496 Mag backfiring?
 

My dad boat, 330 SS formula. (T-496 Mag's, W/Bravo 3's) randomly started a problemp once motor has a load on it. will idel fine, and will get on plane but you cant push it over about 25 ish or it starts hicupping.


throwing these codes.

191 Fuel level 2
118 steer ch hi
75 fuel level ckt hi
94 pikot low

I know the frist 4 are normal but these.....

36 Sea Pump Cont Hi
152 IAC OUTPUT
151 Fuel Pump Relay Ck
77 Cam Sensor
152 Cranksensor.


whats going on?

Wow! That's a lot of codes all at once.

Did you try clearing them to see if the return?

I will. But iw as not on the boat when it happend.

I know the first 4 are allways there. but the other 5 at once sucks..

No one has any help here?

Rylar? nothing?

A guy who went by dave_n used to be on here all the time and he knew everything about the 496's.

When I had a 496 I remember seeing the cam and crank sensor warnings occasionally. I don't think that's anything to worry about. The IAC seems to only effect the performance at idle. I don't know about the sea pump warming. Some of those warnings could have occurred a while ago. Diacom shows what hour they occured at. So, if you reset the codes, some might not come back.

Are you getting any alarms? I have the pcm 555 manual in front of me but it is real vague. I would make sure the harness is plugged in tight to the ecm, and check all other connectors.

swap out relay with other motor,,,put your hand over motor with good relay,,,have someone else turn on key,,,do not start just turn key to run,,,you will feel the fuel pump relay engage for two seconds then click off,,,swap it to the motor your having trouble with,,hope this helps

Can't take those codes at face value. Is it starving for fuel?

Clear it and read it again. The cam and crank faults appear seemingly when the wind blows. what does the freeze frame data say?

need more info. How are you able to determine that all 5 happened at once?

The starboard engine is running rich but seems to have no power. It will not go over about 3100 rpm even in neutral. It seems to vibrate when accelerating. The port will go to about 3300 but then starts to backfire

Checking the codes with the scan tool showed many codes; several are just because we do not have that part or sensor so I have tried to omit those.

Starboard:
152 I A C output
151 Fuel pump relay ck
77 Cam sensor
132 Crank sensor

The port doesn't have any except the ones for no sensors.



Starboard Port
Flow rate. 4.91. 4.99-5.1
Fuel level. 1022. 1022
Sensor power. 4.97 VDC. 4.97 VDC
Sea pump press. 24 KPA. 25 KPA
Spark advance. -5 + 4. All over. All over
IDC D Cycle. 34-36 34-37

Whatever it is affects both engines at roughly the same rpm and load. Highly unlikely that both engines develop faults at the same time so check what they have in common such as fuel delivery. Perhaps you have a partially clogged fuel pickup or something similar.

Good luck,

Dan

I have ben telling him fuel for the same reasons.... bad gas, fuel filters something....

What model year are the engines? I suspect from the codes that on the Starboard engine the IAC has gone bad, replace it.
The fuel pump relay circut high could either indicate a bad relay (not expensive, replace or swap it for one on the other engine to prove out and if code goes away then replace the original bad relay.
The engines not pulling to higher rpms and backfiring could be a fuel delivery problem or bad fuel (water, etc.)problem. Change all the filters primary if there and fuel water seperators and pur some fuel out of the old filters to see if water or a lot of debris present. You can meausre the fuel pressure under looad with a fuel pressure guage and make sure its about 41-43psi at idle and stays above 40 psi at full loads.
Depending on what year the engines are and what version cool fuel system you have there are some other things with respect to the fuel pumps and filter screens you can check.
Also, when this is happening is a beeper going off when the engine hi-cup or stall. the crankshaft and camshaft sensor codes come in when a 496 Merc engine stalls many times and should be cleared when the engines restart.

Another Question; who and were is the marine mechanic your dad should have on call for a boat this size and what is he doing for you?

Best Regards,
Ray @ Raylar

we work on our own stuff for the most part. rebuilt many motors, and palyed with many types. so no mechnice, just us.

I have new IAC for both and new fuel filters, and plan on chcking for water in fuel as well.

should have some more updates after friday playing with it.

thanks,

did new fuel filters, no change.

cleaned throttle bodies, no change.

New IAC valves, No change.

anyone know if a 2004 496 mags, have o2 sencors?

thinking that or plugs and wires maybe?

There are no O2 sensors on Merc 496 engines. The sensors in the stock exhaust manifolds are exhaust manifold coolant temperature sensors and you have no codes there apparently.
I still think you are having a fuel feed problem since its affecting both engines apparently.
Have a fuel pressure guage connected on each engine one at a time and measure the fuel pressures at idle, cruise and WOT. It should be about 41-43psiat idle and should only drop a pound or so under load.
Another easy thing to check on the early Merc 496's is the small in pump inlet screens on the primary fuel lift pump that's located down below the feul water seperator. Remove the brass fitting carefully on the inlet side of the pump and look up inside at the small screen and see if its clogged with any debris. If so clean it and retry the engines.

Best Regards,
Ray @ Raylar

I had backfiring and power loss on an '06 496, and I changed all the filters etc... It ended up being an injector, had them all serviced the following year and that took care of it. I used Marren Fuel Injection and was pleased with the results. (injector.com)

Plugs in the port motor and its ALIVE.. will do starborad as well.