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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3863
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Jeff I am dealing with a 300xs that stopped running while idling

Customer Question

jeff I am dealing with a 300xs that stopped running while idling in gear. engine turns over but doesn't start. No power to the bottom 2 20a fuses, and no burnt fuses.
Submitted: 2 years ago.
Category: Boat
Customer: replied 2 years ago.
What I have done so far: Verified ign switch is ok at switch, lanyard switch tests ok, battery is 950cca and is fully charged.
I swapped main power relay with known working trim relay and no difference. do you have a pin out on the main power relay and a pin out at the engine 14 pin connector? I have a conversion harness from 14 pin to the old 8 pin but do not know what the breakout is on either end.
Expert:  Charles replied 2 years ago.
Hello, my name is***** will be assisting you today. Would you please post the serial number of the engine?
Customer: replied 2 years ago.
1E002675
Expert:  Charles replied 2 years ago.
Do you hear a warning beep when you turn the key to ON?Do you hear the fuel pumps run when you turn the key on?Have you checked for spark?
Customer: replied 2 years ago.
Yes 1 beep. Fuel pumps do turn on. I have not checked for spark. No power to the coil fuse so assumed no spark.
Expert:  Charles replied 2 years ago.
Are you near the engine now?If so, there are pat numbers embossed on the coils. Could you please post the numbers from one of the coils?
Customer: replied 2 years ago.
2066 879984
Expert:  Charles replied 2 years ago.
Ok, Do you have a mulltimeter? There is a bulletin on this coil.
Customer: replied 2 years ago.
I will tomorrow morning. Tell me what to test and I'll do it first thing.
Expert:  Charles replied 2 years ago.
This bulletin here will walk you through the test, and what the results mean. Tomorrow I have to be at the shop for a bit and will not log on unitl after 2PM CST. http://www.marinepartsexpress.com/Merc_Prod_Bull/PCM%20Failures%20Due%20to%20Failed%20Ignition%20Coil%20Bulletin%20No.%202007-25R2.pdf
Customer: replied 2 years ago.
Ok no problem. Will low fuel pressure cause the no power to coil fuse thing? I don't see a fp sensor anywhere. I'll test fp and ap in the am as well.
Expert:  Charles replied 2 years ago.
There is not a sensor for fuel or air pressure on the engine. Just temp of intake air, water temp, Baro/MAP, engine temp, TPS, CPS, air comp temp, shift switch, water in the fuel, The fuel pressure does not control the coils in no way.
Customer: replied 2 years ago.
Ok ill test in the am. If the coils or pcm are shot I assume I'm in for a big bill? It has 39 hrs on it is the worst part. Oh well hope for the best.
Expert:  Charles replied 2 years ago.
Yeah that would be a large bill. The PCM is around $1900, plus just over $100 for each coil.
Customer: replied 2 years ago.
Ok Charles, I had a chance to do the tests on the PCM and all the coil packs. Everything was ok, within specs. Resistance at PCM was .5 ohm. A relief in a sense but back to square one. I wont be back here until sometime this afternoon, so let me know the next step.
Question: What are the wires at the main power relay? solid red 12v+, red w white stripe? red w purple stripe? and yellow w purple stripe? trying to figure out what activates this relay.
Customer: replied 2 years ago.
I also understand coils are weird and there may be an intermittent fault once they're hot etc. Is there an upgraded newer coil that does not potentially fry the pcm?
Expert:  Charles replied 2 years ago.
Red.white and the red.purple are the activation side. Yellow/red is for the start circuit
Customer: replied 2 years ago.
Thi sis what I have: Red has 12v all the time, red/blue has 12v all the time, red white has nothing yellow purple has nothing. this is with the ign key on or off, doesn't matter. From what you say, the yellow/purple should switch on with ignition switch and the red/white sends power to? Do you have a schematic?
Expert:  Charles replied 2 years ago.
I do not have that wiring diagram here at the house. It is at the shop. Have you already swapped the main power relay with one of the trim relays?
Customer: replied 2 years ago.
Yes I did.
Expert:  Charles replied 2 years ago.
Everything was still the same?
Customer: replied 2 years ago.
Yes no change.
Expert:  Charles replied 2 years ago.
How are the wires attached to the back of the key switch?
Customer: replied 2 years ago.
Switch is connected to harness by bullet plugs. Switch itself is sealed. I checked the switch, it checked ok.
Expert:  Charles replied 2 years ago.
Unplug the bullets fr the red, purple and the yellow/red. Touch all together, will the engine crank them?
Customer: replied 2 years ago.
I don't see my reply. Did it, it continues to crank without starting. Did the yellow red momentarily as that's the starter activation wire.
Expert:  Charles replied 2 years ago.
Locate the yellow/red wires coming from the control box. remove them from the circuit. Hook the yellow/red from the key switch directly to the yellow/red coming from the engine harness, does the spark return?
Customer: replied 2 years ago.
I just saw this Charles. I did the test of the neutral safety switch, engine still cranks as before. To be clear, the engine cranks but does not start.
Expert:  Charles replied 2 years ago.
Do a resistance test on the crank position sensor. Let me know what you get on it.
Customer: replied 2 years ago.
Infinite. It's the sensor below the flywheel?
Expert:  Charles replied 2 years ago.
Yes, red and white wires to a two wire plug. move it around as you test the resistance.
Customer: replied 2 years ago.
No change, no short to ground either. I moved connector wire and flywheel by hand, still infinite resistance.
Expert:  Charles replied 2 years ago.
Ok, I got stuck on the coils, but there is the problem. the CPS is bad. It should read 330 Ohms.
Customer: replied 2 years ago.
That will cause there to be no power to the fuses?
Customer: replied 2 years ago.
While I have you, should I update/upgrade my ignition coils?
Expert:  Charles replied 2 years ago.
this will not cause the loss of power to the coils, but is will cause a no spark. When you test for power to the fuses, is it with-in the first 5 seconds that you have the key on?
Customer: replied 2 years ago.
You're right. I was missing the first 5 second part. Alot of extra work, but I relearned something I knew. Basics first...
Do you have a part no for the cps? Input on the coils?
Expert:  Charles replied 2 years ago.
828358 2 is the part number. for the coils, since you are running good, right now, I would buy them one at a time and when you get all 6, replace them.
Customer: replied 2 years ago.
I have ordered the CPS and will replace it, hopefully that will solve this. Can you access TSB# ***** to see if it addresses replacing the coils? A long shot but I'm concerned leaving the old ones on and hurting the PCM.
Expert:  Charles replied 2 years ago.
Your 300XS is not listed on the bulletin, but here it is.
http://www.marinepartsexpress.com/Merc_Prod_Bull/40%2050%2060%20EFI%20FourStroke%20and%20OptiMax%20Ignition%20Coil%20Service%20Repair%20Bulletin%20No.%202009-26.pdf

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