Help with building your Speeduino, installing it, getting it to run etc.
LPG2CV wrote: Sat Mar 11, 2023 5:56 pm Hi Earnest :)

Unfortunately, that is spam on your topic. :( Not to worry about it though. I will see if it can be removed :)

Yes, adjust the throttle plates if rpm is to high at idle. You may possibly want to disconnect IAC in the first instance, as it may stop you getting a good warmed up idle.

TPS is used for Aceleration Enrichment (AE). Larger thottle openings need a liitle more fuel added to compensate for the lean spot when opening the thrott;e plate. Before adjusting the AE, the VE table needs tuning first, as AE is relative to the current VE value. You are some way away from attempting this. :)
@LPG2CV - thank you for the assistance.

Mentioned the IAC system in the above posts, always working, passive system uses engine vacuum to activate the reed valves.

Yes, VE table first. Was just wondering about TPS and how it fits in the system.

Doing more reading and looking into the vacuum system for Speeduino. Found some posts regarding a 4 way sensor array that compares 4 vacuum points and sends Speeduino or the Squirt family the lowest signal from the 4. I have my vacuum system connected so that the same side cylinders are connected together, then a hose from each cylinder bank is routed and connected to the other cylinder bank, and from there one hose goes to the on board MAP sensor:
Vacuum System.jpg
Vacuum System.jpg (61.19 KiB) Viewed 757 times
Have read the posts by gpineau, he used one vacuum connection with a small vacuum reservoir (Home Depot fittings I'm thinking). Gpineau found that the vacuum signal to the ECU was reduced significantly and he could better tune the idle.

Have also read other forum threads where the fellow used one line per into a small reservoir and from there, one hose into the MAP sensor.

Once the engine is tuned for initial idle, can connect a set of vacuum gauges to determine what each cylinder vacuum is and use the most appropriate. Honda is very generous in its vacuum settings. As long as the vacuum between cylinder banks is within 1 1/2 inches of Hg for the FI models, all is well.

Something to consider sown the road.
The MAP signal concepts are simple and effective in specific conditions. More cylinders to the MAP, the more even and averaged the signal is. Route your tubes and collect them however you like, and to the MAP. Tubing lengths or equality has no particular benefit. Try different reading modes to find the best one for signal stability.

If the signal is too jumpy in every mode (confusing the ECM and causing instability), then you can try a buffer. A buffer is a small plenum in the MAP line that again smooths and averages the signals. A popular and convenient buffer is a small fuel filter. While this has benefits, it can also introduce signal lag if the buffer is too large, so only use one if necessary. There are other approaches to idle and off-idle transitions.
LPG2CV wrote: Sun Mar 12, 2023 6:20 am @psig
I'm trying to work out what the reed valves do?
When Honda designed the CFI system for the Gold Wings, it found that during deceleration and start up the engine cylinders were being starved for air. During deceleration this was most unpleasant. Honda designed a passive IAC system that would draw air into the engine cylinders during engine operation. The greater the engine vacuum, the faster the air would be drawn into the engine cylinders. The IAC air inlet to the engine cylinders is after the throttle plates. Thinking air is only drawn into the cylinders during the intake stroke.

I posted a Picture of the IAC System earlier. These are the pictures of the Reed valve and IAC air hose routing.
IAC Hose routing:
IAC System hose routing.jpg
IAC System hose routing.jpg (52.29 KiB) Viewed 736 times
IAC Valve:
IAC 2.jpg
IAC 2.jpg (30.79 KiB) Viewed 736 times
Reed Valve:
Reed Valve - 1.jpg
Reed Valve - 1.jpg (77.22 KiB) Viewed 736 times
Reed Valve Outlet to Cylinders:
Reed Valve Outlet To Cylinders.jpg
Reed Valve Outlet To Cylinders.jpg (75.64 KiB) Viewed 736 times
Reed Valve with end covers off:
Reed Valve 3.JPG
Reed Valve 3.JPG (277.32 KiB) Viewed 736 times
Last edited by Rednaxs60 on Sun Mar 12, 2023 7:05 am, edited 1 time in total.
Only allowed 5 pictures.

This is the schematic of the reed valve:
Reed Valve Schematic.jpg
Reed Valve Schematic.jpg (52.69 KiB) Viewed 736 times
The IAC valve has an internal bimetal strip that when heated, closes the orifice - could be the other way round, to allow air to flow through the IAC valve. It is powered by the same circuit as the fuel pump. This is the internals of the IAC valve:
IAC 1.jpg
IAC 1.jpg (36.19 KiB) Viewed 736 times
The IAC system works well.

Another bit of trivia. The US CFI models were different from the Canadian models in that the US models pumped air into the exhaust after the exhaust valves to meet US, specifically California emission standards. Canadian models did not require this at the time.

US Model cylinder head with air recirc tubes attached;
Cylinder Head with tubes.jpeg
Cylinder Head with tubes.jpeg (165.14 KiB) Viewed 735 times
CDN model cylinder head. Notice the absence of air tube holes:
Canadian FI Cylinder Head.JPG
Canadian FI Cylinder Head.JPG (287.56 KiB) Viewed 735 times
A bit of trivia, some applicable to what I am doing, some good to know.
The IAC valve. By your diagram, one side of the valve connects to both of the reed valves. Where does the other side connect to?


The hoses that attach from the reed valves, to the throttle bodies. Which side of the throttle plates do they exit. The engine side, or the airbox side?

Are you attaching the map sensor to this system, or is the another set of hoses for that?

Sorry I'm so curious :D
LPG2CV wrote: Sun Mar 12, 2023 8:27 am The IAC valve. By your diagram, one side of the valve connects to both of the reed valves. Where does the other side connect to?In my post above you see the IAC VV connections. One from the air chamber to the IAC VV - filtered air, the other to the IAC system. The coolant lines are for cold weather operation so the IAC VV does not freeze.


The hoses that attach from the reed valves, to the throttle bodies. Which side of the throttle plates do they exit. The engine side, or the airbox side?The hoses from the reed valves exit on the engine side of the throttle plates bypassing the throttle plates. This picture shows which side the air is drawn into the cylinders, just after the throttle plate(s) (cylinder side)
Air Chamber Underside 2.jpg
Air Chamber Underside 2.jpg (47.1 KiB) Viewed 702 times
Are you attaching the map sensor to this system, or is the another set of hoses for that?The MAP sensor is attached to the injector holders.

Sorry I'm so curious :D
Don't be sorry, I ask questions all the time, for specific or curiosity reasons, information is knowledge and it's good to share. Trivia, the 1985 Honda GW Limited edition FI model was designed for the north American market (US and Canada) and to be sold only here. The 1986 Honda GW SE-i FI model was manufactured for the US market and sold only in the US. Any Limited Editions or SE-i GWs elsewhere are transplants.

"Are you attaching the map sensor to this system, or is the another set of hoses for that?"The MAP sensor is attached to the injector holders.. This picture shows the MAP vacuum hose connection(s) on the injector holders. The hoses are routed to a single connection point to join the right/left cylinder banks, then a single hose to the MAP on board sensor:
Vacuum hose .JPG
Vacuum hose .JPG (89.63 KiB) Viewed 702 times
The reed valves control the flow of air to each cylinder, replace the stepper motor design. Good design in my opinion, one less component to fit and worry about when space is limited.

Was thinking about wiring. Going to bypass the OEM wiring harness for the coil driver and coils, except for the signal from the ECU to the coil driver. Want to determine if there is a difference in engine operation. My rationale for this is that I have noticed that when I pulled the plug wires to check firing, I noticed that the impact of doing this was not the same for all four plugs.
Pulling a spark plug lead, does not means its electrical. You have two coils. If you swap them over, does the fault follow. If the fault stays on the same cylinder, then it's not the coil. Same process with spark plugs.

Have you tested compression on all four cylinders? Are they within 10%

Poor compression could be rings/bore. A burnt/bent valve/seat. Tight valve clearance. Head gasket.

If you test and record the pressure on a suspect cylinder. Then squirt oil in the cylinder to seal the rings/bore. Test again. If the pressure increases, it's most likely the bore/rings. No increase, suggests valves/head gasket.
Thanks for the comments. Complete engine rebuild 2021/2022. Rings, bearings, and such. Heads redone in 2019. Compression 260 PSI all round, better than the 90 PSI and falling that was the before. These engines will operate until there's nothing left.

Had same plug issues before rebuild and after. Have 3 sets of coils and same issue. Valves setup IAW Honda specs for hydraulic lifters. Generally numbers 3 and 4 cylinder are less aggressive so to speak when plug wires pulled. Have used different coils on these cylinders, no change. No way t test spark units except for continuity and voltage at the spark unit and wiring harness connector.

New plug wires as well. Plug caps were replaced with new in 2016.

It was mentioned that the electronic components could be deteriorating with time, ECU or spark units. Will be looking into this this time round.

An issue that does rear its ugly head when going from old to new, is that you tend to live with the degradation of a system and think everything is good. It's like motorcycle suspension, cars as well, you don't realize how bad it is until you renew/upgrade.
FYI, what you call the IAC is actually a thermal cold-start air valve, as referenced in the Wiki here. I have one on my Honda scooter for cold start, increasing cranking air supply and after-start rpm. Air reduces over time as the bi-metal spring heats and closes the air port partially. The reed-valve units are for air balance, anti-reversion and backfire protection. While their existence needs consideration, they should have little impact on tuning and operation if functioning properly.
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