496 Mag HO RPM issue


A

abvip

New member
[FONT=&quot]I am stumped on an issue and posting here is my Hail Mary. I have read many posts and tried everything others have done and I can think of.[/FONT]

[FONT=&quot]2009 Formula 370 SS, 496 Mag HO. DTS 1A306986 (STB) 1A306867 (Port)[/FONT]

[FONT=&quot]The STB engine lags about 200-400 RPM vs port on most everything over 1000 RPM. Up to 1000 they are dead on. At WOT and trim in I can get about 5000 on my port engine and only 4600 on STB. It is not a drive problem as the split occurs in throttle only mode as well as while underway. Issue started late last year and is still present even after the following attempts to fix:[/FONT]

[FONT=&quot]-Both gen III cool fuel modules removed, insides sand blasted, cleaned and new filters installed[/FONT]
[FONT=&quot]-New fuel pressure regulators on both[/FONT]
[FONT=&quot]-New low and high pressure fuel pumps[/FONT]
[FONT=&quot]-Injectors removed and professionally cleaned and tested[/FONT]
[FONT=&quot]-Fuel regulator vacuum hoses swapped[/FONT]
[FONT=&quot]-Ran boat off remote tank, eliminated fuel/fuel tank issues[/FONT]
[FONT=&quot]-New spark plugs[/FONT]
[FONT=&quot]-New wires[/FONT]
[FONT=&quot]-Swapped MAP sensors[/FONT]
[FONT=&quot]-Swapped cam position sensors[/FONT]
[FONT=&quot]-Swapped throttle bodies[/FONT]
[FONT=&quot]-Rinda scan tool/diagnostics show no unusual codes[/FONT]
[FONT=&quot]-Cylinder misfire test shows even RPM drop for all cylinders under load[/FONT]
[FONT=&quot]-Fuel pressure at idle, under normal load and at WOT all match on both engines[/FONT]
[FONT=&quot]-Vacuum on fuel regulator hose match at idle and higher RPM on both engines[/FONT]
[FONT=&quot]-Compression test checks all cylinders[/FONT]

[FONT=&quot]The only thing I'm not sure of if there is some change in the PCM fuel trim or if that is even possible. I also find it odd that the RPM are totally even up to 1000 and then it's very apparent that something occurs right above 1000 to cause the split. Is there something opening/closing at that RPM that might be getting stuck?[/FONT]

[FONT=&quot]Looking forward to thoughts on how to attack this next. Thanks in advance![/FONT]

[FONT=&quot]Alex[/FONT]
 
Sounds like props. If it?s convenient, I would switch them and see if the problem follows them. Have they been tuned lately?
 
GSENT said:
Sounds like props. If it?s convenient, I would switch them and see if the problem follows them. Have they been tuned lately?
Click to expand...

Its not props, says it happens in Throttle Only Mode

Has posted on other forums, and I'm thinking it needs to be re-calibrated. Something in the DTS and Axis system has changed values. Doing a re-cal may show up what the problem actually is. Hope someone here has more knowledge then me
 
Can you see data output from dtc to throttle etc pots? I would measure each throttle pot output volts and compare. See if they are synced through out range. You already eliminated etc,s. Check throttles.
 
Can you see data output from dtc to throttle etc pots? I would measure each throttle pot output volts and compare. See if they are synced through out range. You already eliminated etc,s. Check throttles.
 
This is really basic stuff, but did not see it in your post. Have you cleaned the air cleaner and throttle body? What about the IAT sensor?

Sent from my moto z3 using Tapatalk
 
Drumerjb said:
Can you see data output from dtc to throttle etc pots? I would measure each throttle pot output volts and compare. See if they are synced through out range. You already eliminated etc,s. Check throttles.
Click to expand...

TPS voltages and throttle position percentages were synced throughout throttle lever range
 
eric_b said:
This is really basic stuff, but did not see it in your post. Have you cleaned the air cleaner and throttle body? What about the IAT sensor?

Sent from my moto z3 using Tapatalk
Click to expand...

Yes I cleaned the flame arrestors, throttle body and plate. I even swapped that stuff between the two engines and saw no change. I don't have an IAT sensor but I did swap MAP sensors...no change.
 
So you have NO iac’s on those motors? They do have a tendency to get hot and at melt around connectors. Worst case is they may cook something in the pcm…
 
You must log in or register to reply here.
Back
Top