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#575286 - 07/19/21 12:35 AM Occasional pop, then more frequent 8.1GI  
Joined: Jun 2004
Posts: 9,114
Silverbullet Offline
Admiral
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Admiral

Joined: Jun 2004
Posts: 9,114
Boise, ID
As a refresher, we have a Volvo 8.1 Gi-b in out Cobalt with about 500 hours on it.

Runs pretty well. It's been mostly trouble free.

Late last season, at WOT I had a very occasional single loud sharp pop from the engine. It almost sounded more like something hitting the hull vs an engine noise.

Then it went away.

Today, it came back. It was more consistent, not quite as loud and the last time it happened it seemed to give a couple in a row and the engine seemed rough after we came off plane. The motor did smooth out after a bit, but we kept it mild as we came back to the dock.

I'll start with plugs and wires and looking for anything loose or missing. If I can get one of the old laptops to hold a charge long enough I do intend to take my mefi-scan out on the boat to try to log some data and see what's going on. With it being more consistent now, I am hoping I can capture the cause.

Anyone want to throw out other things I should check before I take it to a mechanic. Good thing I already bought the new to us camper.

Fuel filter was changed last fall. Tank has 91 ethanol free in it and the boat has been ethanol free for at least 9 years.


James
2002 Cobalt 226 VP 8.1GIDP
2007 Chevy 2500HD Crew Cab Duramax
1988 Suburban 3/4 Ton
2000 Subaru Forester


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#575287 - 07/19/21 11:19 AM Re: Occasional pop, then more frequent 8.1GI [Re: Silverbullet]  
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Cape Cod, MA
You are on the right track doing a scan of your MEFI Wondering if you can run the boat and record the data vs. just scanning for codes.

Wondering if you should do a compression check and even a cylinder leak test if you've got the stuff . . . one thought comes to mind . . . valve got hung up a bit and the piston came in contact with it idn


Regards, Ted

Formula 330SS
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#575288 - 07/19/21 02:53 PM Re: Occasional pop, then more frequent 8.1GI [Re: Silverbullet]  
Joined: Oct 2003
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captkevin Offline
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Chicago, IL
That doesn't sound good. Fingers crossed it is something simple.


2004 Rinker 232
2010 Dodge Ram Crew Cab Laramie 4x4
#575289 - 07/20/21 12:23 AM Re: Occasional pop, then more frequent 8.1GI [Re: tpenfield]  
Joined: Jun 2004
Posts: 9,114
Silverbullet Offline
Admiral
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Joined: Jun 2004
Posts: 9,114
Boise, ID
Originally Posted by tpenfield
You are on the right track doing a scan of your MEFI Wondering if you can run the boat and record the data vs. just scanning for codes.

Wondering if you should do a compression check and even a cylinder leak test if you've got the stuff . . . one thought comes to mind . . . valve got hung up a bit and the piston came in contact with it idn





I'll take it out next week with the mefiscan and record the data and put my son's gopro in the engine compartment to record the sound from inside.

I hope it is not valve contact. That would suck. But, I'll do the basics that I can, record the data and go from there. We only have 6 weeks left of boating season.


James
2002 Cobalt 226 VP 8.1GIDP
2007 Chevy 2500HD Crew Cab Duramax
1988 Suburban 3/4 Ton
2000 Subaru Forester


#575290 - 07/20/21 09:47 AM Re: Occasional pop, then more frequent 8.1GI [Re: Silverbullet]  
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Justification Offline
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Justification  Offline
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Fruit Heights, Utah
The Scan should find any electrical and sensor issue, but in the mean time pull the distributor cap and check for arcing between posts. Check your plug wires, and even pull the plugs.
a single pop could be a misfire caused by a plug going off when it shouldn't or not going off when it should. Getting worse over time sounds like normal wear and tear on basic tune up items, on even a low hour engine.


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#575291 - 07/20/21 11:34 AM Re: Occasional pop, then more frequent 8.1GI [Re: Justification]  
Joined: Jun 2004
Posts: 9,114
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Boise, ID
Originally Posted by Justification
The Scan should find any electrical and sensor issue, but in the mean time pull the distributor cap and check for arcing between posts. Check your plug wires, and even pull the plugs.
a single pop could be a misfire caused by a plug going off when it shouldn't or not going off when it should. Getting worse over time sounds like normal wear and tear on basic tune up items, on even a low hour engine.


No distributor, but I am wondering if I am losing a coil pack as each cylinder has it's own.

Plan to check plugs and wires first. Pull plugs. Ohm the wires, etc.


James
2002 Cobalt 226 VP 8.1GIDP
2007 Chevy 2500HD Crew Cab Duramax
1988 Suburban 3/4 Ton
2000 Subaru Forester


#575292 - 07/20/21 11:37 AM Re: Occasional pop, then more frequent 8.1GI [Re: Silverbullet]  
Joined: Oct 2003
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captkevin Offline
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Chicago, IL
Was thinking along same lines.

Check all the easy fixes


2004 Rinker 232
2010 Dodge Ram Crew Cab Laramie 4x4
#575301 - 07/25/21 08:05 AM Re: Occasional pop, then more frequent 8.1GI [Re: Silverbullet]  
Joined: Apr 2006
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kdl Offline
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kdl  Offline
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Central Mass
Agree, start with plugs. A few years back mine went from running really good to hardly at all. I was surprised how fast it went down hill. New plugs fixed it. I don't recall if I had the popping.
I now change the plugs every few years. Overall great running motor. Let us know what you find.


2005 Cobalt 246 8.1 Gi
"Paradise..."

2001 Key Largo 190 CC
"After Five"
#575302 - 07/26/21 04:08 PM Re: Occasional pop, then more frequent 8.1GI [Re: Silverbullet]  
Joined: Feb 2003
Posts: 11,966
Frantically Relaxing Offline
Admiral
Frantically Relaxing  Offline
Admiral

Joined: Feb 2003
Posts: 11,966
My old 1970 Dodge Coronet R/T (440), my old '56 Ford F-100 (390 cop car motor), our old '78 CruiseAir motorhome (440 dodge), my sons old Honda Civic (many years ago), and the wife's '89 Mustang GT Convertible (5.0, still have it), ALL of these vehicles developed misfires that were found to be caused by bad spark plug wires.
Just sayin' wink


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