Tach and Oil Pressure Flucuates 500 efi
09-25-2008, 08:37 PM
#11
Registered
Thread Starter
I have had the same problem for the last 3 yrs. I changed plug wires, cleaned wires on the back of the gauges, checked grounds and still no change but no worse either. Strange thing is after I run for a while and shut down the motors when I re-start they jump more for a few minutes and then settle down to normal range until I push over 3800 rpm's and the bounce is more prevalent.
I was trying to avoid replacing the tachs because they are gaffrig and I did not want to have a mis-match with Livorsi tachs. Just a little annual.... but I think most of us are with our boats.
I was trying to avoid replacing the tachs because they are gaffrig and I did not want to have a mis-match with Livorsi tachs. Just a little annual.... but I think most of us are with our boats.
I might add that this started after I put the engines back in after having them out.
07-04-2010, 11:15 AM
#12
Registered
Cure for fluctuating tach problem
I had the fluctuating tech problem on my Formula 353 w/ twin HP500 EFI's. Went through all the troubleshooting stuff discussed here: swapped tachs, plug wires, checked grounds till sunrise, etc.. No joy until...
Turned out the problem was the ground connection between the distributor base and the block. The issue was caused by the paint job on the block which insulates it from the distributor base. The easy cure, suggested by to me by someone at Mercury Racing, is a jumper wire between the distributor cap hold-down screw and and engine-block ground. Worked like a charm. Its dead simple hook up a temporary jumper to validate that it solves the problem for you.
This may also cure other guages jumping around as revs increase through the 2000-3500 rpm range.
Note that the engine will operate flawlessly without the distributor-base grounded to the block. This grounding apparently serves to ground out electrical noise from the ignition appearing on the tach signal wire.
Turned out the problem was the ground connection between the distributor base and the block. The issue was caused by the paint job on the block which insulates it from the distributor base. The easy cure, suggested by to me by someone at Mercury Racing, is a jumper wire between the distributor cap hold-down screw and and engine-block ground. Worked like a charm. Its dead simple hook up a temporary jumper to validate that it solves the problem for you.
This may also cure other guages jumping around as revs increase through the 2000-3500 rpm range.
Note that the engine will operate flawlessly without the distributor-base grounded to the block. This grounding apparently serves to ground out electrical noise from the ignition appearing on the tach signal wire.
07-05-2010, 07:44 PM
#13
Registered
Thread Starter
I had the fluctuating tech problem on my Formula 353 w/ twin HP500 EFI's. Went through all the troubleshooting stuff discussed here: swapped tachs, plug wires, checked grounds till sunrise, etc.. No joy until...
Turned out the problem was the ground connection between the distributor base and the block. The issue was caused by the paint job on the block which insulates it from the distributor base. The easy cure, suggested by to me by someone at Mercury Racing, is a jumper wire between the distributor cap hold-down screw and and engine-block ground. Worked like a charm. Its dead simple hook up a temporary jumper to validate that it solves the problem for you.
This may also cure other guages jumping around as revs increase through the 2000-3500 rpm range.
Note that the engine will operate flawlessly without the distributor-base grounded to the block. This grounding apparently serves to ground out electrical noise from the ignition appearing on the tach signal wire.
Turned out the problem was the ground connection between the distributor base and the block. The issue was caused by the paint job on the block which insulates it from the distributor base. The easy cure, suggested by to me by someone at Mercury Racing, is a jumper wire between the distributor cap hold-down screw and and engine-block ground. Worked like a charm. Its dead simple hook up a temporary jumper to validate that it solves the problem for you.
This may also cure other guages jumping around as revs increase through the 2000-3500 rpm range.
Note that the engine will operate flawlessly without the distributor-base grounded to the block. This grounding apparently serves to ground out electrical noise from the ignition appearing on the tach signal wire.
You don't know how much I appreciate this info.
07-05-2010, 07:52 PM
#14
JB Marshall
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Thanks very much. I've trying to solve this problem for more than 3 years with no luck. I got this repsonse while I was at the lake yesterday. I had to go into town and I picked up a couple clips to test to see itf it would work. Took the boat out and the tach never jumped once. Ran it all day today and it never jumped once today either. I will wire it up permently now that I know it works.
You don't know how much I appreciate this info.
You don't know how much I appreciate this info.
+1
Thanks
06-19-2012, 01:56 PM
#16
Offshoreonly Advertiser
Offshoreonly Advertiser
Wybmauty hit the problem right on the head. This is 90% of the problems and are caused by painting parts on the engine.
Cure for fluctuating tach problem
--------------------------------------------------------------------------------
I had the fluctuating tech problem on my Formula 353 w/ twin HP500 EFI's. Went through all the troubleshooting stuff discussed here: swapped tachs, plug wires, checked grounds till sunrise, etc.. No joy until...
Turned out the problem was the ground connection between the distributor base and the block. The issue was caused by the paint job on the block which insulates it from the distributor base. The easy cure, suggested by to me by someone at Mercury Racing, is a jumper wire between the distributor cap hold-down screw and and engine-block ground. Worked like a charm. Its dead simple hook up a temporary jumper to validate that it solves the problem for you.
This may also cure other guages jumping around as revs increase through the 2000-3500 rpm range.
Note that the engine will operate flawlessly without the distributor-base grounded to the block. This grounding apparently serves to ground out electrical noise from the ignition appearing on the tach signal wire.
Cure for fluctuating tach problem
--------------------------------------------------------------------------------
I had the fluctuating tech problem on my Formula 353 w/ twin HP500 EFI's. Went through all the troubleshooting stuff discussed here: swapped tachs, plug wires, checked grounds till sunrise, etc.. No joy until...
Turned out the problem was the ground connection between the distributor base and the block. The issue was caused by the paint job on the block which insulates it from the distributor base. The easy cure, suggested by to me by someone at Mercury Racing, is a jumper wire between the distributor cap hold-down screw and and engine-block ground. Worked like a charm. Its dead simple hook up a temporary jumper to validate that it solves the problem for you.
This may also cure other guages jumping around as revs increase through the 2000-3500 rpm range.
Note that the engine will operate flawlessly without the distributor-base grounded to the block. This grounding apparently serves to ground out electrical noise from the ignition appearing on the tach signal wire.
06-19-2012, 02:26 PM
#17
Registered
Thread Starter
Since this came up I will let you know that it did fix my problem temporarily however it was not long after I had the distributor fail. So I think in my case it was just a distributor going out. Because once I replaced the distributor I did not need the ground wire anymore.
