2003 DF140 need some help

[Lunchmoney]

New member here...
Have twin 2003 Suzuki DF140 4 strokes with separate fuel systems. Port engine starts right up and is very responsive to throttle advancement. Have something going on with the starboard side in comparison to the port side. Starboard engine symptoms are:
Sometimes hard to start without advancing the throttle slightly when warm, won't start without advancing throttle slightly when cold; acceleration is slow to respond to throttle advancement once started and in gear. It will accelerate up to about 3K rpms and stays there despite the throttle being depressed all the way. When this happens, I'll monkey with the throttle for a few seconds going up and down and then it takes off and will accelerate up to 5K rpm or so just like normal and runs strong. It idles fine once warmed up. Backed off the throttle fairly quickly one time and it cut off. Check engine light came on and did a series of beeps but it quit before I thought about the sequence and it never went off again the rest of the day.
Heard maybe the MAP sensor needs to be cleaned or replaced. Heard it could be the TPS (throttle position sensor) but I don't see where that would throw a code and can't find any reference to a TPS in the manuals. Also heard might have air seeping into the fuel system throwing the ratio off. From researching, I'm leaning towards the MAP sensor. Any input would be great. Thanks.

[Solarman]

It might also be the IAC valve dirty, or sticking my first thought.

Good luck.

[catacom225]

Df 140

Have you checked the engine holder for corrosion, try running it with the hood off. If its not giving a error code then start with the basics, run a separate fuel source, replace filters etc.

[Lunchmoney]

Thanks for the input so far... What / where is the engine holder? I've read about a white wire that get corroded and causes problems... Is that what you are referring to?

[Beginner's Luck]

If you thought of the different components as Lego blocks, the engine holder would be the block directly under the engine. If you remove the port side cover there is a steel plug that screws into the aluminum engine holder, it corrodes and eventually lets exhaust gasses escape inside your engine cowling thereby confusing your sensors. Inspect this area for a hole, or remove your cowl while this condition is present and see if that fixes it. I had issues with the IAC (idle air control valve) before, but my engine would ignite and then die suddenly. I'm thinking that the IAC only controls air volumes at idle though, not the upper or mid ranges. When I had an issue with the white wire, if I remember right, my starter would spin but the engine wouldn't fire. Wish I could help more.

[Lunchmoney]

That's a lot of help. Thanks to all that provided input thus far. I just bought this boat so I'm trying to work out the bugs. Unfortunately she's in storage at the coast which is about 325 miles away. Going down in a few weeks and I'm trying to get to a position where I can resolve this issue when I hit town again. I guess I'll clean the MAP sensor, the IAC sensor, change the fuel filter, check this plug for obvious holes or corrosion and anything else I can come up with betwixt now and then. I could hire a local to work on it and hopefully fix it but I'd rather do it myself and save the cash, plus I'll gain knowledge and experience for future use.
This plug that is steel, does it have a sensor on the back of it? Why is it there? Steel plug in aluminum threads is going to be a problem at some point. Dissimilar metals... WTH Suzuki? Is there a source for replacement plug made of aluminum? Even if that's not my problem now, I will address it this winter before it becomes a problem. Thanks again for the help!

[Moonlighter]

The steel plug is like a welsh plug - it just stops up a hole in the casting - many people speculate it was there for an O2 sensor on the car version of this engine. So there are no sensors etc on it al all. Just a simple plug.

You will find it located a couple of inches below the fresh water hose attachment on the port side of the engine - as has already been mentioned, you probably need to take the lower cowls off the engine to see if properly.

If the surrounding area is in good condition you can replace using the plug listed below. But if the corrosion has spread to the surrounding alloy or the threads damaged too much getting the old plug out, welding up, or, a much bigger job, replacing the engine holder entirely, may be required.

And yes, it was a dumb thing for Suzuki, back in the early days, to put a mild steel plug into an alloy casting. They redesigned the engine holder casting back in 2008 to eliminate that plug so it is no longer an issue since that model year.

You can get a replacement alloy plug for it, or, some people have just had the hole welded up by a suitably qualified aluminium welder using some heavy plate alloy. If you do an "advanced search" on this forum for Something like "DF140 engine holder **** plug" you will find references to it. Also try a similar search on ebay as I think the fellow that makes them sells via there.

Edit: found it for you!

Suzuki Outboard DF140 Engine Exhaust Port Replacement Drain Plug DF Aluminum | eBay

[Lunchmoney]

Great info! If the one on the starboard engine has corroded to the point it's allowing exhaust gases to escape, that could be my problem I suppose. The engine is pulling in exhaust fumes instead of clean air but it seems like it would stall out and not idle if that were the case. I guess it would depend on the amount of fumes escaping. If the engine is cold, it won't start without advancing the throttle slightly then it starts right up and idles fine. Once I leave the dock and begin to accelerate, it's sluggish or slow to respond to me pushing the throttle forward. After a few seconds it'll grab and take off and then run like a champ all day at speed or on the troll. I don't think it's anything major. I really don't think it's fuel as it always gets non-E and the port engine does fine. With a four stroke, you shouldn't have to prime the bulb or advance the throttle any before starting I'm told. It should be turn key and start. I'm thinking with my keyboard at this point. I appreciate everyone's help!

[Lunchmoney]

Found out the previous owner had these plugs removed and the holes welded shut in both engines already so that's not the problem. Guess that's good news and bad. Back to the MAP and IAC sensors I guess.

[redlowrey]

Found out the previous owner had these plugs removed and the holes welded shut in both engines already so that's not the problem. Guess that's good news and bad. Back to the MAP and IAC sensors I guess.

In your first post you said that if you played with the throttle it would come good and go to 5k rpm, this tells me you might have a problem with your neutral switch on the engine. When the engine is in neutral the ecu will see 0 volts on pin five, when you put it into gear it will see 2.5 volts, if the ecu see's o volts on pin 5 while the engine is running it will limit the rpm to 3000 and fix the timing at 8 degree's. With the engine not starting sounds like there is not enough air bypassing the throttle plate, it might only need an iac air bypass adjustment. Do this simple test remove the rubber plug on the throttle body and turn the bypass screw out or anticlockwise two turns then start your motor without using the warm up leaver. If it starts up all right it might idle a bit faster but it tells me it only needs more air at start up and a air bypass adjustment.

[Lunchmoney]

I'll adjust the air bypass screw first and see if that corrects the hard to start issue. If no change, I'll proceed to cleaning the MAP sensor and IAC sensors.
As far as the neutral switch, I guess it's OK to crack open the ECM to expose the pins while it's running? I have a good digital voltmeter that I can use to check volts on pin #5. If I bump it into gear and still showing 0 volts, that means the switch is malfunctioning correct? As stated, I'll monkey with the throttle a bit and it'll eventually get up and go. Would that mean that the neutral switch is working sporadically? If me working the throttle back and forth gets it to eventually accelerate beyond 3K, would that indicate the neutral switch begins to work again or is it bypassing it somehow? can I ohm through that switch and check it somehow?
Tons of great info here from everyone, thanks again!

[redlowrey]

I'll adjust the air bypass screw first and see if that corrects the hard to start issue. If no change, I'll proceed to cleaning the MAP sensor and IAC sensors.
As far as the neutral switch, I guess it's OK to crack open the ECM to expose the pins while it's running? I have a good digital voltmeter that I can use to check volts on pin #5. If I bump it into gear and still showing 0 volts, that means the switch is malfunctioning correct? As stated, I'll monkey with the throttle a bit and it'll eventually get up and go. Would that mean that the neutral switch is working sporadically? If me working the throttle back and forth gets it to eventually accelerate beyond 3K, would that indicate the neutral switch begins to work again or is it bypassing it somehow? can I ohm through that switch and check it somehow?
Tons of great info here from everyone, thanks again!

...You don't have to crack open any thing, remove the port cover remove the plastic cover in front of the ecu then pull the ecu forward. all the pins are numbered, pin 5 brown, just slide a thin needle down the side of the pin and connect up your multimeter key on 0 volts in neutral 2.5 in gear. When you check your map sensor pin 29 white, key on engine off, should see over 4 volts, crank the engine and when it starts should see about 1.5 volts and if you rev the engine you will see it toggle between 1 and 4 volts.

[Lunchmoney]

...You don't have to crack open any thing, remove the port cover remove the plastic cover in front of the ecu then pull the ecu forward. all the pins are numbered, pin 5 brown, just slide a thin needle down the side of the pin and connect up your multimeter key on 0 volts in neutral 2.5 in gear. When you check your map sensor pin 29 white, key on engine off, should see over 4 volts, crank the engine and when it starts should see about 1.5 volts and if you rev the engine you will see it toggle between 1 and 4 volts.

Great details! Thanks!

[Lunchmoney]

What are yawls thoughts on the diagnostic software? Bring that I have 2 - 13 year old motors plus I have a new 115 on another boat, would it be worth my investment? I have a laptop already. It appears to be readily available online for purchase. I'm better with wrenches than computers but if it would save me one trip to the dealer it would pay for itself.

[seapro]

I would check spark on individual cylinders by pulling spark plug wire to see if it is in one cylinder. If it is check moisture around the spark plug electrode. i am have the exact issues cylinder 4 is fouling due to moisture until warms up and dries out then runs fine the rest of the day. Next day cold start same issues,