2002 340 DA 6.2 MX MPI iginition issue

GuyFM

GuyFM

New Member
Jul 18, 2019
14
Boat Info
2002 Sea Ray 340DA
Engines
Mercruiser 6.2MX MPI V-Drives
2002 Sea Ray 340 Sundancer with twin Mercruiser 6.2 MX MPI motors with 500 hours, having this issue above 3,000 rpm. Marina service has set timing, replaced cap & rotor, spark plugs and wires and they can not figure out this issue. Batteries are new, new alternator, fresh fuel (in fact they replaced both inline filters and water/separator filters) and this issue persists.

 
It's changing RPM so fast... are the engine RPM's ACTUALLY changing?

If not, this isn't an engine issue which is why changing the things they did made no difference. Try "exercising" the cylinder selector switch on the back of the tach. Make sure you end back up on "8".
 
How does it sound and perform? Don’t look at the gauge, listen and feel, does it hit your rated WOT rpm?

I agree with Lazy Daze. Could just be a gauge issue.
 
Thank you for your questions. It looks like a bad tachonometer but it is not an instrument issue, the tach is reading correctly. There is a loss of power as shown, it's as if the ECU is, for lack of a better term, "bumping" into limp mode. I'm not sure what the correct term is. My GM dealer friend suggests that the 6.2 MPI is "extremely sensitive" when it comes to setting the timing on these 6.2 MPIs. I thought I'd post here for ya'll thoughts. Could the marina simply not know how to set base timing? Or should I start swapping parts between the perfectly running starboard running engine?
 
May be the ignition sensor? The original sensor is a common fail item due to poor grounding.
 
Are you talking about the sensor that is inside the distributor under the rotor? If so, this model year engine does not use that sensor. If not, can you please elaborate? Thank you!
 
Serial number OM313031 350 MAG MX 6.2L MPI INBOARD (2002) that ignition sensor is not used. Again, thank you for your input!

Here is another video of the issue
 
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My port engine (2002-340-6.2’s-v-drives) started doing the same thing with anything over 3000rpms yesterday, after filling up fuel tank. All fresh filters last Sumer. Was thinking maybe a water/dirt disturbance after fueling.
Keep us posted.
 
We are still working on this issue and will let you know. Make sure your distributor has not come lose - these motors are sensitive to timing. I recently discovered that Mercury had a service they offered around 2006 to reprogram the ECU to "loosen" the parameters for limp mode due to timing control being too tight, for lack of a better term.
 
There is an intermittent arc under load (>3000rpm) on the coil. The plugs, wires, cap and rotor are new so re-checking plug gaps and will take a very close look at the coil checking for a carbon track/crack and will do Ohm test of the new Merc wires. The marina service said they swapped coils and the problem did not follow the coil. Will update again.
 
RESOLVED! Fuel starvation issue. The fuel line from the tank to the fuel pump had internally collapsed!
 
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Update. It was not a fuel starvation issue - however the injectors were dirty - it was the CRANKSHAFT POSITION SENSOR which was rubbing against the reluctor wheel. The 4.6L 5.7L 6.2L GM engines from this period (circa 1995 - 2002) have plastic timing covers. Abnormal wear on the front crankshaft bearing can cause the crankshaft to wobble at high RPMs and the reluctor wheel makes contact with the sensor causing havoc. GM put out a service bulletin to add shims to the sensor

https://i.imgur.com/F1y2Guk.jpg
F1y2Guk
 
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If your crankshaft wobbles at high rpm, you have a much bigger problem than shimming your sensor.
 
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