2003 Mobius LSV misfire, replaced a lot already

[rothda1011]

The problem starting showing up originally only under high loads like pulling a wakeboarder out of the water with full ballast, but is now happening during normal operations sometimes. What's frustrating is that it will run great sometimes in all conditions and then for whatever reason starting missing. It does not ever seem to happen right away, but after some use it now will always happen. It's getting worse too - last night it was missing while just cruising around at 20 mph. It does not seem to be RPM related at all. When I say missing I mean you can hear it and feel it - it is quite pronounced.

Here's what I've done. Replaced plugs, wires, coil, ECM, distributer cap and rotor, fuel filter, fuel/water filter, completely drained the gas tank, added heet and sea foam. I purchased a MAP sensor from Amazon that was obviously not the right part as the boat would not even start with it installed, but given it starts and runs fine most of the time with the existing one installed I've mostly ruled that out, but I could be talked into trying another one. I've also checked the fuel pressure - it's a solid 30psi all the time.

If you were me what would you try next?

[parrothd]

The problem starting showing up originally only under high loads like pulling a wakeboarder out of the water with full ballast, but is now happening during normal operations sometimes. What's frustrating is that it will run great sometimes in all conditions and then for whatever reason starting missing. It does not ever seem to happen right away, but after some use it now will always happen. It's getting worse too - last night it was missing while just cruising around at 20 mph. It does not seem to be RPM related at all. When I say missing I mean you can hear it and feel it - it is quite pronounced.

Here's what I've done. Replaced plugs, wires, coil, ECM, distributer cap and rotor, fuel filter, fuel/water filter, completely drained the gas tank, added heet and sea foam. I purchased a MAP sensor from Amazon that was obviously not the right part as the boat would not even start with it installed, but given it starts and runs fine most of the time with the existing one installed I've mostly ruled that out, but I could be talked into trying another one. I've also checked the fuel pressure - it's a solid 30psi all the time.

If you were me what would you try next?

Check the wiring under the dash near the key area, I had a loose wire that would vibrate when hitting waves or randomly that would cause the boat to misfire. Probably a good idea to check the safety lanyard to. Found the problem by jiggling the the wires to see what would happen while it was running.

[rothda1011]

Check the wiring under the dash near the key area, I had a loose wire that would vibrate when hitting waves or randomly that would cause the boat to misfire. Probably a good idea to check the safety lanyard to. Found the problem by jiggling the the wires to see what would happen while it was running.

Thanks! I'll give that a shot. With yours did you notice gauges flickering or anything as the wires would jiggle loose?

[parrothd]

Thanks! I'll give that a shot. With yours did you notice gauges flickering or anything as the wires would jiggle loose?

No flickering, if you're seeing flickering check all power & ground connections all the way to battery and alternator. Mine was actually the switch plate was missing backing screws, which would slightly vibrate depending on the water conditions and jiggle the wires enough.

[rothda1011]

No flickering, if you're seeing flickering check all power & ground connections all the way to battery and alternator. Mine was actually the switch plate was missing backing screws, which would slightly vibrate depending on the water conditions and jiggle the wires enough.

I have no flickering, sorry I was just asking if you did to see if it's something I should be looking for. Thanks again!

[SONIC]

A little more info may help diagnose.
Is a single cylinder misfire or is the whole engine cutting out momentarily (that would lean me toward the loose wire theory above)
Any lights flickering or anything at the same time?

[secondsupra2004]

The problem starting showing up originally only under high loads like pulling a wakeboarder out of the water with full ballast, but is now happening during normal operations sometimes. What's frustrating is that it will run great sometimes in all conditions and then for whatever reason starting missing. It does not ever seem to happen right away, but after some use it now will always happen. It's getting worse too - last night it was missing while just cruising around at 20 mph. It does not seem to be RPM related at all. When I say missing I mean you can hear it and feel it - it is quite pronounced.

Here's what I've done. Replaced plugs, wires, coil, ECM, distributer cap and rotor, fuel filter, fuel/water filter, completely drained the gas tank, added heet and sea foam. I purchased a MAP sensor from Amazon that was obviously not the right part as the boat would not even start with it installed, but given it starts and runs fine most of the time with the existing one installed I've mostly ruled that out, but I could be talked into trying another one. I've also checked the fuel pressure - it's a solid 30psi all the time.

If you were me what would you try next?

Ignition control module. Mine failed in the middle of the lake, no warning but there are other threads similar to yours where it started going bad and dealt them a fit. Is your engine a 5.7 Assault TBI?

[rothda1011]

Ignition control module. Mine failed in the middle of the lake, no warning but there are other threads similar to yours where it started going bad and dealt them a fit. Is your engine a 5.7 Assault TBI?

It is a 5.7 TBI. I'll look into the ignition control module. Thanks! Don't happen to have a part number handy for that do you? If not, I'll find it!

[rothda1011]

It does not feel like everything cuts out all at once, but it feels like more than one cylinder too? I have not witnessed any flickering, but haven't really been looking either. I'll pay way more attention next time out. Sorry for the lack of clarity - your questions are great though!

[rothda1011]

A little more info may help diagnose.
Is a single cylinder misfire or is the whole engine cutting out momentarily (that would lean me toward the loose wire theory above)
Any lights flickering or anything at the same time?

It does not feel like everything cuts out all at once, but it feels like more than one cylinder too? I have not witnessed any flickering, but haven't really been looking either. I'll pay way more attention next time out. Sorry for the lack of clarity - your questions are great though!

[secondsupra2004]

It is a 5.7 TBI. I'll look into the ignition control module. Thanks! Don't happen to have a part number handy for that do you? If not, I'll find it!


The Indmar # is 556096. I bought it from Inboard Online . https://inboardonline.com/search.php?search_query=556096
It was pricey ($200.00) , but I wanted to go with the factory original and make sure it worked. Takes 15 minutes to replace. When I received it, it had numbers on it that I crossed to a Standard Ignition Products number of LX-384. I bought this one as a spare, but have not tried it yet. I'm 99% sure it is a direct replacement though.

[rothda1011]

The Indmar # is 556096. I bought it from Inboard Online . https://inboardonline.com/search.php?search_query=556096
It was pricey ($200.00) , but I wanted to go with the factory original and make sure it worked. Takes 15 minutes to replace. When I received it, it had numbers on it that I crossed to a Standard Ignition Products number of LX-384. I bought this one as a spare, but have not tried it yet. I'm 99% sure it is a direct replacement though.

Thank you very much!

[rothda1011]

The Indmar # is 556096. I bought it from Inboard Online . https://inboardonline.com/search.php?search_query=556096
It was pricey ($200.00) , but I wanted to go with the factory original and make sure it worked. Takes 15 minutes to replace. When I received it, it had numbers on it that I crossed to a Standard Ignition Products number of LX-384. I bought this one as a spare, but have not tried it yet. I'm 99% sure it is a direct replacement though.

So, I'm dumb. I already replaced that! In my original post I said ECM, but meant to say ICM. Dang!

[secondsupra2004]

So, I'm dumb. I already replaced that! In my original post I said ECM, but meant to say ICM. Dang!

You didn't mention it, but do you have a scanner or even a simple code reader? I bought a scanner and can check code faults and view live data while its running. Scanner is pricey though, ($500.00) . Code reader is about $60.00. Hate to see you keep throwing parts at it.

[rothda1011]

You didn't mention it, but do you have a scanner or even a simple code reader? I bought a scanner and can check code faults and view live data while its running. Scanner is pricey though, ($500.00) . Code reader is about $60.00. Hate to see you keep throwing parts at it.

I do not, but will be picking up a simple one (or making one) before I do anything else. Thanks for the suggestion.

[rothda1011]

I do not, but will be picking up a simple one (or making one) before I do anything else. Thanks for the suggestion.

Just used a diy code reader (https://www.themalibucrew.com/index.php?/forums/topic/17763-diy-mefi-code-reader-mefi-2-3-4/) and it's showing no codes! dangit. Any other suggestions?

[rothda1011]

The problem starting showing up originally only under high loads like pulling a wakeboarder out of the water with full ballast, but is now happening during normal operations sometimes. What's frustrating is that it will run great sometimes in all conditions and then for whatever reason starting missing. It does not ever seem to happen right away, but after some use it now will always happen. It's getting worse too - last night it was missing while just cruising around at 20 mph. It does not seem to be RPM related at all. When I say missing I mean you can hear it and feel it - it is quite pronounced.

Here's what I've done. Replaced plugs, wires, coil, ECM, distributer cap and rotor, fuel filter, fuel/water filter, completely drained the gas tank, added heet and sea foam. I purchased a MAP sensor from Amazon that was obviously not the right part as the boat would not even start with it installed, but given it starts and runs fine most of the time with the existing one installed I've mostly ruled that out, but I could be talked into trying another one. I've also checked the fuel pressure - it's a solid 30psi all the time.

If you were me what would you try next?

Just used a diy code reader (https://www.themalibucrew.com/index.php?/forums/topic/17763-diy-mefi-code-reader-mefi-2-3-4/) and it's showing no codes! dangit. Any other suggestions?

[mmandley]

You might look into replacing the actual distributor its self. My buddy has an 06 Supra and was having the same issue, only high rpm, normally 5-10min after surfing and he replaced everything you did and in the end it was the actual distributor failing.

[liteweightstickers]

What did your plugs look like when you changed them? Were ALL of them the same color? Did any of them look particularly clean?