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2003 hamerhead 375 not running under load


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That's precious little info! My first concern would be fuel starvation - are you certain the fuel filter is clean? Not sure what fuel pump yours will have but some (all?) have a suction screen in the inlet port and this may be partially blocked. Are the hoses from the tank to the fuel pump inlet in good condition and not collapsing internally?

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I have replaced plugs, wires, fuel pump, fuel regulator old regulator was dropping in pressure new regulator goes up in pressure per indmar specs. Replaced distributor module and pick up coil, base timing is set to 10 degrees btdc all fuel lines are clear. Have had a certified indmar check with his diagnostic tool 3 times, it is not showing any codes

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Have not replaced the temp sender unit the gauge is reading 160 degrees. Any idea where the temp sender for the ECM is located? Any idea where I could find a wiring harness for this engine? Bakes marine has a lot of PDF files but I could not find one for my engine. Also I have had the air intake sensors unplugged and plugged back up with out unhooking the battery, will the ECM set up a memory?

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The knock sensor on my 2005 Monsoon 340 is screwed into the cylinder block drain port on the right side just in front of the starter.

Popping through the air filter above 2200 is an interesting symptom. To me, that suggests you are getting ignition in the inlet tract somehow. Could it be a valve timing issue, maybe timing chain slipped a tooth somehow, allowing inlet valves to be open when cylinder combustion occurs? Maybe a sticking inlet valve or lifter? Maybe burnt out inlet valve(s)?

Can you crank it with the kill switch active so that it doesn't fire. Does it crank over evenly or are there distinct points where it speeds up suggesting one or more cylinders have significantly less compression than the others?

Did this just start randomly occurring or might it coincide with something like an engine rebuild...?

Bear in mind I'm not a mechanic - just a burnt out old sparky!

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Getting ready to do a compression check on all 8, have had the valve covers off and had the valve train look at by a engine builder he said the valve train was fine. I am the second owner of this boat, the hammerhead 375 which was factory was replaced with a new 383 from indmar a year and a half ago the 383 from indmar is a long block every thing is off the old engine

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You said the base timing is 10 before TDC; was that done with the ECM in timing mode? It sounds like maybe you set the timing at idle, but not in timing mode. Check that first.

It seems like you could get backfire from a hung or lazy injector also.

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I did set the base timing with a jumper wire in the A and B port of the diagnostic tool port that sets the rpms to 900-1100 rmps I then set the timing to 10 degrees btdc after that I pulled out the shunt wire and the rpms went back to around 720 rmps

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Took the intake off the RTV sealant looked really bad, any idea what the intake bolt torque specs are or does it matter? Thanks

You torque them with an inside bolts firts crisscross pattern in 3 steps- 27 then 106, then 133 in-lbs

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Your symptoms are very similar to the ones I had after an engine rebuild. Boat ran fine until it was under load. If would then backfire and stumble at about 2200 rpm. The engine rebuilder had the timing off by 1 tooth when he installed the distributor. This was confirmed by my mechanics diagnostic computer. Just another thing to check if you current work doesn't solve the problem.

Good luck.

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You torque them with an inside bolts firts crisscross pattern in 3 steps- 27 then 106, then 133 in-lbs

Isn't that for the plastic Vortec intake manifold with the spider injector? Does the HH have that manifold?

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That's what I thought. You should still try to verify this, but if it were my engine I would do three rounds of 15 ft-lbs, then 25 ft-lbs, then 30 ft-lbs in a criss-cross pattern starting on the inside center.

Use a high quality gasket or at least a decent non-hardening sealant. I'm not a fan of RTV where gasoline can contact it because it dissolves. With a port injected engine, gasoline should not be in the intake at all, but YMMV.

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Just did a lake test no change at all, think I am going to have to take it to the dealer. Is there anybody know of a indmar machanic that knows how to work on a hammerhead in Tennessee?

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Did a lake test and there was no change, engine still revs up to 5 thousand in netral but will not tun under load over 2200 rpms. Does anyone know if the diagnostic service computer from indmar has changed sense they went to lap tops? Just wondering is a service tech can get more info from this new software?

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