496 mag running issues
 

hey everyone new to the forum here. i have a 2006 496 mag and last season i starting having a problem with it. before the season started i did a gimbal bearing seals ect in the drive, oil change, the two fuel filters in the cool fuel gen module and checked everything else. the boat ran fine for the first 5-6 trips after that my alarm was going off if the boat would go over 3000 rpm. i would have to power all the way down to idle then i would be able to take off again. it runs fine under 3000 rmp. it feels like i loose fuel pressure and it just shuts down. i just got the boat back home and checked the fuel pressure. cycled the key 3 times to get maximum pressure and the gauge reads 45psi, at idle its at 37psi. could my problem be the high pressure fuel pump in the fuel pump? any help would be appreciated thanks. bryan

Maybe overheating alarm? Did you suck up some crap and clog the heat exchanger?

i havent checked that yet i just got it home and the first thing i checked was the fuel pressure. ill take a look at that and make sure its not clogged.

When the alarm goes off what type of beep is it? Do you notice the engine breaking up or the tach fluttering? Have you plugged into the ECM to read the codes? I have a few thoughts but need some more info. I have ALOT of experience with this motor, and tracking down a gremlin...Let me know.

its a solid alram (constant), it feels like it goes into a limp mode like sputters until i bring it down to idle. once i bring it down to idle the alarm will go off and i can take back off as long as a dont go over that certain rmp. i havent scanned it yet. i personally dont have a scanner i would just hate to take it to someone pay them and nothing show up.

If you have an alarm, a scan should reveal the problem. Don't waste time guessing.

These are the conditions that produce a constant alarm
Coolant overheat
low oil pressure
overspeed
sea pump psi low
port and stbd exhaust overheat

When is the last time you replaced the sea pump impellor?

So - I spent roughly 2 summers, and thousands of dollars searching for a very similar issue. I did use a scan tool, and I replaced a number of parts based on the ECM data. However none of it resolved the issue. It ended up being the routing of the knock sensor wire in too close proximity to the spark plug wires. I would run the boat and it would alarm anywhere from 2800 - 3200 which was the cruise range for my boat, but the alarm would stop if I reved past the RPM range, or dropped back to idle. Since you were in the area of the fuel system cooling maybe you moved the spark plug wire or the knock sensor wires. I would suggest you take a very close look at this before you lay out any cash. While the ECM will give you good info - if it isn't sticking a hard code - it won't help. If you do get a scan, I can tell you this issue caused both cam/crank sensor codes as the ECM was having issues determining if the faulty signal from the knock sensor... I just love electronics! Oh btw I did go through coil packs, fuel filters, fuel rail insp. and cleaning, fuel pressure checks, plug wires, plugs, etc...etc...

my impellor was replaced when i did my gimbal bearing, fuel filters ect... that was all done less than a year ago.

The alarm went off so you have fault codes stored in the ECM that may direct you to a simple fix. Scan it first and then start doing other things. It could be difficult to start just replacing things without the fault codes. Check EM!

Best Regards,
Ray @ Raylar

i read on the mercury service bulletin that if the fuel pressure is more than 44psi when cycling the key to replace the cool fuel module and in the water test is says if its lower than 40psi to replace the module. could 1psi cause a problem? i didnt really run a in water test i just started with the muffs on the drive and it was at 37psi at idle. if it was a wire or something i dont see why it would have ran fine for my first 5-6 trips roughly 6-8hrs of operating time then start acting up but i dunno.

ok thanks ray. do you reccommend any shops up in the corona/riverside area?

Yah, talk to Gary @ G& S Marine in Corona, he should be able to scan and maybe help locate your issue. Hope its easy and inexpensive fix.

Best Regards,
Ray @ Raylar

Thanks I'll give him a call.

Is there a normal amount of water coming out the exhaust? Does the exhaust feel hot when the alarm sounds? Backflushing of the raw water side components is easy and good maintenance even if that isn't the problem.

An infra-red heat gun is really handy to have on board to check engine and oil temps. Point it on the oil pan to get oil temp. Point it at the oil filter too.

http://www.amazon.com/Raytek-MT4-Non.../dp/B0002198GY

Seriously - Don't overlook the routing of the knock sensor wires. I know it sounds goofy, but I can't stress this enough. My boat has twin 496's and the port motors issue, - similiar to yours- was fully documented with Merc and they were unable to identify a problem over the course of 3 years. Its a freebie to look at, just make sure the wire routing is nowhere close to a plug wire.

Eric

Ok I'll take a look at it today when I get home. Thanks

Does the knock sensor sit right behind the starter? If it is the wire is pretty much resting on one of my spark plug wires.

So on a 496 MPI motor there are 2 knock sensors, one on each side of the block. I attached a picture to help you visualize it, however it will have a bolt through the center. Think of it this way - its just a microphone looking to detect any type of detonation. If it gets interference from the High frequency plug wires - it sends incorrect signal to the ECM and the ECM attempts to adjust the timing or fuel supply to compensate for what it thinks is detonation.. There is a very small greyish/white single wire coming off of it to a black connector. It should be routed very closely along the edge of the block around to the back of the bellhousing where it connects. If the wire is coming off at a funny angle - just loosen the bolt and rotate it to help you route the wire better. All I can tell you is I chased this issue too long to find out this was the problem. I had certified merc mechanics run the boat, tech the boat, and converse with Merc to no avail...Until I stumbled across a technical article that lead me to this...Good Luck!

http://s8.postimage.org/f364xz5d1/MAL9_33502.jpg
jpeg image hosting

I had a few grains of sand jammed in the water pressure sensor on the impeller housing. Guradian alarm would go off if I ran it over 3000 rpm it would reduce power until i brought it back to idle, then the alarm would fo off.

I bought a new sensor and while replacing I inspected the old sensor. I tapped it a few times and the sand came out.......

http://www.mercruiserparts.com/Show_...ft+and+Pistons #12 is knock sensor,,one on each side of block

thanks for the info. im pretty sure i found it and it is resting on one of my spark plug wires. i also decided to take my water pump apart and found scouring on both sides of the pump on the brass. i read in another post that this can cause problems. my boat has 292 hours on it im the second owner. i was gonna post some pics of everything but cant seem to figure it out. i might not have enough post yet.

There you go. Computer codes would not have shown either of those issues.

Everything everybody said is all good advise. My two cents is to look at your IAC Valve. (Idle Air Control) It is easy to get to (rear of engine, on top). You will likely be able to look at it and see that it or it's connector are melted. If nothing else, remove it, and see if the valve works smoothly back and forth. It is likely rough or frozen. I have two 496's and they both cooked their IAC's at about 500 hrs. My friends have all lost their IAC's. Exact same symptoms you listed. Scanner showed that the Knock Sensor and Crank Location Sensor was bad, but they were not bad. I even carry a spare IAC now. Good Luck!

Change your IAC (Idle Air Control).

At 292 hours i would also change the boost pump cause it's gonna go soon anyway. You should check for fuel pressure using a fuel pressure gauge on the fuel rail. Do a search on this forum and you'll find some good info on both the IAC and the boost pump issues. Nuther thing due to hours and many tanks of gas, is to pop the injectors out one by one and tap out the grit that accumaltes in each one and pop'em back in.

Good luck

thank you i appreciate all the help im getting on here i plan on moving my knock sensor wires away from my spark plug wires, replace my water pump with a hardin pump and ill check the IAC. then hopefully take it for a water test. if anyone else has anymore tips tricks ect... shoot them my way. thanks again guys

When my IAC was bad, it only effected the performance at idle. The motor did not go into guardian mode at all. A scan clearly revealed the problem. The iac output level is like a heartbeat line, when it was bad, it just displayed a flat line. BTW, I use diacom software. I didn't have the cooked wire problems though.

I also saw on some car tv show that you can clean iac's with carb cleaner and they will be good as new. I guess it could hurt to keep that one as a spare.

The only thing I would caution - is not to do too many changes at once, or you will never know the actual cause. Troubleshooting and root cause analysis is a critical process. If you have the luxury, clean up the wire routing, go for a ride, swap IAC go for a ride...etc...try to narrow down the cause.

Ya I was gonna do my water pump and reroute of the knock sensor first. Then I was gonna take it out and see what happens I'm not too far from a local lake I can test at then go from their. I'll prob leave my rear seat and hatch off during the test so I can get to the motor and check things.

Is their any way to function test the IAC or does it have to be done with a scanner?

I don't think it's the IAC. As mentioned I think that affects idle. Do the other stuff. A steady alarm is supposed to be over revving (not your problem), low oil pressure or high engine temperature. The knock sensor wire thing is interesting too. I'd back flush the heat exchanger when you do the raw water pump. You will like the Hardin SS pump.

I would agree with thirdchildhood, had the same issue with my port engine a year ago or so. Scans showed no codes but the temp was about 10 deg higher on the guage, I back flushed the raw water side from the heat exchanger inlet & the problem went away. The p/s & oil coolers can get partially plugged you wont notice at idle on muffs but under load it would show up immediately. I run on the missouri river so i can pick up junk all the time. Hope that helps, Randy

Ok thanks. Ya I was planning on ordering the Hardin pump. Is the only place to get it is from Hardin or cp?

Thanks randy I appreciate the input. I'm gonna order the pump today and go from their prob get it in the water next weekend. I couldn't find any shops around me that carried that pump.

I got mine from CP.

Ok cool I'll prob get mine from their since their located in ca hopefully get it in a few days. Thanks

I got my Hardin pump in last night it def sucks more water than my old pump. I'm taking it out tomorrow for a test run hopefully I won't hear the alarm. I just wanna thank everyone one here that posted all the good advice.

Well I went testing today alarm was still their. Took it an got it scanned and was the water pump psi sensor. Replaced the sensor and now it's back firing really bad at 3k and above. Should I start with the spark plugs and do a compression check while they are out? What is the correct compression psi these motors should be at? Thanks

Spark plugs is a good idea. Bad plug or two will do this and not show up on scanner. Also make sure plug wires from coils are on correct plugs especially if they have been unplugged or removed for any reason. Compression test is good idea also. Should be about 155-160 psi all cylinders with throttle open. Disconnect main injector plug near ecm to do test as you do not want all that fuel pumping into cylinders when cranking. Open throttle wide open also.
You might also have some bad plug wires. You can check that with engine running , hatch open in the dark at night no lights on or to much background light and look for arcing around the plug wires where they run by manifolds,etc.

Hope you find your gremlin easily.

Best Regards,
Ray @ Raylar

Thanks for the info ray. I hope I can figure this out before the season starts.

I just pulled the plugs and found one plug cracked. Gonna throw some news ones in and go test it again.