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IAB vacuum

Garygin

Garygin

Regular Contributor
I have an issue . Honda 225 IAB vacuum is opening as soon as the engine is started. I’m wondering if it could be the IAB solenoid.
Any help would be greatly appreciated.
Thanks, Gary
 
Yep. Stuck open solenoid is the likely culprit. BUT it could be the ecu. First time since I've been on this forum that I have heard of that happening. Do some research on what electrical circuit triggers the solenoid. See chapter 18 in Helm Shop Manual.
 
Solenoid. I'm guessing here, but the solenoid should be relatively easy to test. It's normal state is closed. So with it disconnected, see if you can blow air thru it. If so, it's stuck open.

Well, ok. You got me curious. Will go back to my office and do some research.
 
Gary. If you have the Helm manual, first read page 18-15 to understand how the IAB works. Then see pages 5-66 thru 5-68 to test. Once you get thru the gobblygook, essentially you apply 12 volts to the solenoid and see if it works. If it does, back track the wiring to the ECU.
 
Ok Chawk man.
I checked everything. What I found was that there is no continuity between the black pin on the 2 pin harness to ground .so what the book says is to replace the ECM. I checked the IAB solenoid and it checks out fine. It has continuity , and when 12 volts is applied you can hear the check valve opening and air will pass through.
I’m not an electrical guy .So I’m hoping someone will chime in and give me their opinion
Thanks Gary
 
I'll try to look at the wiring diagram. These ECU's seldom go bad, so I suspect that it's something else.

One would normally think that without the ground, the solenoid would not work. HOWEVER, the Honda injectors and coils are activated by applying ground. It may be that the solenoid activates the same way - i.e. completing the ground activates the solenoid. I just don't know one way or the other, but will take a look at wiring diagram when I get some time.
 
FYI . When I hook the solenoid to its 2 pin connector and energize it you cannot hear the check valve open. I only hear it when I put 12 volts directly to the terminals on the solenoid. Also if I check the Y/BK wire on the 2 pin and a ground I
Have 12 volts
 
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Make sure your #5 fuse is good. Test it.

Read page 5-67 carefully. Here is the way I interpret that page. Apparently, as I suspected, the ECU completes ground to the solenoid to activate it. See page 5-10 - the 26-pin connector.

1. With key on, you should get 12 volts at the Y/BL wire (Pin # 1) and engine ground. Check it with a voltmeter.

2. Now, Key off - check for continuity between the harness black wire (#2 pin) and engine ground. There should NOT be continuity.

If continuity, you likely have a problem with that ground wire or pin. Make sure the pin is not corroded on either side of the plug. If you do get ground on the #2 pin, that would explain why you have vacuum at the IAB diagram at start up.. That is, the ECU supplies the ground when it detects 3950 rpm, and that activates the IAB solenoid.

If black ground wire OK, then pull the 26-pin connector to the ECU and closely inspect pin 9 - see page 5-68.

I want to emphasize that I am not a marine tech and this is simply the way I'm interpreting that Helm manual.
 
I checked everything. I ran all of these tests yesterday. I followed your instructions as the manual and tested again. I figured it can’t hurt. I have the same results. #5 fuse is good, 12 Volts from Y/BL to ground. No continuity between #2 pin and ground. I pulled the 26 pin connector pin and socket look new. Really don’t want to buy a new ECM, but it looks like that’s where I’m headed.
 
One final check. Key off. Pull 26-pin connector from ECU. Check for continuity between the # 9 pin on the ECU to ground. There should be no continuity. If so, I would then conclude a bad ECU. But as I wrote earlier, they seldom fail.
 
Ok . I checked from the #9 pin to ground and there is continuity. So are thinking what I’m thinking .. New ECU?
 
Unfortunately, yes. But before spending that kind of money, maybe you ought to check with a certified Honda Tech who has Dr. H.
 
Hi Gary, I don't believe your IAB has anything to do with the lack of RPM. Your IAB should Close (activate) at idle in order to direct airflow via a longer intake tract to stabilize idle airflow. Prior to start up, valve flap is fully open. At aprox 30% thottle, flap starts opening shortening intake tract thereby accelerating air flow into the intake manifolds to increase volumetric efficiency improving both power and economy. What you think is opening at start up is actually closing the shorter tract. So I suggest you check fuel pressure , compression, and spark under full throttle. I have seen the IAB valves completely siezed in half open, open and closed with the owner not reporting any noticeable performance issues.Hope this helps
 
Ian - Thanks for jumping in. We went down this path because Garygin reported that the IAB was pulled fully open at start up, indicating that vacuum had activated the IAB diaphragm at idle. According to the shop manual, that is not supposed to happen until the ECU detects 3950 rpm when the IAB solenoid is activated.
 
Solenoid releases vacuum, there is almost no manifold vacuum at that rpm. If you watch a MAP sensor you'll see max vacuum at idle and almost atmosheric pressure at wide open throttle.So solenoid is holding long tract ( IAB) flap closed. That's the way I have always understood it, but as I said, I haven't ever known a malfunction of this feature to affect a drop off in performance as Gary is experiencing.
 
Gary - Ian's explanation is most likely correct. I sincerely apologize for taking you down this path. Bottom line - IAB diaphragm SHOULD be activated at idle - i.e. arm pulled into diaphragm. At 3950 RPM, solenoid releases vacuum to diaphragm, which releases the arm to change the angle of the IAB baffles.

So, you are back to the original problem with limit at 3950 RPM.
 
iang6766 said:
Hi Gary, I don't believe your IAB has anything to do with the lack of RPM. Your IAB should Close (activate) at idle in order to direct airflow via a longer intake tract to stabilize idle airflow. Prior to start up, valve flap is fully open. At aprox 30% thottle, flap starts opening shortening intake tract thereby accelerating air flow into the intake manifolds to increase volumetric efficiency improving both power and economy. What you think is opening at start up is actually closing the shorter tract. So I suggest you check fuel pressure , compression, and spark under full throttle. I have seen the IAB valves completely siezed in half open, open and closed with the owner not reporting any noticeable performance issues.Hope this helps
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The IAB valves are completely functional. I have had it apart several times . The only thing that I haven’t replaced is the IAB solenoid, but I tested it . When I connect it to the 2pin connector you cannot hear it click. When I put 12 volts to directly it sounds fine , and it checks to the manual as far as ohms reading. This is the part that I think is the problem. I DO NOT have continuity to ground from the #9 pin on the ECU. By the manual it says I should. If not replace ECU. Thoughts?
Gary
 
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