Engine dies when it get hot

[chiron]

I have been struggling to make my A4 reliable. The tow guys are getting to know me on a first name basis. Since I purchased my boat last fall I have been suffering from random engine failure and some excessive smoke when it has been running for a while. I have been reading this form religiously for months trying to diagnose my (I mean my engines) problem. I have been tearing things apart one by one and have found things wrong each time. Water in the fuel, emptied the water separator. Moisture in the distributor, new cap and rotor. Carburetor, cleaned and rebuilt. Fuel tank, cleaned that out and got the piece of tape floating around the pickup tube out. Coil getting too hot, replaced that. New plugs. New fuel lines and polishing filter.

The problem happens after the engine has run for a half hour or so and then it sputters out and dies. The compression is good on all cylinders and the plugs all look the same a little soot but nothing excessive. I looked into exhaust back pressure and thought well I haven't looked into that yet.

Now I have opened up a can of worms and I guess I should go fishing. I checked the exhaust hose after the riser and found the hose to be in great shape. I did find some crud in the water mixing riser thing and attempted to take it off as to no avail. So I tried to pull off the manifold which I can not get off all the way due to the riser hitting some framing member and now will go back with a hack saw to finish the job and get things all cleaned up.

Sorry for the rambling, venting a bit. Here is the question. Once I get the manifold off I figured I might as well check into the valve adjustments. Could poorly gaped valves cause the engine to die once it comes up to operating temperature? Or am I just chasing ghosts. What all could cause an engine that fires right up when cold and runs like a champ to die once it warms up.

One more thing does anyone know anything about this? I don't have space for a lift muffler or a standpipe and don't know if this is replaceable.

Thanks everyone
Chad

[smosher]

When it shuts down how soon after does it restart ?

Right at shutdown try a little starting fluid to see if its gas or spark related.

[Will Jacocks]

Make sure your tank has a vent that allows air to get in so you don't end up with a suction that keeps the fuel pump from pulling the fuel.

[tenders]

A slowly failing or impaired fuel pump could cause your symptom too. When it's sputtering, does adjusting the throttle and/or choke affect it?

[hanleyclifford]

Just a couple of ideas. Try changing your coil and condesnser (not at the same time). They have been implicated in problems such as you describe. Regarding your exhaust system, you do have the option of a water lift. Check out my album on this site. We have the same exact boat!

[jpian0923]

I have one of those mixing elbows. I had a complete blockage and soaked it in muriatic acid solution. These videos show the result.

[YOUTUBE]N_6x-vB9VDo[/YOUTUBE]

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[chiron]

When the engine dies I immediately check the usual culprits. The coil, which is new, has spark as do all the spark plugs. I have electronic ignition so no condenser to be problematic. The fuel pump seems to be working due to fuel in the float chamber, but since I am taking out the manifold and have access to the pump I will rebuild it for piece of mind. The tank vent is clear. When the engine dies I can sometimes get it restarted in 10 to 20 minutes but it always starts right up like nothing happened the next day. I can sometimes keep it running by messing with the throttle but the choke never seems to help. I have tried pulling one plug wire at a time but she really prefers all cylinders firing. Why is it that buying a sail boat is tuning me into a mechanic?

Chad

[ndutton]

Man, those are classic overheating coil symptoms (half hour run time before shut down, fuel good, starts right up after cooling down). You say upon shutdown the coil has spark as do all the plugs. There's a big difference between having spark and having a hot snapping SPARK.

I didn't read where you checked the coil temperature at shutdown. Might want to check that next time.

[tenders]

> When the engine dies I can sometimes get it restarted in 10 to 20 minutes but it always starts right up like nothing happened the next day.

A classic "bad coil" symptom, sometimes "bad condenser" which you clearly don't have. However, you said in your first post:

>Coil getting too hot, replaced that.

What led you to conclude it was "too hot"? Is the coil still getting hot? I'm wondering if you have a coil with the correct resistance installed, or have something going on in the ignition circuit that makes the proper coil work incorrectly.

> I can sometimes keep it running by messing with the throttle but the choke never seems to help.

Classic "bad fuel pump" symptom, or at least "bad fuel delivery." If you can consistently affect the situation with throttle or choke it almost completely rules out an electrical problem. I would personally want to rule out fuel issues in a robust way before going too far down other time-consuming paths. You've been commendably methodical and logical so far.

[Dave Neptune]

Idea

Chad, yes classic electricle symptoms except for the part about the choke making a difference. The coil problems are USUALLY off or on not weak unless the coil does not recieve a good charge.
First thing I'd change is the condenser and check to be sure that the distributor has a good ground to the block! I have seen heat make a defective condenser do wierd things, especially if the ground path isn't real good.
If the above doesn't work then I'd look at fuel preassure cold and hot since the choke made a difference.

Dave Neptune

[tenders]

He said throttle sometimes helped, choke made no difference, and with electronic ignition he has no condenser.

[Dave Neptune]

Oops!

I was probably slowly writhing as it was posted.

I'd still check the ground paths on the ignition side and I think I'd take a look at the key/switch for integrity as well.

If the choke didn't help don't worry about rebuilding the pump until you have this gremlin at bay.

Dave Neptune

[Kurt]

Have to chime in here for a minute. I read that you are in the process of looking into exhaust backpressure issues and are going to (or have) take off the exhaust manifold. Excessive exhaust backpressure would not cause the symptoms you are describing of running great until warmed up and then dying. Exhaust backpressure will cause poor engine performance when your engine is hot or cold. By poor engine performance, I primarily mean poor power and inability to achieve proper rpm's under load and in neutral when revved. While taking your manifold off for inspection and cleaning (if necessary) is a good preventative maintenance measure on an engine that has an unknown history (at least to you), I think you have bigger fish to fry right now and this may turn into an exercise in frustration for you as I don't believe it will solve your primary problem. BTW - the part in your picture, as somone else mentioned, is a water mixing elbow and is definitely a replaceable part. Others have suggested more likely culprits than excessive exhaust backpressure in regards to your issue.

[Kurt]

Oh - and to answer your other question - I don't believe valves in need of adjustment would cause your problem either. If poorly adjusted valves was your problem, you would likely notice poor performance symptoms other than your engine dying when hot.

[chiron]

While diagnosing this problem earlier in the winter I suspected a bad coil. Seems that if it gets too hot it can produce a weak spark and resemble a fuel related shut down. In the process I discovered moisture in the distributor when the engine got warmed up and replaced the cap and rotor with one that had a vent hole in it. Don seemed impressed when I figured that one out. The spark in the distributor was grounding itself out when enough moisture built up inside and the cylinders were cutting out one by one till it died. At that time the problem seemed to go away but now is back. So maybe my new coil is getting to hot. I did grab on to it the other day after the engine died and it was too hot to hold onto. Is that too hot and what could cause a coil to get too hot. I thought I read somewhere in this form about mounting the coil somewhere off the engine to help keep it cool. Any ideas on this? Would the flame thrower coil possibly help? I have the standard coil supplied by MMI.

Now for the can of worms. Since I thought I would check the exhaust and could not get it off I attempted to remove the manifold but could not slide it off the studs before the water mixing elbow hit some framing on the boat. At this point I was committed to removing both due to the manifold gasket getting ruined once I popped it off. Took the hack saw and cut off the exhaust. pulled both parts and will clean them out just for fun since they are just fine, also inspected the valves and all is well. So besides lots of unnecessary work at least I got to drink a beer and go to the boat.