350 MAG MPI fuel pressure problem

[Vortec]

Hello everyone, I have a question . I have 1999 350 MAG MPI (serial L305046) that I have low fuel pressure problem with.
I connected my gage to fuel rail port and with ignition ON engine OFF I am getting 35 PSI and it drops 5 PSI after 1 minute (which per manual #24 sounds right) but when I start engine it drops to 25 PSI on idle and 20 PSI at 2000RPM in neutral (do not have chance to check it under load) which sounds low, I tried disconnect vacuum line from pressure regulator while engine running I'm at back at 35 PSI. The boat lost some power and RMP's do not go past 3900 RPM. I am leaning toward pressure regulator failure . Am I on right track?
Thanks.

 

[Fun Times]

Re: 350 MAG MPI fuel pressure problem

Hi there, welcome to iboats! Your engine fuel pressure should for the most part hold very close to 30 PSI. Since it's moving all over the place it very may be the regulator but it could also be a fuel restriction someplace between the boat tank and fuel pump or a fitting sucking in air someplace, A kinked or internally splintered fuel line interrupting the fuel flow.

Before just installing new expensive parts, there are a few tests you could try doing in order to help pinpoint a better direction of what may be wrong. If you haven't already done so, you should pull the fuel filter off and check it for any type of debris and install a new filter. Next use a small separate fuel tank with a new fuel hose in place of the boat's fuel tank to see if you get your PSI back. Then to see if the fuel pump is able to produce the required fuel pressure and beyond, carefully pinch off the fuel return line somewhere near the fuel filter base. The fuel pressure should rise up to 50+ PSI during key up.

Also if or when possible, take a look at your fuel regulator to see if you can find a color scripted onto the regulator. You need to know if it's pink or blue. Pink = 30 psi while blue = 43 psi. Though yours should be at 30, there is an off chance yours could be at 43 psi. If you can, let us know what you come up with, Good luck.

Close to the same symptom your having,
http://forums.iboats.com/mercruiser...ser-mag-mpi-fuel-pressure-problem-289594.html

 

[amajamar]

Re: 350 MAG MPI fuel pressure problem

I don't want to hijack this thread in any way, but I have a similar engine, Horizon 350 Mag MIE Gen+ SN: OL677287 which is in a 2002 Sea Ray 310, and I am going to change the fuel pump and cooler. I was also going to install a new regulator while I was at it. I ordered the Merc part number, 807952A 1, and received one with a pink mark. I am working with the Seloc manual for 2001-2008 which shows that engine with a fuel rail pressure of 43, however that would be a blue mark on the regulator.

Can someone please verify that I should be using the pink regulator? When my SN is searched with Merc, it does show it as a 1998 engine, (is this odd in a 2002 boat?) so maybe it is correct but I can't verify with my 2001 Seloc book.

Thanks in advance and sorry to the OP for butting in on this thread! :tape:

 

[Fun Times]

Re: 350 MAG MPI fuel pressure problem

Hi there amajamar, welcome to iboats as well! Below are the differentness of each of your engine models.

MIE - (350 MAG H.P. (1998M )) MIE 350 HORIZON 630V 2.0 3RSR MAG MPI (MIE) (GEN+)
Serial No: 0L677287 Model No: 3F495AJM1 Catalog No: 804703 99

MIE - (350 MAG H.P. (1998M )) MIE 350 MAG MPI SKI STD EXHAUST TOURN SKI (GEN +)
Serial No: 0L305046 Model No: 3941179M1 Catalog No: 827680 98

Going by part number, part number look up and the service manual, both of your engines should definitely use a 30 PSI regulator.
There are two ways of identifying each regulator. By color paint mark on it's mounting flange and/or by a small ring that is on the regulator's hose fitting.

See page 1B 9 & 10,
http://www.atlanticmobilemarine.com/service manual 5&57.pdf

Where the confusion is setting in with your manual and a little bit of my post above as well is engine serial numbers 0L302200 thru 0M299999 use the pink 30 PSI while the very next serial number change 0M310000 thru 0M316999 uses the blue 43 PSI.

S/N 0L302200 thru 0M299999 is around the 1998 till about late 2001 while 0M310000 thru 0M316999 is from about early 02 thru early 03. It's not unusual for an 02 boat model to have an 01 engine model.

I referenced the blue 43 psi as a precautionary measure to look out for because as I read some similar post online there seems to be bit of confusion of what the fuel pressure should actually be in and around these engine models. To help future members, it would be nice if both of you could confirm the color of your original regulator (if any) when you replace it.

When looking up Mercruiser engine and drive parts, it will be normal to see 1998M on any engine model made after 1998 as that is when Mercruiser was to (supposed to) completely stop using engine year as a designation point and went to using serial number breaks like seen above. Outboards stop in 06.

Hope this helps.

 

[amajamar]

Re: 350 MAG MPI fuel pressure problem

Hi there amajamar, welcome to iboats as well! Below are the differentness of each of your engine models.

MIE - (350 MAG H.P. (1998M )) MIE 350 HORIZON 630V 2.0 3RSR MAG MPI (MIE) (GEN+)
Serial No: 0L677287 Model No: 3F495AJM1 Catalog No: 804703 99

MIE - (350 MAG H.P. (1998M )) MIE 350 MAG MPI SKI STD EXHAUST TOURN SKI (GEN +)
Serial No: 0L305046 Model No: 3941179M1 Catalog No: 827680 98

Going by part number, part number look up and the service manual, both of your engines should definitely use a 30 PSI regulator.
There are two ways of identifying each regulator. By color paint mark on it's mounting flange and/or by a small ring that is on the regulator's hose fitting.

See page 1B 9 & 10,
http://www.atlanticmobilemarine.com/service manual 5&57.pdf

Where the confusion is setting in with your manual and a little bit of my post above as well is engine serial numbers 0L302200 thru 0M299999 use the pink 30 PSI while the very next serial number change 0M310000 thru 0M316999 uses the blue 43 PSI.

S/N 0L302200 thru 0M299999 is around the 1998 till about late 2001 while 0M310000 thru 0M316999 is from about early 02 thru early 03. It's not unusual for an 02 boat model to have an 01 engine model.

I referenced the blue 43 psi as a precautionary measure to look out for because as I read some similar post online there seems to be bit of confusion of what the fuel pressure should actually be in and around these engine models. To help future members, it would be nice if both of you could confirm the color of your original regulator (if any) when you replace it.

When looking up Mercruiser engine and drive parts, it will be normal to see 1998M on any engine model made after 1998 as that is when Mercruiser was to (supposed to) completely stop using engine year as a designation point and went to using serial number breaks like seen above. Outboards stop in 06.

Hope this helps.

Thanks so much for you rapid response! I will certainly report back here what I find when I remove the old pump. I have other questions that I will be starting new threads on soon. The link you provided to the Merc manual will be very helpful, thank you for that! Regarding having the proper Seloc manual, are there significant differences between my 1998 engines and the 2001 and up manual that I have, especially when it comes to repair sequences?

 

[Vortec]

Re: 350 MAG MPI fuel pressure problem

Thanks for your replies. So today I tried to pinch return line and I still did not get anything over 33 PSI engine off, I removed pressure regulator and do not see any pink or blue paint all I can see is NR-1 marking. But if you are saying mine should be set at 30 PSI ,does 20 psi in neutral at 2000 RPM sound low?. Does it really means that my regulator messed up? Thanks.

 

[Fun Times]

Re: 350 MAG MPI fuel pressure problem

Thanks for your replies. So today I tried to pinch return line and I still did not get anything over 33 PSI engine off, I removed pressure regulator and do not see any pink or blue paint all I can see is NR-1 marking. But if you are saying mine should be set at 30 PSI ,does 20 psi in neutral at 2000 RPM sound low?. Does it really means that my regulator messed up? Thanks.

Yes it is low at 20 psi.

If you haven't already done so, then for more testing you'll still want to hook up an external fuel supply with a primer ball and put some pressure to the system while making sure the fuel filter is full and checking fuel pressure that way too.
But in the end if your sure the filter is in good shape and full of fuel for the block off test you just did then that would indicate the pump is not able to produce the required pressure either due to a bad pump or lack of fuel supply getting to the pump to do the test properly. So before buying a new pump, another test should be in order in my opinion.

Some reading for you on fuel pumps in general not necessarily specific to your engine model though they are close enough to help give general ideas of what you can do to the fuel pump if desired. http://www.boatfix.com/merc/Bullet/98/98_04.pdf
http://crowley-cloudfront.s3.amazonaws.com/media/mercuryBulletins/001/04/2004/EN_01.PDF
Search Results - Crowley Marine

Do you know if you have a low pressure fuel pump located between the fuel tank and water separating fuel filter assembly? Some do some don't is the reason I ask.

 

[amajamar]

Re: 350 MAG MPI fuel pressure problem

Hi there amajamar, welcome to iboats as well! Below are the differentness of each of your engine models.

MIE - (350 MAG H.P. (1998M )) MIE 350 HORIZON 630V 2.0 3RSR MAG MPI (MIE) (GEN+)
Serial No: 0L677287 Model No: 3F495AJM1 Catalog No: 804703 99

MIE - (350 MAG H.P. (1998M )) MIE 350 MAG MPI SKI STD EXHAUST TOURN SKI (GEN +)
Serial No: 0L305046 Model No: 3941179M1 Catalog No: 827680 98

Going by part number, part number look up and the service manual, both of your engines should definitely use a 30 PSI regulator.
There are two ways of identifying each regulator. By color paint mark on it's mounting flange and/or by a small ring that is on the regulator's hose fitting.

See page 1B 9 & 10,
http://www.atlanticmobilemarine.com/service manual 5&57.pdf

Where the confusion is setting in with your manual and a little bit of my post above as well is engine serial numbers 0L302200 thru 0M299999 use the pink 30 PSI while the very next serial number change 0M310000 thru 0M316999 uses the blue 43 PSI.

S/N 0L302200 thru 0M299999 is around the 1998 till about late 2001 while 0M310000 thru 0M316999 is from about early 02 thru early 03. It's not unusual for an 02 boat model to have an 01 engine model.

I referenced the blue 43 psi as a precautionary measure to look out for because as I read some similar post online there seems to be bit of confusion of what the fuel pressure should actually be in and around these engine models. To help future members, it would be nice if both of you could confirm the color of your original regulator (if any) when you replace it.

When looking up Mercruiser engine and drive parts, it will be normal to see 1998M on any engine model made after 1998 as that is when Mercruiser was to (supposed to) completely stop using engine year as a designation point and went to using serial number breaks like seen above. Outboards stop in 06.

Hope this helps.

To confirm, I did find that my regulator had a pink mark on it. I changed the pump, cooler, and regulator out today and found something interesting. The vacuum line to the regulator was pinched up next to the head and melted pretty much closed. Could that cause an overpressure situation at low speed and idle? I was thinking that I may have a stuck open injector, as I found that the engine oil smelled like there was some gas that got into the crankcase, and I am wondering if this could have been a contributing factor.