Problems with my 502(s)...
 

Hope this is right place for this...

1996 Wellcraft Excalibur with twin 502s. These are pre-"cool fuel" 502s - I least I think so. To my knowledge they are original to the boat and have never been out. Engines likely have about 400 hrs on them.

Background -
I purchased this boat from the second owner in the Annapolis area in 2006. He was a knowledgeable, open wallet owner and I never really had any engine issues for the 3 years I owned it there.
Life changed in 2009, and I moved to CA. I replaced both outdrives with Merc Factory new BIIIs just before I left, because one was starting to clatter a bit. At the same time, the engines were winterized, fogged, and the boat was shrink wrapped on the hard stand. The plan was to get established in SoCal, then have the boat shipped west.
Never did.
10 years later, I'm living in Dallas and brought the boat here last year to use on the local lake.
When the boat arrived, I told the marina mechanic - whatever it needs, or might need...
There was much to do - but the engines both were fine. Both started instantly, ran cool, used zero oil, no leaks...

Boat went in the water, and I cautiously took it out a couple of times for 30-45 minutes, to just check things over - all with zero engine issues. I didn't hammer on it (I never do), but had it running for a few sustained runs up 4000 RPM. On the third such run as I was returning, the Stbd engine required more throttle to match the port... After that, it would never go above 2000-2200 RPMs.
That was last year. The mechanic here replaced all fuel filters, and cleaned the FI pump. Said there was some residue and gunk, but nothing too bad. Note that the engine always starts instantly. Sometimes when returning after a test run, the engine would die when pulled to idle. Always idles fine cold.

One noteworthy item is the boat never had ethanol gas before coming to TX. The marinas here have ethanol in the gas. Before shipping to TX, I had a company come and drain (suck) the 10 year old gas out before shipping.

Since then, I've read everything I can and this year I'd like to actually use my boat. The Marine mechanics here are, shall we say, problematic... I would gladly pay someone to do this work, but .... Looks like I'm going to have to DIY...

I bought a fuel pressure (thx to some of the tips / info here) gauge and checked the pressure on battery power and with engines running. On the key, pressure is low 20s. At idle to 1500 RPM, it was 30.5 psi. I think the pressure is supposed to be around 43psi.
Here are the engine numbers:
OF802268
OF264092
Thinking I might have a restriction from the tank, I used a 5 gallon can to remove that possibility. Pressures were exactly the same - both engines.
So, next I changed both fuel filters and Racor water separators - carefully inspecting the gas that came out of them. The filters and gas were perfectly clean. Ran the engines for a bit in the slip to make sure there were no bubbles. Hooked up the pressure gauge and battery pressure was a littler lower, but idle - 1500 RPM was still exactly 30.5 psi.

Note that I always pinch the line from the Fuel pressure regulator during idle testing to see if the pressure moved or spiked and it never moved.

I have never been a fan of "replacing parts in hopes of it fixing a problem" methodology of troubleshooting, but I'm getting desperate.
At this point I'm ready to think my problem is the 20 year old high pressure FI fuel pumps have worn, perhaps exacerbated by the introduction of ethanol and sitting for 10 years. They aren't cheap or easy to change, but if the smart guys here advise that to be the next step.... I will.

TIA
M

Clean and flow test the injectors. Not saying that will eliminate the problem but is surely due.

Likely pump or injectors

0F802268 comes up as a 454 MPI and has a VST.
Cool fuel came out starting with serial number 0K147350 and up
The other serial number is a Bravo drive

https://www.mercruiserparts.com/7-4l...m-454-v-8-19-1

The motor uses a mechanical fuel pump on the raw water pump which feeds the VST. The VST fuel pressure should be 37 psi and mechanical pump should be 3-7 psi.

What brand gauge did you get?

The VST has a screen in the bottom and can get clogged, and can be damaged very easy if not careful.

Since both are doing the same and only one has the issue, I would reach down on the starboard side of the block under the manifold and disconnect the wire off the knock sensor. Try to run again and if it comes back up, slow back down and reconnect. You don't want to have it disconnected if you have a knock.

If the knock wire runs along next to in line with the plug wires, the wires can emit enough of a pulse for the module to pick up[.

Have the wires been changed?

Your tank is likely full of crap. Common in boats that sit. The crystallized fuel can be plugging pickups.

If your gauge is correct your fuel pressure is low. Since both motors are the same and low (in 20s running is unacceptable) , Id be suspicious of gauge. Id run clean fuel, cleaner etc thru fuel system on hose , change filters then pull injectors and have cleaned and flowed. Another OSO member did pretty much what your doing except he skipped the part about pulling the injectors and subsequently AFTER he melted a piston he had me flow and clean them and there were several that were unacceptably low. Even though you had all the fuel "pumped out" , I wouldn't be surprised if there wasn't 10 gallons left floating around in there that pickup wont suck out. 10years later would be some vile ****!

Another thing to add... replace all of the rubber lines going from the tank to the inlet of the fuel filter/separator. I had a similar problem with low pressure and it was because of a split in the supply line. It was not leaking fuel but was sucking air.

Had the same issue, cracked line sucking air, but no fuel leak

Thats what I’m thinking. 10 year layup, something dryrotted and cracked, hoses, gaskets, o-rings.

BUP is a mechanic in Texas, reach out to him.

BUP is in Arlington, TX. In your back yard.

Crap. I did get the engine numbers wrong.
They are:
Stbd ; OF602868
Port ; OF764092

The injectors were (supposedly) removed and cleaned before the boat went into the lake. Doesn't mean they couldn't have been fouled by the new batch of gas with any slag from the tank.
I have considered that crap and varnish are in the tank. The process to clean it / have it cleaned would be very difficult. It's hard to access and I don't know of any company nearby that can / would do it. I'm in Dallas - not Miami or Newport...
I just this week changed all fuel filters. Cut them open, they had very very little grit or contaminants. The water separator is 10 micron. Wouldn't a ten micron filter catch anything that would foul the system components?

That said, clogged / dirty injectors wouldn't cause lowered pressure in the fuel manifold. Poor running - yes. It is now on my short list to do, but perfect injectors won't fix low fuel pressure problems.

Codes were checked last year. No codes.

I had not considered the knock sensor. Would it throw a code? Does it lower fuel pressure as part of it's function? Does it re-set when the ignition is switched off?

Someone mentioned this small screen in the VST. I know it is the last restriction before the injectors... It was removed and cleaned as part of last years trouble shooting... I read somewhere to just remove it with the ethanol gas or it would cause problems. Later I think I read it's 10 micron so the same filtration as the water separators. Thoughts? How difficult is it to access and clean / replace..?

The gauge is new from Harbor Freight. New gauge, one hose... what could be wrong? The running pressure was (always, exactly,) 30.5 psi. Not 20s...

I'm sure BUP is a great guy (sorry, person...), but a marine mechanic somewhere in Texas is no help. If he is in the Dallas area, I'd love to talk. FYI, the marinas here charge outside mechanics a 20% upcharge so many won't work offsite. Can't fathom how that's legal, but you can imagine my frustration. I would be WAY happy to pay someone with the right tools and knowledge to trouble shoot this issue. But I won't pay 20% extra to have someone guess and throw parts at a problem and hope...

Not to criticize - but I'm surprised only two jumped on the pump as a problem. The low pressure is definitive. The knock sensor can be definitively be checked - so that I can verify. Slag in the tank? Air leaks in the fuel lines (that appear perfect and new)? I am very reluctant to throw time and $$$$ at fixes without knowing they are fixes. I understand boating isn't cheap. I work as a commercial pilot, so to guess and hope isn't part of my DNA....

I guess I was hoping someone would chime in that had early 502s, had seen fuel pressure of 30.5 and fixed it by fixing / replacing XXXX...
I do appreciate the inputs guys.

SN's check out 502 with VST

MEFI-1 is not that good. It does have a code 43 which is knock circuit failure
MEFI-2 tad better with code 43 meaning knock detected

Will a MEFI-1 remember the code, mine didn't. I was out having fun with the same motor as yours, many years ago. Went to take off again and could not get on plane. Could only get around 3200 rpm, motor didn't sound bad just no power. Longer story, but the knock sensor detected a knock because I laid the wire along side the plug wires because it looked neater. SInce then I have repowered again so VST is on a shelf in a box

If a knock is detected the timing is retarded

I asked about the fuel pressure gauge because HF not being known for quality equipment, I'm thinking your pressure is ok, the gauge is just off. The hint was because pressures are the same between both motors but only one having issues

I asked about if new wires were installed because the guy may have laid the wire along side them. Might have even done it just doing plugs to be nice (sort of)