Mercruiser 5.7L Fuel Pressure Regulator ?
 

Engine is a 2003 5.7L 350/300HP.

Narrowing down a low fuel pressure issue. Removed the cool fuel fuel pressure regulator ( a real bear to get to and remove )
A few questions:

• I'd like to test the fuel pressure regulator's function while out of the boat - is this possible ? If so, how do you do it ?
• Or, I'd replace it - is there an aftermarket or GM equivalent to this part ? The part # is: 861126A 1
• The fuel filter screen that sits under the pressure regulator is still seated in the cool fuel housing - it looks good from what I can see, besides it's in there pretty well and might be a PITA to remove. Does the fuel flow through the FPR into the screen or from the cool fuel housing, screen into the FPR ( this will let me know which side of the screen would have gunk - if any.

Lastly, there's a brass nut on the end of the fuel pressure regulator - is this removable or is it one with the unit ?

Thx

Bump

The regulator opens when the fuel pressure exceeds its setting, in your case is 43 psi. When it opens it sends the fuel back to the fuel filter

To test the Reg, remove it and use air. Slowly increase pressure watching a gauge to see when it opens.

To test the pump, you need to run it with a gauge which can read 100 psi and connect gauge to the output of the pump by itself.

Ok - great - I can do those tests.

sounds like I’ll have to put a ‘test’ cover plate over where FPR normally seats to do fuel pump test. Correct ?

which direction does fuel flow ? Forward to aft or vice versa ?

will I do damage to fuel pump by inhibiting fuel flow with the gauge in place ?

No, remove the fuel pump from the cool fuel tube to do the test

Comes in from the filter thru the pump

No, but only do it for a short period. The pump either pumps up above 60 psi or it doesn't. 10 to 20 seconds will tell you that

Quote:

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To test the Reg, remove it and use air. Slowly increase pressure watching a gauge to see when it opens.

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Which end do I blow air through - the brass coupler side ?

THE cool fuel side is the outlet return)

Ok
thanks...

Blow into the inlet.

I just tested the FPR.

There are (3) openings once removed from the cool tube;

• one that sits down on the cool fuel tube - there's an O ring
• The brass coupler that connects to a fuel line
• the vacuum hose nipple

The only location that has any effect on air flow is when I connect the air source to the first option - the one that seats onto the cool tube. This does not allow any air through at 35-40 PSI, it starts to allow a slight air flow at about 40 PSI. At 43 PSI, it flows.

Is this the right test ? If so, it sounds like the FPR is OK. Is this a correct assessment ?

FUEL PUMP

If so, I will need to test my fuel pump. Something I loathe to do, just because I have to remove it from the h*ll hole its in. Is there an easy way to test the fuel pump while it's in place ? If not, and I pull the fuel pump - how do I test it while out ?

Do I provide a fuel source to pull from, connect to (+) and (-) source, connect PSI gauge to output side and read the results ?

Thanks !

Yes, your Reg is good

Can do the test with the module connected, but will need to hot wire the fuel pump
Connect gauge (At least 100 psi) to fuel line coming from the pump
With Reg installed turn pump ON and pressure should hold steady.

If Reg is removed and hole is blocked with plate and gasket, pressure should be at least 60 psi with pump ON

Can also do it with pump removed on the bench and supply gas from a can. In all cases (except for test with Reg installed) need to bleed off the air for accurate test

Hey all. I have now inherited this problem! I bought ABL1111's boat and have been trying to diagnose a hard start/low power issue as it seems he may have been too. My gauge tells me 20 psi fuel pressure at idle and above (neutral. out of water). Is there a link to somewhere to the troubleshooting steps for low fuel pressure? I cant find anything in the manual.

If you pinch off the return line (from pressure regulator back to fuel filter head), while the pump is running (have to jump 12V to the positive side of the fuel pump relay), and the pressure increases, then the regulator is bad. Prior post by ABL seemed to indicate regulator was OK with air test so you probably just have a bad pump.

Thank you. Would that be a pretty definitive test for the main fuel pump? If it doesn't make pressure that way, the pump is bad?

Also, I find it odd that there is a regulator on the fuel rail as well as at the cooler/main pump. Would I need to take that one out of the equation to accurately test the fuel pump?

The regulator on the rail was a holdover from the old fuel system. When the "cool fuel" system on the lower port side of the motor was implemented (instead of the old VST system), Merc just put a blockoff in the fuel rail that made the old regulator useless (they then renamed it a pulsator). The regulator on the rail is a dead end. You don't need to touch it to test the fuel pump.

Definitive, well, mostly, yes. If you jumper 12V to trigger the pump, and while it's running, you pinch the return line and you can't get to 60 psi, the pump is weak / failing. A healthy pump should be very capable of hitting 60psi with the return line pinched off (and be sure to *immediately* release if you do in fact see 60, you never want to exceed that pressure.

Awesome. Thanks again. I did notice that the "return" was plugged after that reg. Funny tho. If you want to you can still pay $369 for it!

So now. Fuel pumps. The OEM one is NLA. Is there one we like better than the Sierra? I see the prices are all over the place, and I assume quality somewhat follows that number. I typically don't buy junk if I can avoid it.

I put in a cheapo from "the ROP shop", it works fine, delivers the same pressure as the OEM pump on my other motor. Durability remains to be seen, it's only been a month or so. Usually cheap is cheap, but I'm not convinced that all these pumps aren't coming out of the same Chinese factory anyway.

Pinched the return at the filter housing. Almost immediately pegged a 100 psi guage. Seems like the pump is good.

Blocking off the return will cause the pressure to exceed the Reg setting and damage it. As you have found the return was plugged to try and compensate for a weak pump.

You can still get the old pump and Reg, just not from Merc. Merc sells only the conversion kits
The pump use to be made by Airtex

I'm not sure I follow. According to his test, my pump is good and I need a regulator, yes? If it makes 100psi with the return pinched, and 20 psi with it open, it seems like the regulator has failed, but the pump is good?

Ohhh. I get it. I was speaking about the factory block off of the return from the pressure regulator in the fuel rail. Nothing was done to the motor that wasn't factory.

Latest test. Engine running. Return fully open. 20 psi. By just pinching the return slightly I got it to go to 45 but I stopped there. Pretty sure it would have easily gone higher. Sounds like a bad regulator to me. I hope so. That's so much easier to change than the pump. lol.

What is the psi spec on these things (350mpi’s) anyway ?

edit: okay, just back read. Should be 43psi ?

oh great, just saw this notice:Mercury Marine is having an 8% price increase May 15.

Unfortunately all orders placed after noon EST May 13 will be at the new prices.
Back to subject:

Okay, 43psi it is. :) See#13 description.


https://cimg1.ibsrv.net/gimg/www.off...ba022ceea1.png

Yup. 43 psi and I'm at 20. lol. But by manually regulating I'm able to get and maintain 45 with the engine running. I'm going to try a reg. If the pump wasn't such a bear to swap I'd do that too, but that is going to require a lot of swearing to get done.

Looks like I'm not getting notified of a response via email. What I have for Reg861126A1 Cool Fuel Gen 2 (43 psi) BLUEMallory 9-33206, Merc 892681

Kinda funny. Someone on a FB group pointed out that the OEM part is made by Keihin and is the same reg as a honda civic. See photos.....IDK if I trust it enough to do it, but its interesting for sure.

https://cimg6.ibsrv.net/gimg/www.off...db509533ee.jpg
https://cimg7.ibsrv.net/gimg/www.off...d721c5b27b.jpg

Btw, which fuel system do you have ? Some systems use a regulator down near pump, which makes the regulator on the fuel rail just a dampner if you will.

That's what I have. The reg on the rail has it's return blocked from the factory. The reg that works is mounted on top of the cooler.

I believe there is a 30psi keihin nr-1 and a 43 psi nr-1. So, be careful.

Yeah. I think with the OEM part only being 179 and coming with the o ring and filter, I'll just get the right one. Irwin can have it for me tomorrow.

Okay, here you go :) honda fpr and everything including an install mess up to avoid. Lol.

https://forums.iboats.com/threads/lo...ag-mpi.720696/

Alldodge, you get around. :) :thumbs

Old reg would go to 19 psi with key on (Priming. Not starting) t. New reg goes to 43! Bad reg. Haven't started it yet. I think I'll wait for the fuel that I spilled to dissipate first. No idea if this will fix my hard cold start, but it was certainly an issue.

So I think I found my low fuel pressure problem. Now FPR brought me right to 43 psi. I opened the old one up and found a bit of a mess.
https://cimg3.ibsrv.net/gimg/www.off...153b59c2a6.jpg
https://cimg5.ibsrv.net/gimg/www.off...5273f4ffb3.jpg

Looks like plow trucks frames and rocker panels up here. Yikes !

How is that even possible even in salt water? I replaced one this week because one engine was running 300 RPM lower than the other. I’ve been chasing this for a year. Computer throws no codes. I have recorded both engines and they both run the same.

My thoughts are that the vacuum line fell off at some point or seawater was drawn in at the connection. It is a very loose fitting vacuum port. I know the PO had a bilge flooding event while fishing. I know he rinsed and cleaned the bilge and motor after, but you'd never rinse this out.

I'm happy to report that the new fuel pressure regulator solved the cold start issue 100%. It now just starts right up and idles nicely. Getting my distributor rotor phased properly solved my drivability problem as well. I ran the boat at 40mph and 4300 rpm the other day. ABL thinks it ran at 5-5300rpm at 40, but I think that either he remembers wrong, or his old analog tach was off. The ECU shows the motor having 0.0 hours above 5k rpm.

I do think I should be a bit higher in the rpm range, but I also discovered that the trim limit was set wrong and I was missing 1.25" of ram travel. Before I start looking at props, I'll see if this gets me up higher but I'm not terribly optimistic that it will get me a lot. I have 22 pitch props on now and I suspect I'll need to drop down. I'm also not getting nearly enough lift out of this 23' SeaCraft as I do with my 20' boat of the same make/model with an outboard.

I love that you resolved this! ANY advice on my similar situation?? 2007 - 5.7 MAG MPI Alpha/Bravo. Same fuel delivery system. My issue is very hard starts after it's been running then shut down. Only way to get her to start is to push throttle down at least half way while cranking. I put a fuel pressure gauge on rail and got the 38 - 43 bouncing needle while at idle. Once started she runs fine, no issues. Just the restarts are tough. Serial # 0W687532 Tks gang!!

How old is your distributor cap and rotor? You have the "crab" style cap that can be a cause of hard start problems. They only last a year or so before they get flaky.