Mercruiser 4.3 MPI

[Zoubi]

Hello everybody,
I have a problem with a Mercruiser 4.3L MPI - year : 2017 - hours : 21h !

The engine start good and works almost good (not perfect), but it shut down at the idle with no alarm, no mecanique problem..
So I look for again and again, I control every thing, I change the IAC, same problem.

But today I find something ! I disconnect the hose between the PCV valve (on the valve cover) and the intake manifold, after that the engine works good ... (you can see the picture, it is the hose disconnect).

I think it was the PCV valve dead, so I remove the valve cover, but every thing is good.

The engine works good now with the hose disconnect but I want to understand what is the problem ! :O
Somebody have see this problem ?

Thank you.

 

[alldodge]

By disconnecting the hose going to the PCV valve you have created a large vacuum leak. Since the motor runs good with this leak, then the idle air control (IAC) is not working. The IAC is responsible to control the amount of air the motor gets at idle. Since the IAC has probably malfunctioned it stop the flow of air and the motor died

but it shut down at the idle with no alarm, no mecanique problem..

To verify the issue is the IAC, the motor should be scanned for codes. Don't know you have a catalyst motor or not, but the hose remaining off can damage the motor and the cat if you have them

Could also find the IAC and see if the plug connecting it is in place (item 8)
https://www.mercruiserparts.com/bam/subassembly/31507/13808/80

 

[Zoubi]

Thx for your answer !

The engine have not cata .
The engine have been scaned for code with diagnostic computer G3.

I change the IAC by a new ... I don't understand where the problem could be. I check all the system, clean the metal gate (on the number 12)

 

[alldodge]

I change the IAC by a new ..

If you have already changed the IAC, then check that it has been installed correctly and there are no leaks. Also that the electrical plug is installed tight.

If all this has been done then the motor needs to be scanned

 

[Zoubi]

The engine have been scanned with Computeur Diagnostic G3.
The IAC have been change and the problem it is the same with the old and the new. The electrical plug is good.
No leak, new gasket. The engine have 21 hours !

 

[alldodge]

OK, so it was scanned and G3 does not show any faults in the history or freeze frame data.

Reconnect the PVC hose and run it until the engine indicates what the problem is. You can even look at live data to see what is going on with it

 

[Zoubi]

Already done, the engine shutdown at the idle with no fault. G3 says nothing.
I test IAC with G3, but at 100% openning, the engine goes at 750rpm, I think it is not enought. (with a V8, at 100% -> 1200rpm)

 

[alldodge]

It still sounds like the IAC and I understand you have replaced it. When I say IAC this also includes the PCM and connections to/from them. The reason I'm going back to it, is because the motor continues to run with the PVC hose off.

If you can keep the motor running by giving it motor throttle with the PVC hose attached, this also is an indication its the IAC control. Maybe Fun Times or muc can advise of other possibilities

 

[muc]

serial number would help.

what metal gate (on the number 12)?

have you checked the IAC muffler? is it stuck somewhere?

 

[Zoubi]

Yes for me it was the IAC to...
I only change parts 14, 9
I can't change IAC to PCM connection, it's in the electrical motor wiring.

Thank you for your help.

 

[Zoubi]

muc :
I haven't the serial number at this time (it start by 2A.....) I'm in France, I don't know if you have the same here.
The muffler, parts 11 https://www.mercruiserparts.com/bam/...31507/13808/80 ? this one yes.
What you mean by suck somewhere ?
The metal gate is :

Thx

 

[muc]

#11 can get plugged up or fall apart and get stuck somewhere. Do not clean it ---- replace it.

serial number allows me to know what motor you have and is my first step in troubleshooting.

 

[Zoubi]

Ah ok yes, number 11 I change it.
I give you the serial number in a few days

 

[muc]

Or just remove it for testing.

 

[Fun Times]

Zoubi. in your parts link there is a second muffler sort of similar to item # 11....The other muffler is item 6 that sits within the throttle body....Pull the flame arrester off and make sure the muffler is there and not dirty or damaged, etc. etc... Also clean the passage holes that head over to the IAC motor with throttle body cleaner.

Are you able to keep the engine running if you advance the throttle handle any?

Are you a boat servicing dealer or are you using a Mercruiser dealer / or a boat service technician that has access to a Mercruiser dealer G3 scan tool device?

When connected to the G3 scan tool does the test function make the IAC respond? if so what seems to happen?

What did the live data show number wise?

Someone may have to try testing the wiring to the IAC system to see if it seems to be working correctly and within specifications according to the latest service manual that fits you newer model engine year which isn't going to be found online without a servicing dealer helping you out in your area.

The engine works good now with the hose disconnect

The question becomes how good is good as there's usually still a noticeable running difference while that hose is not connected correctly....What does/did the engine idle at when the hose was disconnected? Did the engine still sound a little offbeat vs when things were working normal?

Being a 2017 boat, is the engine still under Mecruiser warranty?....If so it wouldn't be the best idea to be working to deep on the issue such as pulling the valve cover, etc. etc. giving them reasons to not want to work with you should there be deeper issues.

 

[QBhoy]

Sure sounds like an IAC issue but the alarm beeps on the dash when it is. Or it did when mine went. Defo check the muffler sponge isn’t blocked up. I’ll have a think.

 

[Zoubi]

@Fun Times

"The other muffler is item 6 that sits within the throttle body...."
I have not this one ... all 4.3 mpi have ? The engine is new, and never have this, but the first hours, it have any problem.

"Are you able to keep the engine running if you advance the throttle handle any?"
Yes, but I have some acceleration hole.

"Are you a boat servicing dealer or are you using a Mercruiser dealer / or a boat service technician that has access to a Mercruiser dealer G3 scan tool device?"
Yes, I'm a technician

"When connected to the G3 scan tool does the test function make the IAC respond? if so what seems to happen?"
Yes, IAC respond, but not perfect, like I say, at oppening 100% in the manual test, the engine goes only to 750rpm maximum, not more.

"The question becomes how good is good as there's usually still a noticeable running difference while that hose is not connected correctly....What does/did the engine idle at when the hose was disconnected? Did the engine still sound a little offbeat vs when things were working normal?"
With the hoses, the engine doesn't work good, the idle goes to 450rmp -> 500 ->480 ->550-> .... but with the hose disconnect, it is 550rpm fixed.
And in acceleration, I have a hole in 2000-2500rpm, but no with the hose disconnect.