502 MPi - Still popping thru the intake. Need some ideas for troubleshooting.
09-03-2018 | 01:17 PM
#1
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From: Virginia Beach
502 MPi - Still popping thru the intake. Need some ideas for troubleshooting.
Okay, I have a bad alternator on the starboard side (new one ordered), but I’m charging/running off the port motor, and batteries seem to be hovering around 14v, running.
We ran about 20 miles right at about 60 mph, 4100. The boat was running well. We got to a point where we needed to pull back coming into a no wake zone, and at 2800 she started to pop through the intake on the port motor. I’m thinking bad MSD cap (cross firing) or a bad module/coil.
How is do I troubleshoot this? I’d rather not just throw parts at it.
1999 Gen VI 502 MPI.
We ran about 20 miles right at about 60 mph, 4100. The boat was running well. We got to a point where we needed to pull back coming into a no wake zone, and at 2800 she started to pop through the intake on the port motor. I’m thinking bad MSD cap (cross firing) or a bad module/coil.
How is do I troubleshoot this? I’d rather not just throw parts at it.
1999 Gen VI 502 MPI.
09-03-2018 | 01:41 PM
#2
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From: Toronto, Canada
depending on the pop you're experiencing, I'd be looking at your fuel pump, when they sh*t the bed they'll tend to pop in the intake on decel... just my $.002 and without knowing the details hard to recommend any real coarse of action...
09-03-2018 | 07:23 PM
#3
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From: Virginia Beach
Have had no issues until installing steering. We ran a poker run beforehand, and she ran flawlessly.
She isn’t popping on decel; we back off to 3k after a good long run and she starts to do it (did it again on the way back... 30 minutes at 4200). This last go, ran 20 miles at 4200, not even working her hard. Temps good, oil good. We back off because we’re gettign ready to come into the inlet, and she starts to do it. Tach drops a few hundred rpm while popping, and trying to accelerate out of it creates more. It’s like a wire is crossed. A few minutes later she’s back to being fine again.
Im using an MSD cap, rotor, and wires. Maybe the cap is arcing? Regardless, it’s very intermittent.
She isn’t popping on decel; we back off to 3k after a good long run and she starts to do it (did it again on the way back... 30 minutes at 4200). This last go, ran 20 miles at 4200, not even working her hard. Temps good, oil good. We back off because we’re gettign ready to come into the inlet, and she starts to do it. Tach drops a few hundred rpm while popping, and trying to accelerate out of it creates more. It’s like a wire is crossed. A few minutes later she’s back to being fine again.
Im using an MSD cap, rotor, and wires. Maybe the cap is arcing? Regardless, it’s very intermittent.
09-03-2018 | 07:41 PM
#4
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Joined: Jul 2015
Posts: 141
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From: Cedarburg,Wi.
Have had no issues until installing steering. We ran a poker run beforehand, and she ran flawlessly.
She isn’t popping on decel; we back off to 3k after a good long run and she starts to do it (did it again on the way back... 30 minutes at 4200). This last go, ran 20 miles at 4200, not even working her hard. Temps good, oil good. We back off because we’re gettign ready to come into the inlet, and she starts to do it. Tach drops a few hundred rpm while popping, and trying to accelerate out of it creates more. It’s like a wire is crossed. A few minutes later she’s back to being fine again.
Im using an MSD cap, rotor, and wires. Maybe the cap is arcing? Regardless, it’s very intermittent.
She isn’t popping on decel; we back off to 3k after a good long run and she starts to do it (did it again on the way back... 30 minutes at 4200). This last go, ran 20 miles at 4200, not even working her hard. Temps good, oil good. We back off because we’re gettign ready to come into the inlet, and she starts to do it. Tach drops a few hundred rpm while popping, and trying to accelerate out of it creates more. It’s like a wire is crossed. A few minutes later she’s back to being fine again.
Im using an MSD cap, rotor, and wires. Maybe the cap is arcing? Regardless, it’s very intermittent.
Last edited by drumerjb; 09-03-2018 at 07:45 PM.
09-03-2018 | 08:12 PM
#7
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From: Virginia Beach
502 fuel injected, 1999 Gen VI.
I don’t think this is a lean up. The engine doesn’t load up, it just starts popping. It’s more like a rhythmic pop pop pop and rough running, then it goes away.
Tune up done at the beginning of the season: new cap and rotor, wires and plugs. The plugs on this engine were perfect when I changed them. The computer says nothing is wrong, no codes.
This one has 480 hours, top end and injectors done (bad valve seats) at, I want to say, 300 hours (previous owner).
This sounds either eletrical (spark happening at the wrong time) or mechanical (like a valve open).
I don’t think this is a lean up. The engine doesn’t load up, it just starts popping. It’s more like a rhythmic pop pop pop and rough running, then it goes away.
Tune up done at the beginning of the season: new cap and rotor, wires and plugs. The plugs on this engine were perfect when I changed them. The computer says nothing is wrong, no codes.
This one has 480 hours, top end and injectors done (bad valve seats) at, I want to say, 300 hours (previous owner).
This sounds either eletrical (spark happening at the wrong time) or mechanical (like a valve open).
09-03-2018 | 10:10 PM
#8
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Posts: 141
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From: Cedarburg,Wi.
502 fuel injected, 1999 Gen VI.
I don’t think this is a lean up. The engine doesn’t load up, it just starts popping. It’s more like a rhythmic pop pop pop and rough running, then it goes away.
Tune up done at the beginning of the season: new cap and rotor, wires and plugs. The plugs on this engine were perfect when I changed them. The computer says nothing is wrong, no codes.
This one has 480 hours, top end and injectors done (bad valve seats) at, I want to say, 300 hours (previous owner).
This sounds either eletrical (spark happening at the wrong time) or mechanical (like a valve open).
I don’t think this is a lean up. The engine doesn’t load up, it just starts popping. It’s more like a rhythmic pop pop pop and rough running, then it goes away.
Tune up done at the beginning of the season: new cap and rotor, wires and plugs. The plugs on this engine were perfect when I changed them. The computer says nothing is wrong, no codes.
This one has 480 hours, top end and injectors done (bad valve seats) at, I want to say, 300 hours (previous owner).
This sounds either eletrical (spark happening at the wrong time) or mechanical (like a valve open).
also get it warm and do cyl compression test.
It's one or the other mechanical or electrical. You can pull plug wires and inspect Spark color and consistency at appropriate RPMs where missing is occurring. you need to isolate whether it's mechanical or electrical or fuel first
Last edited by drumerjb; 09-03-2018 at 10:16 PM.
09-03-2018 | 10:18 PM
#9
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From: Virginia Beach
Right now (running on the hose) it’s fine. Sounds good, no problems.
The problem here is that it’s very intermittent. Today, it didn’t happen until slowing down on both the coming and going legs of our trip. Even then, it was for a short time. When this first started, I could shut it down, and it would run okay after. The other night, I ran the boat hard (trying to beat sunset in unfamiliar waters) and not one hiccup.
I hate throwing parts at something as that’s not the way to fix anything. I was hoping someone would chime in with “I had the same issue.”
The problem here is that it’s very intermittent. Today, it didn’t happen until slowing down on both the coming and going legs of our trip. Even then, it was for a short time. When this first started, I could shut it down, and it would run okay after. The other night, I ran the boat hard (trying to beat sunset in unfamiliar waters) and not one hiccup.
I hate throwing parts at something as that’s not the way to fix anything. I was hoping someone would chime in with “I had the same issue.”
