2001 21v Running rich 350 Mag MPI Ski

[snowmandopeman]

Hey guys me again, so replaced all the plugs after I found 3 that were pretty fouled up and no more misfire, I did notice after taking the boat out for a couple of hours this evening the exhaust smells like unburnt fuel. I'm starting to think the engine is running rich which caused the plugs to foul up. I am going to go ahead a replace all the ignition components and run a compression test and leak down test just for safe measure. Does anyone know what else may cause a rich running condition so I can diagnose those components as well? Thanks for the help.

[snowmandopeman]

Thank you Gumby you are a wealth of knowledge and I appreciate the assistance. I did some looking around for the 3 wire pick up and was only able to find the 2 wire is there a certain site where I can find that? For all those other parts do you typically use OEM or is there another brand that is considered as reliable and possibly cost less, just not sure how picky these engines are.

[snowmandopeman]

I actually found the parts when I looked up the part number is showed the 2 wire sensor but after a closer look it said a new part was superseded and it was the 3 wire so got everything ordered!

[snowmandopeman]

Good call, not going out till next weekend and all my parts should be here tomorrow, Ill replace all those parts and clean the throttle body. freeheel4life ill check that vacuum line also, I couple other places I was doing some reading mentioned the same thing. Thank you, ill report back how she runs this weekend!

[snowmandopeman]

gumby So I replaced the Cap, Rotor, Plugs, plug wires, Fuel/water separator, cleaned the throttle body and MAP sensor, and replaced the ignition sensor already had the 3 wire one on there but did it anyway. went to take the boat out today and ran awful, popping out the throttle body really loud hissing sound from intake and there was a misfire, it ran worse than it did before. I'm going to go through it again this week and hopefully I can figure something out. this is really weird as it was running amazing all summer.

[snowmandopeman]

I did not replace the IAC or TPS I removed them both and the throttle body when I cleaned the throttle body. I have not been able to locate any vacuum leak but I will investigate further. Still have to check the spark plug wires again I’m almost certain I have them in the correct order but can’t hurt to double check. I tested the IAC and it seems to be functioning just fine it is missing the muffler so that could be what’s causing the extra intake noise as for the TPS I have it on order I did run some tests on it and it seems okay but figure might as well replace it.

[snowmandopeman]

Oh you’re all good man it wasn’t taken that way at all. I am in agreement 100% I ordered all new parts so just waiting on them at this point. I did get my fuel pressure gauge today and just hooked it up, with the boat acc on fuel pump primed but engine not running I am getting 14-15 PSI this seems low to me.

[snowmandopeman]

It’s brand new just opened it so it should be but I’ll double check. If it checks out probably need a new fuel pump it seems.

[boatwakes]

Been following this one and yes, the fuel pump needs to be replaced, pressure should be 30psi +- 2. I did a write up on it here https://www.tigeowners.com/forum/tec...ol-fuel-system and it includes parts and part numbers required to do it properly. Also, there is a Manifold Air Temp sensor on serial numbers 0L304600 through 0M31009, Mercruiser P/N #805223T. It's located in the top of the intake manifold just behind the throttle body and is mounted vertically. We've seen them get coated in oil vapor from the PCV and start causing whacky readings. The MAT sensor and Engine Coolant Sensor work together to provide the fuel curve on those engines so look at the ECT (PN (#805218T))as well as your thermostat (which MUST be 160*) PN (#8M0109441) and your dash temps to figure out if you need to replace the thermostat. Those engines look like they run at 175 on the gauge but when we connect the computer it's around 165. If the the t-stat is stuck open the fuel curve never leans out and thus will cause the engine to run rich. The injector pulse width cuts in half when the ECM sees engine temps at 140* and above, below that it's still in warm up mode.

[snowmandopeman]

Okay so went a did a compression test, just for piece of mind. when I was taking out the plugs I noticed 3,5,7 were already looking a bit rough and have only been run for about an hour since being brand new. So I’m fairly certain those three cylinders are the culprits. I have ordered the new TPS, IAC and coolant temp sensor which I will replace either way when they arrive. Would these sensors cause this fouling or non ignition in those specific cylinders only or would it be across all cylinders, or do you think it could be a leaky/ faulty injector which would be localized to those individual cylinders.

I have an appointment at a mechanic to scan the ECM for any issues and give it a once over. I’m not going to be able to get in the water for 2 weeks due to being out of town so I don’t mind tinkering a little bit before then.

Compression

1 195

2 200

3 192

4 195

5 190

6 190

7 195

8 195

[boatwakes]

Your compression is fine but an engine of that age with original injectors is ready to have them cleaned or replaced. We run them with before and after flow readings for customers and have always had them come back to say how happy they were to have engine power restored. It honestly sounds like you've got a few issues to resolve but adding injector cleaning or replacement to the equation, especially since you've noticed a build up on those cylinders so soon, would be nothing but a good thing. I would suggest replacing the items one at a time and running the boat in between to find out exactly what your issues were.

[snowmandopeman]

boatwakes thank you, I found a shop locally that will test and clean them, just trying to go through the engine and clean/ replace anything that could be causing my issues. At this point the IAC valce and TPS are all back ordered till October so unless the injector cleaning fixes my problems my season is probably over unfortunately.

[boatwakes]

I really wouldn't worry about either of those, when they fault they throw a sensor code which alarms two beeps every minute. The IAC generally doesn't let the engine start without applying throttle, which opens the throttle plate letting air in, and will usually stall once throttle is returned to idle. It's very rare for the TPS to fail and I have replaced 1 in my tenure. Post your serial number so I can check if you have the Manifold Air Temp sensor.

[snowmandopeman]

l673424 it almost seems like its cross firing from one cylinder to the other which might be causing the back fire through the intake. I did also did notice it is idling around 1000 rpm. I believe it does have the intake manifold temperature sensor.

[snowmandopeman]

Okay so just fired it up after cleaning and replacing a few sensors. Actually sounded like it was running much better no more back fire through intake manifold, at first then after a few mins started misfiring again and running rough. I did notice after revving it up it died when settling back down, once I restarted it I noticed the serp belt squealing and the belt was not moving. Thinking one of the Serpentine components it seizing up? I also noticed the temperature gauge at the helm was fluctuating heavily would go to 175 then rev slightly and back down to almost zero.