Rpms not even on 496 mag ho

Throttles uneven and not running the same on both engines. Butterfly opening at the same time so it isn't the controls. When the port is at the wall at 4000 rpm, the starboard control is only half way up. 496 mag ho on both sides. Replaced the plugs, wires, checked the TPS, pulled and had the injectors profesionally cleaned, checked fuel rails and pressure. There's no real shake in the engine and you can't tell there's any kind of miss, but I'm losing power and rpms. Anyone have any suggestions??

The prop hub may be bad and slipping???

When not under load (out of the water or in neutral) do they both rev up equally?





Careful in your description,"wall"

What you should be saying is,

when at full throttle under load in the water the port engine is running 4000 rpms and the starboard engine is only 2000 rpms.........The words you use are unfamiliar........
Throttles are uneven??? you mean RPMs for the same throttle position are uneven!


It only confuses ......

Ayuh,.... Long list of things checked, but I didn't see the fuel filter,....

It's Contents might be a clue,...

All filters changed 3 on each side. Separate tanks. Volt tested the TPS, fuel pressure at 38 which is a match to what the computer is saying is the correct pressure. No load they are even in location and rpm. Only under load they are off from each other. If it was a hub it would be freewheeling (rpms up) and I would hear and see it in the water. I do mean the throttles are uneven. They are physically in different locations. One is hitting the end of its travel, or the wall of the throttle housing and the other throttle is backed off and about halfway to the wall or its terminal location. Both engines at 4000rpm though.

Unfortunately I do not have any EFI troubleshooting back ground...........

But when an issue happens and you have two motors and one is running correctly........Swapping suspect parts is the easiest way to start.


Like distributor caps.......There have been known issues with some cross firing.....

Even though the fuel pressure is correct maybe swap fuel lines to see if problem moves, or use a separate/external fuel tank for that one engine that would indicate a fuel delivery issue fro tank (s)

Also only 2000 rpms may indicate a limp mode issue??? Not sure but worth looking into........maybe a sensor had gone bad that would cause a limp mode condition??

Not much else I can add........sorry.

Try this:

1. Be DAMN sure the throttles are opening the butterflies ALL the way.

2. If so, then run the FJ Dyno Test. To wit:

Set both engines at the same, comfortable cruise setting based on rpm. Open the throttle all the way and note the rpm. Return to the cruise throttle setting, then do it for the other engine. Compare both the rpms achieved and how quickly the motors accelerated. Then get back to us.

Jeff

Butterfly opening all the way and even to the other engine control. I have already done the fuel swap, there are separate tanks in my boat with no cross over. Sensor bad and limiting the engine sounds about right. I'm going to hook up my computer to it tomorrow and see what I come up with in that end.

Swamp the PCM's(Computers) From engine to engine and see if the problem travels. Careful with the computers They are $1800.00 EA.

The reason for the PCM Swap is there is no way to know if the PCM is bad except for replacing it with a known good PCM.

How did you check the fuel pressure? While underway or at the dock?

Post the serial number.

No worries, we will get this figured out for you.

Threw the computer on it and it came up a code for the Star exhaust gas temp, hi. Steering cir hi. Pitot hi. I also got IST 2,4,6,8 codes. In other words, one side of the whole motor was shut down. I pulled the top back off and rechecked the lines and found the bank plug disconnected and the exhaust sensor disconnected. The pitot was blocked but I don't care. I plugged it back in and bang , she was clean and smooth. No more alarms. My fault for not rechecking the harnesses when I put them back together. Thanks for the help though. The computer gave me the answer from the beginning, I just wasn't listening to it.

Thus the name .....CLUELESS...................sorry I had to...............lol

The key to working on things is not to answer the phone or text while working. When I was putting it all back together I answered the phone a couple of times and was in a group text. You never get back to the same rhythm that you had from the start once you stop.