Runs great, then shuts off, then runs great

[jacques debauche]

Our A4 has been running like a charm until last week. Restarting after a race, the A4 caught immediately and ran perfectly for about three minutes. It then shut down instantly (as though the ignition were switched off). It restarted immediately, ran for another few minutes, then shut off again. This repeated several times until we tied up to our mooring. Since the coil was suspected, we replaced it - no change in symptoms. There are three more suspects: 1) a problem involving the electronic tachometer (but disconnected it - no change), 2) a problem with the ignition switch (but wiggling it and its wiring doesn't cause problems) or 3) an intermittant failure of the solid state ignition module, but my experience with solid state electronics is that they usually die completely, so this seems unlikely. Both the character of the stopping (abrupt) and the OK condition of the fuel system indicate that the problem is electrical, but what? Our next move will be to run a temporary jumper from the positive side of the battery to the positive terminal of the coil to check for any intermittant in the ignition circuit. Any other suggestions?

[hanleyclifford]

Check to see if there is an intermittent short where the primary ignition wires enter the distributor housing.

[jacques debauche]

Good suggestion - I've always been a little nervous about that groove filed into the distributor cap to accespt the solid state ignition module wires.

[jhwelch]

This is not quite in line with your sympotms, but do you have an electric fuel pump which is also wired to run when the starting key/button is pushed? If your pump is not running other then when starting you might get 3 minutes run time out of what fuel is in the carb. bowl, but the shutdown would have more of a sputter to it.

[tenders]

I was gonna say fuel pump too. Is it possible the oil pressure switch (which turns off the fuel pump on low oil pressure) is miswired?

[joe_db]

Some electrical fuel pumps are wired to the a connection on the starter solenoid that was originally intended to bypass a ballast resistor in the ignition circuit. Thus the fuel pump runs when the starter is engaged but would then quit if the fuel pressure safety switch is bad.

[jacques debauche]

Not fuel pump

The possibilty of the fuel pump cutting out because the oil pressure switch opens was considered, although that would be unlikely to cause such an abrupt shutdown. However, just to make sure, I jumpered the switch, and it made no difference. Back to the drawing board.

[anglosax]

coil connection

I had similar symtoms on a A4 - would just stop for no reason and restart and run as normal until next time - Bypass all the wiring loom and temporarally connect the coil direct to battery and run - You will have to break the connection to stop engine - good luck
Otherwise I would look at float valve in Carb - 3 minutes sounds like a chamberful of gas

[joe_db]

Try ether. If it runs, no fuel was the issue. If not, maybe no spark.

The possibilty of the fuel pump cutting out because the oil pressure switch opens was considered, although that would be unlikely to cause such an abrupt shutdown. However, just to make sure, I jumpered the switch, and it made no difference. Back to the drawing board.

[jacques debauche]

Float valve

Interesting suggestion about the float valve. In a previous boat I had a float valve that would stick even with 3 psi fuel pressure on it. And as you say, the engine would run a few minutes before dying. However, it was a slow protracted fuel starvation death, not an abrupt dropping dead. I didn't believe that a float valve could stick with that much pressure on it, but in a post mortem of the faulty carburetor (after it was replaced with a new one) that proved to be the problem.

As for connecting the positive side of the coil to the battery directly, that is already on my to-do list the next time I can get onto the boat. If nothing else, that would eliminate the ignition switch and associated wiring from the "usual suspects". The boat is a Tartan 30 with the ignition switch half a boat length from the engine under a lazerette cover where it can get wet, so an intermittant switch is a strong possibility.

[Crash]

Gonna only say this once..

I had similar issues with my engine out in the Bay as she would start up for a few minutes then quit like it was an electrical problem too. I'd restart her up and she'd run for another few minutes and quit again. Usually after the 3rd time she just wouldn't turn over so I had my crew practice their seamanship skills and dock her under sail. (yeah you guessed another reason for my "handle" here..)

Well as it turns out I ran out of gas. Now with my pants squarely around my ankles "Dionysus" was a newly acquired boat and the gas gauge didn't work and I had no idea what the fuel consumption was.....but now I do.

Crash

[edwardc]

... or 3) an intermittent failure of the solid state ignition module, but my experience with solid state electronics is that they usually die completely, so this seems unlikely. ...

Sometimes an electronics failure will be heat sensitive. Your electronic ignition might run for a few min until it warmed up and something internal went "open", and cooled and recontacted as soon as the current stopped flowing.

Just another possibility to consider. If you've still got the old points & condenser, a quick swap-out could confirm or eliminate it.

[JOHN COOKSON]

More Stuff To Check

Check the wire from the coil to the oil pressure safety switch.

Try running a hot wire to both the coil and the fuel pump at the same time. This will bypass a whole lot of stuff and should give you some diagnostic information. For example if the engine still cuts out there is the fuel pump, coil, electronic ignition to consider. If the engine runs normal there may be a wiring problem. And so on.

Since this problem started after sailing there is a possibility crud was stirred up in the tank and is blocking the fuel pipe inlet.

The posts in this thread should keep you busy for awhile. Good luck to you.

TRUE GRIT

[CalebD]

Bon chances Jacques Debauche.

I'm pretty sure that everyone else here knows more about this then I do so you can take my suggestions with une petite graine du sel.
I should have mentioned these rudimentary procedures that we do with our old 1967 A4 when I spoke to you last Wednesday but I was caught up in hearing the symptoms and wanting to get out to our boat to race. Since you did not race we got a first place finish.
When the engine shutoff occurs we routinely drain our Zenith carb from the 1/2" bolt that closes the main passage in the carb. If you can catch the draining gas in a clear container you can check for crud that may have been blocking the float valve. Sometimes a few quick taps with the handle of a screw driver will also help dislodge any crud that may be messing with the float needle assembly. I suppose it is also possible that your float is set at too low an angle and keeps the needle set at closed - not sure why that would occur except if the float's legs are easily bent by your boat heeling from sailing. Perhaps you need a new float assembly for your carb if that is the case as the metal legs will deform more easily once bent a few times from fatigue.
The angle in the legs of the float determine if the needle will open and close properly. If the angle is wrong then the needle can stay firmly in the closed position that will not allow any more fuel in. If the angle of the float legs is wrong in the opposite direction then the valve can stay open allowing gas to drip from your carburetor (ask me how I know this).
I think I need to order a new carb float for our boat as we are now smelling plenty of gas when the fuel petcock is open.
I hope that is helpful as it is about all I know.
My best.
Caleb D.
Tartan 27' #328 'Odalisque'

[Serendipity]

Do tell...same ole problemo

We have been dealing with the same problem for several weeks too. starts, or starts with ether and runs 3 minutes...slowly konks out, but usually doesn't just stop like a kill switch. played the fuel chase game, rebuilt carb, replaced fuel lines, filter, same result. bought new carb. None the better. bypassed oil pressure sensor, primed fuel lines, same: starts and runs, then quits, then difficult to start. good compression (88-91 psi) Replaced plug wires, plugs, kill switch. then we hired a mechanic!
he saw fairy yellow sparks at coil while cranking, rather than bright blue and informed us we needed a coil replaced. replaced coil. Same symptoms still! I am gonna replace the 1-yr old electronic ignition and see how that goes...along with all wiring.

the possible problem of bad fuel has not been fully trouble-shot. we started this problem in midwinter, after lots of rain...but I would expect the Racor filter to show crud or water when drained from the bowl to a mason jar, right?

-Team Serendipity