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DarkMantle

Merc 8.1 tach not reading

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I took the boat out for a short run today. First for the season just to check it over, and low and behold the rpm reads zero. The engine is running fine. Any clues as where to look first?  Being EFI and no distributor I'm assuming this comes right off the ECM. Wondering if this is wiring off the guage. Also my trim only works in the up direction in the trailer switch position. Down is normal and fine.  The soft touch just stopped working. So I have a couple electrical gremlins. Wonder if they are related somewhere in the ground circuit. 

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Your tach should have a rotary switch on the back that changes it from 4 to six and 8 cylinders. With a screwdriver carefully move it around to all three positions several times. Then return it back to original position. This cleans the contacts and may fix your tach problem. Worked for me. 

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sometimes my tach goes a little haywire---reads low or high or jumps around.  If I simply tap my finger on the tack it goes to normal

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16 hours ago, MonkeySeaII said:

sometimes my tach goes a little haywire---reads low or high or jumps around.  If I simply tap my finger on the tack it goes to normal

Ahhh. The US Navy meter calibration program. Was on one ship and 50% of the gauges had cracked glass from that method. :slap:

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On 08/05/2018 at 11:03 PM, CKSNAP said:

Your tach should have a rotary switch on the back that changes it from 4 to six and 8 cylinders. With a screwdriver carefully move it around to all three positions several times. Then return it back to original position. This cleans the contacts and may fix your tach problem. Worked for me. 

Thanks everyone. CK that was the trick. Saved me a lot of grief. Probably would have been chasing my tail. 

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3 hours ago, Pops said:

Ahhh. The US Navy meter calibration program. Was on one ship and 50% of the gauges had cracked glass from that method. :slap:

LOL.  Sometimes it works on your kid's head too!!:)

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On 5/8/2018 at 8:30 PM, DarkMantle said:

I took the boat out for a short run today. First for the season just to check it over, and low and behold the rpm reads zero. The engine is running fine. Any clues as where to look first?  Being EFI and no distributor I'm assuming this comes right off the ECM. Wondering if this is wiring off the guage. Also my trim only works in the up direction in the trailer switch position. Down is normal and fine.  The soft touch just stopped working. So I have a couple electrical gremlins. Wonder if they are related somewhere in the ground circuit. 

Trim limit side of the trim sender is pooched - that's why you're forced to use trailer position double detent on the shifter to raise the drive. Will require a new trim limit/sender kit to be installed on the gimbal ring - requires the boat to be out of the water for this, but the drive can stay on. Seeing you have a 496 Mag with the SmartCraft style trim sender, Mercury part # 8M0107462 is the latest part number. Part # 25 in the part schematic below.

 

NOTE: recommend placing your drive in the Bravo 1 position to allow for faster hole shot and less bow rise when getting on plane. When the 'celery' stick for the rear power trim anchor pin is repositioned to the Bravo 1 position from the Bravo 3 position, the trim sender needs to be recalibrated to allow the trim sender gauge to be accurate. Doing both at the same time makes a lot of sense to me. You're boat won't give you adverse handling by going to Bravo 1 position. Some boat makes and models don't react well to the Bravo 1 position - thankfully your boat isn't among them.

Recommend pulling the drive anyway if it hasn't been off in a couple of years to grease the splines, check condition of bellows, gear oil reservoir hose, rear shift cable, engine alignment, etc. With the drive off, it makes it a little easier to route and install the new trim sender/limit wires up through the gimbal housing. Use Mercury Xtreme grease to lube the drive yoke splines, etc.

Hope this helps.

Chris

21193.GIF

 

Image result for bravo 1 position chaparral

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4 minutes ago, Shepherd1 said:

Trim limit side of the trim sender is pooched - that's why you're forced to use trailer position double detent on the shifter to raise the drive. Will require a new trim limit/sender kit to be installed on the gimbal ring - requires the boat to be out of the water for this, but the drive can stay on. Seeing you have a 496 Mag with the SmartCraft style trim sender, Mercury part # 8M0107462 is the latest part number. Part # 25 in the part schematic below.

 

NOTE: recommend placing your drive in the Bravo 1 position to allow for faster hole shot and less bow rise when getting on plane. When the 'celery' stick for the rear power trim anchor pin is repositioned to the Bravo 1 position from the Bravo 3 position, the trim sender needs to be recalibrated to allow the trim sender gauge to be accurate. Doing both at the same time makes a lot of sense to me. You're boat won't give you adverse handling by going to Bravo 1 position. Some boat makes and models don't react well to the Bravo 1 position - thankfully your boat isn't among them.

Recommend pulling the drive anyway if it hasn't been off in a couple of years to grease the splines, check condition of bellows, gear oil reservoir hose, rear shift cable, engine alignment, etc. With the drive off, it makes it a little easier to route and install the new trim sender/limit wires up through the gimbal housing. Use Mercury Xtreme grease to lube the drive yoke splines, etc.

Hope this helps.

Chris

21193.GIF

 

Image result for bravo 1 position chaparral

That's great information thanks. So it is possible to change the switch, drive on?  I have to pull the drive to change the upper steering pin because it's leaking, but that's a winter job. Had the drive off last fall for new bellows and shift cable, and new gimbal bearing. 

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On 5/11/2018 at 7:26 AM, DarkMantle said:

That's great information thanks. So it is possible to change the switch, drive on?  I have to pull the drive to change the upper steering pin because it's leaking, but that's a winter job. Had the drive off last fall for new bellows and shift cable, and new gimbal bearing. 

I'd just replace the trim sender this winter when you have the square/square shaft seal replaced. If the gimbal ring is loose, highly recommend replacing at that time the gimbal ring, square/square shaft, and tiller arm as well. 

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