454 won't go above 2000

[b0mbtrack]

Mercruiser 454, I'm not sure the year or model number as the block was replaced years ago with a marine power engine. It is a multi port, MEFI 7.4L, fresh water cooled. The engine runs great up to about 2000-2050 then doesn't go above that. It doesn't skip a beat at any rpm below that, it runs nice and smooth. It hits about 2000 and just stops going up. It doesn't pop like its lean, and it's not backfiring at all. It actually sounds good at 2000 it just doesn't want to go above it. The engine has been completely tuned up, I ran it on my own fuel tank directly at the engine. I changed the riser gaskets incase water was getting passed at higher rpms. No change in performance after any of that. I ran the engine on the computer and it's not running in safe mode. It has a IAT fault (reading -32 degrees) but I don't see a IAT on the engine. TPS is fine. The spark advance goes up to about 24 then starts to back down to about 19 and I'm not sure if that is normal. It actually starts to go back down around when it starts to act up. Thanks in advance.

 

[b0mbtrack]

I'm thinking something is wrong with the spark advance. Does anyone know what the max should be? It doesn't sound right to me that the spark advance starts to go back down after reaching about 24.

 

[Maclin]

Not sure what IAT is, but some engine programs limit RPM until the engine warms past a certain temperature point.

 

[Scott Danforth]

Intake Air Temp.

and yes, your 7.4 liter should have one.

 

[MikDee]

Intake Air Temp.

and yes, your 7.4 liter should have one.

Just curious Scott, isn't that an Idle Air Temp sensor? Used on fuel injection engines in place of a choke?

 

[b0mbtrack]

Everywhere I look the IAT is called Intake Air Temp. I think the "choke" is IAC Idle Air Control. According to the books the IAT should be located in the large plenum opposite the throttle body. It is definitely not at that location and I can't find it anywhere on this engine. I know it should be two wires, tan and black. Any idea if it could have been located anywhere else? It is also not on the throttle body. Would this sensor even cause this problem?

 

[b0mbtrack]

Here are some pics of the engine. The numbers given are all I have for it. One picture is a close up of a plug where I believe the IAT should be. I'm still trying to find out how the spark advance should work on this one.

 

[b0mbtrack]

OK figured out how to get pics up.
The IAT should pretty much be behind/under the relays in the following picture.
This plug is there instead
These are the only numbers I've got to work with.

 

[b0mbtrack]

Checked fuel pressure today just to be safe and it was a good 34-35psi. Someone told me to check out the crank sensor and the sensor in the distributor so I'll see tomorrow with the computer what the crank is doing. Not sure if there is a procedure to check the distributor sensor but I'll check the manual.

 

[b0mbtrack]

No crank sensor on this one and no change with ICM inside distributor.

 

[Fastatv]

Has the TPS been moved whatsoever...or replaced? Is there a means of pulling codes on this engine?

 

[b0mbtrack]

The TPS is working correctly according to the computer. The only code to come up is for the IAT (intake air temp) however, this engine isn't equipped with an IAT. I get rid of the code and no changes to performance and the code comes right back.