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TexasPilot71

Engine noise - “popping” or “missing”

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Well here's my 2 cents. Secondary ignition problems don't show up within a norrow rpm range, they are more susceptible to engine load and get worse as load increases. Not a camshaft as they also worsen under rpm and load along with weak valve springs.Is it popping from intake or exhaust? Next I would get a DVOM and find the signal wire on the throttle position sensor. Unhook the cable and sweep the throttle plate open to close. Use a tpin to backprobe the wire. With key on you should see a smooth increasing and decreasing voltage sweep. You are looking for approx half a volt closed and 4.5 at full open.If anything looks un ordinary you can also take the sensor off and do an ohm reading across the supply and signal terminals. When installing make sure your base voltage reading remains the same. If that checks out I would next get a good timing light and check your base and total timing and also watch for any odd variations as the timing increases and decreases. You should not see more than 34 or so degrees of total timing. This may be very difficult to do but you can do it in neutral. If you see the timing wigging out it could be an ignition module issue. Hope this helps.It doesn't sound like an engine mechanical issue. Also a crank sensor usually only acts this way when there is debris on the signal plate and won't resolve under higher rpms. JK.

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No codes avail on the engine ?

Last check. See if the throttle linkage has rubbed thru a ignition wire at that 1 lever rpm place.  300 rpm dead spot is very odd. Need a GREAT mechanic on this one. 

I would expect a HUGE BILL to find this weird one.

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2 hours ago, Mi3sons said:

Well here's my 2 cents. Secondary ignition problems don't show up within a norrow rpm range, they are more susceptible to engine load and get worse as load increases. Not a camshaft as they also worsen under rpm and load along with weak valve springs.Is it popping from intake or exhaust? Next I would get a DVOM and find the signal wire on the throttle position sensor. Unhook the cable and sweep the throttle plate open to close. Use a tpin to backprobe the wire. With key on you should see a smooth increasing and decreasing voltage sweep. You are looking for approx half a volt closed and 4.5 at full open.If anything looks un ordinary you can also take the sensor off and do an ohm reading across the supply and signal terminals. When installing make sure your base voltage reading remains the same. If that checks out I would next get a good timing light and check your base and total timing and also watch for any odd variations as the timing increases and decreases. You should not see more than 34 or so degrees of total timing. This may be very difficult to do but you can do it in neutral. If you see the timing wigging out it could be an ignition module issue. Hope this helps.It doesn't sound like an engine mechanical issue. Also a crank sensor usually only acts this way when there is debris on the signal plate and won't resolve under higher rpms. JK.

Good advice, thanks!  I'll show this to my mechanic as it's a bit above my head.

2 hours ago, cyclops2 said:

No codes avail on the engine ?

Last check. See if the throttle linkage has rubbed thru a ignition wire at that 1 lever rpm place.  300 rpm dead spot is very odd. Need a GREAT mechanic on this one. 

I would expect a HUGE BILL to find this weird one.

I don't have a code reader, but I have a Vesselview 7 and it's not showing anything.  I suspect it should show any codes thrown, but I have not seen one yet.  After all, it runs off the diagnostics port.

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well a similar issue on a thread here reported the exact symptoms and found to be a

"The problem was a bad fuel pressue regulator. Mechanic installed it last week. Boat runs better then ever. Good luck!"

 

Run a pressure check. Popping noise is lean condition. 

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1 hour ago, BajaDriver said:

well a similar issue on a thread here reported the exact symptoms and found to be a

"The problem was a bad fuel pressue regulator. Mechanic installed it last week. Boat runs better then ever. Good luck!"

 

Run a pressure check. Popping noise is lean condition. 

Thanks for the link.  That's exactly the first thing we're doing on Saturday.  Checking the fuel pressure.  Praying that's it!

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25 minutes ago, BajaDriver said:

I’ll keep my fingers crossed

Thanks!  I ordered a pressure regulator today just in case.  If not, I can just send it back.  Amazon!

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Fuel pressure is good. No obvious vacuum leaks. Leaning toward a bad tank of fuel. Going to install a fuel/water separator filter, maybe hook up a fresh outboard tank of fuel and see if it doesn’t clear up. If not, then next steps will be injector cleaning. 

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Tiny band of rpms ?  Vibration of electrical ignition wire getting zapped  / touched to a ground point ?  or even a loose connection ?  Corroded connection ?

Does it miss at the same speed & way in Neutral ?

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1 hour ago, cyclops2 said:

Tiny band of rpms ?  Vibration of electrical ignition wire getting zapped  / touched to a ground point ?  or even a loose connection ?  Corroded connection ?

Does it miss at the same speed & way in Neutral ?

No popping in neutral.

And after riding with my mechanic yesterday, we discovered it’s popping even above the original 3600-3900 band Where I heard it. So anything above about 3500 RPM under load will produce the popping. 

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The injectors can be tested individually while still installed with a test pigtail and a Merc hand held. I'm still leaning toward a coil. W

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8 hours ago, TexasPilot71 said:

Fuel pressure is good. No obvious vacuum leaks. Leaning toward a bad tank of fuel. Going to install a fuel/water separator filter, maybe hook up a fresh outboard tank of fuel and see if it doesn’t clear up. If not, then next steps will be injector cleaning. 

Dang it! Well fuel, injector, etc. 

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Pull all the spark plugs. Look for the odd color or chipped insulator. It could still be a bad rotor or cap. Long run of baddies in stores ?

Some body has to eliminate Fuel or electrical system. 

What happened this week end ?

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2 hours ago, cyclops2 said:

Pull all the spark plugs. Look for the odd color or chipped insulator. It could still be a bad rotor or cap. Long run of baddies in stores ?

Some body has to eliminate Fuel or electrical system. 

What happened this week end ?

Last weekend I replaced cap, rotor, plugs, wires, and fuel filter.  No better.  This past weekend we hooked up a pressure gauge and got normal readings while the engine was "popping".  The plugs I removed last weekend all look good except a few looked like they might have been running a little lean (grey color...not more "burnt" like the others.  They were only about 18 months old.  Mechanic looked at them and agreed.

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17 hours ago, Wingnut said:

The injectors can be tested individually while still installed with a test pigtail and a Merc hand held. I'm still leaning toward a coil. W

Thanks.  Is there any way to test the coil or the crank position sensor?  How about the injector test?  Pigtail?  Merc hand held?  Never heard of them.

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You put a fuel pressure gauge on the fuel rail, then turn the key on without cranking and note the pressure.  Let's say it's 43 psig.  You then hit the test button on a specific injector and note the pressure drop.  Let's say it's 3 psi.  Then you repeat the process with the remaking injectors.  If they are higher or lower than the average then you have a bad actor.  The test just opens the injector for a precise period of time as commanded by the hand held.  Injectors are expensive and if you find a bad one you change it.  No reason to fool with the remaining 7 as they tend to be very reliable.  W

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44 minutes ago, Wingnut said:

You put a fuel pressure gauge on the fuel rail, then turn the key on without cranking and note the pressure.  Let's say it's 43 psig.  You then hit the test button on a specific injector and note the pressure drop.  Let's say it's 3 psi.  Then you repeat the process with the remaking injectors.  If they are higher or lower than the average then you have a bad actor.  The test just opens the injector for a precise period of time as commanded by the hand held.  Injectors are expensive and if you find a bad one you change it.  No reason to fool with the remaining 7 as they tend to be very reliable.  W

What is this "test button"?  Is it on the injector itself, or are you talking about a piece of diagnostic equipment?  I do get 43psi at "key on".

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If you send me a valid e-mail address I will send you the test procedure direct from the Merc manual. Simply put, you unplug each injector, and plug on the test pig tail. Then the other end of the pigtail gets connected to the hand held scan tool. You establish a base line fuel pressure, and then with the key off, you depress the test button on the hand held which fires that injector for a specific pulse width (duration in milliseconds). You then record the new fuel pressure reading and repeat the procedure for the remaining 7 injectors. Too much pressure drop indicates a sticking injector which closes too slowly. Too little pressure drop indicates a partially plugged injector. No pressure drop indicates that the injector has failed electrically, is plugged solid, or is stuck fully closed. W

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