Before I chase a rabbit down the hole and replace a lot of expensive ignition parts am I expecting to much in idle quality with my engines? They are 320 HP Vortec's that shake at idle but manage to hit peak rpm at wot. Being they are fuel injected I would anticipate a smooth idle but camshaft profiles could cause the choppy idle. Anyone know if I'm looking for something that isn't attainable
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Volvo Penta GXI-C idle quality
- Thread starter woodshoes
- Start date
If all ignition & fuel delivery parts are healthy, idle should be quite smooth. Is it rough both at idle in N and in gear?
Especially if you don't yet have a marine diagnostic scan device & MEFI diagnostic manual and appropriate connector adapter , I would suggest removing the distributor cap and replacing that and the rotor if you see any metal corrosion. Flat top "crossover" caps tend to have short lives. Don't try to clean off corrosion and reinstall.
(The manual will advise to always perform a scan 1st to potentially help avoid wasting more time and money.) It's hard to check the IAC, TPS, MAP sensors, etc., w/o a scan device.
That device will also allow you to check whether the distributor is clocked to the correct cam retard angle for that exact model and year. That spec changed quite a bit from year to year. A power balance check is also easier with simple key command on the scan device to sequentially shut down one cylinder's injector or spark pulse at a time to see if dropping any cylinder does NOT drop RPM.
If you have been running it on good quality stabilized fuel the Platinum/Iridium plugs should likely be OK, but if new cap & rotor don't help you may have to check them.
Maybe take a fuel sample, confirm it smells good and strongly fresh, and let it settle out in a clear container for visual inspection.
Min. idle rpm is controlled by the ECM, so if 1 or more cylinders is dead or weak more all the injectors open a little longer to bring rpm to spec.but it might not be smooth in that case.
Throttle body clean of carbon? Flame arrestor clean ? Plug and coil wires on securely and in good shape?
Especially if you don't yet have a marine diagnostic scan device & MEFI diagnostic manual and appropriate connector adapter , I would suggest removing the distributor cap and replacing that and the rotor if you see any metal corrosion. Flat top "crossover" caps tend to have short lives. Don't try to clean off corrosion and reinstall.
(The manual will advise to always perform a scan 1st to potentially help avoid wasting more time and money.) It's hard to check the IAC, TPS, MAP sensors, etc., w/o a scan device.
That device will also allow you to check whether the distributor is clocked to the correct cam retard angle for that exact model and year. That spec changed quite a bit from year to year. A power balance check is also easier with simple key command on the scan device to sequentially shut down one cylinder's injector or spark pulse at a time to see if dropping any cylinder does NOT drop RPM.
If you have been running it on good quality stabilized fuel the Platinum/Iridium plugs should likely be OK, but if new cap & rotor don't help you may have to check them.
Maybe take a fuel sample, confirm it smells good and strongly fresh, and let it settle out in a clear container for visual inspection.
Min. idle rpm is controlled by the ECM, so if 1 or more cylinders is dead or weak more all the injectors open a little longer to bring rpm to spec.but it might not be smooth in that case.
Throttle body clean of carbon? Flame arrestor clean ? Plug and coil wires on securely and in good shape?
After watching a few YouTube videos it is apparent that I have some idle quality issues and your response confirms it, thanks. I'm going go the tune up route on them because I have a couple seasons on the plugs, caps and rotors which are all considered consumables. The wires are of unknown age, in placesince I bought the boat four seasons ago. I replaced the IAC valves late last season to cure a hot start and stalling problem. The flame arrestors are cleaned every spring and fuel filters replaced also. If that fails to solve the rough idle I'll have no choice but seek diagnostic help from the dealer. Thanks again for the advice.