496HO Computer on a 496Mag?

[Wizard29]

Long story short, trying to help my father in law with an issue he's having with his boat. We suspect he's got a bad computer. We want to try to swap computers to see if that's actually the problem.

He's got a 496Mag (375HP) and I have access to a 496HO (425HP) computer with the same part number (885557) we could swap out. However, I've read that the HO computer programming is different and will not run on the Mag, which makes sense. However, he said he spoke to Mercruiser and they say the computers can be swapped and the programming is the only difference between the two engines, which doesn't make a lot of sense.

I was under the impression the HO has a different cam and a couple of other things. In any case, can we really run the HO computer on the Mag? I'm thinking no, but anybody know for sure?

 

[Mandelon]

Sounds like the computer will work, it just needs to be programmed with the correct settings for the other engine.
So you need a laptop and access to the correct settings, and the software to run all that.

 

[mjc]

For a test the programming shouldn't resllmatter that much. Especially just to test.

 

[Wizard29]

Sounds like the computer will work, it just needs to be programmed with the correct settings for the other engine.
So you need a laptop and access to the correct settings, and the software to run all that.

I should clarify...Will it work without changing the programming? The HO computer would be borrowed and we wouldn't want to change parameters.

 

[Singleton]

Call a Merc shop and ask - they might even have loaner sitting on shelf you could borrow

 

[LargeOrangeFont]

I should clarify...Will it work without changing the programming? The HO computer would be borrowed and we wouldn't want to change parameters.

Will it plug in, start and run? probably.

Will it be tuned correctly under load? Probably not.

Is the tuning difference enough to matter? No idea.

 

[gqchris]

Long story short, trying to help my father in law with an issue he's having with his boat. We suspect he's got a bad computer. We want to try to swap computers to see if that's actually the problem.

He's got a 496Mag (375HP) and I have access to a 496HO (425HP) computer with the same part number (885557) we could swap out. However, I've read that the HO computer programming is different and will not run on the Mag, which makes sense. However, he said he spoke to Mercruiser and they say the computers can be swapped and the programming is the only difference between the two engines, which doesn't make a lot of sense.

I was under the impression the HO has a different cam and a couple of other things. In any case, can we really run the HO computer on the Mag? I'm thinking no, but anybody know for sure?

What are the symptoms? This is what mine did when it went bad. It had to be sent to Whipple for "Clock Fix".

 

[Mandelon]

My 496 ran shitty one trip. Turned out to be plugs. They were fine...until they weren't. Super simple fix.

 

[Wizard29]

The problem he's having is he will be cruising along and it's like someone turned the key off and back on real quick. Doesn't die, but loses power for about one second, beeps, and then keeps going. Been through the wiring, breaker, switches...computer is really the only thing left to check. Usually only does it once or twice per day completely randomly.

No other problems or alarms. It wouldn't have to run perfect for us to check, but well enough to run up and down the lake for a day to see if the problem still exists.

 

[Ace in the Hole]

Paging @Shlbyntro

 

[Shlbyntro]

It should work for testing on trailer purposes only, I definitely would not go run it around. But be forewarned: Ecms don't usually go bad for just any reason, they are usually knocked out by a dead short in one of the many plethora of sensors or electronic engine components; or more commonly bad grounds/battery connections. If you do indeed have a bad ecm, there is a chance that whatever caused it can hurt your buddy's computer if it hasn't been caught/rectified yet.

 

[DaveH]

yes the tune is really the only difference. it should start and run. FWIW you probably have an intermittent connection is your ecu harness. Highly doubt its the ecu.

 

[dribble]

My 496 ran shitty one trip. Turned out to be plugs. They were fine...until they weren't. Super simple fix.

Every 30 hours like clockwork. From day one.

 

[lbhsbz]

Try it. If it runs on the trailer, take it out on the lake…just take it easy. Nothing ever blows up at 1/2 throttle due to the tune

 

[Blackmagic94]

Loose quartz crystal on pcm mother board.


whipple does this repair for 450 bucks


when it comes loose it has zero power

 

[OLDRAAT]

Grounding issues?

 

[HubbaHubbaLife]

It should work for testing on trailer purposes only, I definitely would not go run it around. But be forewarned: Ecms don't usually go bad for just any reason, they are usually knocked out by a dead short in one of the many plethora of sensors or electronic engine components; or more commonly bad grounds/battery connections. If you do indeed have a bad ecm, there is a chance that whatever caused it can hurt your buddy's computer if it hasn't been caught/rectified yet.

Just thinking bout you.... how's the Cobra project?

 

[Shlbyntro]

Waiting to pick it back up in October after it cools down a scoach. Next step is loading her on a trailer and taking her to paint. Unfortunately and more urgently, the Lightning needs a radiator and the Ranger just roasted 4th gear in her 6 month old manual transmission. So the Fairlane gets to live outside for a little bit while I change the radiator and send the transmission in for a warranty rebuild.... Then the Cobra can go in for paint and the power/drivetrain will be installed while the body is off

 

[HubbaHubbaLife]

Waiting to pick it back up in October after it cools down a scoach. Next step is loading her on a trailer and taking her to paint. Unfortunately and more urgently, the Lightning needs a radiator and the Ranger just roasted 4th gear in her 6 month old manual transmission. So the Fairlane gets to live outside for a little bit while I change the radiator and send the transmission in for a warranty rebuild.... Then the Cobra can go in for paint and the power/drivetrain will be installed while the body is off

Oh paint... thats a great stage. Interior to follow?

 

[Shlbyntro]

Oh paint... thats a great stage. Interior to follow?

Followed by electrical and plumbing

 

[HydroSkreamin]

The problem he's having is he will be cruising along and it's like someone turned the key off and back on real quick. Doesn't die, but loses power for about one second, beeps, and then keeps going. Been through the wiring, breaker, switches...computer is really the only thing left to check. Usually only does it once or twice per day completely randomly.

No other problems or alarms. It wouldn't have to run perfect for us to check, but well enough to run up and down the lake for a day to see if the problem still exists.

If it’s a DTS engine, check or change out the clean power harness. Corrosion or general lack of contact on the pins can cause this.

As previously mentioned, the PCM connections could be suspect as well, and where I’d be looking if it’s a mechanical (non-DTS) engine.

Regardless, do you have access to the fault history? I’d definitely be looking for encoder faults. That vintage could be a possibility as well.

 

[Shlbyntro]

If it’s a DTS engine, check or change out the clean power harness. Corrosion or general lack of contact on the pins can cause this.

As previously mentioned, the PCM connections could be suspect as well, and where I’d be looking if it’s a mechanical (non-DTS) engine.

Regardless, do you have access to the fault history? I’d definitely be looking for encoder faults. That vintage could be a possibility as well.

I'm fairly certain that the Motorola triple nickel is indicative of a mechanical control engine, 1st or 2nd gen 496.

 

[HydroSkreamin]

I'm fairly certain that the Motorola triple nickel is indicative of a mechanical control engine, 1st or 2nd gen 496.

Not true. Same PCM on all L6 and L4 Verado, 525, 600&700SCi, 850/1075/1200 SCi as well. Slightly different p/n, as well as supercession to PCM03, 07, and 08, externally physically the same.

Mechanical version end in 01, DTS and supercharged versions end in 02.

 

[Shlbyntro]

Not true. Same PCM on all L6 and L4 Verado, 525, 600&700SCi, 850/1075/1200 SCi as well. Slightly different p/n, as well as supercession to PCM03, 07, and 08, externally physically the same.

Mechanical version end in 01, DTS and supercharged versions end in 02.

Agreed. But I believe the "555" is absent from the pn of those newer ECMs. I have never seen a 496 with a "555" numbered ECM that didn't still have cables.

 

[HydroSkreamin]

Agreed. But I believe the "555" is absent from the pn of those newer ECMs. I have never seen a 496 with a "555" numbered ECM that didn't still have cables.

You’ll have to trust me on this one then, I guess. I was involved with the rollout of this product in August 2000, and both DTS and mechanical engines were supported by PCM555.

 

[Shlbyntro]

You’ll have to trust me on this one then, I guess. I was involved with the rollout of this product in August 2000, and both DTS and mechanical engines were supported by PCM555.

If true, the only conclusion I can come to is it must've been a very rare option back then because merc 496s and mpi 350s make up the vast majority of my work.

For the sake of this thread though, @Wizard29 what say you on you and your buddy's boat, cables or DTS?

 

[Wizard29]

If true, the only conclusion I can come to is it must've been a very rare option back then because merc 496s and mpi 350s make up the vast majority of my work.

For the sake of this thread though, @Wizard29 what say you on you and your buddy's boat, cables or DTS?

Pretty sure it's cables. Boat is an '06 Ultra Stealth and nothing too fancy.