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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 15634
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 1999 Campion with 5.7 liter Mercruiser GM engine

Customer Question

I have a 1999 Campion with 5.7 liter Mercruiser GM engine Bravo 2 drive. Engine starts and runs great cold, for about 15 minutes, but spits and pops in the 2500-3800 rpm once hot, under load, worst at minimum plane (3300 RPM). It is OK at WOT. Changed
fuel filter (it was water free), checked carb strainer (clean), installed new ignition coil and new diz cap and rotor. No improvement, although old coil looked gunky (thought I had found the smoking gun). So, problem is still there. Ideas?
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.
Hello my name is ***** ***** am I speaking with? Is the engine carbureted or fuel injected, if you have the serial number that would be best. When you say it pops, is it popping in the intake, or exhaust? How old is the fuel, and when did this problem start?
Customer: replied 1 year ago.
2 Bbl carb, . The engine stutters and pops in the range stated , OK at WOT, OK at all RPMs unloaded. Problem started after about 4-7 hours running this year. I have gone through one tank of fuel. The boat had previously been stored for a couple of years.
Customer: replied 1 year ago.
If you need some other info beyond what I told you in the initial description, tell me and I will get it and send to you tomorrow. (it is 9:30 pm here and dark)
Customer: replied 1 year ago.
Hello, still there Jason? My name is Mark
Expert:  Jason replied 1 year ago.
Hi Mark. Sorry for the delay. Another customer had requested a phone call and I had to take it. Can you tell me if it is popping in the exhaust or intake?
Customer: replied 1 year ago.
It sounds like a big periodic miss more than anything. It is not a backfire, so maybe it is intake. It almost sounds like a quick shot of super retarded timing, then normal, then return to the problem. But OK at WOT and idle.
Customer: replied 1 year ago.
It sounds like timing is too far advanced when you take off from dead stop if you nail it when this stuff is going on. You can hear some ignition knock.
Expert:  Jason replied 1 year ago.
You said you went through 1 tank of fuel. Have you tried running it off of another fuel supply yet, like a portable outboard style tank?
Customer: replied 1 year ago.
Not yet. Because it runs great cold across the range, or at no load or at low load, or at WOT, I was thinking fuel is not the problem.
Expert:  Jason replied 1 year ago.
You said it sounded like it said the timing was to far advanced. Have you checked it with a timing light?
Customer: replied 1 year ago.
Not yet. I ordered Seloc manual but don't have it yet. Don't know special procedures for setting up to check it. Will after I get the Seloc.
Expert:  Jason replied 1 year ago.
I'm about to hit the sack here on my end. Shoot me the engine serial number sometime tomorrow and i'll look and see which ignition system you have, and I can tell you how to go about checking the timing and wat to look for. Have a good night,Jason
Customer: replied 1 year ago.
Mercruiser engine serial number is ***** Knock sensor. Is PT #16184069. ICM is 861254-1. Best regards, Mark
Expert:  Jason replied 1 year ago.
Got it. It is a thunderbolt 5 system. On timing get the engine good and warm and then hook up a timing light to the #1 plug wire and check timing at idle. It should read roughly 8 degrees before top dead center. And then slowly advance the throttle and you should see the timing mark move to the left. The biggest thing is at idle make sure the timing mark is steady, and not jumping around.
Also, on the side of the engine is the knock sensor. Unplug that and give it a run and see if it is any different.
Let me know how you make out.
Expert:  Jason replied 1 year ago.
Hello, just checking in. Any progress?

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