posted an updated on my Honda Pacific Coast fuel injection project, I was moving ahead with using a VT1300C throttle body. I had started to make 3D cad files to have a metal adapter 3D metal printed to fit everything together. Alas, I discovered that the VT1300C throttle body will not work on the PC800 due to the geometry of the PC800 engine and the VT1300C throttle body. There just isn’t any manageable way to make an intake runner to couple the throttle body and the engine together. The picture above shows a mockup with some moulded rubber hose. Yeah… not going to work.

Thus I moved back to using the PC800 carb that I had started modding several years ago.

I pulled off the fuel injectors and fuel injector retention clips from the VT1300C throttle body to use on the PC800 carb-converted-to-throttle-body. Turns out that they work pretty well together. Note that this isn’t the end orientation of the retention clips.

I then worked on installing a throttle position sensor off of a set of CBR600RR throttle bodies I had purchased some time back as part of this project. I used some allthread and JB Weld to make a mounting point on the right hand side of the carbs. The bolt that runs through the carbs from the throttle cable wheel to the spring on the other side works well for turning the potentiometer inside the TPS.

Another view of the gloppy mess of JB Weld.

I used some washers and nuts to hold everything together.

I also had to make some plastic spacers due to size issues with the nuts.

I’m a bit surprised that it worked as well as it did.

No issues with clearance.

It tucks in nicely next to everything.

Next I worked on placement of the injectors and their associated parts. Surprisingly, I found that I didn’t need to cut any additional material from the old PC800 carbs to fit the injectors and their retainers into the top of the engine area.

Looks good here, too!

More test fitting.

I cut up some allthread to make retaining the injectors and the high pressure fuel lines a possibility.

Then I bent the allthread so that I could use some JB Weld to hold the allthread to the PC800 carbs.

Both sides bent up and ready for JB Weld.

Putting a layer of JB Weld on.

It got pretty goopy using normal JB Weld.

The next day I used some JB Weld in the stick form like I had originally used on the injector bungs to finish the job and make everything very secure. I ended up going with the normal stick rather than the high temp stick. Hopefully that doesn’t give me problems later.

Closeup of one injector mounted in place. I trimmed the allthread short so that everything fits into the space above the engine without interference.

Test fit in the engine. Everything looks good.

Plenty of clearance.

Good on this side, too.

Next I worked on getting the fuel lines plumbed in to clear the stock air box.

Everything looks good here, too.

Then I took some time away from the carbs/throttle body to modify a Bosch idle air control valve to work as the IAC for this project. The spring was old and tired so I had to open the unit up to modify things internally. I ended up moving the retainer for the spring about 1/8th of a turn and using some JB Weld to hold everything in place. This is a Bosch 0 280 140 505. I bought mine on EBay for a few bucks compared to quite a bit more as a new part.
I still need to get a vacuum cap for the top large barb and a three wire plug for the bottom to interface with the MicroSquirt. That will probably happen this afternoon. Wiring is straight forward for the three pin Bosch units.
Next up, I modified a brass water pipe fitting to work with the temperature sensor that I installed in the PC800 air box to work as the intake air temperature sensor.

Here’s the IAT installed in the air box.

Another view before I gooped it with RTV sealant.

Sealant on the bottom.

Here it is as a test fit.

I then worked on installing the wiring in the bike in a clean way around the throttle body. I used some convolute tubing to tidy everything up.

Then I mounted the air box onto the carbs and connected everything up.

Then this happened! 😀

Yes, the bike ran (just a little) on my first try starting it up with fuel injection. I have no fuel leaks (so far) and I have the start of an idle tune. There are still some things to do to the bike before I can button everything up and tune beyond idle. I discovered today that I misplaced the breather tube that connects the head cover outlet on the rear cylinder to the air box. The Honda part number is P/N 17225-MR5-000 and it is no longer made or available. Luckily I found one on EBay that should be here within five days. I also still need to install the Bosch IAC valve on the bike although that doesn’t have to happen right away. Both the vacuum lines that will connect to the IAC and the air box barb that will connect to the breather tube have their holes currently plugged so it will not impact initial tuning.

Were it not for being such a rainy day, I would be down in the garage working on the tune. However, I don’t want to risk burning up everything in the garage since I can’t put stuff outside due to the wetness falling from the sky. My next real chance will be on Friday. Maybe then I’ll start getting a decent tune put together and be able to button up the wiring.

May 28, 2014July 4, 2020

Starting up the MicroSquirt for the first time

Today I powered up the MicroSquirt for the first time on my Honda Pacific Coast PC800 fuel injection project. I bought the MicroSquirt several years ago but life got in the way and only recently have I been able to get serious about the project again.

The main contributions to the project I did today surrounded verifying that wiring is correctly installed and calibrating sensors. This is also my first time using the TunerStudio MS software. I am still debating if I will purchase the advanced functionality or stick with the standard free version.

Here is a screen capture of the TunerStudio MS software running with the MicroSquirt. I did not enable the fuel pump today so what you see here is simply a static test. I did try some cranking though to verify that RPM sensing from the negative terminal on one of the spark generators was working correctly. After initially having a bunch of noise problems, I found this post on a forum dedicated to the MicroSquirt. It led me to add a diode and 1K ohm resistor in parallel on the RPM sensing wire. I also moved the wire to a slightly different position to avoid any noisy AC signals from the stator or the other spark generator wiring. That seemed to solve the problem. Also, it will provide protection in the future to not blow out the opto-isolator as some people had reported happening on the forum post.

Above is a screen capture of a log file that I generated to see what RPM the engine cranks at. The average seemed to be around 340 RPM. I think this is about correct although I’m not sure if the Pacific Coast’s stock ignition control unit operates in wasted spark mode or if it only delivers spark to the cylinder when it is the appropriate time for a spark.

One thing that graph doesn’t show but another graph did is that I have some serious voltage drop with the way the system is currently configured. Without running the high pressure fuel pump, I was seeing as low as 9 volts on the MegaSquirt. Hopefully that isn’t entirely accurate. It isn’t in the danger zone for forcing a MicroSquirt restart but it is pretty low for getting a good spark. More research will have to be done on this once I have the final pieces in place.

In other news, I found a Bosch P/N 0 280 140 551 idle air control valve that is a two wire PWM setup with spring return. The only problem seems to be that in the fully off state, the valve goes a bit too far and becomes partially open. There is a brass set screw that seems to set how far back the valve turns. However, it was sealed in place with some factory goop. After chiseling the goop out, I wasn’t able to get the brass screw to spin and instead was stripping out the hex keyhole. I think that I am going to try drilling the brass screw out and replace it with a press-fit pin that i drive into the correct depth. This wouldn’t be a problem if the MicroSquirt had stepper control built in. I might still go back to DIY Auto Tune and buy the stepper IAC mod kit for people with the DIY PNP MegaSquirt. I previously had an email conversation with the good folks at DIY Auto Tune about grafting one of those kits onto my MicroSquirt. It wouldn’t be easy but it is possible to do. On the other hand, I might find that I can tweak the tune well enough to have the PC800 reliably start without an IAC. Time will tell.

Up next on my to-do list is to bring the throttle body assembly to the university with me to try using the 3D scanner to capture CAD geometry data. I am planning to develop a custom adapter to go between the throttle body and the engine intakes. As luck would have it the rubber carb boots from the PC800 are the correct size to fit on the VTX1300C throttle body. I plan to design the adapter in a CAD package, 3D print a prototype in plastic to check for fitment, and then send out to an additive manufacturing house for a 3D metal print.

On the spark control front, DIY Auto Tune is now making a quad spark control unit that is much less expensive than other alternatives. I only need to control two sparks but it would still work for my application. Then the issue would be dealing with the oddly designed pulse trigger wheel inside the PC800 crankcase. The MicroSquirt firmware isn’t really designed to support such an oddly shaped trigger wheel pattern. I would probably have to replace the existing trigger wheel with a custom wheel to make it easier to tune the spark. For now, I am sticking with the stock ignition control module. Maybe later I’ll get more ambitious and run spark off the MicroSquirt, too.

Progress is being made slowly but surely. I haven’t encountered anything insurmountable yet. It’s just a matter of slowly and methodically working on the motorcycle to bring it to life with fuel injection.