Problems with my 502(s)...

TheBigToy

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May 3, 2020
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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
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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51,362
most likely the ethanol is cleaning the crud from your tank and pumping it into your injectors

if the tank(s) were not cleaned from sitting, (just having the old gas siphoned off), then you have lots of varnish and gunk in your tank.

clean your tank

then clean your injectors.
 

alldodge

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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?
 
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alldodge

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Could also use a 12V resistor type LED and a paper clip to see if there are any codes. The MEFI 1 was not that great for providing much info, but it can help.

Install LED, install paper clip, turn ignition ON and do not start.
Start counting flashes

If there are no codes it will flash 14 (flash, pause, flash, flash, flash, flash then pause and will repeat


Click image for larger version  Name:	DLC with LED code reader.jpg Views:	10 Size:	47.7 KB ID:	10876351

Or can buy a code reader
https://www.rinda.com/marine/marine.htm
 

tpenfield

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Yea, I recognize that engine serial number . . . similar to mine. Not sure what to make of the 0F26XXXX number.

Sound like you don't have 502's :noidea:

502's MPI's seem to start at serial # 0F802600

0F802268 is in the range of a 1995 502 EFI
 

TheBigToy

Cadet
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May 3, 2020
Messages
11
Crap. I did get the engine numbers wrong.
They are:
Stbd ; OF602868
Port ; OF764092
 

alldodge

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Copied from your OSO thread, most not all

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...

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)
 

TheBigToy

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May 3, 2020
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11
Thx, Dodge.

Excellent input across the board. Thx for taking the time.

I will look - and hopefully find - the knock sensor and wire on my engine(s) and test as you suggest.

The plugs and wires were changed last year - but it did run for a bit, before having issues... will be my first check.

I don't like Harbor Freight in general... Unless I'm buying one time use tool.... With this, I was really hoping it would point to a smoking gun: One engine with normal pressure, and the bad one with not-normal pressure.... And then another check with engine pulling gas from a clean source to further define the problem.

When they both were the same, and both low with gas from the can - I was ready to pull my hair out.
 
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