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Engine Missing and Surging

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omegahart

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I got my alternator rebuilt by a local marine shop and installed it today. Double checked all connections and headed out this evening for a test run. There was in immediate improvement in cranking, getting on plane, and I ran 36 mph at 4,200 to 4,400 rpm. Spent about two hours running up and down and lake. Ran on both batteries. Alternator was putting out a steady 14v. Ran the best since I purchased it.

Idled over to an island to watch a sailboat race and the engine started missing. Voltage bounced from 12 v to 14 v and the rpm was steady but speed was up and down. Limped back to the dock and turned on dock light, voltage dropped suddenly from 14v to 12v. Tried turning on several accessories and the voltage guage would drop to 12 v and creep back up after they were shut off. Boat cranks fine but stammers and misfires. No loose connections anywhere to be found. I cannot run at much more than idle which shows on the rpm guage to be about 300 rpm but it can't be right. If I rev the boat to about 1,500 rpm the voltage drop is not very bad but all the lights and blower dim as different electrical components are turned on.

Any ideas?
 
Battery bad and killing the other battery.

With the price of a new alt, being so cheap why have them rebuilt is beyond me.

DB electrical they are on ebay also.

Ok not raggin just trying to educate.

Ok pull the batteries and have them test, with the alt again. Any auto zone will do it for free.

Ether with new or known good battery and alternator run one battery, no switch straight up.

Still a problem post we will go from there.

I want to be clear. One battery, no battery switch, good cable, make sure of the cable, make sure of a clean main ground.

Make sure starter connection, main barrel plug ALL connections good.
 
Update:

Both batteries checked out ok on all tests at Autozone.

The alternator is a Mando and Autozone's tester needs an AC Delco code to do a proper test. They did a general test and the alternator failed twice. Does anyone know an AC Delco code to properly test the Mando?

When I had the alternator in the shop I checked all the wires to the Perko switch. Had to replace the connector for the power cable for the trim pump, a connector for a pump breaker, and one end of a red power cable to battery #2. All other wires appeared to be in good shape.

Will continue to check leads from the alternator, starter, choke, etc.
 
Took alternator back to shop. Checked out several times on machine and passed all test. Was present for testing. Reinstalled alternator directly to one good battery bypassing the perko. Checked all grounds and found the main ground is split to a grounding block. The nut was only hand tight. Was cheking the main power harness and it looked very good and clean. Did find that the wire loom covring the harness had been melted where it crosses the exhaust. Damage was covered up with another piece of larger wire loom. The tan (water temp) and the white/purple were melted and had exposed wire. SELOC shows the alternator wire to be red/purple but there is only a white/purple in the harness. Cranked on muffs and fired right up and idled well. Have not had time to test on the lake for extended run yet. I am only showing 300 rpm at idle on the RPM guage and a hair less than 12 volts on the voltage guage. Would think 300 is to low. Did not run up the rpms to see if the voltage guage jumped to 14.
 
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"...only showing 300 rpm at idle on the RPM guage..."

Adjust the RPMs to idle specs. Maybe 600-650 RPM; you did not give the engine model.
 
Since I can't get on the water until Friday, I have been reviewing the pages in the Seloc manual regarding the Thunderbolt IV ignition system. When I purchased a new distributer cap and rotor, the rotor cam attached to a new sensor wheel. When I replaced the rotor and sensor wheel, I did not use Loctite 271 as specified. It this an issue and could it be related to my current problem?
 
A lot of people don't (or won't) use the 271. Lack of it isn't likely to cause your issues.

Not too many engines will idle at 300 rpm....you may wanna check your tach. At least rotate the selector switch a few times - just remember to set it back to 8 cyl.
 
I checked all the wires to the ignition coil and starter. All looked good but somewhat corroded. Cleaned and reinstalled. Put on a new set of plug wires to replace the origninal 1994 mercury wires. Got 12+ when turned the key. Boat fired up first turn of the key (has not been run since 7/6). Sounded great, still had low RPM on guage but a solid 14 + volts on guage. Shut off and turned the setting on the back of the RPM guage a few times. Restarted and was showing about 500 rpm at idle at 14+ volts on guage. Turned on the blower and the voltage guage dropped to about 13. Turned off and returned to 14. Turned on the bilge, dock lights, stereo, curt. lights, etc. and there was barely any drop in voltage. Turned on the blower and it dove to 13. Shut off each accessory one by one and the voltage returned to 14 but the blower sounds like it is going to take off. It is a Attwood turbo 3000. I would think the dock lights and stereo would pull as much power as the blower. Wondering if I should replace the 14 year old blower before the test run in the morining as it may be damaged and pulling to much power.
 
Wondering if I should replace the 14 year old blower...
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It wouldn't hurt anything but your wallet a few dollars. I replaced my 18 yr. old 3" blower w/a 4" one. I had to replace the plastic outlet pan to accept the 4" hose. I also added another 3" inlet hose and hung it in front of the carb.
 
You may also want to check the wiring to the switches for your accessories. Many times, the installers will tap off the ignition switch, for B+, for everything switched off the dash. If the current load exceeds the rated capacity of the harness (or they used undersized wiring) you can have a real mess on your hands.

Before replacing the blower, measure its current draw to see if it is at the spec value. That will give you a good indication of the motor's condition, electrically anyway.
 
I would say that your electrical system is working well enough for a thorough run. The 1v drop from 14v to 13v when accessories are brought into the equation is normal. I would be concerned if the voltage dropped lower than 12v when accessories were included.
In an electrical circuit when amperage draw increases, voltage decreases and when voltage increases amperage draw is being decreased.
13v won't hurt your blower any, you probably never heard it run at full speed before when the electrical circuit was messing with you.

Also remember that your gauges are usually just a rough indicator of what the electrical system is at. For a more finite answer use a good quality Volt and ammeter.

Bert
 
Rain and lightening this afternoon so no test run. Replaced the Atwood Turbo 3000 with a Sureflow Yellowtail blower. Tested the leads before installation at 12v. Cranked on first try and had no reduction in voltage even though the new blower is 12 v, 5 amps the the Atwood is 12 v, 2.4 amps. Ran all accessories and blower and got no drop on the guage and only heard a small change in the bower. This blower is much quieter but is pushing a lot of air. Still only had about 300 rpm. Increased the idle speed to about 600 rpm. Sounds good. Real test at 11 a.m. My emergency backup boat will be a 28ft Scout Abaco with twin 300 Yamahas.
 
Got to spend the day on the lake yesterday. No problems with the engine misfiring or powering up or down. Got 36 mph at about 4200 to 4400 rpm. Able to cruise at 3000 rpm with bow up in rough water without powering up or down. I can hear the new blower when it is turned on and barely when the engine is cranked. The extra rpm at idle drown out the blower. I can actually see the rpms drop when the shift interrupter kicks in. No noticable voltage drop with the blower or other electrical componets. Small change in tone of blower when dock lights on but not other components. No large drop in voltage with both blower and dock lights on. Hopefully all the cleaning, reconnecting, and wire repairs with the new blower have fixed the problem.
 
Well, the problems continue. Have been pulling the kids on the tube the past few weekends and have a problem. Engine starts right up, ildes well, and engine sounds great. After about 45 minutes of running at 3000 rpm (25 mph) the engine flutters. Can barely hear it over the wind but the rpm guage drops 200 ot 300 rpm and the surges 500 or 600 rpm. If I accelearate to 3500 rpm it will run good for a few minutes and begin doing the same thing. Runs without issue through no wake zones, idles perfect, jumps up on plane before and after the problem, and always starts right up. 1994 Thunderbold IV. New distributor cap, rotor, plugs, plug wires, good batteries, new alternator, and new starter. All contacts from alternator to wiring harness cleaned and tightened. Any thoughts?
 
omegahart said:
Well, the problems continue. Have been pulling the kids on the tube the past few weekends and have a problem. Engine starts right up, ildes well, and engine sounds great. After about 45 minutes of running at 3000 rpm (25 mph) the engine flutters. Can barely hear it over the wind but the rpm guage drops 200 ot 300 rpm and the surges 500 or 600 rpm. If I accelearate to 3500 rpm it will run good for a few minutes and begin doing the same thing. Runs without issue through no wake zones, idles perfect, jumps up on plane before and after the problem, and always starts right up. 1994 Thunderbold IV. New distributor cap, rotor, plugs, plug wires, good batteries, new alternator, and new starter. All contacts from alternator to wiring harness cleaned and tightened. Any thoughts?
Click to expand...

surging is fuel contamination...check for fuel condition/ water..

check fuel tank vents for security/condition fuel cap seal condition ..
 
That is what I was thinking but wanted to be sure before smelling like gas for a few days. Read the post on cleaning out the tank and will follow. Does the vent connect diretly to the tank or split off the main fuel line? I get a lot of fuel blowing out when fueling. I do have two access panels to the tank and the floor over the tank can be removed if I have to.
 
I get a lot of fuel blowing out when fueling.
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Vent attaches to the tank usually on the other side of the fill tube. You may have a low spot in the vent line. Fill the tank 3/4 full at 1/2 speed.
 
Could be the tach. Disconnect the pink wire,(check for the wire colors in your book),at the tach. The tach won't work but it is a simple test. A bad tach will cause all kinds of problems like you stated. 300 rpm is suspect. It won't run at that rpm.
 
Looks like Moodrifter may have picked a winner. Pulled the gray wire from the tach this morning and she ran great all day. Ran about 30 minutes at 27 mph with no missing. Pulled the kids on the tube for about 45 minutes before rain (lots and lots of rain) ended the day. Had full power through the throttle with no missing. Will give it a go again next weekend for a longer test.
 
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