2006 Merc 496 Mag won't always spark/start & possibly IAC/PCM issues too.

[jmsmieja]

Hey everyone. Read through the current posts. Just wanting to confirm I've diagnosed correctly before spending more money.

I just bought an '06 Chaparral with the Merc 496 Mag. When water testing, it beeped once at about 2-3k RPM and then throttled back on it's own. Did it a couple more times. I googled, found the IAC issues, and then the dealer replaced the foam filter and said they cleared IAC codes (filter was pretty dirty).

Knowing the IAC was cheap to replace, I bought the boat and replaced the IAC when the problem resurfaced for me. That didn't fix the issue (even with an OEM IAC).

Now I'm thinking it's probably the PCM driver.

It doesn't do this constantly. I let the boat warm up, take it out, and then it does it a small handful of times when I first try and cruise around between 1500 and 3k RPM. It then goes away on it's own, coming back only after letting the boat sit at anchor for an hour or more.

Is there anything else I should look into before I tear out the PCM to have it diagnosed and repaired? I don't plan to just buy a new one.

Thanks for the guidance!

 

[alldodge]

When water testing, it beeped once at about 2-3k RPM and then throttled back on it's own

Don't see this being an IAC issue. Once the motor is above 1500 RPM the IAC is no longer used.

The single beep is the issue unless its a solid and continuous beep. If continuous then this could be the neutral over speed switch

 

[jmsmieja]

The single beep is the issue unless its a solid and continuous beep. If continuous then this could be the neutral over speed switch

It's probably between a 1 to 2 second single beep.

 

[alldodge]

The 555 PCM doesn't have a single beep in the warning fault listing. It has continuous and 2 beep faults. This could be due to corrosion in a connector. The continuous faults are

ECT overheat
Oil pressure
Drive lube
Over speed
Port or Starboard overheat
Sea pump low

The sea pump pressure low happens quite but most the time once it starts it continues, It could be also be the PCM and the best method to find the issue is with a scanner.

 

[QBhoy]

TPS, SW pressure sensor and more likely distributor cap and rotor would likely solve it.

 

[jmsmieja]

Just a heads up for everyone. The boat finally died on me while cruising a couple weeks ago. Would crank strong but not fire. I checked all the spark plug wire connections, and eventually it just decided to fire and run. The boat went back to working as before for the rest of the weekend.

I had a professional come hookup to it a few days later, and sure enough the boat wouldn't even start. It was throwing a MAP sensor, cam position sensor, and crank position sensor fault all at the same time. Guardian was also kicking in. No juice to the spark plug he checked. He tried cleaning and reconnecting the "barrel" harness connection to the engine, but the problem remained. 3 hours later he was stumped, and then the engine fired and ran again like nothing was wrong.

Still waiting for him to hear back from Merc on what to do next before throwing parts at it. In the meantime, it's anyone's guess if the boat will start and stay running. Tried to use it today in fact, and it wouldn't start at all. Finally after 3 hours it fired right up, but then died 2 minutes later.

I'm checking for other posts related to the above sensors, and plan to start a new one since the IAC was not even faulting at this point in time.

 

[jmsmieja]

2006 Merc 496 Mag won't always spark or start

Hi everyone,

I have a 2006 Chaparral with the Merc 496 Mag (EFI). Serial number OW632XXX. It recently died while underway, and I couldn't get it to fire. Checked all the spark plug wire connections, played around for a bit, and it magically started again and ran as usual. Worked all weekend after that.

I had a mechanic come out the following Monday to hook up to it and see what faults it was logging. The boat would crank strong but wouldn't fire/start for him. It was throwing simultaneous MAP sensor, cam sensor, and crankshaft sensor faults. It was also logging Guardian faults/logs. He confirmed that no juice was going to one of the spark plugs, even after bypassing the dash with a CDI remote start module. He cleaned and reconnected the "barrel" connector to the engine, wiggled a bunch of other connections, and couldn't really turn the problem on & off.

In the end, after 3 hours of troubleshooting, he couldn't find the root cause. The boat was running when he left, but he didn't know why. Now I'm waiting for them to hear back from Merc. I tried the boat tonight multiple times, and it wouldn't fire. Eventually on the last try it did fire like normal, but then died after about 60 seconds.

Anyone aware of or had a similar issue with this vintage of 496 Mag with EFI? I'm tired of waiting for an answer and can't seem to find a close comparison on all the forums I've been searching.

 

[alldodge]

Suggest not starting another thread because while this probably doesn't have anything to do with the IAC it does still have issue with the motor and PCM. You can get a Moderator to change your thread title if you think this will help

I'm seeing fault with all the sensors as a failing in a feed to the sensors which would be the 5V line. When the motor won't start check the voltage on the 5V line of any of the sensors, they are all feed by the same line

 

[jmsmieja]

...When the motor won't start check the voltage on the 5V line of any of the sensors, they are all feed by the same line

Hi AllDodge. I did this today. Boat started just fine when I got to it in the morning. Then refused to fire after doing some troubleshooting (don't know why...). While it wasn't firing, I measured the 5V supply to the MAP, TPS, Crank Pos Sensor, and Cam Pos Sensor. All 4 had 5V going to them the entire time.

Just a heads up, while the boat was actually starting, one by one I disconnected the above 4 sensors, and then tried to start the boat to see what would happen. The one that seemed to replicate the issue I've been having is the crank position sensor. I already have the (automotive equivalent) part on hand, so I will try to swap that tomorrow. I will also get my hands on a Cam pos sensor, as that also prevented the engine from starting when disconnected (but acted a little bit differently than I'm used to).

Any other insight would be greatly appreciated. Maddening to have it work/not-work whenever if "feels like it".

 

[alldodge]

Wish I had another idea, but with all the sensor throwing codes lead me to the 5V, and that didn't answer the question. I'm out of ideas

Did the scanner list which code numbers?

 

[jmsmieja]

Did the scanner list which code numbers?

Hey AllDodge. I didn't get that detail, since it was a mobile marine mechanic that did that diagnosing.

That being said, I did fix the issue today. With a new crank pos sensor and cam pos sensor in hand, I went to work changing out parts. Boat wouldn't start right out of the gate, so I swapped the crank sensor first. Did not fix the issue. I was pretty much out of time, so I re-did a bunch of electrical connections again for the heck of it, shook the harness around a bit, and then the boat started. So then I started shaking various parts of the harness with it running, and voila, I was able to start stuttering the engine when shaking the harness in a certain spot.

Turns out, there's a small capped fuse block with 4x 20A fuses on one of the harness breakouts. I had already looked at it to see that the fuses were good, but today I pulled all the fuses, and then looked at the fuse sockets. Sure enough, one of the sockets was clearly spaced open wider than the rest, and the fuse pulled out very easily. I was able to replicate the problem by pulling that fuse with the engine running, and then could make the problem go away by putting the fuse in and making sure it had good contact. I didn't have a pick small enough to try and bend the socket "blade" more closed, so I simply bent one of the fuse legs/tines to make sure it would have tight contact. Boat has started and ran fine multiple times since.

One last share. In true DIY mechanic fashion, I created more work for myself. The crank sensor was hard to unbolt due to a power steering hose in the way, so I decided to disconnect it at the "quick coupler" at the steer cylinder. Oil came flowing constantly out of the cylinder and hose, giving me an oily bilge to deal with, and air in the steering system that I have yet to work out all the way. Figures right?

Thanks again to everyone who weighed in to help, and I hope this saves someone else down the road. If I ever dig into what that fuse was for, I'll post it here.

 

[alldodge]

Good the hear, those intermittent connections are the hardest to find