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My apologies for the long post but I am at my wit's end on this one!!! Coming home on one engine is getting really old (thank you Capt. Patrick for the oversized rudders!!).

Well, this is the second season I have had an issue with my port engine cutting out at idle. I've self diagnosed, had a mechanic look at it, and consulted with other knowledgable gasser gear heads to no avail.

Here is my set up-

Vintage 1980's 454/340 hp Mercruises with velvet drives.

Port engine - approx 950 hrs since 2005 rebuild.
Starboard engine - approx 1250 hrs since 2000 rebuild
Rochester quadrajet carbs


Two seasons ago I started to periodically experience this repeated scenario with the port engine-
Cold start - no problem
Run at cruise for 30 or more minutes - a o.k.
Stop and anchor, drift, or tie up at another marina for 30 minutes or up to several hours
Restart engine and idle at 750 rpm - no issues
While untying or pulling anchor, engine starts to sputter so I bump the throttle a bit, it sputters and cuts out
Try to restart, engine sounds like it wants to fire for a moment, then nothing.
After several additional attempts over the course of several hours, still nothing.
Many hours later after the engine has cooled - cold start, no problem

Here are the things I have done in an attempt to find a resolution-

1) changed ALL fuel filters, including the small one where the fuel line enters the carb.
2) swapped ignition modules with the "good" starboard engine.
3) rebuilt quadrajet carb.
4) replaced quadrajet carb with a new O.E.M. replacement from National Carborators out of Jacksonville

Unfortunately I recently had to switch mechanics due to the retirement of my guy who serviced the engines for 14 years. For some reason there is a shortage of gas mechanics in my area that have knowledge of working with old technology!

I'd love to donate these motors to and artificial reef program and just be done with it, however I am not currently in the right economic situation to handle a proper repower.

Thanks in advance for any suggestions or resolutions!!

I have had similar problems. I have very little skill as a mechanic but the professional I use is very good. Mine turned out to be fuel pump issue. I could be wrong but I believe it was providing to much fuel and flooded the carb. Had something to do with the tolerances being a bit oversized on a rebuilt engine.

Please don’t laugh at my non technical explanation but it took a while to diagnose and I’ve become quite skilled at handling the boat with one motor. Same thing rebuilt port motor and that’s the side that caused problems.

I believe the fuel pickup on the original tank was lower to the port motor which picked up the ethanol gunk. The reason why my starboard motor has continued to last

I have a 1986 Porsche with almost identical symptoms that have been driving me nuts and look forward to hearing the resolution.

I had this problem with my Chryslers. Turned out to be a bad coil. Replaced. Been fine since.

Had the same problem---replaced the coil--still had the problem----replaced the ignition module----problem fixed.

I have electric fuel pumps-----over the years replaced them as well---experienced similar problems with them as well.

I had a very similar issue on my 1980's vintage 350 engines. It turned out to be this sensor under the distributor cap. It was an easy and inexpensive fix and the problem was gone! Good luck.

See part #8

https://www.mercruiserparts.com/bam/sub ... 92/1074/60

Mack,
One sure way to diagnose fuel issues is put a pressure guage between fuel pump and carb and run till you have the issue.
If the engine quits and there is good pressure, not fuel. If it quits and fuel pressure is dropping off, then back track to fuel pump, blow lines out and check rubber sections for internal collapse and check tank pickup and vent.

If the pressure stays good, then start at electrical. Coil, pickup, wiring connections, corroded internal ignition switch.

If the engine quits and won't restart, check for spark. You can buy an in line spark check rather than air gap ground a wire.

Don' t over look the simplicity of corroded wires and connections on a boat heating up and creating issues.
A good mechanic can make or has a simple bypass harness so that the basic electrical functions can be taken directly to the battery to bypass much of the electric.

When faced with this issue in my past career, I would take the boat out with all my diagnostic stuff and run the boat till it created the issue. At that point it doesn't take long to figure it out by going down a check list, block diagram of trouble shooting.



Amberjack,
One of the common issues I find now in the custom car business on older cars is rust in the tank blocking fuel flow. Like what I described above can be done on cars also.

pretty much all of what Bruce just said for sure. From experience with GM and quadrajets, 1) quadrajets are terrible, never over look ,even on remanded one, an internal leak causing a massive engine fuel flooding event especially hot. I don't think you can still get a new one, only remanded units. They develop internal cracks and should have a welded and machined and or sealed fuel bowls as they often leak from there. 2) on my old 350's, I used to carry extra distributors in the boat due to them failing so often. So the check for spark when the even is happening is very necessary.

I'd rule out the electrical problem first, you can do this easily by checking for ignition sparks. One easy way to do this is just by putting a timing light on a plug wire when cranking. If it is an electrical problem, the fix is usually a fairly pretty straight forward find and replace mission. With 2 engine you can do it economically, swapping parts until you find the smoking gun. In my experience coils are temperamental, but usually all or nothing. The pickup sensor in the distributor is the same but both should be swapped or replaced if you are not getting spark. After that you are looking at an ignition or thunderbolt module on Mercs. I never had one that needed to be replaced.

From what you describe, I'd bet it is a fuel related issue. I think Bruce's gauge approach would be an ideal way to start. It sounds like air, vapor lock or some kind of intermittent pump issue.

If it is electrical, it will be easier to confirm and repair, so I'd start by looking for ignition sparks as soon as it happens again. If plugs are not firing you are 1/2 way to resolution.


Hope this helps,
Mike

Had the same issue, changed out the coil to a high performance coil.. no more issue. My original coil was a cheap auto store coil. The coil is soaking.

Good luck

Thank you for all of the comments. My sense is that it is a fuel problem, however since I have already swapped the carborator I am going to hit the electrical side and eliminate the possibilities from there.

Stay tuned!

I think I jinxed myself----but lost an engine this weekend----I have electric fuel pumps----my oil pressure switch had a crack and shut down my fuel pump.

I replaced the switch today---but fuel pump is not working----where should I start to track down the problem. I have 1995 carbed motors with Delco MSTS.

Jump the switch and see if it runs.

Those switches can come normally open or normally closed.
You want normally open, closing upon oil pressure. Did they give you the correct one?

Jump the switch like Rawleigh suggested to check.

Mack I had a cutting out issue with my crusader 454 and it was the pick up coil under the distributor. When the motor got hot the glue would get soft and the wires would come away and cut out. When it was cold it ran great. Changed it out retimed motor and it ran great.

Was not sure how to jump the switch with 3 wires——power/fuel pump/starter? For future reference please advise.

As could not jump the switch-put new switch on good motor -started right up so switch is good.

Secondary problem—getting no spark—-I can hear the fuel pump and she will crank- but no spark.

Again, it’s a Delco MSts system—could the crack in the pressure switch short the coil or ignition module? Is there a way to check or should I start switching parts off the good motor?

Pretty sure I isolated the problem to a bad ignition module. Replacement parts are priced from $80 for Sierra--$150 Volvo---$225 for a Mercruiser------I have seen Delco prices for $45-------Is there a difference for the marine versions?

Craig Mac wrote:Pretty sure I isolated the problem to a bad ignition module. Replacement parts are priced from $80 for Sierra--$150 Volvo---$225 for a Mercruiser------I have seen Delco prices for $45-------Is there a difference for the marine versions?

Looks like the difference is $35.00, $105.00 and $180.00 depending on which one you buy.



I honestly do not know if there is a difference and/or spark proof...but could not let that bad bit of a joke go.

Carl

For what it's worth, I have used a bunch of Sierra parts over the years, and never had a problem with any of them--perfect fit for the original equipment, and lasts just as long.

as others have mentioned there is a pickup coil inside the distributor. I had issues with one of my 3.0L engines with the same thing, the boat would run fine cold for 1/2 hr then the tach would start bouncing and the engine would run rough. At that point I'd have to back down to 1000 rpm.

Testing it with an ohm meter cold it would test out fine, one trip I did the test again with it hot and finally figured it out.

the EST ignition timing procedure is pretty specific and you have to put a wire between two leads to get the module in the right config to properly time the motor.

Don't replace before checking out. If you think its bad disconnect it. It provides knock sensor and map sensor input to the advance curve which with your setup, carbs isn't as critical as injection.
The est module will provide the default advance curve for the distributor. Disconnect the 4 wires at the distributor connection. Run the engine to check if the problem has gone away.

I think we have found a fix.

Took awhile to replicate the issue but finally did last Friday. Started with the electrical side and all was well. Disconnected the fuel line from the carb and cranked it - virtually no fuel pumping out. Not sure why this was happening after running the motor at cruise then letting it sit for awhile, however it appears the fuel pump is the issue.

Replaced the fuel pump today and ran it at cruise for about an hour. Let it sit and it restarted fine and idled. Fingers crossed that this is the end of it!

Thanks for everyone's comments and suggestions! Much appreciated.

Glssd yo hear the problem is resolved. The pump must of had a weak diaphram.

Tony- yes, that is also what my mechanic said. Not sure why it was only an issue when the engine was warm and at idle, however we are now running with a new fuel pump.

Amberjack,
One of the common issues I find now in the custom car business on older cars is rust in the tank blocking fuel flow. Like what I described above can be done on cars also.[/quote]

Yes, in fact it was a fuel issue. I found a new mechanic and had him put it up on the rack based partly on information feedback here. We drained all the old fuel--19 gallons of dark brown, premium gasoline. We also replaced the fuel filter which had not been replaced in the 20+ years I've had the car. Runs great, sounds great, fun to drive again!