Merc 4.3 l fuel injected stalling when warmed up. Intermittent problem. Sn 1a330717

[Davidalex]

The engine runs fine at high speed and when started up in the driveway or at the boat ram. Usually runs fine when leaving the ramp at low speed.There is an intermittent problem when the engine has been run at high speed and then brought back to trolling speed, the engine wants to stall out. Giving it more throttle and seems to run well. A couple of times I have noticed the idle rpm running around 1000 rpm when brought back to neutral. I have changed the cap,rotor, fuel filter, idle air control valve. I don't think it is ignition or fuel related. Help would be greatly appreciated.

 

[alldodge]

Howdy

My guess is it is fuel related, the injection system is not getting enough fuel because something that is controlling the amount is not working correctly. When you come off planning speed the throttle plates close down, the IAC takes over, vacuum inside the intake increases and the fuel pressure drops a bit, along with timing be retarded back to base timing.

To start with the easy stuff,
Did you clean the IAC port and use a new gasket when installing the new IAC?
Was the IAC muffler removed and/or replaced along with cleaning the port (item 6)
http://www.mercruiserparts.com/bam/subassembly/31507/13808/80

Is the vacuum line connected between the throttle body and the fuel pressure regulator, also is the hose intact with no breaks or cracks?
Can you feel a suction on the vacuum line (item 25) at the fuel regulator with motor running and line removed?
http://www.mercruiserparts.com/bam/subassembly/31507/13808/60

 

[Davidalex]

Thank you for your response. I did clean the IAC port from inside the throttle body's with carb. Cleaner. The muffler was gone I presume the it was gobbled by the engine. I cleaned the port again and installed a new muffler. I also installed a new throttle position sensor, in order to get the old one off I removed the IAC adapter. I didn't change flat gasket in front of the IAC or the two Orings on the adapter. I had suction at the fuel regutalor. I started the engine and the engine was I idling at about 1000 rpm. I checked for air leaks and found it was leaking around the IAC or around the adapter. My game plan is replace the adapter Orings and the gasket in front of the IAC and run the engine again. Any other suggestions you have would be greatly appreciated.

 

[alldodge]

Nothing right now, and sorry I didn't mention about no harsh chemicals on the IAC (carb cleaner). The tip and parts are plastic and can be melted by the stuff

 

[Davidalex]

I changed out the Orings on the IAC adapter and the gasket between the IAC and the IAC adapter. Started the engine and everything seemed normal, rpm around 650, I was able to shift and give it and give it throttle. Ran it up to temp (160). And still was normal. The following day I launched the boat, started it, everything seemed norm. Kept at no wake speed for probably 15 minutes, everything was normal. Took the engine out of gear and the engine stalled out. Started it up and the engine ran rough, wouldn't idle down with out stalling, had to goose the rpm to about 1500 rpm to ake it back to the ramp. Any other suggestions would be appreciated.

 

[Bondo]

Ayuh,..... Welcome Aboard,.... Insteada just changin' the fuel filter,.....
Check the contents of the one on there now for anything other than clean fresh gasoline, 'n then slap on a fresh filter, 'n try it,....

 

[alldodge]

If you can keep the motor running at higher rpm (above 1000 rpm) and when you idle down it dies, in most all cases this is the IAC.

If you get a Noid light, but here is the IAC test

 

[Davidalex]

I was wondering, if the problem I am having is intermittent will it show up on the omb test. The test procedure calls for testing the 4 IAC harness terminals. The IAC harness connector has 2 terminals. I know I'm reaching but could the problem be the mapt sensor and if so how could I test it. Thanks in advance for your help.

 

[alldodge]

I was wondering, if the problem I am having is intermittent will it show up on the omb test. The test procedure calls for testing the 4 IAC harness terminals. The IAC harness connector has 2 terminals. I know I'm reaching but could the problem be the mapt sensor and if so how could I test it. Thanks in advance for your help.

I think your mixing the TPS with the IAC. In post 2, the first link illustrates the TPS is item 2 and the IAC is item 8. The TPS has two terminals and IAC has 4.

You mention "omb", did you mean ohm test? If so what are you going to ohm?

 

[Rick Stephens]

AllDodge

Great posts.

 

[Davidalex]

I got my abbreviations mixed up I meant obd. My question is if this test is performed first as IAC functional test indicates, is it going to indicate a problem if the engine is not malfunctioning when the test is performed. I have started the boat in my driveway and the engine has run normal on several occasions. The IAC functional test step 4 also states to test 4 IAC harnass terminals. My IAC has 2 terminals, the tps sensor has 4.

 

[Fun Times]

Being a 1A starting serial number, what year is the boat?

Being a newer engine model, something's have changed as far as sensor designs and unfortunately there isn't any updated wiring diagrams available online along with a lot of the testing procedures found in older manuals are almost sort of invalid such as in a situation like this. The older IAC's were a 4 pin while the newer ones are 2 pins. The old TPS's were 2 or 3 pins and now has 4. Wiring diagrams for the MPI system is no longer found in service manuals any longer, they are in paper form which is sent out to dealers as they are produced for a certain engine model...This stated in 2007.

If your lowest RPM you are truly able to obtain is 650, then that is still to high. Before 2006/07, the MPI idle speed was 600 but the later models after 06 or 07 went to as low as 540 RPM when engine is warm at 160 degrees.

Were you ever able to get the engine to die on the garden hose at home or only while under load in the water? Since it seems to be dying during shifting, it could have something to due with the mercruiser shift interrupter switch binding up which affects the ignition system or more probable something different is happening that is just out of range to make the engine not run correctly but not bad enough to set a fault code sounding a warning horn. It could be anything from a sensor to a throttle cable not adjusted correctly holding open/closed too much with the throttle body plates....Also possibly affecting shifting....Among other things as well.

The MPI system may need to be scanned by someone that knows the system pretty good to see if any of the live data parameters seem out of specifications.

You could try pulling out a few easy to get to spark plugs to see if they appear to be overly carbon fouled since you mentioned the MAPT sensor which yes if there is something not right with the MAP or engine vacuum systems, then it could have an effect with what you're describing.

Being that you have the flat distributor cap, it may be causing issues as well or the distributor shaft assembly may not be properly phased in too which will cause issues too.

Is the boat new to you or did this just seem to start out of the blue?

Davidalex's IAC pin connector would resemble this as it matches his part number,

http://www.ebay.ca/itm/Sierra-Idle-Speed-Control-Motor-Replaces-Mercruiser-862998-/322204451365

 

[79_banshee]

Could be way off but maybe voltage regulator cause it's fuel injected. If the computer isn't getting or seeing the right voltage it may not run right. Not sure if boats have them but may have somthing to do with it

 

[alldodge]

Gee wiz, Merc doesn't want anyone to work on their stuff except them. Going to need to remember 2007 and the 1A. Might be that only folks like you FT and muc will be the only ones to help. Appreciate the info

 

[Davidalex]

The boat is a 1997 Proline repowered in 2008, engine, lower unit and controls. I have had it since it was new. The manual says the idle rpm should be 600 rpm. I am reading the tach mounted to the boat, the reading I'm getting is pretty much what it has always been. I have duplicated the problem on the garden hose no load on the boat. The IAC connector is as shown in the above picture (2pin). Does anyone have a procedure for testing this IAC .the problem originally occurred last year, it happened a couple of times then did not occur again until this year. I would say the problem occurring now is more likely.

 

[Davidalex]

I brought the boat in to a authorize Mercury dealer. The mechanic told me after 2 1/2 weeks dold me that they had tested everything. They talked to Mercury rep and they said that after all the testing they did if left the ecm module. They say that there are no guarantees that it will work and once they open the box I own it. I don't think it's the Ecm module and would like to find another mechanic in he Boston area. Does anyone know a good one?

 

[79_banshee]

It very well could be the ecm they can do funny things. Sometimes they short out on the inside. I've seen it lots in heavy duty trucks.

 

[alldodge]

If unable to find another mechanic I would suggest giving a call at the link below. Bob can check it out and find out if it just needs reflashed or something simple

https://www.obd2allinone.com/mefiecms.asp

 

[Davidalex]

The Mercury mechanic installed a new elm module and engine still has the same problem. They are trying to get a hold or the Mercury tech rep. The boat yard claims that can't call him direct, his cell number is blocked. They have to call Mercury and Mercury will contact the guy and he will then call him. They also claim that Mercury will not send a tech out unless the engine is under warranty. The boat yard has had the boat now for almost 6 weeks. I was assured that the ecm has been flashed. I want to thank all of you for your help, I'm considering calling next, if anyone has any further suggestions I would appreciate them.

 

[Dannyendres]

Would the IAC mess with a boat starting? On a 5.0