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OK Mechanics. Need some help & advice


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I'm a gear head but ford guy. First thing that comes to mind is the cats if one is going out or both when you go to give it more gas it should act just like you are saying. Pull one of the new plugs from each side and see what they look like see if the ground strip burn on one of the plug is way higher than the other if so that is your side because it will cause extra heat in the cylinder. (Ground strip burn is the L part that the spark goes to. You will see the difference in the part that has gotten hot and the rest) Example this is one I got way to hot on nitrous and melted it.

IMG_2427_zps902e088e.jpg

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Definitely not a mechanic, but I'm going to guess TPS (throttle position sensor.) Not sure about your motor, but on mine it was only $40 and 10 minutes to change...might be worth the time & money just to eliminate it as a possible culprit.

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Does it run better cold? ECM could be doing what it is supposed to do but getting bad data. There are 2 temp sensors o e for the ECM and one for the guage. IAC will cause rough idel but not much else.

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Does it run better cold? ECM could be doing what it is supposed to do but getting bad data. There are 2 temp sensors o e for the ECM and one for the guage. IAC will cause rough idel but not much else.

REW, just curious, where is the second temp sensor for the ECM? I replaced the one on top of the intake manifold and it ran fine for a while but started acting up again when transitioning from cold to hot (right around 130F).

BS, the TPS and IAC are two sensors up on the throttle body. Like Formulaben mentioned, the TPS is a cheap part to throw at it. One thing that you may want to do is to disconnect the battery completely so that the ECU re-learns after replacing the IAC and/or TPS. I didn't do that when I changed mine out and my problem returned after a few weeks. I haven't had a chance to get back up to work on it but your problem sounds a lot like mine but mine only happens when transitioning from cold to hot.

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You can test the TPS with a multimeter

tps sensor test.

using multimeter set to dc volts,
probe dark blue wire with needle probe(red lead), (black lead to ground)
ignition on engine stopped
voltage should be around .5vdc. His could be a little off.
slowly open throttle, voltage should increase up to 4.5vdc at wide open throttle. This could be a little off main thing is in the ball park.
should be no flat or dead spots or voltage spikes. This is the key part!!

  • Like 2
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  • 4 weeks later...

The best explanation we can come up with......There were enough stored codes (because of the water in the fuel) that it sent it into limp mode. Then during the process of diagnosis we created a few more so the tech cleared the codes. He also changed out a set of brand new spark plugs because of some light fouling though but at that point he was just trying to cover all the bases cant blame him.

Sure wish we had a mefi scan tool during this process.

She ran well today.

Edited by Lance B. Johnson
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is water in the fuel from dragging the vent while surfing?

There are a lot of surf hours on this boat and has never done this before. The vent hose has a big loop in it and racor installed.

Nevertheless we aren't ruling that out as a possibility. There is also the possibility that the gas cap wasn't tightened enough because that is the one we typically use for filling the boat and it is very much under water while surfing.

Edited by Lance B. Johnson
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should note also that there was indeed a lot of water in the fuel. I know his original post kinda alluded to the fact that it was a little cloudy but later we drained the gas into clear containers and there was an estimated 3 gallons of water in the fuel. Surprised it ran at all.

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what does a mefi tool show that you can't see on the dash? Aren't all the codes visible in the settings (diagnostics?) menu on the dash?

I have no idea. never used one except it would be nice to be able to clear the codes and see data.

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A scan tool will let you see the current values for sensors and engine parameters to help you figure out what is and isn't working. Injector pulse width, spark advance, engine load, etc.

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Shawn,

Scan tools these days offer a lot more then just access to codes. However I usually only work with cars so I am not sure how much information a MEFI system can produce. But I can be reasonably certain that it would be a lot more then what the dash will tell you.

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Might also be worth looking at having the injectors serviced in the off season. Fuel lines don't hold up as well anymore with the additives they are putting in the gas and it has been known to get past the filters and stuck in the injectors. Water in the fuel won't help the injectors either.

Not a cheap service, but something I'd look it if the problem persists.

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