496 Mag backfiring?
06-07-2012, 11:05 AM
#11
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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
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
Last edited by Raylar; 06-07-2012 at 02:33 PM.
06-07-2012, 12:13 PM
#12
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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,
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,
07-09-2012, 10:29 AM
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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?
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?
07-09-2012, 12:51 PM
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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 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
07-09-2012, 01:11 PM
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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)
