500efi Rough Idle @ Warm
06-23-2019, 09:35 AM
#1
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Thread Starter
500efi Rough Idle @ Warm
Ran our boat yesterday...Throw the boat in, fire both motors start and run perfect at cold. After cruising for a little while, come off plane and during idle notice our port motor is running rough / hunting for idle. Almost sounds like mis-firing...can see the tach bouncing up and down. Get to our destination hang out for a bit...fire both motors back up running perfect again at cold. They both run great under load and higher rpms, no issues. Get to no wake and notice port motor doing the same thing on the way back.
Did some research and it it sounds like the first things to check are IAC, ECT, and maybe crank sensor? I was gonna personally start with IAC but seeing as they are $100 is there a cheaper thing to check before changing it?
Should mention spark plugs are relatively new (last year). Spark wires are all new from last year. The cap and rotors are old...
Did some research and it it sounds like the first things to check are IAC, ECT, and maybe crank sensor? I was gonna personally start with IAC but seeing as they are $100 is there a cheaper thing to check before changing it?
Should mention spark plugs are relatively new (last year). Spark wires are all new from last year. The cap and rotors are old...
Last edited by 1MOSES1; 06-23-2019 at 09:41 AM.
06-23-2019, 09:42 AM
#2
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sounds like fueling at idle or it has a touch of reversion.really need a scan tool and some way to measure fuel pressure,you don't have a crank sensor,you do have a pickup coil inside the distr.
06-23-2019, 09:54 AM
#3
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Fuel pressure check is a good call. Does the rough idle at warm vs. cold tell me anything to check?
06-23-2019, 10:27 AM
#4
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iTrader: (6)
move the IAC from the good running engine to the other one and see if the problem follows
06-23-2019, 10:58 AM
#5
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iTrader: (9)
stock 500 efi do not have a crank sensor nor a cam sensor and the IAC of this style do not have the issues like they do in the 555 computer controled engines. This IAC has a low failure rate is basically my point here. It happens but its low %. The TPS goes bad in more cases that the IAC. Just saying
Ignition tune up complete and new coil prob will help and of course u have the MULTEC injectors. the paper weights Do not buy any of these components online or ebay. Junk knock off stuff.
Ignition tune up complete and new coil prob will help and of course u have the MULTEC injectors. the paper weights Do not buy any of these components online or ebay. Junk knock off stuff.
06-23-2019, 03:52 PM
#6
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Thread Starter
stock 500 efi do not have a crank sensor nor a cam sensor and the IAC of this style do not have the issues like they do in the 555 computer controled engines. This IAC has a low failure rate is basically my point here. It happens but its low %. The TPS goes bad in more cases that the IAC. Just saying
Ignition tune up complete and new coil prob will help and of course u have the MULTEC injectors. the paper weights Do not buy any of these components online or ebay. Junk knock off stuff.
Ignition tune up complete and new coil prob will help and of course u have the MULTEC injectors. the paper weights Do not buy any of these components online or ebay. Junk knock off stuff.
do the 500’s have TPS? I’m gonna start with caps and rotors given it should be done anyways. Then swap IAC’s and go from there.
VIP Member
06-23-2019, 04:33 PM
#8
Banned
iTrader: (9)
the internal coil winding from heat cause the issue in the MULTECS I can not tell u how many people have chased that issue thinking its ignition related but was the Multecs..
IF I WAS YOU I would do a coil with spark plug wires and cap and rotor. First. The coil issues is heat related as well so they can be fine for however long it takes up till the heat related issue takes over -- then coil will act up.
Also what is coolant temps running and when the issue takes place ???
I just change all my caps and rotors to a USA maker and have coils coming that are bare min 15 % higher output for the big blocks that use the same distributor.
98 percent of all caps and rotors come from china and Mexico - even Mercruiser and Merc racing caps and rotors come from Mexico
As a side note Voodoo Rob owns twins 600 sci Merc racing engines and He just did some testing with 16 of my coils I sent him. He will tell you straight up - the coils are a huge Winner for his app --- he is running them as we speak. Just saying. Of course his coils are not like yours but I have the same person doing all of my coils from here on out (for all these marine engines ). Externally they will look the same but internally is the huge difference. The coils I sent Voodoo Rob are double the output of what Merc racing has for the 600 sci and the 700 sci. Im going to get him to post how it went for him.
IF I WAS YOU I would do a coil with spark plug wires and cap and rotor. First. The coil issues is heat related as well so they can be fine for however long it takes up till the heat related issue takes over -- then coil will act up.
Also what is coolant temps running and when the issue takes place ???
I just change all my caps and rotors to a USA maker and have coils coming that are bare min 15 % higher output for the big blocks that use the same distributor.
98 percent of all caps and rotors come from china and Mexico - even Mercruiser and Merc racing caps and rotors come from Mexico
As a side note Voodoo Rob owns twins 600 sci Merc racing engines and He just did some testing with 16 of my coils I sent him. He will tell you straight up - the coils are a huge Winner for his app --- he is running them as we speak. Just saying. Of course his coils are not like yours but I have the same person doing all of my coils from here on out (for all these marine engines ). Externally they will look the same but internally is the huge difference. The coils I sent Voodoo Rob are double the output of what Merc racing has for the 600 sci and the 700 sci. Im going to get him to post how it went for him.
06-23-2019, 05:16 PM
#9
Registered
my thoughts. Wires get hot and start missing. If boat ran fine and really nothing changed I would look at how old the basic ignition stuff is.
06-23-2019, 06:45 PM
#10
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Thread Starter
Will report back tomorrow...hoping to source coil and cap locally. As mentioned all of the spark wires are new as of last year. Quite frankly I spent too much on them to be bad in 1 year.
