Anyone else having Mercruiser Dist. Cap issues?

N

Nomore10s

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Mar 28, 2008
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29717
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Recently had my 350 MAG MPI 5.7L Mercruiser engine tuned up. Replaced plugs, distributor cap, rotor, V8 wire set, water-separating fuel filter, in-line fuel filter, etc. with all new Mercruiser parts. Bay tested for 15 min. & engine ran fine. Next day, engine runs rough and loses power over 2000 rpm. Ran cylinder compression test and fuel pressure test and everything checked out OK. Started replacing all items one by one until we discovered the distributor cap was causing the problem. Replaced the distributor cap with a new Mercruiser cap and had same issue again 2nd time out. I have a 3rd cap now with the same problems. My mechanic has been buying his parts from Kellogg Wholesale Marine in CT. There are 2 other boats at my marina with similar engines that were tuned up at the same time. We are all experiencing similar problems. I suggested the mechanic source new distributor caps from somewhere else.
Anyone else having the same issues?
 
Yup, had a bad new distributor cap for my mercruiser 5.0 MPI. I took her out last Saturday for the first time. Ran well for about 45 minutes. I anchored out for a few hours. When I restarted the engine it ran rough, I got out of the no wake zone and tried to get up on plane and couldn't get her above 10 mph. Crawled back at 5 mph. On Tuesday I told my mechanic the problem. A few hours later he called and said it was a defective cap and he replaced it, bay tested it and said all is ok. I started it and ran it at idle for about 5 minutes, seems to be ok, but I havent taken her out yet.
 
Captain

Have you replaced the starters in your MAG 350's?

If so what was the part number? I want to buy a spare for mine.

Joe
 
Relplaced ours with a premium NAPA cap and new rotor awhile ago.
I want to figure out what's what, BUT it seems there are two design approaches:
1. Spring loaded center contact in CAP, Fixed center contact in ROTOR
2. Fixed center contact in CAP, Spring loaded center contact in ROTOR
They should be matched, so only one component has the spring loaded contact.
My personal preference is 2. above, but either should work as a SET.
So I wonder if the cap and rotor matched, or the "failure" was actually a mismatch.
 
How often do you need to change the caps ? I do it every year along with the gas filters. But I have never had a real reason to do it other than that is what I did last year.

I also used to change plugs every year, but now since I get the 3-5 year type $15 each, I have my mechanic check a couple to see if they should be changed.
 
How often do you need to change the caps ? I do it every year along with the gas filters. But I have never had a real reason to do it other than that is what I did last year.

I also used to change plugs every year, but now since I get the 3-5 year type $15 each, I have my mechanic check a couple to see if they should be changed.
 
I wish I had made note of this thread when it was first posted. I had this happen to me this weekend on both my newly tuned engines. It turns out that Mercury and Sierra (same factory) have a whole 'lot' of mis-cast caps out there...specifically the 'crab' or 'spider' caps of a radial design. It's so bad Mercury told me the only way to guarantee getting a good cap is to buy a GM cap.

Jeff
 
Update to my post of 6/5. Turns out that my second distributor cap was also bad, took her out on the second cap and within ten minutes the engine ran rough again. Turned around and crawled back to the marina again. Mechanic immediately installed a third cap, he said the third cap was an aftermarket brand although I didnt get the name of the brand. Since then, (about two to three hours of boating time) the engine has been running well. Incidentally, my mechanic did speak to Mercruiser and they acknowledged the problem. He also said it happened to another boat in our marina.
 
quote:
Originally posted by Radiowaves

How often do you need to change the caps ? I do it every year along with the gas filters. But I have never had a real reason to do it other than that is what I did last year.

I also used to change plugs every year, but now since I get the 3-5 year type $15 each, I have my mechanic check a couple to see if they should be changed.

I usually do plugs and caps/rotors every other year and keep an old cap and rotor aboard in case of emergency.
It never hurts to have a few extra parts handy, you never know when someone might need something to limp home with.
Some things can be a pain to get to in my bilge, but the plugs aren't terrible. The caps are right out there making them real easy to change.
You could probably go a lot longer than every other year if you wanted to, but caps/rotors, and plugs are fairly cheap.

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