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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10740
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have problems with my bayliner with a chevy 350 stalling under load at 2000 rpm. Then d

Customer Question

I have problems with my bayliner with a chevy 350 stalling under load at 2000 rpm. Then difficult to start.
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello.Could I get the engine serial number please? If you run a jumper wire from a 12 volt source to the + of the coil will the engine start better?
Customer: replied 1 year ago.
I am not on the boat so I don't know the engine serial number. It is a chevy 350 as I understand it and the boat is from 1979. it is attached to a Volvo Penta 280 not duo prop.Yes, when I run a 12 volt jumper from the battery it seems to start a lot easier and quicker.
Expert:  Tan replied 1 year ago.
With the key on we need to check the voltage at the points. Have you replaced the points and condenser? I will have to locate a wiring dioagram to see if this uses a ballast resistor or a resistor wire. Do you know if there is a ballast resistor befor the coil? This will be a long ceramic block about 2.5 inches long and 3/4 of inch wide? I actually need the engine model number AQ????
Customer: replied 1 year ago.
I have enclosed a picture for you. It has a ballast resistor. There is an electronic ignition unit under the distributor cap. When cranking over the engine the volt meter on the instrument cluster says it is down below 10 volts.
Customer: replied 1 year ago.
It is an AQ 280. here is the serial number for the outdrive in the picture
Expert:  Tan replied 1 year ago.
We need to check the voltage when cranking at the ignition coil. If your voltage is to low then we have a corrosion issue, bad ballast resistor weak battery. With electronic ignition you shouldn't need a ballast resistor. Now since you say it start better with the jumper wire we know we have a voltage issue. When the engine start acting up we need to see what the voltage at the coil is doing. If you are loosing voltage the engine will run poorly. So we are at the point we need to do some voltage tests. Did you happen to run the boat with the jumper wired connected to the coil + ?
Customer: replied 1 year ago.
I have run it with the jumper wire connected from the battery to the positive terminal of the coil. it seems to run fine that way. Even with the key in the on position, when I disconnect the jumper wire, the engine will cut out, This seems odd to me because most times it starts and runs just fine without the jumper. I found that the line from the key to the positive side of the coil had a butt splice that I pulled apart with my hands and I spliced it back but it is still suspect in my mind.
Expert:  Tan replied 1 year ago.
This is why we need to test the voltage at the coil +. With key on you should have 7+ volts the higher the better. Now if your voltage is low then we need to check voltage coming from the key switch to the ballast resistor. You could have just a bad ballast resistor. Low voltage will cause loss of spark. So check voltage on both sides of the ballast resistor key on. What is your reading.
Customer: replied 1 year ago.
ok, I will check that at noon PST and get back to you. So we only need 7 volts on the coil to make a spark, interesting. I have a timing light as well and I was going to check to see that I have a spark on all the plugs. it just seems that maybe there are two problems here, a fire and a fuel issue, if you will. I mean if I jump the coil why would it still stall? The problem is intermittent and only happens when I have been out for a while and I'm drifting around trying to get it started which I don't particularly like. I don't know that I could duplicate the problem just tied up to the dock. Oh yeah, the boat is in a slip in Monterey, CA.Anything else I should check while I am there. I was thinking to take the anti-siphon valve out and take a looksee. Make sure the fuel tank vent is clear (on a different boat I had a wasp nest in there and couldn't figure out why it didn't simlarly shut down after a while on the water). Also I was thinking to check fuel pressure but my gauge is not very good (reads 3 PSI at rest) and I don't have a connecting barb. I was thinking to purchase a 0-15 PSI fuel pressure gauge from Summit Racing and mount it just before the carb.
Expert:  Tan replied 1 year ago.
Ok you could have an issue with fuel also. We have to eliminate one then find out about the other.Now what you can do is get a gas can and a piece of fuel hose run the engine on that fuel supply. This will eliminate any kind of a fuel issue with the boat side fuel system. A fuel restriction can give similar symptoms as loss of spark.Run the engine on the alternate fuel source. If it runs better or about the same connect a jumper wire connecting 12 volts to the + side of coil now run boat on alternate fuel source and the jumper wire does it run better? Check you voltage without the jumper when the engine start to act up. Your fuel pressure should be about 6+ psi at 1800 rpms.
Customer: replied 1 year ago.
I went to the boat and checked a few things. The outdrive PN(###) ###-#### ***** number is ***** the block has raised letters on it that say 30 CM and(###) ###-####. I checked the voltage like you asked; Batteries = 12.7V, (key on) incoming to Ballast = 11.03V, (key on) outgoing from Ballast to coil = 5.73V. The ballast has some notations on it: "USE ONLY WITH EXTERNA..".(seems cut off) and below that "12". on the opposite side it says "503" and below that "MADE IN USA". Just for giggles I ran the blower end of the vacuum in the main tank fill line and air comes out the adjacent vent. I'm guessing that connecting 12V to the coil instead of the incoming side of the ballast is a mistake. Your thoughts?
Expert:  Tan replied 1 year ago.
Ok the ballast is bad. The voltage coming out isn't enough. The vent test you did only verifies we don't have a clogged vent. This doesn't help with eliminating a fuel starvation issue with the boats fuel system. We still need to run the engine on another fuel source. If you have debris in 36 year old fuel tank it can cause a fuel restriction and the engine will not run at higher rpms. So replace the ballast resistor and run the engine on a different fuel source. We know we are not getting enough voltage to the ignition. I don't know what kind of electronic ignition you have but it ran the way it is connected at some time so replace the resistor. Post back with findings.
Customer: replied 1 year ago.
Ok, I will replace that resistor and do the alternative fuel source test and report back. Thanks!
Expert:  Tan replied 1 year ago.
Your welcome.........I will be here till 7PM PST.

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