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Barefoot57
09-08-2010, 06:41 PM
2002 LQ9 motor. <25 hours on engine oil. Mobil 1 filter. Engine oil looks good and is at correct level. Engine not overheating (160-180). Not entering a "limp" mode. Dual batteries (strd & deep cycle). Just changed over the tranny to 15w40 from ATF (< 1 hr). New plugs (< 1hr).


I am getting an audible alarm that I have no clue what it is about. I can be in idle and get it, not get it until I am at "high" speed, or not get it all. There is no "check engine" light at any time. When I do get the audible alarm, I shut the motor down, restart, and there is no alarm. One thing that I am leaning towards, but do not understand is, the oil pressure. Even at low RPM's, I am about 60 psi. When I open the throttle a little, I am 80+ psi. Then, for unknown reasons, I am at 0 psi. The alarm will sound at any psi in the 0-80 range. I'm thinking the sending unit crapped out for sure. But, the fact that the alarm will sound anywhere makes me wonder if there are not other issues. I have read other threads indicating a range of problems to make this alarm sound. I doubt I am logging trouble codes because there is no check engine issue. This makes me think taking it to the shop is a waste of time and $. Therefore, what should I be checking? How should I be verifying correct oil pressure?

**Issue was occuring intermittently before tranny fluid change and plugs. After the changes, alarms everytime between starting and shutting down because of alarm.

Thanks!

G.Luke
09-08-2010, 08:50 PM
I am having a somewhat similar issue. My audible alarm goes off whenever oil pressure gauge indicates just above zero. This only happens when at "hot idle." I checked true oil pressure by hooking up a mechanical oil pressure gauge and found out that my oil pressure is within parameters. It sounds like your pressure sending unit is out of whack since your oil pressure is bouncing all over the place. It should pretty much range b/t 40-60 when cold from idle up to cruising speed. Your specs are listed in the owners manual. According to Larry at Indmar, "The spec for oil pressure is 4 psi at idle with oil hot and minimum 18 PSI at 2000 RPM with hot oil." That is for the LTR (5.7liter 330hp). Yours should be pretty similar. I would start with changing the oil pressure sending unit. http://www.skidim.com/prodinfo.asp?number=R020001. Also search threads for warning alarm. You'll see that its a pretty common problem in many early 2000s models