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2005 5.7L MPI dumping under load

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DinghyCaptain

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been chasing this for a little bit off an on and im starting to scratch my head...

2005 Crusader Captains Choice MPFI 5.7L with the "New returnless fuel system" 330hp

the engine seems to be losing fuel delivery under load at RPMS but im not getting very far chasing down why so maybe its something else.

symptoms. engine will run all day at low rpms, idle to about 2000rpms roughly. under no load (neutral) seems to run fine as well. if you put the throttle to it in gear she starts to pick up like normal, and then drops out like the throttle was pulled back after 15-45 seconds.

i started with filters, fuel pressure at the rail is 60-75psi at idle and during the priming period before startup, the electronic pickup pump seems to be pumping fuel but i dont know at what psi and i cant find what psi its supposed to be running at (im assuming 3-7)

boat has 2 fuel tanks, switching between them makes no difference so i dont believe its a tank related problem

symptoms started all of a sudden while out with the boat, and have only gotten marginally worse over time, but roughly stayed the same... literally slowed down over a wreck to scan for fish, went to pull away and it started acting up...

my next course of action is going to be to check the psi at the pickup pump, and run a test pump and fuel line from a portable tank to the high pressure pump to try and isolate the issue...

thanks in advance
 
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Independent of the fuel pump design details, the ECU drive the injectors for varying time periods....so the pressure in the injector rail is the one to be focused on.....mid 40's (43-45 PSI) is nominal spec for that timeframe.....and it needs to be checked, under load, across the RPM band....if its not consistent, there's an issue .....
 
makomark said:
Independent of the fuel pump design details, the ECU drive the injectors for varying time periods....so the pressure in the injector rail is the one to be focused on.....mid 40's (43-45 PSI) is nominal spec for that timeframe.....and it needs to be checked, under load, across the RPM band....if its not consistent, there's an issue .....
Click to expand...


i thought all these "newer" chevy's ran high psi rails, like 60-75psi?
 
The MEFI 4/4B Diagnostic Manual gives the spec for the 2005 MP 5.7L as 57-62 psi @WOT with engine under load.

The same numbers at WOT (57-62) are also given for the 2002-2004 MP5.7L engine (what I have) but they add the note that the pressure should be 49-54 PSI at idle. I don't know why no idle fuel rail pressure is given for the 2005 engine. Maybe it was inadvertently left out, or maybe the fuel pressure regulator is not controlled by the Manifold Air Pressure in that year engine and it is always suppposed to be the higher pressure.

But Mark is right, focus first on whether you have spec pressure in the rail when your problem occurs. If it falls, you could have a flow blockage or perhaps a failing low pressure fuel pump. If you have pressure and still have an apparent fuel problem, you may have a bad wire/connector on one of the two injector driver circuits. Carefully inspect the plug where these wires come out of the MEFI. You would be well served to get a copy of the Diagnostic Manual. I have posted several times in the past where this can be found.

Good luck.
 
John - the Crusader MEFI-4 manual I have says nominally 45 PSI for the 5.0 & 5.7 and nominally 60 PSI for the 6.0 - I didn't look for the value on the 8.1L.

Some earlier engines used a regulator referenced to the intake (vs the atmosphere) and will show variation w/ MAP value....
 
My manual was issued by PleasureCraft and is dated 11/05 (November 2005?)

Both the 5.0 and 5.7 show the numbers I gave for MY 02-04 (page 5-148). Only the higher range is given for 05 (page 5-150). The 8.1 is 37-43 at idle and 44-48 psi at WOT in the 02-04 section.

Now the 6.0 is interesting. In MY 03 it is 49-52 psi @ idle and 57-60 psi @ WOT. But in MY 04 is says 59-61 psi (idle and WOT). So they apparently dropped having the fuel pressure slaved to the manifold vacuum. In 05 all of the engines give WOT only, but I suspect they all have the new constant fuel pressure scheme so that number is good for idle as well.

I believe the reason for the lower fuel pressure at idle in 02-04 is because the injectors or drivers were limited to no less than 1.8 milliseconds. The rated flow at 3 bar was (if I remember right) about 24 (22?) lbs per hour with the nozzles selected. In any case they needed the lower pressure to get the desired .7 gallons per hour at idle and the higher pressure to get sufficient fuel flow at WOT. I would guess they must have improved the injectors in 05 so that they could go with an even shorter on time at idle and thereby simlplify the fuel pressure control. Or maybe they reduced the flow rate (smaller nozzles) and discovered they could leave the injectors on longer at WOT to make up for it. As you likely remember from a past discussion several years ago, these things don't fire cylinder by cylinder but rather in two banks so timing of the flow can't be too critical.
 
@DinghyCaptain I forgot to mention a common cause for strange behavior in these engines.....and that is the cam retard setting. It is critical for smooth running at all rpms, and unfortunately it can only be set (measured) with a Rinda scanner.

Basically, the timing (base and advance) are determined by the MEFI controller on these engines. It senses crankshaft position and fires the spark at the correct time for the load and rpm. When the distributor cap is loosened and turned this adjusts cam retard (NOT timing). Timing is not user adjustable. There are no moving parts other than the rotor in the distributor and the rotor is always in the same exact relationship to the crank and top dead center whether the engine is at idle or at maximum advance. So.....if you think about it for a minute you will realize that the ideal adjustment would turn the distributor cap to have the rotor not quite yet pointing at the correct distributor contact when the spark fires at idle. As the spark advances with higher engine rpm it will eventually be pointing a little past the correct distributor contact. In both cases it can jump the gap. But if the adjustment (called cam retard for some reason) is off, then either the idle or the high rpm (full spark advance) will have trouble getting a good spark to the plugs.

So if you cannot find your issue with the simple, cheap things that have been suggested, you really should get a scan done and be sure your cam retard is correct. The spec calls for 43-47 degrees.

Now if you are a real shade tree mechanic type, and if you believe the other engine is correct (it does run OK, doesn't it?), then you can set the cam retard (maybe) without the scanner. Carefully study the distributor on the good engine and find something on the base that points at something on the engine. Then go to the other engine and see if it is exactly the same. If not, loosen the 10mm bolt on the bottom and carefully turn the distributor until it lines up perfectly with what you observed on the other engine. I did this after a head job (distributor had been removed) thinking I might get the cam retard adjustment close. When I scanned I was actually withing spec, so it can be done!

And get a Diagnostics Manual. You will be amazed at how much information and help is in there.

Good luck.
 
CaboJohn, thank you for all the insights...

I was told by the boats previous owner that the engine did have a sensor go bad on him a few times that caused weird running problems but he couldnt remember exactly what it was, though he did seem to think it was a cam or crank position sensor... i could likely reach out to the shop he used to use for work on it and see if they would know what was failing on him and the symptoms that it presented with... i havent been thinking sensors or ignition since the problems ive been having have truly seemed so much like fuel starvation, but next time i get down to the boat i'll be all set up to check pressure at the rail as well as coming off the pick-up pump to finally confirm if this is actually a fuel problem hopefully.

admittedly i havent had the time to dedicate to diagnostics as i would like... its been a crazy year for me lol

thank you, and MakoMark for the help! i'll report back as i discover more

as for manuals, i have the 05 owners, parts, and a 2001 Marine/Industrial service manual (which i was told is the newest available and is the newest i can find?), and a MEFI 4/4B Diagnostics manual... if theres anything else recommended?

also, just for clarification, the boat is a single engine, so unfortunately if for some reason the distributor is out of adjustment shade-treeing it sounds like its gonna be a problem haha, but everything does seem to be clamped down and secure as its supposed to be so im gonna hope its still where it was when she was purring like a kitten lol... damn boat made a flawless 13hr trip for me from Shark River NJ to the Chesapeake bay only a few running hours before she randomly started ****ting the bed like this, and as i said before, she was running perfect all morning as well
 
John: Ironically, the crusader manual I have is the mefi-4/4B and is also dated 11/05......and the 6.0 section indicators the regulator is NOT referenced to the manifold.....the 5.0, 5.8 & 8.1regulators are manifold referenced.....could have been newer injector or the desire to use up a boxcar load of regulators....or a handful of other things....

I'd suspect the cam retard is fine and a sensor is a more likely candidate.....now, if the engine had the distributor removed.....
 
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