2004 MCX running rich

[73blue]

Ok so I've searched all over these forums (been a huge help btw) but I can't find my problem or a solution anywhere. I have a 2004 X-10 with the MCX engine, app 400 hours. This spring the boat overheated and I replaced the thermostat and water pump. No more cooling problems. Now the boat starts fine, runs smooth until warm, then the issues begin.
On takeoff the boat really bogs down and acts like its choking out. Every once in a while it will slightly backfire. When I turn it off and restart it the idle drops to 300 rpm. With a slight nudge of the throttle it will increase to 600 and stay there. I think I've lost a couple mph top end, but I've propped down and weighted, so that may be in my head. It does top out about 4600 rpms. When I'm riding behind it (I'm 260, so it puts a load on it) there is a little smoke but no soot buildup or anything. And man is it drinking gas!
Obviously something is throwing off the air/fuel ratio and feeding the engine way too much fuel. Here's what I've done/checked so far:
Changed spark plugs
Cleaned K&N
Checked Oil
Checked fuel pressure @ key on/engine off, idle, 1/2, and w/o
Checked TPS w/ volt meter
Changed Coolant temp sensor
Run Seafoam through it
Finally had a dealer plug his comp in- no codes, everything looked normal on the hose

I thought it may be the MAP sensor but the tech said it would def throw a code. He seemed to think it was a leaking injector or the IAC. I put the fuel pressure gauge on, turned the key on to pressure up, turned key off, and it bled down about 1 lb/min. My mechanic friend said a leaking injector would be a much faster bleed, which leaves me with the IAC. Figured I'd check with yall first before I kept jumpin at things.

[notnowgus]

I know this sounds crazy, but have you disconnected the battery for a minute or two to see if that changes anything? When all else fails, disconnect!

[73blue]

To update: Changed the IAC, no change in engine trouble. Any help would be appreciated.

[73blue]

Unhooked battery, changed MAP, still nothing. Any ideas?

[73blue]

Ok now I'm confused. Saw some threads on here that said my fuel pressure at the rail should be around 58 psi, which is what I have at key on. My owner's manual says 35-45 psi. Which is it? Also checked the pressure again under load when the boat was acting up, slight oscillation in needle at idle and wot, but at 2000 rpms it was bouncing from 40-70 psi. Whats the deal? Fuel pump? Pressure Regulator? Any help would be appreciated.

[2000XPSD]

check the IC and for the a dirty IAC
Fuel pressure should be with key on engine off 41-47psi

[73blue]

Already put in new IAC (see earlier post). IC? Sounds like fuel pressures too high. Regulator?

[mgurley]

Did you remove any plug wires? Did any plug/wires get unusually wet?

[73blue]

I've checked the plugs. No noticible difference with any. They look normal.

[JimN]

Ok so I've searched all over these forums (been a huge help btw) but I can't find my problem or a solution anywhere. I have a 2004 X-10 with the MCX engine, app 400 hours. This spring the boat overheated and I replaced the thermostat and water pump. No more cooling problems. Now the boat starts fine, runs smooth until warm, then the issues begin.
On takeoff the boat really bogs down and acts like its choking out. Every once in a while it will slightly backfire. When I turn it off and restart it the idle drops to 300 rpm. With a slight nudge of the throttle it will increase to 600 and stay there. I think I've lost a couple mph top end, but I've propped down and weighted, so that may be in my head. It does top out about 4600 rpms. When I'm riding behind it (I'm 260, so it puts a load on it) there is a little smoke but no soot buildup or anything. And man is it drinking gas!
Obviously something is throwing off the air/fuel ratio and feeding the engine way too much fuel. Here's what I've done/checked so far:
Changed spark plugs
Cleaned K&N
Checked Oil
Checked fuel pressure @ key on/engine off, idle, 1/2, and w/o
Checked TPS w/ volt meter
Changed Coolant temp sensor
Run Seafoam through it
Finally had a dealer plug his comp in- no codes, everything looked normal on the hose

I thought it may be the MAP sensor but the tech said it would def throw a code. He seemed to think it was a leaking injector or the IAC. I put the fuel pressure gauge on, turned the key on to pressure up, turned key off, and it bled down about 1 lb/min. My mechanic friend said a leaking injector would be a much faster bleed, which leaves me with the IAC. Figured I'd check with yall first before I kept jumpin at things.

The MAP sensor shouldn't have a problem when the only incident that you can think of is an overheat. One that would affect the air/fuel mix is the ECT (Engine Coolant Temperature) sensor. If the motor was hot enough, it's possible that the harness to the ECT melted and the wires shorted together, causing the sensor to read erroneously. Normally, the wires shorting would cause an overheat indication (low resistance - high temperature indication) but it's also possible that the sensor is bad. If you can't read a code, do a visual check of all wiring that is in contact with the motor.

Do a compression test, if this hasn't been done yet.

[73blue]

I replaced the ECT and checked the connections a few days ago. I'll try to do a compression test tomorrow. What do you think about the fuel pressure? Thanks for the responses btw.

[JimN]

I replaced the ECT and checked the connections a few days ago. I'll try to do a compression test tomorrow. What do you think about the fuel pressure? Thanks for the responses btw.

The first thing I would do is stop throwing parts at it. Anything that causes this will be measurable. That means a code will show up if it's a sensor. The IAC should be re-parked if a new one is installed and it won't necessarily go to the correct position immediately. This doesn't send any feedback to the ECM- it just does what its told and there's a "home position" that is used as the reference point.

[notnowgus]

I have seen oxygen sensors on sbc's go bad without giving a trouble code (in trucks). Did the 04 MCX have an O2 sensor?

[2000XPSD]

Already put in new IAC (see earlier post). IC? Sounds like fuel pressures too high. Regulator?

ic= ignition control reference....but after reading your post again don't bother checking, it's tough to check it. the IC btw is where the injectors get there pulse timing...via the ecm

but sounds like high fuel pressure...check real good for vacuum leaks. the fuel reg is vacuum driven off of intake manifold.
Compression test like jimn said is a good idea too...a burnt or bad valve = high manifold pressure = high fuel pressure

check the pcv valve for the hell of it...and wiring like jimn said but add to the list vacuum hoses too

and to reset the IAC pintle postion:
1) turn off ign for 10 sec
2) start eng for 5 sec
3) ign off for 10 sec
4) restart and check idle...that's it

the pintle distance should be preset from the factory but if you want to check it then it should be 28mm tip to body flange

[2000XPSD]

I have seen oxygen sensors on sbc's go bad without giving a trouble code (in trucks). Did the 04 MCX have an O2 sensor?

no o2 sensors in a 04