Low voltage at coil |
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Skier85
Newbie Joined: January-09-2017 Location: Phoenix, AZ Status: Offline Points: 14 |
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Posted: June-08-2018 at 11:18pm |
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So I have a 1985 ski supreme that has the standard 240hp pcm351 in it. Now I had running on the water and ran great got back to the dock and was letting it idle and then proceeds to turn off as it ran out of gas. Get it back and start to do some investigating. Checked for spark and got spark but just weak spark. So check the voltage at the coil. 4.25v go back to the resistor and on the low side get ~5v then check the high side and get 9.7v. Now after some digging around on the forums I see these are on the lowers side of where the voltage should be. So decide I should work back and see where the draw is coming from... well check the voltage at the starter solinoid. 12.75v full battery voltage. Move to the 40amp push breaker 12.75v. Go to the two leads at the electric choke and get 9.7v. Now that is where I got hung up. There is something drawing the power before it gets to the choke. Here is where it get a little odd and maybe someone could help with this side. Crawl under the dash and start testing away. So from the fuse holder, 11.6v move to the amp meter as I notice a few power wires over there and test from fuse holder ground to positive post of amp meter and get 11.7v and on the negative side of the meter I get 11.6v. I’m assuming that is ok. Next move to the ignition switch and 10.8v. I will attach some photos of the wiring. Maybe something looks off. During my investigating, I unwrapped a pink or what should be red wire that was spliced into the charge wire coming from the alternator going to the harness plug. This was how I received it from the previous owner,,, but have to assume it would have a home just not sure where. there is a photo of the wire in here too. I also found that wire to be hot but it touching the manifold and getting a spark. when testing from ground to the mystery wire i get 12.75 battery voltage.
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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Could that pink "should have been red" wire be an orange wire?
Since you have an ammeter, the wiring diagram from TRBenj for a mid 80's PCM 351 doesn't quite work for you since it's for a boat with a voltmeter. That wire would normally go to the output side of the main breaker for battery charging (backwards through the breaker to the solenoid to the battery) but since you have an ammeter that wire isn't hooked up and the orange wire goes to the ammeter and then a short red wire to the ignition switch (or might be spliced into the red wire on the ignition switch) and that red wire goes back to the main breaker output for battery charging. (it's a long and winding road to charge the battery with an ammeter setup) So short version, tape the end of that wire so it can't short out on anything. Your drop of 11.7 volts on the ammeter outlet to 10.8 at the ignition switch seems excessive for a short piece of 10 gauge wire Also I hope that's black paint and not charred insulation on the wires on the back of the ammeter. Have you unplugged the 8 wire connector at the back of the engine. They can tend to build up corrosion and cause voltage drop in the wires both to and from the dash like your purple wire from the key to the ballast resistor for example If it's real bad the contacts might fall apart as you pull the connector apart. It can be scary pulling that connector apart The spade connectors on the wires to and from the ballast resistor don't look original, are you sure you have good connections there ? |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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Did you ever check the points or electronic module, rotor, cap,condenser?
Your problem could be there since the boat was running with the voltages you measured right up till it quit. |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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John, Do you have an EI module in the distributor? If so, try disconnecting it and then see what happens with the volts. Also, try disconnecting the electric choke and do the same. |
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Skier85
Newbie Joined: January-09-2017 Location: Phoenix, AZ Status: Offline Points: 14 |
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So the engine, does have some points in the despributor. And I had cleaned and checked the gap on the points. When I first cleaned them they were a bit dusty, but didn’t see any burn or arc makes on them so they visually seem to check out. Now I did put a newer coil and ballast resistor, and a condenser inside the distributor. And that’s when she came to life. As to plug at the back of the engine, I did have it disconnected and doesn’t appear to be to corrode. But nothing can ever be too clean! As for the orange wire. I belive you are correct about it being orange rather than red.
It is it is spliced off the orange wire off the charge post of the altenator. Now there is a purple wire coming from the 8 pin plug going to a splice of green wire to the regulator and red wire which goes to the electric choke. I’m getting some signal out of the ammeter. But as you can see the brass is not as shinny as it once was.. I is possible that that could cause a the drop. I will see if I can pull them off and see if I can clean and check to see if it makes a difference! Could a bad altenator cause it drop like that? |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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Hi John
I went out a got some numbers from a good running points equipped PCM this morning. The results might surprise ya Engine off battery volts 12.7 you had 12.75 Upstream connection to ballast resistor 9.0 you had 9'7 Downstream side of ballast resistor 4.9 you had 5.0 Coil positive terminal 4.5 you had 4.25 You're probably wondering why I had essentially the same numbers and the boat runs fine. It's because these voltages were taken with the points closed which is grounding the coil With the points open I had 10.5 at both connections on the ballast resistor and 10'5 at the coil positive too since the coil is not grounded and is not doing any work. So to me you have some normal voltages in the points closed condition and if you check with the points open or take the positive wire off the coil and check voltage you'll have better numbers like I did. With the engine OFF there's a lot better chance of the points being closed than open. I'd pull the points out for a good lookover/cleaning and maybe even replacement. Gap them at about .018 inches or if you have a dwell meter set the dwell to about 30 degrees and see how things are. I have an untaped wiring harness on the workbench to look at and your two questionable splices are normal. Both the orange wires as mentioned previously and the other one with purple(power from the key) red (power to the choke) and green(excitation to the alternator) is how it was built. If you're not too familiar with points setups, you can find plenty of info with a CCF search or a google search. So, in the end, your boat should start with the voltages you've found if the ignition components are good |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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And again KENO comes to the rescue. He performs an autopsy on a perfectly good motor.. Thanks Ken.
Your a true asset to CCF |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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Aw shucks Duane It was pretty easy to check and give him some numbers and besides I got to look at the points, rotor and cap. The coil being grounded or ungrounded by the points in his case makes quite a difference in voltage readings Besides, if Pete was to have tried this, he'd pop the distributor cap on the Tique and find that electronic conversion that it took him 11 years to discover he had |
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Skier85
Newbie Joined: January-09-2017 Location: Phoenix, AZ Status: Offline Points: 14 |
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Well said Duane. KENO this isn't the first time I have seen you coming in with all the invaluable data. Thank you for the info it is a huge help. Im hoping to look for the points and distributor a little closer. I must have over looked some key details. I will report back with findings!
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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Hi John
One thing I should mention is that you can bypass the ballast resistor and see if it starts as a quick test to see if it's a voltage issue. That will put your supply voltage to the resistor right to the coil. If you run it for an extended time that way, you'll eat up your coil and/or a set of points but for a quick test you'll be fine. I've driven one that way for a couple of hours with no issues but don't know how long would be too long It's probably very dependent on the coil you have. And another thing............about the time you're convinced it's electrical maybe it'll turn out to be fuel related. |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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I figured out that I was wrong about Pete taking 11 years based on the comment below from 2009 post I stumbled across
He knew it had an electronic conversion all that time but was afraid to look under the cap. Maybe after 11 years he got brave or thought it might have an issue.and had to look Good maintenance practices Pete |
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Gary S
Grand Poobah Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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But 11 great white north years divided by 3 boats = 1 Florida year
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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Can always count on you Gary
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Skier85
Newbie Joined: January-09-2017 Location: Phoenix, AZ Status: Offline Points: 14 |
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KENO you are truly might be the troubleshooting guru! So looking at the points check out to be fine... I did find that my original distributor did eat a advance spring as you can see. so off to go hunting for new springs but. More to KENO troubleshooting skills, I pull the spark arrestor off the carb after a few cranks only to find the primary boosters pouring fuel into the engine with the engine still. looks like its time for a rebuild. I have to imagine over fueled engines don't like to start well. |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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KENO you are truly might be the troubleshooting guru! I pull the spark arrestor off the carb after a few cranks only to find the primary boosters pouring fuel into the engine with the engine still. looks like its time for a rebuild. I have to imagine over fueled engines don't like to start well./QUOTE] The guy's good. Plus he will take his stuff apart to prove it!! |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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We'll just call it experience You have to give yourself some of the credit, you looked and found the fuel issue after it was mentioned. Your distributor springs were discontinued long ago and are next to impossible to find. Your distributor is a Prestolite with the clip down cap. The big spring in your picture appears to be a little rusty but otherwise good. The funny loop on the end and the slack is how it's built. The small missing one is what usually breaks like yours did. It's a much lighter spring that's always under tension and controls your advance rate up to around 3500 to 4000 rpm when the big spring comes into play. There are spring kits for other brands that really don't have anything close to right. I found a homegrown "backyard hack" solution for the light spring that works well. I'll take some pictures and post them later today with a write up to go with it. |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11093 |
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Hi John
A while back I found a spring that works pretty well to replace your broken small spring. Most hardware stores should have it. It's a Hillman #119 spring. See the picture below. It's a little different than the original but definitely better than a twisted stretched old one, or in your case none at all In the same clip down distributor that you have it gave a pretty decent advance curve.when used in conjunction with your original big heavy spring. It won't break the bank, it cost about a dollar, so it's worth a try. Buy a few in case you mess up a spring or two.. They're a general purpose spring so I figure the quality control isn't the highest because you can find them with the loops on each end parallel to each other or at around 90 degrees to each other. Get the ones that are parallel, you may have to weed through a bunch but it'll make life easier than having to put a little twist into it to make them parallel. Some may call it a hack job, but it works and will keep your timing the way it should be. |
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peglegtoo
Newbie Joined: July-09-2018 Location: Mass Status: Offline Points: 16 |
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this post should be in the faq. thanks ken
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