496HO issues at high and low RPMs
#1
Registered
Thread Starter
Join Date: Apr 2012
Posts: 41
Likes: 0
Received 0 Likes
on
0 Posts
496HO issues at high and low RPMs
I have a 2002 Mercruiser 496 MAG HO w/ ~450 hours on it that's giving me trouble. Here's what's going on:
Other than that it seems to run great around 3000-4000 RPMs. I just got back from a 150 mile cruise with no problems except at the low and high RPMs.
Any ideas what's up? Fuel pressure maybe?
Thanks.
- A continuous alarm (guardian?) goes on when at or near full throttle for more than a few seconds, until I throttle all the way down. This has gotten progressively worse over the last few times I've taken the boat out.
- The "check engine" alarm on MercMonitor used to come on at the same time as the continuous alarm, now it's constantly on (plus 2 beeps every few minutes). MercMonitor doesn't report any more specific alarm.
- Last week I had someone check the ECU and it had thrown an oil pressure code. Oil level was a little on the low side, so we topped it off and reset the code. Oil level is fine now.
- The engine had a little trouble starting this morning. It was a much quieter start than usual and seemed to be struggling until it warmed up after a minute or two.
- Slightly above idle it sometimes sounds like it's kind of sputtering or something.
- It's stalled a few times at low RPMs, usually when throttling down from just above idle. That may have been due to low fuel tanks though.
- MercMonitor is reporting an obviously incorrect oil temp of 32 degrees F. Other gauges seem to be working. Oil pressure was ~20, water temp ~170, water pressure ~3, can't remember the rest.
Other than that it seems to run great around 3000-4000 RPMs. I just got back from a 150 mile cruise with no problems except at the low and high RPMs.
Any ideas what's up? Fuel pressure maybe?
Thanks.
#2
Registered
Join Date: Feb 2007
Location: Sweden
Posts: 161
Likes: 0
Received 0 Likes
on
0 Posts
Standard problems on those engines are the IAC and the sea water pressure sensor.
A malfunctioning IAC can contribute to hard starting, stalling.
The pressure sensor most often causes alarms at or near wot.
A malfunctioning IAC can contribute to hard starting, stalling.
The pressure sensor most often causes alarms at or near wot.
#3
Charter Member #1171
Charter Member
Get it scanned,,,,,thats the beauty of new motors,,,,,simple diagnosis
__________________
I want to live in a world where a chicken can cross the road and not have its motives questioned.
I want to live in a world where a chicken can cross the road and not have its motives questioned.