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Distributor cap

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crc

New member
Hello,
I just purchased a 2003 boat with a merc. 350 mag mpi motor. The previous owner put a non-marine distributor cap on and according to him from that point forward the tachometer stopped working.
I am going to replace the cap and button with the marine version. After looking at the cap, there is a connection, on the port side toward the stern of the distributor, that is vacant. I haven't been able to find any loose or hanging wires that may connect to it. Can anyone tell me if I should have wire connected there and if it is for the tachometer?
Thanks
 
If he put non-marine ignition components on the boat, you should treat everything else he says in the proper perspective.

The connection on the distributor is for its module and isn't used per the shop manual.

The cap and the tach are independent items...your tach drive comes straight from your ECU...you can pull the tach and get it tested or maybe borrow one for debugging purposes.
 
crc said:
Hello,
I just purchased a 2003 boat with a merc. 350 mag mpi motor. The previous owner put a non-marine distributor cap on and according to him from that point forward the tachometer stopped working.
I am going to replace the cap and button with the marine version. After looking at the cap, there is a connection, on the port side toward the stern of the distributor, that is vacant. I haven't been able to find any loose or hanging wires that may connect to it. Can anyone tell me if I should have wire connected there and if it is for the tachometer?
Thanks
Click to expand...

Ayuh,.... Yer motor has the T-Bolt V distributor don't it,..??

How can ya put a Non-marine cap on it, if it ain't never used used, other than on a boat motor,..??
The cap has gotta fit the body,..?? the rotor has to fit the shaft, 'n Merc glues their's on...

Got a Picture of whatever it is ya got,..??

I'm confused here...
 
Trying to figure out how to post the pics /i do have. It is the cap with a flat top and plug wires come in each side. The cap is held on by two screws. By non-marine I am told the main difference (and probably the only difference) are the contacts are not brass.
 
Check that the connections are good to the tach, while you are laying on your back under the dash cycle the tach switch back and forth a few times and set it for 8.
 
I'll take a stab here and suggest that the new cap may be this Merc style.... yes/no?



If the engine runs well, then the cap must be distributing the spark correctly.

This should (in theory) have no bearing on the tachometer function.

Did the PO make any other changes to the TB ingition system?


.
 
To post the pic, you'll have to use the go advanced button.

If the tach is ok, then you have a wiring issue or (less likely) a tach driver issue inside the ECU...not much left to go wrong.
 
Ricardo, thanks for the pic yes that is it. The previous owner did not cover the boat well enough during winter months and the engine compartment held alot of moisture. The first time I saw the boat it had alot of moisture in the engine comp. and had been sitting since Sept '12. On the test ride the engine had a slight miss. The PO used the dist cap as the excuse for the miss and mentioned the tach stopped working at the same time he replaced the dist cap. No other changes I'm aware of so far.
 
Good question.
If "A" drive, you'll have a shift interrupt system that is perhaps part of the issue.

Use your engine serial number and follow the link that Boat_Tech posted.
Merc has always been good w/ serial numbers relating to the service manual sections.


.
 
It has the Bravo outdrive and I will get the serial number Sat or Sun, could not read it from the pics I have.
 
crc said:
The previous owner put a non-marine distributor cap on and according to him from that point forward the tachometer stopped working.
Click to expand...
Another thought would be since the previous owner was working in & around the rear of the engine, he most likely has disrupted the main wiring harness 10 pin cannon plug at the rear of the engine giving it a loose connection. It is real common to lose a connection to a gauge or two along with power or ground to the ignition circuit intermittently acting as a engine miss due to vibration.

crc said:
On the test ride the engine had a slight miss. The PO used the dist cap as the excuse for the miss and mentioned the tach stopped working.
Click to expand...
Though rare, it's possible that your non working tachometer may be shorting out interanly or the wiring to the back of the tachometer is touching someplace causing the engine miss while running. Usually a shorted out tachometer will keep the engine from running at all due to no spark, but things happen especially when moisture is involved.

Master mechanic said:
Check that the connections are good to the tach, while you are laying on your back under the dash cycle the tach switch back and forth a few times and set it for 8.
Click to expand...
Doing this procedure seems to help fix a high percentages of sporadic, non working tachometers.:)
 
Boattech my serial # is in the 0M56XXXX range however when I tried the link it did not work.

Master Mechanic this is new to me ..... what do you mean by set the tach to 8?
 
crc said:
.............. this is new to me ..... what do you mean by set the tach to 8?
Click to expand...
I believe that he's refering to the cylinder number adjustment that some tachometers offer.
On the underside, there may be a small port with a very small adjustment screw within.
Some are straight slot... some are hex key.

At the perimeter, it may read; 4 cyl, 6 cyl or 8 cyl .

This screw sets the contacts that select the algorythm that the instrument operates on.
By moving this screw back and forth, you may re-gain continuity at the contacts.
It costs you nothing to try it.

.
 
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