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1993 mercury efi missing

  • Thread starter deputychiefdavis
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D

deputychiefdavis

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I was running at about 5000 RP

I was running at about 5000 RPM and it started missing. I checked compression and have 110 to 120 in all 6 cylinders. I replaced the plugs and still have a miss.Any sugestions
 
Bad plug wire? coil starting t

Bad plug wire? coil starting to go? switchbox?

Is it missing at lower speeds as well?

Need to start troubleshooting/testing the ignition system to see what isn't working properly...

Post your serial and can dig up some specs/proceedures for testing..
 
I think this is the serial num

I think this is the serial number. I had it rebuilt about 4 years ago. It is a 2.5 LXRI 200 #0D207354. It misses at all speeds but will get up on plain with no problm but I can not get more than about 5200 RPM. It feels like I am missing 1 cylinder. Not sure how to check plug wires or coil. Thanks for your help
 
"Jeff, 5200 rpm is close to ba

"Jeff, 5200 rpm is close to bang on at WOT - dropping your pitch by 1 or 2 would take it up a bit, but your range is 5000-5800, so that really is fine.

I have just finished horsing around with a 90 horse that had "phantom" ignition problems, including a miss at all speeds, intermittently. Turned out to be a couple bad connections (corroded ends on the stator and trigger at the switch box).

But I would definately use Ralph's suggestion and see if you can isolate the miss - is it occuring on a single cylinder or multiple - that will help determine the next troubleshooting step..."
 
It appears to be one cylinder.

It appears to be one cylinder.How do I use a timming light to find out what cylinder is missing. I am running a trophy 4 blade prop 24 pitch. At WOT I am turning 5600 RPM.Puts me at about 60 MPH according GPS. Do not know if that is good or bad.
 
Your top rpm/speed sounds bang

Your top rpm/speed sounds bang on for that particular set-up.

A buddy is the best method of finding the bad cylinder. You need to run with the hood off the motor and hook the timing light to one wire at a time until you find the culprit - so having a "spotter" while you drive the boat is a definate plus.

It's a little too difficult to try and control things and watch the timing light for that "missed" flash which will be apparent with each corresponding miss on the motor...
 
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