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MCM 5.0 EFI possible fuel issue?

K

kuneha

New member
Hello.

I have a Regal Cruiser with the MCM 5.0 EFI V8 Engine.

There appears to be a fuel issue and I would like your thoughts and opinions.

Main symptoms: Boat accelerates to 30mph, then 25, then 20 until eventually it won't go over 10mph.

The work done on the engine so far is: service (including distributor cap and rotor arm), new fuel pump, new MAP sensor, new batteries and few other things.

First, when the fuel pump was changed (cool fuel) they didn't put the vacuum line back on the fuel pressure regulator. I did some reading on this and it appears that this line simply connects to the flame arrestor so I am not sure if this operates via vacuum to operate or just for safety in case the regulator fails. I cannot put the vacuum line back as I don't have the means to lift the engine slightly to access the cool fuel box when the regulator is located. The line just connects to the flame arrestor and is disconnected and dangling on the other end.

I did some basic diagnosing and this is what I have found; when I rev the engine from idle to say.. 2000RPM or so with a quick throttle stab, the injectors dumps so much fuel to the point where the engine nearly dies, it seems to be flooding it. I can physically see it turn from a fine mist to a waterfall almost. It does look like a clean injection however, the injectors seem to have a healthy spray pattern and doesn't appear to drip. The engine doesn't always die, it slightly coughs but eventually regains itself.

Another issue is when I put rev the engine to a fixed RPM the engine creeps up in RPM. To make it clear, if I rev to 1500RPM and leave the throttle there, the engine will go to 1500RPM, 2 seconds later it will rise to 1700RPM and then usually another jump to 1900RPM. During this, I can see the injector spray change every time the RPM creeps up. It becomes a spitty/pulsing type injection that becomes more finer and less spitty/pulsing and more consistent as the RPM creeps up incrementally. I notice this when driving the boat as well.

I want to do a fuel pressure test but apparently I need a special T piece to connect a gauge to but where I am in the UK, sourcing these parts are terribly difficult. I'm lucky enough to be able to just get the service parts let alone special diagnostic tools and fittings.

Any thoughts?
 
do you have an auto junkyard over there, just cannibalize 2 gm throttle body motors with one having the tap for rail pressure and connect them with a rubber hose and a double female connector block. Unscrew your fuel line, screw the adaptor in, reattach fuel line to other end.
 
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Bt Doctur said:
do you have an auto junkyard over there, just cannibalize 2 gm throttle body motors with one having the tap for rail pressure and connect them with a rubber hose and a double female connector block. Unscrew your fuel line, screw the adaptor in, reattach fuel line to other end.
Click to expand...

I can try and see what I can do.

Do you think the vacuum hose being disconnected from the fuel pressure regulator would cause these issues?
 
That's how the regulator regulates. With it back on (correctly), however, things should return to normal.

You said the hose connected to the flame arrestor? That doesn't sound right; it should go to a vacuum source. Check that out.

I hate EFI!

Jeff
 
fastjeff said:
That's how the regulator regulates. With it back on (correctly), however, things should return to normal.

You said the hose connected to the flame arrestor? That doesn't sound right; it should go to a vacuum source. Check that out.

I hate EFI!

Jeff
Click to expand...

It confused me as well but it is apparently for safety incase the diaphragm inside the regulator fails; so that if fuel leaks out it gets pulled in to the throttle body rather than all over the floor.

Screen Shot 2017-08-15 at 13.35.44.jpg
 
I would attach it but the cool fuel system where the regulator is located is underneath the engine with no clear access without removing the engine mount and slightly lifting the engine. Is this something I can do with a small car jack just to tilt the engine a few inches?
 
kuneha said:
I would attach it but the cool fuel system where the regulator is located is underneath the engine with no clear access without removing the engine mount and slightly lifting the engine. Is this something I can do with a small car jack just to tilt the engine a few inches?
Click to expand...

It easily unbolts from the studs that hold the engine mount to the block. The mount does not have to be removed and the engine does not have to be lifted.
 
I wish that were the case but it appears not with my particular boat. The actual casing of the cool fuel module cannot be removed as its extremely tight under there. I remember when the fuel pump was changed that the mechanic said this is what he had to do to gain access. It's a shame he didn't put the vacuum line back on to the fuel pressure regulator.
 
re: "It's a shame he didn't put the vacuum line back on to the fuel pressure regulator."

then it is his responsibility to replace the hose... If he does not, find another mechanic. Every mechanic eventually makes a mistake. What separates the honorable ones from the bad ones, is what they do when they inevitably make that mistake. You should not have to do anything other that point it out to him.
 
sandkicker said:
re: "It's a shame he didn't put the vacuum line back on to the fuel pressure regulator."

then it is his responsibility to replace the hose... If he does not, find another mechanic. Every mechanic eventually makes a mistake. What separates the honorable ones from the bad ones, is what they do when they inevitably make that mistake. You should not have to do anything other that point it out to him.
Click to expand...

The mechanic was the Marina's mechanic but he was apparently fired for poor service so there are no mechanics stationed at the Marina. One has to find their own unfortunately.
 
sandkicker said:
re: "It's a shame he didn't put the vacuum line back on to the fuel pressure regulator."

then it is his responsibility to replace the hose... If he does not, find another mechanic. Every mechanic eventually makes a mistake. What separates the honorable ones from the bad ones, is what they do when they inevitably make that mistake. You should not have to do anything other that point it out to him.
Click to expand...

Focusing on the regulator vacuum line is a waste of time. It is not the cause of your issue.

Really need a serial number to point you in the right direction.
 
Docksidemarineservices said:
Focusing on the regulator vacuum line is a waste of time. It is not the cause of your issue.

Really need a serial number to point you in the right direction.
Click to expand...

Slightly upsetting to read as I was hoping this would finally be the fix as it is a problem that seems somewhat plausible. I will get the information to you as soon as possible. The boat is an hour away from my home and so getting to and fro is a bit tricky.

What information are you looking for specifically just in case I cannot find any serial number?

Thanks.
 
I managed to get a fuel pressure reading and various RPM (not under load) and it appears to be at 30±2 PSI or so and it holds steady so this seems find to me.

I had a small look at the fuel pressure regulator and it does look a bit old. Perhaps the original? - I managed to get the pipe on to it but it appears to have made 0 difference to how the engine runs. Thoughts?
 
Couldn't find it. Access is terrible and I'm getting annoyed with it all.

Fuel pressure was a solid 30 psi when under load so that seems alright. Engine wouldn't go over 2800RPM with WOT regardless of fuel pressure. The fuel spray pattern on the right injector didn't look as fine as the left but seemed healthy enough. I give up.


Access to anything on this boat is awful. I'm good with a set of spanners and quite mechanically inclined but this is beyond me. I genuinely give up. My boat can sit there and rot.
 
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Now, don't get pissed at me, but wouldn't it make sense to junk that damn EFI nightmare and put on a 4 barrel carb? Lots of parts out there reasonably priced and, as you stated, you're entirely capable of doing the job. You'd need a fuel pressure regulator set at around 6 psi--Holley makes a nice one. The rest of that EFI crap could be removed and/ or blocked off.

My 305 - 230 hp with a 4 barrel runs great and gets good gas mileage. Watcha think!

Jeff
 
Just to update this thread as I know people often try to find these types of thread for answers but the OP never usually returns to tell people if they ever found the problem.


The boat has been taken out of the water and I've managed to take off the other riser to inspect the flaps.. both were missing.


I removed the drive and found them in this exact position:


IMG_20171006_125656.jpg



Flapper has blocked the exhaust entirely.


I've not tested the boat yet but this seems the likely cause.


Regards.
 
kuneha said:
Just to update this thread as I know people often try to find these types of thread for answers but the OP never usually returns to tell people if they ever found the problem.


The boat has been taken out of the water and I've managed to take off the other riser to inspect the flaps.. both were missing.


I removed the drive and found them in this exact position:


IMG_20171006_125656.jpg



Flapper has blocked the exhaust entirely.


I've not tested the boat yet but this seems the likely cause.


Regards.
Click to expand...

Was it running hot too?
 
Docksidemarineservices said:
Then I doubt this is the issue. Not saying it will not cause your problem...but doubtful because of no temp issues.
Click to expand...

I seem to have mixed opinions on this. Some have said the blockage isn't close enough to the engine to see an overheat but it's close enough to cause exhaust back pressure which is causing the low power.

Thoughts?
 
fastjeff said:
Now, don't get pissed at me, but wouldn't it make sense to junk that damn EFI nightmare and put on a 4 barrel carb? Lots of parts out there reasonably priced and, as you stated, you're entirely capable of doing the job. You'd need a fuel pressure regulator set at around 6 psi--Holley makes a nice one. The rest of that EFI crap could be removed and/ or blocked off.

My 305 - 230 hp with a 4 barrel runs great and gets good gas mileage. Watcha think!

Jeff
Click to expand...
Dunno where you are on this but to add to Jeff's advice...the EFI cam often does not have a lobe for a mechanical fuel pump. Just be aware of that if you decide to go old school. It'll be about $1000 all in to change to a carb with your plumbing etc.
 
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