496 Fuel Pressure
08-07-2007, 06:34 AM
#11
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Person on another forum was going thru same thing and couldn't fix it until he switched gas brands. After switching he supposedly has no more problems.
08-07-2007, 08:42 AM
#12
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Keep in mind that as soon as you turn the ignition key, that energizes the fuel pumps which repressurize the fuel rail. You can hear them pumping and then quit when the set pressure is reached.
I don't think its that deep. The reason I say that is because it runs too good to have a bad injector. And I just changed the plugs and they all looked good. If I had a bad injector or even 8 bad injectors for that matter that lost pressure that quick and dumped that much fuel that quickly it would never start.
The one thing I forgot to mention was that i purposly waited for the pressure to drop all the way to zero after the pump cycled off and it started perfectly normal when it's cold. Somethings not adding up here.
The one thing I forgot to mention was that i purposly waited for the pressure to drop all the way to zero after the pump cycled off and it started perfectly normal when it's cold. Somethings not adding up here.
08-07-2007, 12:09 PM
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That is good to know and coincides with my limited experience. I thought that the pumps were just making up the difference between my slightly lower static fuel pressure when the engine is not running than when it is running.
08-19-2007, 07:55 PM
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I've been teking Ray's advise and cranking while the boost pumps are still running and has seemed to work, no hard starts lately. I decided to go ahead and replace the boost pump and I still get the same result where the pressure starts drop as soon as the boost pump shuts off the pressure drops fast down to 10 psi eventually 0. Cool Fuel 2 system (03') Engine still starts fine even at below 10 psi??? No fuel leaks or anything. Fuel pressure is solid at 43 psi at idle on the hose. At 2500 RPM it seems to drop a bit down to 40 psi. Seems to run alright, no stalling, missing etc. It did seems to labor a bit getting onto plane, but I had a heavy load.
Where could the presuure be going to? Leaky injector, think that would show more of a performance issue though. It runs rich,(Transom needs to be washed at the end of the day) but all stock 496 around that vintage seem too.
Any ideas?
Where could the presuure be going to? Leaky injector, think that would show more of a performance issue though. It runs rich,(Transom needs to be washed at the end of the day) but all stock 496 around that vintage seem too.
Any ideas?
08-20-2007, 02:19 PM
#17
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496 problems
Some of the questions answered here will depend on the year of your 496 Merc engine. On pre-2004 Mercury was still using coolfuel 2 whch had the two fuel pumps in different places and a seperate fuel water seperator. On 2004 and later Merc wnt to Coolfuel 3 which has both pumps and the fuel water seperator in one housing with just one pressure line up tot the engine fuel rail. The earlier systems have more system to prime and sometimes when the motor has been sitting a long time without starting it will take longer in the older coolfuel system to fully prime the system and build the 42-44 lbs of fuel pressure . On the 496 setups the pumps are on a relay which when the key is turned to the run position turns them on for about 5 seconds from the ECM signal and then they will shut off unless the motor is started immediatly after or during the beep. If you wait to crank the motor with the ignition still on the motor will try and start with the pressure present which can be low due to normal dropoff and it can make the motor harder to start.
My suggestion is to start the motor as soon as you turn on the ignition or if not then turn the key off, wait about 10 seconds and then try restarting. The fuel pressures you list are good and as they should be so pressure on sart is not a problem. If you have an active fault code or a problem with a cam sensor fault it can take the motor longer to start and if the cam sensor circut is bad it sometimes won't start at all. If you have fuel pump or filter problems it can show up as hard starting but its easily recognizable because the motor just won't pull full power under load and will show obvious signs of fuel starvation and stalling.
Hope this helps.
My suggestion is to start the motor as soon as you turn on the ignition or if not then turn the key off, wait about 10 seconds and then try restarting. The fuel pressures you list are good and as they should be so pressure on sart is not a problem. If you have an active fault code or a problem with a cam sensor fault it can take the motor longer to start and if the cam sensor circut is bad it sometimes won't start at all. If you have fuel pump or filter problems it can show up as hard starting but its easily recognizable because the motor just won't pull full power under load and will show obvious signs of fuel starvation and stalling.
Hope this helps.
THanks Ray.
I have a problem, possibly fuel related. (2002 Twin 496 HO's)
Running at 4000 RPM+ the starboard motor just quits. Like if I turn the key off. Most of the time it starts right back up, so I guess it does not actualy dies. But... running at 60 MPH+ and one of the motors shuts off is like droping an anchor in the water.
Totally unsafe starboard turn. Possibly going in "guardian mode". I wonder why and only the starboard motor does it.
IT's one think that a motor all of the sudden does not run well or misc. problems but shutting off like this.. GGGRRRRRRRRRRRRR I almost flipped.
HELP !!!
Thx .
P
08-20-2007, 06:19 PM
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Paradox:
First thing you need to do is find out whether engine is going into a Guardian strategy, ie codes or alarms. If this is what has been happening, these guardiian power reductions will be recorded in the ECM history and they will point directly most of the time to your problem. If no codes are found in recent history to coincide with this shut off, then I would suspect you have a wiring harness power or bad or intermittent electronics -electrical conections problem.
If this is the case, on that motor, start disconnecting and reconnecting all the sensors and connectors one by one, look for partial disconnects, corroded or wet connections or just loose or patial connections. Make sure you undo and check the 10 pin or 14 pin main harness connector also. Also make sure all ground and battery connections are corrosion free and tight both at the battery switches, batteries and at the motor. A little contact non-flamable contact cleaner may be helpful. I suspect that one of these two scenarios is your problem Hope this helps,
Regards,
Ray @ Raylar.
First thing you need to do is find out whether engine is going into a Guardian strategy, ie codes or alarms. If this is what has been happening, these guardiian power reductions will be recorded in the ECM history and they will point directly most of the time to your problem. If no codes are found in recent history to coincide with this shut off, then I would suspect you have a wiring harness power or bad or intermittent electronics -electrical conections problem.
If this is the case, on that motor, start disconnecting and reconnecting all the sensors and connectors one by one, look for partial disconnects, corroded or wet connections or just loose or patial connections. Make sure you undo and check the 10 pin or 14 pin main harness connector also. Also make sure all ground and battery connections are corrosion free and tight both at the battery switches, batteries and at the motor. A little contact non-flamable contact cleaner may be helpful. I suspect that one of these two scenarios is your problem Hope this helps,
Regards,
Ray @ Raylar.
08-20-2007, 08:34 PM
#19
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Thanks Ray
All connections are OK. I will have the computer check out the history. The last time the starboard motor quit, it did infact died. Started right up but I heared a small low picth klinking, knocking noise in the rear. Random, intermittent. I did not use the starboard after that. Put... put to the docks was not fun with one motor. If it is a lifetr or cam issue, then it's time for the Raylar 525 HP kit anyways. I need a great price and a deal Ray..
Thanks Ray
All connections are OK. I will have the computer check out the history. The last time the starboard motor quit, it did infact died. Started right up but I heared a small low picth klinking, knocking noise in the rear. Random, intermittent. I did not use the starboard after that. Put... put to the docks was not fun with one motor. If it is a lifetr or cam issue, then it's time for the Raylar 525 HP kit anyways. I need a great price and a deal Ray..
08-21-2007, 08:56 AM
#20
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The symtoms your explaining point to a cam or crank sensor. There is another recent thread on here stating that Merc told the particular shop that the crank sensor will not throw a code but will inhibit to 90%.
We have experienced the exact same symtoms as you are explaining on another boat. The boat shut down just like someone shut off the key at 3500rpm. Started right back up and then quit and progressively got worse. It stored some cam sensor errors but was told those are common (and they are as I've seen them on my own and I haven't had any problems) but did not show as active until I got it running crappy on the hose. It then showed as an active code. We replaced the cam sensor and it fired up and ran like new. For a week or two anyway. The problem recurred and at that point we changed out both the crank and cam sensor and it has run with no issues for a year.
Got to love these electronics!!
Dave
We have experienced the exact same symtoms as you are explaining on another boat. The boat shut down just like someone shut off the key at 3500rpm. Started right back up and then quit and progressively got worse. It stored some cam sensor errors but was told those are common (and they are as I've seen them on my own and I haven't had any problems) but did not show as active until I got it running crappy on the hose. It then showed as an active code. We replaced the cam sensor and it fired up and ran like new. For a week or two anyway. The problem recurred and at that point we changed out both the crank and cam sensor and it has run with no issues for a year.
Got to love these electronics!!
Dave
