496HO rough idle
 

Went boating Friday, no prior issues.

I filled up the gas (on land), put boat in. It took a few tries to start. I had to advance the throttle a little. It idles rough. I left the marina got on plain and it seemed to run fine the rest of the day. I ran it all the way up to 5000 rpms, performance was usual.

I get home. start flushing the motor and it's idling real rough and down around the 575 area. It normally idles around 650. I put a new water seperator on and no change.

Do you think the IAC could be the problem. The motor is not throwing any codes. A scan is included below.

The only other thing is a few days ago lightning struck a tree pretty close to where my boat was parked. Do you think something could of fried?

The strange thing is it ran fine other than the idle.

DIACOM ® Diagnostic Status Report

07/25/2008 18:22:27


1. VEHICLE CONFIGURATION

Engine Make: N/A
Engine Serial No: N/A
Model Year: N/A
System Type: MerCruiser PCM555

2. PERFORMANCE DATA

Parameter Description Value Unit

Available Power 100 %
Baro Pressure 14.66
Battery Voltage 13.95
Coolant Temperature 152.60
Engine Speed 578 RPM
Fuel Flow Rate 1.60 GPH
Fuel Level 1022 #
IAC Duty Cycle 43.03
Lake/Sea Temp 431.60 °F
Manifold Absolute Pressure 10.86
Manifold Air Temperature 140.00
Oil Pressure 49.58
Paddle Wheel 0 Hz
Pitot ADC 0 #
Port Exhst Cool Temp 122.00
Sea Pump Pressure 2.57
Sensor Power 5.02 VDC
Spark Advance 1.38
Starb Exhst Cool Temp 100.40
Throttle Position 0.00
Throttle Sensor Voltage 0.58
Trim Position 0 #
Trim Volts 0.00 VDC

3. TROUBLE CODE STATUS

Current ECM Codes

Sensor Fault, click Read Fault button for details

Trouble Code List:
PITOT CKT LO Code is active
FUEL LVL CKT HI Code is active
STEER CKT HI Code is active
TRIM CKT LO Code is active
FUEL LVL2 CKT H Code is active

Freeze Frame Data:

0 TRIM CKT LO
--------------------------------------------------------------------
FF Baro Pressure 14.66 PSI
FF Battery Volts 12.54 VDC
FF Sea Pump Pressure 0.14 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 132.80 °F
FF Coolant Temp 158.00 °F
FF Demand 0.12 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 530
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.65 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.08 %
FF Available Power 100 %
FF Run Time 178.02 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.12 %
FF Trim Position 0.00 %

1 FUEL LVL2 CKT H
--------------------------------------------------------------------
FF Baro Pressure 14.66 PSI
FF Battery Volts 12.54 VDC
FF Sea Pump Pressure 0.25 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 138.20 °F
FF Coolant Temp 158.00 °F
FF Demand 0.12 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 521
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.65 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.18 %
FF Available Power 100 %
FF Run Time 178.02 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.12 %
FF Trim Position 0.00 %

2 STEER CKT HI
--------------------------------------------------------------------
FF Baro Pressure 14.66 PSI
FF Battery Volts 12.54 VDC
FF Sea Pump Pressure 0.26 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 138.20 °F
FF Coolant Temp 158.00 °F
FF Demand 0.12 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 525
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.65 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.19 %
FF Available Power 100 %
FF Run Time 178.02 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.12 %
FF Trim Position 0.00 %

3 FUEL LVL CKT HI
--------------------------------------------------------------------
FF Baro Pressure 14.66 PSI
FF Battery Volts 12.52 VDC
FF Sea Pump Pressure 0.39 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 138.20 °F
FF Coolant Temp 158.00 °F
FF Demand 0.12 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 479
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.64 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.43 %
FF Available Power 100 %
FF Run Time 178.02 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.12 %
FF Trim Position 0.00 %

Part 2

4 PITOT CKT LO
--------------------------------------------------------------------
FF Baro Pressure 14.66 PSI
FF Battery Volts 12.52 VDC
FF Sea Pump Pressure 0.40 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 138.20 °F
FF Coolant Temp 158.00 °F
FF Demand 0.12 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 479
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.65 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.45 %
FF Available Power 100 %
FF Run Time 178.02 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.12 %
FF Trim Position 0.00 %

5 CRANK SNSR
--------------------------------------------------------------------
FF Baro Pressure 14.78 PSI
FF Battery Volts 11.82 VDC
FF Sea Pump Pressure 0.74 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 84.20 °F
FF Coolant Temp 78.80 °F
FF Demand 0.00 %
FF Engine Speed 377 RPM
FF Engine State Running
FF FPC Total 25.0 Counts
FF Frequency Count 10
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 20.95 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 14.31 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.40 %
FF Available Power 56 %
FF Run Time 176.70 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 0.00 %

6 CAM SNSR
--------------------------------------------------------------------
FF Baro Pressure 14.78 PSI
FF Battery Volts 11.82 VDC
FF Sea Pump Pressure 0.74 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 84.20 °F
FF Coolant Temp 78.80 °F
FF Demand 0.00 %
FF Engine Speed 377 RPM
FF Engine State Running
FF FPC Total 25.0 Counts
FF Frequency Count 10
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 20.95 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 14.31 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.40 %
FF Available Power 56 %
FF Run Time 176.70 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 0.00 %

7 MAP INPUT HI
--------------------------------------------------------------------
FF Baro Pressure 14.78 PSI
FF Battery Volts 11.55 VDC
FF Sea Pump Pressure 0.69 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 84.20 °F
FF Coolant Temp 78.80 °F
FF Demand 0.00 %
FF Engine Speed 314 RPM
FF Engine State Running
FF FPC Total 71.0 Counts
FF Frequency Count 14
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 24.56 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 14.71 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.38 %
FF Available Power 71 %
FF Run Time 176.70 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 0.00 %

8 FUELPUMP RLY CK
--------------------------------------------------------------------
FF Baro Pressure 14.66 PSI
FF Battery Volts 10.14 VDC
FF Sea Pump Pressure 0.16 PSI
FF Boat Speed 0.00
FF Manifold Air Temp 93.20 °F
FF Coolant Temp 167.00 °F
FF Demand 0.00 %
FF Engine Speed 119 RPM
FF Engine State Power Off
FF FPC Total 0.0 Counts
FF Frequency Count 1
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32768.0
FF Manifold Air Pressure 14.17 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.04 %
FF Available Power 61 %
FF Run Time 170.03 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 0.00 %

Fault Log Data
Fault Descriptions Seconds

Battery Range High: 0
Battery Range Low: 0
Block Pressure is Low: 0
Compressor Temp Overheat: 0
ETC Motor Open: 0
ETC Motor Short: 0
Fuel Pressure Sensor Input High: 0
Fuel Pressure Sensor Input Low: 0
Guardian Strategy: 0
Knock Sensor 1: 0
Knock Sensor 2: 0
Low Oil Pressure Strategy: 0
Low Oil Remote Strategy: 0
Low Oil Reserve Strategy: 0
MAP Sensor 1 Input High: 6
MAP Sensor 1 Input Low: 0
MAP Sensor 1 Idle Rational: 0
Oil Pump Output: 0
Overspeed: 0
Port Clnt Overheat: 0
Starboard Clnt Overheat: 0
Warning Horn Output: 0
Water In Fuel: 0

Engine Run Time History:

Total engine run time: 178.07 Hours
0 - 749 RPM: 47.78 Hours
750 - 1499 RPM: 29.90 Hours
1500 - 2999 RPM: 12.82 Hours
3000 - 3499 RPM: 35.37 Hours
3500 - 3999 RPM: 39.12 Hours
4000 - 4499 RPM: 9.32 Hours
4500 - 4999 RPM: 3.70 Hours
5000 - 5499 RPM: 0.07 Hours
Over 5499 RPM: 0.00 Hours

There is a MAP Hi fault in the freezframe memory with a frequency count of 14, and it has occured recently. The MAP is also a little high. Any chance you could email some recorded data to look at?

Hey Dave,

I was hoping you would see this post. I did record a 2 min. file yesterday. I'll try to email it to you.

Dave

Hey Dave,

Would the MAP sensor cause a rough idle? I noticed that in my recording from yesterday the MAP graph was a flat line at 10.86. None of my other recordings ever had such a flat line for the MAP?

Flat line?? That ain't right. Sent you an email.

Thanks Dave, the files are on the way. I hoping it is something simple (and not too much $$) like the MAP sensor.

Dave,
Finally had some time to look at the files. The first two look pretty normal. In the third recording, the MAP is stuck at 10.86PSI, but the PCM doesn't seem to recognize it. Between that and the stored MAP Hi faults, I would say there is no question it warrants replacing the MAP sensor.

Thanks a lot Dave! I just took apart the IAC and it looked clean. I'll call my local merc shop and see if they have a map sensor in stock.

P.S. I hope you weren't effected by the quake?

the 496's have an i.a.c muffler located just above the throttle plate in the little square opening. chances are it is shot and never replaced. an easy check is visual but also the hissing noise at idle. check it, pull it out using a small pair of needle nose pliers.
also just becasue the iac shows response electricly doesnt mean its working physically, sometimes they show a percentage change in duty cycle with no physical changes in the actual idle process because the plunger which is the mechanical part of the unit freezes and doesnt alter the idle. a good sign of this is alot of salt on the arrestor. also do the check key on engine off and listen for a hum from the iac.

good luck.