Fuel pressure???

[rlemn8r]

I have a marine power 496 fuel injected in my eliminator with a legend pump. The manual says it should have 38 to 44 psi fuel pressure. I measured it at the fuel rail and it has 37 to 38 psi. That's at an idle. When you rev it up, pressure goes down to 32psi. Is this normal?? Or should it be steady all the time. Took it out on thanksgiving and it idles fine but wouldn't get up on plane. It just wants to stumble over. Also found when I got home that the vent line for the tank was kinked over. Could this be part of the problem also??

 

[02HoWaRd26]

Time for a new fuel filter possibly, would be my first check based on what you said.
Also shouldn’t be hard to bring up your fp while in idle, that’s where you adjust it, but i would be all over the filter before going any further at all.

 

[rlemn8r]

Time for a new fuel filter possibly, would be my first check based on what you said.
Also shouldn’t be hard to bring up your fp while in idle, that’s where you adjust it, but i would be all over the filter before going any further at all.

Would there be an adjustment up on the fuel rail possibly??

 

[02HoWaRd26]

I’d say one end or the other has to be a fpr
Fuel Pressure Regulator

 

[BDMar]

Don't adjust it if there is even an adjustment. The fuel psi is rated with the vacuum line disconnected from the regulator. With it connected, it will be at the bottom of the range and as you raise the rpm's, the vacuum increases which will lower the fuel psi. In the water in a jet boat the load will increase as rpm's rise and the fuel psi shout be towards the top of the scale. So you need to do a lake test with a test gauge connected.

 

[rlemn8r]

Don't adjust it if there is even an adjustment. The fuel psi is rated with the vacuum line disconnected from the regulator. With it connected, it will be at the bottom of the range and as you raise the rpm's, the vacuum increases which will lower the fuel psi. In the water in a jet boat the load will increase as rpm's rise and the fuel psi shout be towards the top of the scale. So you need to do a lake test with a test gauge connected.

Do you think that a kinked over vent line could make it stumble getting on to plane?? Even when I put gas in, it would burp back out of the nozzle.

 

[02HoWaRd26]

I’m still thinking first things first check the fuel filter

 

[SBMech]

Bad pump or plugged filter. Fuel pressure rises when vacuum falls on an FI engine. That's what the pressure regulator does, acts as a quasi accelerator pump by increasing mixture richness by altering the base time over duration formula mechanically by increasing fuel pressure under load. Since the ecu calibrates it as a base of 38, when it's at 45 under load it's richer.

Check your pressures under load as BD said, remember the volume test is just as important, you can make ample pressure put not produce enough flow as well...rare to see that though.

I doubt the vent would cause this unless the tank was completely sealed. You don't move enough fuel around normally to cause pump cavitation like that. Even then IMO it would take some serious time running hard...and you would hear a definite "whoosh" sound as you opened the tank cap.

 

[rlemn8r]

Bad pump or plugged filter. Fuel pressure rises when vacuum falls on an FI engine. That's what the pressure regulator does, acts as a quasi accelerator pump by increasing mixture richness by altering the base time over duration formula mechanically by increasing fuel pressure under load. Since the ecu calibrates it as a base of 38, when it's at 45 under load it's richer.

Check your pressures under load as BD said, remember the volume test is just as important, you can make ample pressure put not produce enough flow as well...rare to see that though.

I doubt the vent would cause this unless the tank was completely sealed. You don't move enough fuel around normally to cause pump cavitation like that. Even then IMO it would take some serious time running hard...and you would hear a definite "whoosh" sound as you opened the tank cap.

Thanks for the info guys. Will start there first and then the pump..

 

[Yellowboat]

Before you replace the pump, make sure too check the connections and wire going too the pump. Had an issue years ago, where I could not het enough pressure, replaced the filter, pump and reg. Only too find out I had 9 volts at the pump, enough for it to spin, but not enough too build pressure.

 

[Fun Times]

Do you think that a kinked over vent line could make it stumble getting on to plane?? Even when I put gas in, it would burp back out of the nozzle.

Yes in a marine engine having any sort of blockage to the fuel vent system may cause engine run ability issues like you're seeing. Typically one quick test for venting issues would be while you're out water testing the boat, Open the fuel filler cap and see if the engine performs better especially while the problem is happening.
Here's a few other fuel system testing ideas if interested, https://forums.iboats.com/forum/eng...ow-to-testing-your-boats-fuel-system?t=283269

Also while testing the fuel pressure with the gauge connected, if possible on your engine model, temporarily disconnect the vacuum hose at/going to the fuel pressure regulator and see if the fuel pressure rises a few psi.

 

[rlemn8r]

Found out the lower fuel pump was bad. Put on a new one, pumped out the old gas and put in fresh and it runs great. Then sold it yesterday.

 

[Blackmagic94]

Doesn’t fuel pressure need to be tested with vacuum disconnected to get a correct reading.

 

[rlemn8r]

It does. The high pressure pump could keep up at an idle and it had good pressure. But as soon as you hit the throttle pressure went down to 15 pounds. When I tested the high volume lower pump I found out it quit working. Replaced it and put in clean gas and it was fixed..

 

[jongig]

We have a 2005 Merc 496 and this thread was similar. Started and ran fine for 10-minutes and then I couldn't get the boat beyond idle, starving for fuel. Fuel pressure at the engine was 38, mechanic said that was low, I just wasn't convinced and thought I'd do some homework as they want to pull the boat tomorrow and I won't have the boat for awhile. What seemed interesting to me was multiple pumps, is there a pump in the tank and one at the engine? I'm a smart guy but I'd like to understand. I'm more familiar with carbs and thy only need a full fuel bowl with little pressure. If the pressure isn't enough in a injected engine I guess not enough fuel would pressure could cause this but knowing that pressure without volume would also be an issue.

Thanks for the help...

 

[Fun Times]

We have a 2005 Merc 496 and this thread was similar. Started and ran fine for 10-minutes and then I couldn't get the boat beyond idle, starving for fuel. Fuel pressure at the engine was 38, mechanic said that was low, I just wasn't convinced and thought I'd do some homework as they want to pull the boat tomorrow and I won't have the boat for awhile. What seemed interesting to me was multiple pumps, is there a pump in the tank and one at the engine? I'm a smart guy but I'd like to understand. I'm more familiar with carbs and thy only need a full fuel bowl with little pressure. If the pressure isn't enough in a injected engine I guess not enough fuel would pressure could cause this but knowing that pressure without volume would also be an issue.

Thanks for the help...

What is your Mercruiser engine serial number? And boat model type?

Right around 2005 the Meercruiser 496's came with a different fuel system design called the Mercruiser Gen 3 cool fuel module.

The 496 Mercruiser Gen 2 cool fuel system typically ran 2 fuel pumps too but mounted on opposite sides of each other if so installed which the low psi pump would be right around the water separating fuel filter area...But no there wouldn't be a fuel pump inside the fuel tank with the stock Mercruiser fuel system....Mastercraft boats did that.

mercruiser gen 3 cool fuel module - Bing

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[jongig]

Boat is a 2005 Crownline 270CR, on the motor it says 496 MAG, 866090-001, 886557. There is a Motorola sticker next to that, not sure if these are the numbers you're looking for.
Can you offer an idea on fuel pressure, 38PSI?
If there are two fuel pumps would I be able to diagnose any of this myself? Are the two pumps electric? Pumps on the same circuit?
Any chance I'm missing something else?
The marina the boat is at does anything that the boat needs, I don't debate anything, just pay. This is the first time we've had this happen and the boat is in great condition, 330 hours, lightly driven, cared for.

Thanks...

 

[HubbaHubbaLife]

Jump on in, the waters great....

496HO Engine performance issue.... opinions needed

Guys.... I took out my boat twice in past three weeks and it runs solid all the way up to around 4-5 rpms where it feels sluggish and under powered. Kind of missing some umph. It idles fine and never stalls around docks. I was thinking maybe bad fuel so I put some fresh 91 octane in and got some...

www.riverdavesplace.com

 

[jongig]

My 2005 Crownline 496 engine serial number is OW064258, Family 4M9XM08.1BAS. DOM 10/2004. I found the fuel

pump and filter assembly, 2 wires to the pump, I tested the resistance on the pump side, .5ohm, I didn't find voltage on the pump side but I think the pump turns on for a few seconds and then stays off until the engine is running.

 

[Fun Times]

Boat is a 2005 Crownline 270CR, on the motor it says 496 MAG, 866090-001, 886557. There is a Motorola sticker next to that, not sure if these are the numbers you're looking for.
Can you offer an idea on fuel pressure, 38PSI?
If there are two fuel pumps would I be able to diagnose any of this myself? Are the two pumps electric? Pumps on the same circuit?

Meant to get back to you on this, The numbers listed above would be part of the engines main PCM info for the MPI system.

Thanks, You did find the engine serial number (0W064258) which helps tell what fuel system you have and so does the photo you posted which makes it a Gen 3 cool fuel module system.

Here is a link to your engine parts catalog for you if needed, https://www.mercruiserparts.com/496-mag-base-model-0w060000-thru-0w3

Here's the internal parts of your Gen 3 Fuel Module Components ,

Some of the earlier year models with the gen 3 cool fuel module had deteriorating paint inside the cool fuel module which could reach all the way up to the fuel injectors including the fuel damper on the fuel rail which looks like a fuel regulator assembly...So be cautious of that potential issue even when servicing the fuel system...If you need more visual aid to the paint issues or how to open up the module for other regular services like new fuel filters, there are many videos online/YouTube of people going through in detail of what to look for and where, etc.

Has the 2 fuel filters found inside the module been changes out before / recently?

While 38 psi may seem to be close enough to the typical fuel pressure ranges found in some Mercruiser engine model service manuals that show a + & - number of about 4ish psi, the manual for the gen 3 module suggests the range only be between 41 to 43 psi.

The typical numbers found on this design regulators are either 41.77 PSI (288 kpa) or 43.511 PSI (300 kpa)... So depending on what one you have installed and depended on how the reading of 38 psi was taken, 38 psi would start to indicate a weakening fuel pump or delivery issue as it should be a bit higher and closer to the normal range of your regulator installed.

Under a heavy load of boat acceleration you ought to be seeing a fluctuation of fuel pressure though but you should also see a pressure fluctuation by removing the vacuum line off the regulator mounted down on-top of the Gen 3 fuel module while at engine idle RPM.

https://rinkerboats.vanillacommunities.com/discussion/10877/cool-fuel-pressure-regulator

Using a vacuum gauge, there is a way to test the low psi & high psi pumps and regulator suggestion too as it is outlined inside the service manual for the gen 3 cool fuel system linked here for you or your service tech working on the boat for you, http://boatinfo.no/lib/mercruiser/manuals/mercruiser40.html#/32

At 38 psi, it may be a low/weak/lazy fuel pump inside the module much like @rlemn8r mentioned in his post above...But also should question what year rlemn8r engine/boat is too for some comparison of fuel system design ?.

Hope you can resolve the issue at the lowest cost possible, good luck.

 

[jongig]

Fun times, I really appreciate the time you put into this, really great information and exactly the information I was looking for. I would really hope I don't have the painted version as I saw the outcome on youtube, not good and it could take time as the injectors would also have to be at least cleaned. Best hope is one of the fuel pumps is bad.

I can't verify the two filters were changed 10/2019 but the marina charged me for having changed the fuel filter, it doesn't say filters but they should know there is two, they seem competent.

The pressure was 38 when tested at idle, barely running. My thought here is that the pressure being just a little low would keep the fuel from spraying out the injectors. I might guess that the fuel pump doesn't stay on when the ignition is on/motor not running as a safety feature. I can't test anything at this point because the engine almost starts but it will no longer even idle.

I have read in some posts about Mercruiser paying for the replacement parts as they know they screwed up, it's not about the money for me as I just want to get back on the water but if that's the cause I probably won't see the boat for awhile, I will not be a happy boater.

I like my marina but talking to the mechanics I just get an idea they'd rather not talk to me. I'm in business over 30 years and I get the dumbest questions but always see that moment as a opportunity to educate, I always go out of my way.
There's a Crownline dealer down the road and they had a new 265CR on the lot months ago. I had asked them about a bow-deck-pad, they said after three weeks that Crownline sells nothing for my boat. Being a smart one myself I said the 265CR is exactly the same boat mold and seems to be an exact match, they said probably not. WIth their permission I took the pad from the new boat and tried it on my boat, exact match. I then asked them to order one, they said they would get back to me, that's a month ago.

My boat is in great condition but we have such a short season and a few weeks off the lake will really suck.

I have the tools to diagnose this but I'm so hoping the marina gets this done. I may take a ride over this morning to be the squeaky wheel. I am a little anxious working around fuel in such a confined space, I'm very safety conscious and without training or knowledge of this I think I should leave this to the marina.

John

 

[Fun Times]

There's a Crownline dealer down the road and they had a new 265CR on the lot months ago. I had asked them about a bow-deck-pad, they said after three weeks that Crownline sells nothing for my boat. Being a smart one myself I said the 265CR is exactly the same boat mold and seems to be an exact match, they said probably not. WIth their permission I took the pad from the new boat and tried it on my boat, exact match. I then asked them to order one, they said they would get back to me, that's a month ago.

If at all possible, try to work on getting the part number for the mat from using the Hull ID number from the boat on the lot....With the part number first search the part number online and EBay and if not found there then try searching & calling Great Lakes Skipper.com as they buy most of the production boat type manufacturers leftover parts like yours, Four Winns boats, etc. etc.. You may have better luck dealing with an online dealer vs the marina this time of year for boat accessories such as those.

Parts Request

Dear Valued Crownline Owner, Thank you for your Parts Request. Crownline Boats is a boat manufacturer and we have no retail business that involves selling parts direct to consumers, all parts need to be purchased from an authorized Crownline Dealer. To find your local dealer, enter your zip...

crownline.com

Search results for: 'deck pad'

www.greatlakesskipper.com

 

[jongig]

Thanks, Crownline gave me the same advice and I was never able to find the mat. It really doesn't make much sense that they'd not know that they make the exact mat for my boat but that's exactly what I found out. I think I need to find a better Crownline dealer.

Talked to my marina today, they're thinking is that the 38PSI is okay and they're changing the spark plugs to start. I've never heard that engine do anything but hum right along but it would be nice if they were right I guess. I asked about the cool fuel module and they were familiar with the paint peeling issue.

 

[Fun Times]

Thanks, Crownline gave me the same advice and I was never able to find the mat. It really doesn't make much sense that they'd not know that they make the exact mat for my boat but that's exactly what I found out. I think I need to find a better Crownline dealer.

Talked to my marina today, they're thinking is that the 38PSI is okay and they're changing the spark plugs to start. I've never heard that engine do anything but hum right along but it would be nice if they were right I guess. I asked about the cool fuel module and they were familiar with the paint peeling issue.

Keep searching the part number here and there as it may just turn up sometime out of the blue that or have Great Lakes Skipper order one up for you as it may be quicker....Or look up Sea Deck boat flooring as it might be an alternative way of what you're looking for.

From the sounds of how the engine is running spark plugs would just seem to be a starting point but then again the 496's have been known to run very oddly with bad spark plugs so hopefully.

Let us know what they find, good luck.

 

[Lavey 29]

all 496 Mercruiser 42 to 43 psi plus or minus 2. 45 psi max and 40 min also the type of fuel pressure gauge matters as well. If you are using a 20 buck gauge or harbor frieght BS crap the readings can be off because of quality.

 

[jongig]

Water in the gas, can you believe it, I thought about it but dismissed the thought, we go through too much fuel. They're best guess is the bad O-ring on the gas cap and the recent storm. It probably doesn't take much to foul the whole thing up anyway but it's running good. On Monday I wanted to drain the fuel pump assembly just to see what came out but I didn't because I just had second thoughts.

This is such a great thread to read for someone going through this.

 

[Fun Times]

Water in the gas, can you believe it, I thought about it but dismissed the thought, we go through too much fuel. They're best guess is the bad O-ring on the gas cap and the recent storm. It probably doesn't take much to foul the whole thing up anyway but it's running good. On Monday I wanted to drain the fuel pump assembly just to see what came out but I didn't because I just had second thoughts.

This is such a great thread to read for someone going through this.

Awesome the engine is running good again..
They changed the fuel filters?
Any word on what the fuel pressure reads now? ... For future reference of when not running right, it would be good to know what your gauge reads when running good.

Bare in mind that water could also come from your fuelling station source for a number of developed reasons especially from an on water source of a marina.

 

[HubbaHubbaLife]

I wasn't so lucky with my 2006/ 496HO.... $2500 in and counting. I like your story better.

 

[Lavey 29]

if he does not have the latest cool fuel installed, its just a matter of time before the fuel injectors get plugged up with black paint. no one escapes that with the gen 3 cool fuel until the fuel system gets all cleaned out and or new fuel system parts installed and the latest gen 3 cool fuel installed. Ill say it again its just a matter of time and no one with the gen 3 cool fuel ownership escapes the paint peeling causing havoc. End of story

 

[jongig]

Awesome the engine is running good again..
They changed the fuel filters?
Any word on what the fuel pressure reads now? ... For future reference of when not running right, it would be good to know what your gauge reads when running good.

Bare in mind that water could also come from your fuelling station source for a number of developed reasons especially from an on water source of a marina.

I will try to find information on what the fuel pressure is now, good idea. I buy my gas from them..

 

[jongig]

if he does not have the latest cool fuel installed, its just a matter of time before the fuel injectors get plugged up with black paint. no one escapes that with the gen 3 cool fuel until the fuel system gets all cleaned out and or new fuel system parts installed and the latest gen 3 cool fuel installed. Ill say it again its just a matter of time and no one with the gen 3 cool fuel ownership escapes the paint peeling causing havoc. End of story

I think I will follow up on this by talking to them when the boat comes out for the season. If I asked them to give me the fuel module maybe I could rebuild it. I have a complete machine shop, maybe a little sand blasting of the paint. I don't want to go down that road if I can help it. When I talked to them they said they've replaced a lot of them, maybe just replacing it is a better idea. I see they're about $1,200, I'd rather spend the money up front.