Jumpy Tach

[Cool It]

My tach seems to move up nice until it gets to just over 3200 - then it gets very jumpy. It jumps up to 5000 or so until I push the throttle almost about wide open then it comes down to about 3800-4000 . which is to low for wot . It cruises nice at 3200 but after that I have this problem . I have tried changing prop pitch from 17 to 19 but really has not helped -still have the 19 on. any other reasons for all of this???-- 1988 5.0 mercruiser alpha 1 305 Cu 200 hp --22 foot renkin seamaster W/A <br /><br />Thanks<br />Cool It

 

[RatFish]

Re: Jumpy Tach

Get yourself a diagnostic tach to make sure your in dash tach is giving you good readings. You can pick one up at your local auto parts store.

 

[Cool It]

Re: Jumpy Tach

are the diagnostic tachs expensive/ and how do I attach it-- Would I be better off trying a new tach if that is not the problem I can always return it -- or is the diagnostic tach easier to use than installing a new tach<br /><br />thanks<br />Cool It

 

[cobra 3.0]

Re: Jumpy Tach

Wallmart has very inexpensive auto tachs. Instructions are provided with the tach.

 

[Cool It]

Re: Jumpy Tach

I did not see one at walmart or the auto parts store-- what do you consider inexpensive?? I priced tachs at the marine supply about 120.00 <br />Maybe I should check all my wire connections first --maybe there is a problem there. <br /><br />Does a tach just get old and jumpy??<br /><br />Cool It

 

[tommays]

Re: Jumpy Tach

if your going to due you own repiars the money you spend on a shop tack and multimeter are worth about 1 hour labor at a long island boat dealer mines up to 105 dollars and hour at this point make me wish i still had my sail boat sometimes<br /><br />tommays

 

[RatFish]

Re: Jumpy Tach

Cool It,<br /><br />Yes, check your connections and wiring first. Here is an example of a diagnostic tach at sears. It costs $50. It's simple to hook up, directions are in the box. Again, any decent auto parts store will carry something like this. If you do decide to buy one, make sure it covers the full anticipated RPM range.

 

[hoot]

Re: Jumpy Tach

do a through check of the igniton system, especially the coil. the tach reads off of the -post. loose nut maybe.

 

[Cool It]

Re: Jumpy Tach

I do see that the wire from the coil looks like it is worn and even has a slight crack near the connection - rest of wire looks ok -I wiil try to cut and add new connector. but I dont understand how this could be the problem if the tach runs up fine to 3200 and then gets jumpy after that. <br /><br />Thanks<br />Cool It<br /><br />Thanks <br />Cool It

 

[Cool It]

Re: Jumpy Tach

It seems to me that it would be jumpy all the time if there was a wiring problem, but Im no mechanic so please enlighten me<br /><br />Thanks

 

[marunr]

Re: Jumpy Tach

Mine was jumpy just after 3000 rpm and it was a bad connection on the - post as hoot said. Threads were bad which prevented tightening.

 

[RatFish]

Re: Jumpy Tach

Cool It,<br /><br />Vibration, no matter how minor, at various RPMs could be causing an intermittent contact problem somewhere in the wiring circuit. <br /><br />Check the wiring where possible, from the tach back to the engine. Make sure there is no corrosion and all connections are tight. Look for wire insulation that is cracked or missing. If the wire passes through a wiring harness, unplug it, look for corrosion, clean if necessary, plug back together. Also, check your fuse box, remove each fuse, check for corrosion, clean if necessary then put it back in. <br /><br />These are the first (and cheapest) steps I would take.

 

[Cool It]

Re: Jumpy Tach

I did not know that I had a fuse box - the only fuses I see are on the panel for the ignition,blowers and four accessory switches. are there fuse anywhere else is there a fuse for the tach?<br /><br />If I cut the wire at the connection to the coil I dont have much to play with - if I screw up putting a new connector on that will leave me short to make it to the coil -- if this happens can I add wire with a striaght connector??<br /><br />Thanks<br />Cool It

 

[Cool It]

Re: Jumpy Tach

well before I cut this wire I still need to know if I can add to it if I need to or will this ruin the wire???

 

[RatFish]

Re: Jumpy Tach

Wait a minute. Why are you going to replace the connector? Is it corroded? Strands of wire broke going into the connector? Did you trace this wire back to your tach? You should get a manual showing the wiring diagram of the tach circuit so you know you have the correct wires. If everything passes a visual inspection, I would tighten and unplug/re-plug all connections in the circuit.

 

[Cool It]

Re: Jumpy Tach

I know it is the right wire because I diconnected it and my tach stopped working. the reason to change the connecter is just before it there seems to be a small crack in the wire. I dont know if this is the problem but seems to me I should fix it.

 

[RatFish]

Re: Jumpy Tach

Assuming everything visually checks out, give it a shot. If the crack in the insulation is right at the old connector, cut the wire there or a little above it, you should be ok. You only need about 1/8" bare wire for the new connector. When you remove the old connector look for corrosion in the connector and wire. I have also seen wires arch to ground from cracks in insulation. A splice would be ok if you screw up. Make sure you use the same type and gauge wire.<br /><br />EDIT: Check out this link.

 

[cg2er410]

Re: Jumpy Tach

I have the same problem all of a sudden. I installed a new tach 2 years ago and it worked fine until I installed a compass on my dash. Unfortunately with my style of windshield, I was not able to move the compass as far away as I would have liked. I did check for problem with the compass and gauges before I mounted it. I have also removed the compass from the base (it still has the brass adjusting rods in the base) and it may do it. Oh yeah, the problem is intermittent. I checked the wiring at the coil and all is good. I did notice a problem when i try to push the coil wire down, the magstar wires i use have a tight nipple fit and i had to slide it up to get it out of the way to get the connector to seat (i also used dielectric grease on the fitting) and then once i had the connection, i slid down the nipple. seems so airtight it wont seat like it does in the dist cap or the plugs. I did just recently change the plugs, points and condenser and it was after this that I noticed the jumpiness of the tach. when i turn the key on it does not always reset to zero now either. any advice?

 

[Cool It]

Re: Jumpy Tach

hey I just relized with you saying it does not reset to zero -- mine does not come down to zero when I shut the engine off it sits about 1100 --once I start it comes to idle about 600.<br /><br />Cool It

 

[Cool It]

Re: Jumpy Tach

Any help with this last reply about not reseting to zero-- is the tach just shot???<br /><br />Thanks<br />Cool It