350 Mag MPI bogging down under load

[Stingray2000240cs]

Okay, I know this has been discussed and I've read most threads and have purchased parts based on those threads. I've been dealing with this issue since the end of last season. I'm just now starting to put some real time into the troubleshooting process.

I have a 2003 Maxum 2700 with a 350 Mag MPI Serial #0m643181

I've replaced plugs, wires, cap, rotor, and cam position sensor. All with Mercruiser parts. I've done a compression test and all cylinders are good. I checked the fuel injectors with a cheap amazon tool and all injectors flow the same. I checked fuel pressure the other day and I think I'm right about 37-38PSI at idle. I'll need to check this under load.

I have a Rinda Scan tool, but it doesn't give ME a lot of information. Maybe you guys will see something. https://www.youtube.com/watch?v=tadr5WbUBwA&feature=youtu.be

I also purchased a "High Voltage Switch Indexing Tool Service Bulletin SB2011-11R2 Tool" so that I could make sure the distributor is properly indexed, but I haven't used it yet. I've also recently read about a service bulletin 2006-02, but I'm not sure how it would be related. I'll check on that this week at the boat though.

I feel like this may be a fuel delivery issue. With the fuel pressure gauge connected and giving it a bit of throttle the pressure drops. If it's a fuel pump, would it be the boost or high pressure pump? How could I test them? Could it be the Fuel Pressure Regulator not closing with acceleration? Could that be why I'm not seeing 43 PST at idle? Could it be not closing properly?

I appreciate your feedback and guidance on this.

Thanks,
Jeremy

 

[alldodge]

Your fuel pressure should be 43 psi at idle and clear up to WOT. The Regulator is preset and the fuel pump can produce pressures above 60 psi if the regulator gets stuck closed. So your reading below 43 could mean either the pump is weak or there is an issue with the regulator

Your regulator is item 13
https://www.mercruiserparts.com/bam/subassembly/31748/8093/60

Stated compression is all good without stating what they were, so just to verify there all cylinders are within 10% of lowest to highest, and are close to 150 psi?

 

[Stingray2000240cs]

Thanks for the response. I'm having a hard time finding my notes on each cylinders compression, but I did find a note that they were all between 160 and 170.

Also, with the fuel injectors. When I say they flow the same, the test I used was key ON, press a button on the tester and it would pulse a set amount of time. They all started at the same key ON PSI and all showed the same PSI after the pulse. I know that doesn't tell the whole story, but it leads me to believe that they are fine.

 

[alldodge]

Sounding like fuel pressure regulator, but do check pressure under load

 

[Searay205]

Your definitely low on fuel pressure. remember the computer opens injector if fuel pressure is not adequate you don't get enough fuel. may have piece of crap in regulator holding it open. I think alldodge nailed this one.

Unrelated but your water pump pressure appears low at 4000 rpm. 10 psig, i usually see 15 psig in my alpha 1 gen 2. engine temp looked great so i would just watch.

Your fuel burn is wrong, again with low fuel pressure you aren't getting all the fuel. the PCM assumes injector sprays for this duration with 43psig of supply pressure consumes "x" amount of fuel.

 

[Stingray2000240cs]

Great, thanks! I love hearing the specifics based on my video. I've had the hardest time finding info to compare what I'm seeing on the Rinda.

I'm going to see if I can test the fuel regulator by clamping the return line at idle to see if the fuel pressure jumps. I'll also take the boat out for a spin and log fuel pressure at different RPMs. I may not have time to get out there tonight, but I'll get this done tomorrow or Saturday at the latest.

Thank you both!

 

[alldodge]

To test Reg it needs to be removed. Use a air compressor and increase pressure on the lower point until the air starts passing thru the side which feeds back to the filter.

 

[Stingray2000240cs]

This is the Reg test I was thinking of running.

Pinch the return line at idle to see if the Fuel Pressure jumps. Pinching the return should eliminate the Reg and should show PSI in the 80-100PSI range, I'm guessing since I don't know the true specs of the fuel pumps. If it does, then this may show that the high pressure pump is good. If it doesn't, then Fuel pump could be the issue.

Here is a good demonstration that I've been trying to study at the 20 Min mark of this video. https://youtu.be/RyEPOeQB0Zg?t=1206

I'm still planning to test the fuel pressure under load.

 

[achris]

In the video, the best RPM I saw there at WOT was 4300.... WAY too low! You should have been pulling 4600 as an absolute minimum, and closer to 5,000 would be better.

Once you get the fuel pressure sorted out, check those revs again. If they're not up near 4900, then consider a prop change.

Chris.....

 

[Stingray2000240cs]

Yes Achris, I honestly rarely ever get it to 4000 RPMs. The engine runs so rough, I usually just back it down or never get there that high. I'm running 20P props on my B3.

 

[achris]

Have you used the Rinda software to do a 'misfire' test? Very useful for checking that each cylinder is 'pulling its weight'...

Quick run through on the prop selector indicates they are the right props.

Chris......

 

[Stingray2000240cs]

Good idea Chris. I recall the test and I think I ran it and the RPM change was the same across the board. I think part of the issue with the misfire test on my boat is that it fires in pairs so I can't check them one by one. I may be wrong on that though. I'll run it again to confirm.

 

[alldodge]

Only possible issue with closing off the return line is excess pressures can damage the regulator

 

[Stingray2000240cs]

I'm going out today to test the fuel pressure. If I decide to replace the high pressure fuel pump, do you only recommend OEM or is their a quality alternative? Thanks!

 

[alldodge]

Merc doesn't make the pump Airtex does E11004
But have no issue with others

 

[Stingray2000240cs]

I really appreciate that part number. That would save me a ton if I I end up needing one. I wasn't able to take the boat out and test under load. I was by myself and it was windy today.

I'm hoping to have some help tomorrow since it's supposed to be windy tomorrow as well. I have a hard time keeping the nose straight when backing into the slip with a cross wind.

I really didn't make much progress today. I put the pressure gauge back on and I got some slightly different info from the other day. I still idles at about 37-38PSI. I ready a post that said that is normal. The only difference I noticed today that with snap throttle, the PSI went slight above 38, maybe to 42 then slightly below 38 when release then resettled at 38. I think that is all normal. I say this is slightly difference because the other day, I was only able to give it a little throttle and the PSI would drop instantly. I think todays numbers are more accurate. I'll try and get under load info tomorrow.

The local dealer wanted to sell me a pump and cooler today, but I passed.

 

[Stingray2000240cs]

I'm not sure how big a difference a snap throttle test is versus just holding at a specific RPM. If I rev the engine to 1800 RPM per the manual, I should see 43 PSI. I don't, I see about 37-38PSI and can feel it starting to miss.

AllDodge, Airtex doesn't make that fuel pump anymore. At least they are telling me that it's a discontinued pump and that they don't have a replacement listed.

Do you know if that is the same pump in the 861156A03 kit? I tried to get some pics of mine. Do you think this is bad corrosion? I'm trying to determine if I should just get the pump or if I should get the kit and maybe even a new regulator since I'll be in there. It looks like a pain.

 

[alldodge]

That's not bad, most of it is electrolysis fro dissimilar metals, brass, aluminum, stainless

If you look for the merc hp pump there are still folks selling just the pump. If you were in slat water I would say go for the hole kit.

 

[Stingray2000240cs]

Okay, thanks. My boat is in freshwater.

I finally was able to do some testing under load today with the help of a friend. Here is some info that I gathered.

At idle, my fuel pressure was 36.
At 1800 RPMs, my fuel pressure was 37.
I start to see about 43psi around 2200rpms.
The boat is really starting to miss bad as I continue to try and work through it and we only get up to about 3500 rpms today. The fuel pressure is staying at 43pst although the needle isn't rock solid. Kind of like the needle is vibrating, but at that 43psi mark.

I removed vacuum from the FPR and the fuel jumps from 36 to 43 at idle. this tells me that the fuel pump max output is 43psi. I would expect the fuel pump to be much higher and the FPR is what would keep it maxed out at 43psi.

Let me know if any of this adds any value. I'm still leaning towards a new high pressure pump.

 

[alldodge]

Its the pump or the Reg and only way to determine which is to test. I'm leaning toward pump do to the way it reacts