# Suzuki DF90 sluggish/dies at idle



## caylorray (Oct 3, 2007)

My 2004 90HP Suzuki with close to 600 hrs recently started giving me a problem. It's the first time I've ever had any problem what-so-ever with this engine.

-Put the boat in the water, start it up to get it warm, and by the time a buddy gets to the boat from parking the truck/trailer, it starts running sluggish, and dies soon after.

-Attempts at restart fail, it just cranks over, but doesn't quite want to fire up. Wait a short bit, and it'll crank right up. Get it past idle before it starts dogging and it runs perfectly, all the way through WOT.

-At any point, if I drop the throttle down to idle, the engine will die shortly after (unless I nurse it really well). 

-Again, let it sit for a bit, and it starts right up.

-While the eng is running like this, I get a check eng light with flashes, which I found corresponds to the MAP sensor. 

-With the boat sitting on the trailer with rabbit ears attached, it runs perfectly, from idle through WOT, in gear or out of gear, for as long as it sits there; no check eng light.

-A friend knows a mechanic and he said 99% chance it's the thermostat. Just took the thermostat out and tested it. It starts opening ~150 deg F, and fully open 5-10 deg later.

I'm assuming something is causing the MAP sensor to sense a bad pressure reading, then the MAP sensor sends signal to the computer making it think it needs to compensate, and resulting in the shut-down. I just don't know what's causing the manifold pressure to be off. I've looked the eng over and found no visual problems, to include vacuum lines.

Any thoughts?


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## nic247nite (Oct 10, 2007)

Are you hearing any buzzers or horn? Sometimes when your do for a check up things like that will happen, please call me 444-9760 and we will help you and give things to try.


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## caylorray (Oct 3, 2007)

Get a buzzer, but it's just a audible to let you know to look at the gauge. Has nothing to do with scheduled maintenance. 

Right now the one thing I do know is that there's something different between circulating fresh water vs. saltwater through the cooling system. Saltwater causes it to die at idle, fresh water doesn't. I just can't put my finger on it. 

Been googling and found some things that have me interested. Found that if the engine doesn't get warm enough, the computer does some things that might cause it to do what it's doing. Also I've heard saltwater has a different affect on thermostats than freshwater. 

Could it be that freshwater allows the thermostat to open properly, but saltwater is causing it to open prematurely, preventing the engine from getting to required operating temperature? Then perhaps the computer try to compensate, but instead causes it to run poorly?

Maybe with the throttle above idle it locks out that sensor or something, allowing the engine to run right?


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## Telum Pisces (Sep 27, 2007)

When your engine is on the muffs, it's not under a load. Yet when you put it in the water, the pump is having to work/pump the water in making the motor slightly under load. That's the difference that you see. It shouldn't have anything to do with fresh vs. saltwater. So when your boat is in the water, an idle problem is going to show up vs. on the muffs it will not.


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## caylorray (Oct 3, 2007)

> *Telum Piscis (5/29/2008)*When your engine is on the muffs, it's not under a load. Yet when you put it in the water, the pump is having to work/pump the water in. That's the difference that you see. It shouldn't have anything to do with fresh vs. saltwater.


Hmmm, that's true. I just replaced the impeller last year, and I'm getting a good stream from the pee-hole, and no overheat indications. So water supply is not an issue. Yet, everything else being equal, the eng runs perfect with freshwater, but poorly with saltwater. So it has at least 'something' to so with fresh vs. saltwater, even if not obvious. Just not sure what yet.

Again, I've never experienced this problem before, and I've had the engine 4 years, and almost 600 hours. So it's definitely not normal!


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## Tuna Man (Oct 2, 2007)

Are you telling us that the engine will run differentlywhile running it in a freshwater lake/river...and then in saltwater?


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## Telum Pisces (Sep 27, 2007)

> *caylorray (5/29/2008)*
> 
> 
> > *Telum Piscis (5/29/2008)*When your engine is on the muffs, it's not under a load. Yet when you put it in the water, the pump is having to work/pump the water in. That's the difference that you see. It shouldn't have anything to do with fresh vs. saltwater.
> ...


I can almost tell you for certain that there is not a problem with saltwater vs. freshwater. Unless you are taking it to the river and it runs fine and then take it to the bay and the problem occurs, it's not a difference in water. It's the pressure difference between running it on the muff and actually having the water pump suck in water when your boat is in the water. You can take a large tub of fresh water and run yourengine and I can probably bet that it's going to show the problem just as ifyour boat isin the water. 

Have you checked for water in the fuel???


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## caylorray (Oct 3, 2007)

> I can almost tell you for certain that there is not a problem with saltwater vs. freshwater. Unless you are taking it to the river and it runs fine and then take it to the bay and the problem occurs, it's not a difference in water. It's the pressure difference between running it on the muff and actually having the water pump suck in water when your boat is in the water. You can take a large tub of fresh water and run your boat and I can probably bet that it's going to show the problem just as ifyour boat isin the water.
> 
> Have you checked for water in the fuel???


I see what you're trying to say, I think. Using a tub was going to be my next step just to see. 

Are you suggesting that the impeller might not be doing it's job quite well enough, and hose pressure might be hiding that fact? At least that's the thought that leads ME to want to use a tub.

If that's true, then what would explain the eng running fine above idle? Shouldn't it still experience a problem if water isn't circulating well enough? And shouldn't I be experiencing an overheat situation?


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## Telum Pisces (Sep 27, 2007)

> *caylorray (5/29/2008)*
> 
> 
> > I can almost tell you for certain that there is not a problem with saltwater vs. freshwater. Unless you are taking it to the river and it runs fine and then take it to the bay and the problem occurs, it's not a difference in water. It's the pressure difference between running it on the muff and actually having the water pump suck in water when your boat is in the water. You can take a large tub of fresh water and run your boat and I can probably bet that it's going to show the problem just as ifyour boat isin the water.
> ...


What I am saying is that idle problems/issues sometimes do not show up on the muffs because the engine is not under a load. Your water pump/impelleris probably fine. This is a fuel injected motor, right? PM Kenny (sequoia) on here. He should be able to help you out.


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## caylorray (Oct 3, 2007)

> What I am saying is that idle problems/issues sometimes do not show up on the muffs because the engine is not under a load. Your water pump/impelleris probably fine. This is a fuel injected motor, right? PM Kenny (sequoia) on here. He should be able to help you out.


Interesting.

Yeah, it's F.I. Before I bug anyone else any further, I'm gonna use a tub and see what happens. 

Thanks a ton for your replies! It's given me other things to think about, which will hopefully lead me to finding the problem. :doh


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## flipthelip (Apr 7, 2008)

I had the same problem with mine it was back pressure and I think some sensorJEFF @ Posner Marine and found the issues call them local Suzuki dlr


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## caylorray (Oct 3, 2007)

Finally got a tub and ran the engine. Wasn't "quite" as bad as having it on the water, but still ran sluggish and eventually got it to die by going above idle and back to idle.

So, now I see it definitely has nothing to do with saltwater vs. freshwater. Man, I was SO fixated on that!

The research I've done definitely tells me I have a backpressure issue. Now I just need to figure out what's causing it. I've seen mention about a leaking gasket (or gaskets), but not sure yet where that might be on my engine.

Back to Google!


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## DOUBLE "D" & LV (Oct 2, 2007)

Have you thought about just having the computer at a dealer hooked up to it????? You mentioned you are getting a MAP sensor code. The MAP sensor is what works the low RPM running, of course with other sensors as well. After a certain point, the MAP has little to no effect on runability. You may be chasing a ghost by not observing the obvious when it is staring you in the face. I would highly recommend letting someone hook the computer to it and check the MAP and for other sensor issues. I would be able to do it if I still had the program, but since I don't and your gauge is telling me to check the MAP, that would be the first place to go after a few preliminary checks.


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## caylorray (Oct 3, 2007)

Taking it to the dealer is definitely an option. 

The thing I like about troubleshooting problems this way, "chasing a ghost", is I learn so much along the way. 

My wife's Mustang has had a check eng light a few times, and although it took some time to finally figure it out, I did, and fixed the problem each and every time. Although I didn't become an expert, I learnt alot that will help to diagonosing future problems that may arise, like how the O2 sensors operate, and that there are "banks", and so on.

I still have a few things I want to look at on the engine that I think could cause my backpressure problem, ie restrictions in the exhaust relief ports (something I've learned about researching on my own). Once I run out of ideas, I'll be looking for a mechanic.


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