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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10979
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have an apparent intermittent spark issue with my -91 Johnson 70 hp VRO (BJ70TLEIE).

Customer Question

Hi. I have an apparent intermittent spark issue with my -91 Johnson 70 hp VRO (BJ70TLEIE). Normally, the motor starts up with all cylinders firing. I take it to plane and shortly after that the motor loses power and drops from plane. It runs, but not enough power to plane. After a while it wakes up and works normally. The change in motor's operation happens always quickly, without warning.
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.
Hello. My name is***** is usually a coil or power pack issue. To find the problem we have to determine which cylinder is misfiring. This will require the use of a timing light and a friend to drive the boat. This test has to be done when the engine is acting up.Is this a test you can perform?
Customer: replied 2 years ago.
Hi Tan, I'm Timo. Thanks for quick reply. I've already tested this and it's the middle one not getting spark.
Expert:  Tan replied 2 years ago.
Hi Timo. Have you swapped that coil with another good firing coil?
Customer: replied 2 years ago.
Although obvious thing to do, alas that I haven't done... Since it's 10.30 pm here, I'll try that tomorrow. I just have to hope the motor will be acting up. Thanks so far, Tan
Expert:  Tan replied 2 years ago.
Ok great. If the misfire moves the coil is bad. If it stays then we have a bad power pack or a bad timer base. Most likely the power pack. We can test the timer base but only when it is acting up and you have to have a peak reading volt meter to do this test. The power pack is still available(###) ###-#### Timer base(###) ###-####. back with findings.
Customer: replied 2 years ago.
Hi, Tan. Sorry for long silence. I haven't been able to do any troubleshooting yet. If it doesn't rain today I'll test the coils.
Expert:  Tan replied 2 years ago.
Ok that's fine. Keep me posted.

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