Re: 1994 Volvo Penta 5.7GI - major power surge problem - possibly timing - possibly f
Now the boat is going into rpm reduction mode. Runs really good up till about 2200 then kills it until 1200 then regains power. Kinda sucks cuz marina it's slipped at are being total jerks about scanning it....... Maybe limp it 5 miles to very reputable marina for scan ?
Does anyone know what can cause the rpm reduction mode???
Hi Chad: Misery loves company. I have a 1999 TBI 5.7 Volvo GSi that just started doing precisely the SAME thing. With the drive in neutral, the engine will Throttle up to ~2400rpm but then falls back to ~1200 rpm then slowly speeds back up again to 2400 rpm where it falls off again. This cycle will repeat itself every ~8 seconds with NO throttle inputs from me. Mildly amusing for a few minutes! I CAN get around the "fall off" by disconnecting the Throttle Position Sensor (TPS). The engine does not run as smoothly but punches right through 2400 rpm all the way to red line with no problem. At cruise, it seems fine too. Without disconnecting the TPS I could not plane off. I think (I hope?) I might have a bad TPS - say with a "dead spot" in the potentiometer. This is truly a crazy problem. Most inputs to the Engine Control Unit (or Module) ECU/M can cause the engine to enter ?safe mode? and reduce the RPM. ECU inputs include the Manifold Absolute Pressure, Throttle Position Sensor, Idle Air Sensor, Knock Sensor, Coolant Temperature Sensor, Oil Pressure Sensor and a few more in some models. Worst yet, if the ECU is bad, a new one is over $1000! I think I hate boats!
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Recent Update: July 28, 2011
I found my problem ? it was the Oil Pressure Switch! I replaced the sensor for about $30. It?s part 3852215. It is located by the Oil Filter and has a single signal wire attached to it. BTW, disconnecting the signal wire also solved the problem and is an excellent ?get home? tactic but you really do WANT the protection that this (properly operating) switch provides, so the switch needs to be replaced at your earliest convenience if it is defective. These engines actually have TWO Oil Pressure sensing devices ? An Oil Pressure SENDER and an Oil Pressure SWITCH. The Sender is hooked to your Oil Pressure Instrument Gauge. The Oil Pressure Switch senses very low or no Oil Pressure and feeds the S.L.O.W. circuit controller on the engine. This circuit reduces your RPM to less than ~2500 in an attempt to save it from major damage. This condition occurs whenever the SLOW circuit senses no oil pressure or extremely high coolant temperatures (via another switch, this time the engine coolant temperature switch). Anyway, the Oil Pressure Switch was my problem.
Hope this helps!
