Another stalling problem

[T-bird]

The short version; I bought a rebuilt A4 5 years ago installed it myself on my Catalina 30 and it ran well for 3+ years. This year or so it started to die randomly and would not start till it cooled. Lately the run times degraded untill the last 2 weeks it stops after 10 minutes. It starts on the first or second crank and runs well until it shuts down very suddenly, maybe 1 or 2 seconds of falling RPMs then nothing. No shudders or coughs its quite smooth. Heres what Ive done so far; tested the coil 3.4 ohms w/ no external resister (as written on the coil) I also ran my spare coil with the same outcome. I rebuilt the carb. thanks to MMI manual; no change. Thermostat barely hits 140 degrees and I can lay my hand on manifold for a sec. Plugs are hot but clean. Salt water flow is good on my fresh water system. I have electronic ignition, and spark at the plug even with hot engine. The elec. fuel pump was tested and felt relatively coolish. Today after my 10 minute run and shutdown, I jumped a wire from coil to starter terminal after about a hour of cooling. It started but ran for 30 sec before nada. No oil pressure switch. Ill check my raw water impeller, which I ran dry a time or two. Im no mechanic and this gremlin has stumped me at every turn.

[jcwright]

Hello Tbird.

You mention that the fuel pump was tested, but not how. Perhaps you've already checked for fuel pressure downstream of the fuel pump. If not, a fuel pressure gauge is worth considering.

Jack.

[Peter]

Tbird,

Let me second that suggestion - a fuel pressure gauge is an excellent diagnostic tool.

Another possibility is a plugged fuel tank vent. You could try running the engine with the fuel fill cap off - no smoking!

HTH,

Peter

[JOHN COOKSON]

First off let's determine which system is at fault - spark or fuel.

The described symptoms are very characteristic of a failing coil or possibly a failing EI.
Immediately after a shut down, before things cool down, pull the big wire out of the distributor, and hold it near the engine while cranking the engine to check for spark. A blue white arch is good.

ex TRUE GRIT

[Mo]

I would run the engine and have someone there with you. When it dies, have the person turn it over and you check for spark at the plugs immediately. If you have a bad coil you likely will not have any spark or a very weak spark when you try it immediately after it quits. When a coil is failing it heats up and fails to produce a good spark...or none at all. As it cools back down it will work again. A new coil will be required if that is what's going on...it sure sounds like a coil issue.

[joe_db]

I would run the engine and have someone there with you. When it dies, have the person turn it over and you check for spark at the plugs immediately. If you have a bad coil you likely will not have any spark or a very weak spark when you try it immediately after it quits. When a coil is failing it heats up and fails to produce a good spark...or none at all. As it cools back down it will work again. A new coil will be required if that is what's going on...it sure sounds like a coil issue.

Engine stalls - helper squirts a bit of ether in the carb - you hit the starter - engine starts is a gas issue, no change is ignition

[Dave Neptune]

Since a fuel delivery problem will stumble to a stall I think it is out of the question.

Electrical stalls are pretty much a running or not like turning off the key. I have had a coil go intermittent while running IE the engine would stutter and loose RPM's then go back to norm only once in my experience. If it is not the coil as you state you did still see a spark I think you should confirm this.

Now as to the rewiring how extensive and did the "mechanic/electrician" eliminate the trailer plug? The trailer plug can open and close with vibration causing shutdowns as it has been seen many times here on the MMI site.

Perhaps heat has nothing to do with it but if the connections are weak at the trailer plug which would cause the plug to heat then it may open the circuit to the ignition. And this is really reaching for straws.

The timing of your events leads me to the coil as a ten minute warm up is about right for a coil. Be sure you do have spark right after the shutdown if you can make it repeat.

Also check your operating voltage at the battery and the coil with the engine
at around 1200 RPM's so the alt is working, and report back.

Dave Neptune

[Dave Neptune]

Part II

As Mo states the value of help wiggling the trailer plug while the other person is working the voltage values is a good check and also do this while giving the ign key a few wiggles. This may show a few weak spots.

Dave Neptune

[SubtoSail]

+1 on the coil. I have read that the EI will tend to use up coils, although the proper resistance may solve that (the one from Moyer is proper). If EI tends to degrade coils over time, and thermal cycling at the engine mounting position tends to degrade coils over time, I'd consider the coil to be a likely culprit. +1 to check for spark immediately after the shutdown, when the coil would still be in a "failed" state.

A few months ago there was a similar problem reported that turned out to be a failed electric fuel pump. There was enough gravity fed fuel to run for a bit, but the pump wouldn't keep up over time. Is your shutdown pattern affected at all by throttle? ie: will run forever at idle, but dies after ten minutes with throttle.

Quick plug for the simple things: remember not to crank too long when not starting, if your exhaust set up will cause backfill; remember to switch the key to off after shut down as leaving in the on position will keep power applied to the coil, destroying it if it is not the problem already.

[JOHN COOKSON]

I also ran my spare coil with the same outcome.stumped me at every turn.

Do you know the history of the "spare" coil? Was it on the boat when you bought it? It may be a "spare" coil that was left on the boat that doesn't work.

A true spare part is one that you know will work when you need it.

ex TRUE GRIT

[joe_db]

FYI - At high power settings running out of fuel is about 95% as sudden as losing spark. I'll make a video when I get around to it.

I like to flog this in every thread about shutdowns:

https://moyermarine.com/product/the-engine-warning-and-diagnostic-system-ktas_01_564/

You can save HUGE amounts of time and trouble if you can see what went wrong when it went wrong. Note this will not tell you if a coil fails, but it will tell tell you if the coil is not getting voltage.

[T-bird]

Last night I did some tests. After a easy start, and 3 minutes into warm up I measured the "+" terminal coil to block ground at 10.7 Volts at 1100 RPM. While waiting for the engine to fully warm up, it shut down. I pulled the distributer wire held it about 1/2" from a head bolt and got a nice strong arc from a not fully warmed engine. All this happened within 5 min. of startup. I also tested the spark at the plug and got a much weaker spark. Then cranked the engine while spraying either into carb and it would start and run for 1-2 secs. After I started to cool down, I check and drained about a teaspoon of gas from carb. In a day or two I plan to check all these tests with fuel pressure gauge install. Ill try to video and check back in. Thanks again for all your support

[joe_db]

10.7 volts is VERY low unless you have a ballast resistor. Also note ether will fire off from a much weaker spark than gasoline will.
If I had to guess, some combo of rotor, cap, and wires are bad or maybe all three AND you are maybe not getting near enough voltage to the coil.

[ndutton]

This brings up another test, alternator output voltage @1000RPM. Either you have massive voltage drop in your engine harness or your alternator is not working.

Has anyone mentioned trailer plugs in the engine harness yet? They are a known problem.

[T-bird]

Sorry forgot to mention that I no longer have the old trailer plug set-up. I will re-test tomorrow.