300X hesitating during accelaration

[onttr22]

My 2002 - 300X just all of sudden started acting like its running out of fuel, its like its trying to go but surges.

Didn't have much time to test different throttle positions etc and didn't want to do any damage.

Ran fine all day, then we started it up to go home and at about 3500 rpm it started to surge or miss. It definetly didn't want to get up and go.

Came home pulled the plugs and it looks like it was lean for sure.


Where does one start to diagnose ?

I'll try changing filter tomorrow , it was new in the spring.

[simonmotorsports]

Sounds like the MAP sensor.

[EuropeanAM]

Or a fuel supply issue (supply pump, fuel line restriction, etc).

[onttr22]

Dont think there is a supply pump on my TR22, Should I have one with the X on the back ?

I'll have a closer look, I dont hear one when I cycle the key but I guess that could mean its not working. If its there and not working the pulse pump may have an issue trying to pull thru an electric pump.

Also , curious if you have supply pump why would you need a pulse pump ?

Don and Eric thanks for the advice, your both great guy's .

[EuropeanAM]

Many of the factory built 300x engines DID NOT get rigged with an electric supply pump. Most do fine... provided the lines, prime bulb and pulse fuel pump are "healthy".

Now Eric's "monsters".... that's another story! I believe he commonly recommends a supply pump on his EFI setups.

[Largemouthlou]

I ran an electric on mine for a while and didn't notice any difference... I did take the little pulse pump off when I used it also..

[onttr22]

Mine has been running extremely well, up till now. Dont beleive I need the supply pump either but I have one on order as I plan on getting it brought back to new or perhaps a bit better than new this winter with a few goodies and it was recommended to add one.

If I notice a difference i'll let you know. Gonna make sure the existing problem is fixed prior to adding a supply pump.

[Red_Bullet]

I also have an early model 300x. My engine had the same symptoms and maybe the solution for my engine can help you. From people I have talked to, this problem seems to happen mostly with the early 300x's. I don't know if the later models are any different. Anyway read on because your problem sounds just like what happened to me several times.

It is the map sensor. You can confirm this next time the engine acts up. The following diagnosis method came from Mercury Racing. The 300x refers to the TPS when no signal is detected from the map sensor. Just shut the engine down and unplug the map sensor when you experience this problem. It is on the top of the intake. Leave it unplugged and crank it back up and try it again. I'll bet the problem goes away. If it does just change the map sensor.

If the problem persists and you go through several map sensors in a matter of 6 months like I did, try this, it has solved my problem.

I believe the sensor fails due to fuel spray making its way up to the sensor over time. My sensors had some fuel in them (just a film) everytime I would have a problem. So from many years of engineering test experience, this is what I think is happening. The map sensor for this engine is a delco automotive product. These types of sensors are designed for clean dry air....NO LIQUIDS especially like gasoline. In an automotive application they are mounted so far up the intake that they will never experience any fuel or liquids of any kind. I think in this marine application, over time a small amount of fuel spray makes its way inside the sensor and eventually to the sensing element and causes it to fail.

I tested this theory during my map sensor ordeal and haven't had a single problem since....(3+ years). The fix takes 2 brass hose barbs, a brass elbow, and fuel tubing. Install the brass hose barbs into the elbow. Use the silicone rubber nipple jacket from the map sensor and put it on one of the hose barbs. This will provide proper sealing to the intake manifold when you insert it. Then put the shortest piece of tubing you can between the sensor and the elbow. The elbow helps by not allowing any fuel spray to fly straight to the sensor. Essentially what you are doing is adding about 1.5 inches or so of separation between the intake manifold and the sensor. The map sensor is only making a pressure measurement to estimate the amount of air being drawn into the engine, so if you keep all the connections air tight, it won't affect the pressure measurement.

Sorry for going so long with this reply, but your problem sounded exactly like what happened to me. So maybe this will keep you from the many undiagnosed dealer visits I had to endure before the problem was found. Hope this helps, if you want pics or have anymore questions, feel free to ask.

[Largemouthlou]

Good info there!!!

[onttr22]

I'll remove the sensor today and have a look at it .

When you say to unplug it and crank it back up are you leaving it unplugged or plugging it back in then cranking it back up ?

Would love to see a pic if possible.

Thanks

[onttr22]

Took it off and yes there was fuel in the nipple of the sensor.

I also noticed I have some fuel laying in the bottom of my intake, probably 1/2 a cup.

Is this normal ?

I'm thinking maybe bad injector o rings or injector, possibly pulse pump (rebuilding it later today when the kit comes in)

[EuropeanAM]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by onttr22 &raquo;</TD></TR><TR><TD CLASS="quote">Took it off and yes there was fuel in the nipple of the sensor.

I also noticed I have some fuel laying in the bottom of my intake, probably 1/2 a cup.

Is this normal ?

I'm thinking maybe bad injector o rings or injector, possibly pulse pump (rebuilding it later today when the kit comes in)</TD></TR></TABLE>

You shouldn't have that much fuel laying in there, unless you did a fairly substantial amount of "idling" with the engine "trimmed up"

In that case, "gravity takes it's toll".

Simple to test for a leak- connect pressure gauge to system, cycle key to pressurize system. Verify system holds steady pressure for at least 60 seconds after key is turned off.

[Red_Bullet]

Yes leave it unplugged. Then take it for a run down the lake. The engine computer will refer to the throttle position sensor for the fuel mapping. It should run normally when the map sensor is left unplugged.

[Red_Bullet]

I also had some fuel in the intake manifold. Probably a tablespoon or two. I have to do alot trimmed up idling where I fish. I don't know if excessive idling contributes to the map sensor problem, but it might.

[onttr22]

You guys are amazing. The dealers around me haven't even seen a 300X let alone worked on one. Heck I phoned five dealers within an hour drive and no one had a diaprahm kit for the pulse pump. Had to order one. Thank god I was able to get part number from a reliable source for the MAP and pulse pump kit.

Don, I did idle for about 5 mins as the water is way down and I had the motor tipped way up so this maybe the cause . I 'll check it next time at a different launch.

[Largemouthlou]

Don can get ya what ever ya want!! But that is amazing about the pulse pump cause they use that one in alot of motors!!

[Darth VMAX]

Hoping you get everything resolved

Now, How does that BIG OL' TR22 runn with that big power on the back? Those things need 300 horses because of the sheer size! They are a neat boat

[onttr22]

Darth,

I love the boat , yep its a heavy boat but it still flys. I'm still learning to manage the Chime but getting pretty good at it. Handles the big water with ease and at 75 mph its like your sitting in your lazy boy watchin TV. Fully loaded 2 people, livewells full its a 80 mph boat any time. Lightly loaded its down right exciting for me anyways.

Hoping to add another a few hp to it this winter with a fresh rebuild and a bit of Special Simon Dust. Couldn't imagine this motor on a 1200 or 1300 lb boat. Actually seriuosly thinking of dropping a Stroker in front of it , but my wife isn't buying it.

[onttr22]

All is fixed, I rebuilt the pulse pump and changed out the MAP sensor and it runs like new again. I think the pulse pump has been getting weak or the MAP sensor has been acting up for a while because the difference is incredible. Sounds like a different beast.

I'd like to Thank those that helped me solve my problem and to Red-Bullet for his idea of putting a 90 between the intake and sensor and how to diagnos the sensor.

Thanks once again Don and Eric for your help.