Motor stalling 1989 Mercruiser 4.3 V6 175hp

[jrmarsh]

Boat starts up fine in the water, for the first couple of minutes I can get it up to about 1900rpms before it wants to crap out. At first, i can sometimes get it to "surge" if I give it a lot of throttle, then eventually, not at all. Then, upon starting it again I can only get slightly above idle before it dies. It seems to worsen over a short period of time. It also seems to die suddenly as if it isn't getting enough fuel or spark. I've been using an auxiliary tank to rule out water in the fuel. The ignition was converted with a presto-lite ignition module in the distributor that came out of an older, junked boat.

Here is what I have tried so far:
I first had the carb rebuilt, however, after having it rebuilt I did run it and then found a substantial amount of water in the fuel. I've since used an auxiliary tank and run clean fuel through it for about 30 minutes.

It has a new fuel pump that has been tested at 6.5 pounds pressure.

A mechanic put a new coil on it, I have since been told by another mechanic that it is the wrong one (I have a Sierra Thunderbolt on order).

I've been told that the presto-lite ignitions either work or they don't work at all, I've also been told that they are junk.

Is it also possible that there is still water in the carb?, in the bowel?, can I, how do I drain it if this needs to be done?

Even with what I've done so far the symptoms seem to be the same.

Any help would be greatly appreciated.

Thanks,
James

 

[V-Tech]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

For us in the automotive world, (and you have an automotive engine) the rule is to always make sure the ignition system is working at 100% of it's ability before you go after the fuel system. But then, we do not deal with the water in the fuel factor nearly as much. I dealt with similar symtoms earlier in the summer on a boat with the same engine. There was high resistance in the circuit that delivered power to the ignition coil. It is supposed to receive full battery voltage, but was only getting about 10.5 volts. Since it had full battery voltage (12.6 volts) at the back of the ignition switch I just ran a new wire all the way back to the ingition coil, problem completely solved.
On most boats this will be a purple colored wire.
So, measure the voltage at the positive side of the ignition coil with the key in the RUN position and compare that reading to voltage directly on the battery. The voltage at the ignition coil should be within .5 volts of battery voltage.
Other accessories that share power off of that purple wire could also draw excessive current giving you a similar situation if you do have a significant voltage drop to the ignition coil.
Check the voltages and go from there.

With your volt meter, put the positive lead on the positive of the ignition coil and ground the negative lead of the voltmeter to a solid metal part on the engine to get your voltage at coil reading. At the battery, just put the positive lead on the positive terminal of the battery and the negative lead of the voltmeter on the negative terminal of the battery. Sorry if you already knew how to take voltage measurements. Just trying to be thorough

 

[jrmarsh]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Thanks V-Tech for being so thorough in your explanation. Electrical is not my thing so please excuse me if this sounds stupid but the gauge on the gauge cluster reads 14 volts when running.
Regardless I will try your method and see how it reads.

James

 

[mpdive]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Are you running a water seperator?

 

[mpdive]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Thanks V-Tech for being so thorough in your explanation. Electrical is not my thing so please excuse me if this sounds stupid but the gauge on the gauge cluster reads 14 volts when running.
Regardless I will try your method and see how it reads.

James

No such thing as a stupid question. The gauge on the dash is your charging volts as your driving the boat. Battery is 12 volts and the alternator is reponsible for the additional voltage to keep the battery charged. 14 volts is a good thing.

 

[jrmarsh]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Yeah, I've tried running it with the water seperator, bypassing the water seperator and just using an auxiliary tank and still I get the same symptoms.

 

[jrmarsh]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

mpdive: So does this mean that doing the electrical test described by V-tech is a moot point?

 

[mpdive]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Not at all. Your charging system volts have nothing to do with the prescribed test. V-Tech is correct in the procedure.

 

[Volphin]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Double check your engine ignition timing and idle mixture. Sounds to me like you are leaning out. What carb are you running?

V

 

[mpdive]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

You said you ran it for 30 minutes on the auxillary tank. Did it stay running?

 

[jrmarsh]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

You said you ran it for 30 minutes on the auxillary tank. Did it stay running?

In the driveway with earmuffs no problem. Under load in the water it runs up to about 2000 rpms for about a minute then cuts out if I give it more throttle. Upon restarting, it starts to cut out at lower rpms and eventually I have to limp it back in at idle.

 

[mpdive]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

In the driveway with earmuffs no problem. Under load in the water it runs up to about 2000 rpms for about a minute then cuts out if I give it more throttle. Upon restarting, it starts to cut out at lower rpms and eventually I have to limp it back in at idle.

This is not an easy one to diagnose from afar. If it were my boat......, I would take it to the lake with a helper. remove the doghouse and start driving the boat with the arrestor off. When she begins to falter, spray a quick shot of carb cleaner down the throat of the carb and see if the rpm's return. If they do, we are dealing with a lean out fuel condition. This is the best way to make sure your not dealing with an ignition module. coil, etc..malfunction. Who rebuilt the carb? Also if it does shut down, immediately pump the throttle and see if there is a shot of fuel from the accelerator pump. This will verify a full float bowl.

As I said earlier in another post, ignition modules can be erratic. However it really wouldn't explain why it would run on muffs. I'm still leaning towards a fuel sitiuation, and if it is upstream of the fuel pump it will be easier to diagnose providing you running off a remote tank. Lastly, make sure if you do take it out on the water, you run it off the remote tank. It's time to start breaking down the sub systems.

 

[jrmarsh]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

This is not an easy one to diagnose from afar. If it were my boat......, I would take it to the lake with a helper. remove the doghouse and start driving the boat with the arrestor off. When she begins to falter, spray a quick shot of carb cleaner down the throat of the carb and see if the rpm's return. If they do, we are dealing with a lean out fuel condition. This is the best way to make sure your not dealing with an ignition module. coil, etc..malfunction. Who rebuilt the carb? Also if it does shut down, immediately pump the throttle and see if there is a shot of fuel from the accelerator pump. This will verify a full float bowl.

As I said earlier in another post, ignition modules can be erratic. However it really wouldn't explain why it would run on muffs. I'm still leaning towards a fuel sitiuation, and if it is upstream of the fuel pump it will be easier to diagnose providing you running off a remote tank. Lastly, make sure if you do take it out on the water, you run it off the remote tank. It's time to start breaking down the sub systems.

Very good points, thanks for the info. I will try it out in the morning at let you know my findings.

 

[mpdive]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Yes. Do that. I would be curious to know if you keep it running. That will give us something to go on.

 

[Volphin]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

This is not an easy one to diagnose from afar. If it were my boat......, I would take it to the lake with a helper. remove the doghouse and start driving the boat with the arrestor off. When she begins to falter, spray a quick shot of carb cleaner down the throat of the carb and see if the rpm's return. If they do, we are dealing with a lean out fuel condition. This is the best way to make sure your not dealing with an ignition module. coil, etc..malfunction. Who rebuilt the carb? Also if it does shut down, immediately pump the throttle and see if there is a shot of fuel from the accelerator pump. This will verify a full float bowl.

As I said earlier in another post, ignition modules can be erratic. However it really wouldn't explain why it would run on muffs. I'm still leaning towards a fuel sitiuation, and if it is upstream of the fuel pump it will be easier to diagnose providing you running off a remote tank. Lastly, make sure if you do take it out on the water, you run it off the remote tank. It's time to start breaking down the sub systems.

Great plan! Sound advice.

V

 

[MolsonCanadian]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Check for a sticking check valve in the fuel supply.

 

[jrmarsh]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

I had a marine mechanic work on it on Saturday, he tested all the electrical, starting with the wire coming back from the ignition, put in a new flame thrower coil, cleaned some corrosion off the contacts on the distributor, new battery terminals, found a broken spark plug wire, did a compression test (150 pounds all the way around...YAY!) put in new stainless steel plugs, adjusted the carb and cleaned the screen.

He also disconnected the tachometer, apparently, some of them can cause problems with the electrical. I've also read this somewhere too.

Sunday we took it to the water, it fired up and we took it out on the bay. For the first 3 minutes it ran really well, lots of power and very smooth sounding, then, inexplicably, it cut out. Fired her up again and attached a volt meter which my mechanic had me watch to see if the voltage changes during or prior to a shutdown. We ran the boat for a good 10-15 minutes at all speeds and it did not even miss. I took the mechanic to the dock and let him go and went out again. It ran superbly, it was a thing of beauty, both I (and the mechanic) were really impressed with the power, especially since it's a big heavy boat. Then on the way back in, it stalled again. I then realized that the fuel hose going into my auxilliary tank was pushed down very far and was curling back up and the gas was getting low, so, at this point I don't know the exact cause for the second stall, it could have been my rigged fuel supply, or as I suspect and my mechanic says: The electronic ignition module on the distributor, it is a third-party aftermarket presto-lite and I really ought to restore it to the original Mercruiser electronic ignition.

I'm going to hook up the original tank and hoses after I pump a little more fuel out to check for any water and then run it again this Sunday.

BTW: We did check the anti-siphon valve and also the carb to make sure it was sqirting gas. The mechanic did not recommend squirting carb cleaner in the carburator while it is running, or stalling because he did not want to risk damaging the motor should it back-fire.

So, that's where I'm at with it: Cautious Optimism.

 

[achris]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

It just occurred to me that I had exactly the same problem on my old (1994) V6 about a year before I sold it. It would run all day on the muffs, or at idle, but as soon as you started to put some load on it she'd die out. Took me a while but I tracked it down to a corrosion hole in the bottom of the ignition coil. All the oil have leaked out and while it was cold, or had very little load on, the coil worked fine. Ask for some extra power and the spark failed. As I said, it took me a while to find. When I changed spark plugs the problem went away, because the new plugs need less voltage to fire. I changed leads, cap and rotor before I found the hole in the bottom of the coil. The hole was caused by condensation forming on the coil and accumulating on the lowest point.

Good luck....

Chris..........

 

[Lakes84]

Re: Motor stalling 1989 Mercruiser 4.3 V6 175hp

Had something very similar happen. My v-6 merc would run out nice, then die out after 15-20 minutes. Problem turned out to be the coil casing was cracked. When the motor heated up, it would expand the casing and kill the motor. Just my experience.

See you on the lake

Joe