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When to change Distributor Cap and Rotor on Malibu Inboard


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My 21 year old Malibu Response LX got a new engine this spring after the infamous 'Texas Valentines Week Freeze' incident cracked the block and exhaust manifolds. I  noticed a lot of 'Sag' or 'Hesitation' on ski starts with the newly repaired boat. (The mechanic re-used all the engine accessories including the Starter, Alternator, Distributor, EFI, etc.). In the past, hesitation and/or poor top-end was fixed by changing the two fuel filters. In this case, new filters did not help. Next step was to check the timing. The mechanic set the timing to 0BTDC. My EFI system needs a jumper from pins A to B on the Engine Diagnostic Port (Fig 1) to put the engine into 'dumb' timing mode. Changing to 10BTDC improved power slightly. The mechanic recommended changing the Distributor Cap and Rotors.

Inspection of the 21 year old (540 engine hours) Distributor Cap Aluminum points showed extreme Oxide deposits. (Fig 2)

Cleaning/burnishing the flat contact surface with a Dremel Wirebrush fixed the problem (Fig 3)! But, the cleaned surfaces were worn and pitted and I considered this a temporary fix.

I replaced the Cap with a new Brass-Contact Marine grade Delco compatible Cap/Rotor and am back in business! (Fig 4)

When to replace: At least ever 10 years or when you have rough idle or hesitation not fixed by Fuel and/or timing fixes. I read somewhere that Brass Contacts are more durable than the Aluminum ones.

Fig 1: Engine Diagnostic Port with paper clip in Pin A (Cap removed)

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Fig 2: 21 year old, 540 engine hour, Aluminum Distributer Contact on Delco EST Distributor

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Fig 3: Same old contact after wirebrushing with Dremel tool.

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Fig 4: New Marine-grade Delco Distributor Cap brass contact

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Nice job, and great photos.  Welcome to the crew!

If you have original plug wires, it is past time to change them as well.

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16 hours ago, justgary said:

If you have original plug wires, it is past time to change them as well.

Yup! The plugs and wires were changed 2 years ago.

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7 minutes ago, raming said:

Yup! The plugs and wires were changed 2 years ago.

Fantastic.

Did you happen to change your fuel and exhaust hoses while you had the engine out?  It would have been a great time to freshen up all of that rubber.

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7 hours ago, justgary said:

Did you happen to change your fuel and exhaust hoses while you had the engine out?  It would have been a great time to freshen up all of that rubber.

Exhaust Hoses lasted about 18 years. One actually split open after a overheating event. The replacement hoses are the higher grade Silicon Rubber reinforced kind. The fuel lines were inspected and the rubber is still flexible.

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