1999 DF70 WOT Issues

[selfel]

I have a 1999 DF70 (actually the Evinrude version) that I purchased last year on a 22ft pontoon boat. Motor was not run for a couple of years before I bought it, only had 145 hours. Previous owner said IAC valve failed and had a new one that I installed. Cleaned the fuel tank and took it to the lake. Still idled high but seemed to run pretty good, first WOT run got me about 5500 RPMs if I recall. Second try, only about 4000 rpm. Has check engine light and about 10 second continuous horn after start up. Get 2-5-5-5-5-...........check engine light code when key is turned on. I pulled the electric pump, cleaned the screen (pretty varnished up) and installed new HP filter. No change in performance. Pulled the fuel rail and injectors and had a shop clean and flow test them, they said initially they had hardly any flow but were fine after cleaning. All back together but still no more than 4000 rpm. I let it set until last few weeks, bought the Suzuki Diagnostic software, no codes shown. Finally figured out the high idle, the previous owner had the butterfly off of the closed throttle switch with the manual set screw. Got it idling really nice on the inlet air screw with IAC duty at around 30% or so at idle.

Only thing I see from the diagnostics when running is fuel pump duty is only 76% at WOT (4000 rpm) Also, history from the diagnostics shows 494 minutes in the 5000 to 5500 rpm range so confirmation that there is something up now.

In general the motor starts, idles and runs like a top. No missing or hesitation. It's not getting shut down by the computer at 3000 rpms like if you try to rev past that in neutral (it's very obvious then that the ECU is killing injectors and/or coils).

I have to think that the 2-5-5-5-5...... code is the missing piece of info that may get me on the right track. I've seen a couple of posts online of the exact same code and similar issues but never saw any that resolved the problem.

Last thing, plugs are very black and sooty (not wet) so somehow it's running very rich although like I mentioned it seems to run very well up to 4000 rpm.

Thanks in advance for any help that anyone may have.

[selfel]

Just bumping this back up to see if I can get any responses. Still trying to get this thing figured out, and help would be very appreciated.

[Moonlighter]

There is a sticky thread in the top section that lists all the fault codes and what they mean. They are only 2 parts eg 2,5 not 2,5,5,5,5,5

[selfel]

Yes sir, I've reviewed all of those lists. Mine is definitely blinking 2 then 5 but the 5 blinks just keep on repeating forever.

[redlowrey]

Pull the cowl off and see if there is no air restriction, something may have built a nest inside it, for the plugs to be black, the the injectors are spraying plenty of fuel and there is not enough air to burn it.
If the cowl is clear, see if you can run the engine without the cowl, there might be exhaust gas leaking from the engine holder reducing the amount of air that is being burnt.

[selfel]

In all my internet research I did see a post where someone had bird nest in the cowl. I've checked for that as well as confirmed the throttle plate is 100% open when the at full throttle. Current thinking is it may be very over propped, looking for a one to test now. Check engine code is still a mystery but may try replacing that gauge with a known good one to see if it's a problem with that, not the motor. Thank you for the input, I really appreciate it.

[redlowrey]

You should be able to tell straight away if it was over propped, try trimming it out till you nearly blow out and see if it is capable of getting to the rev limiter, seems strange you have gone from 5500rpm to 4000 rpm same prop. What are the compression pressures.

[selfel]

I've trimmed it till it starts to cavitate and it revs well beyond 5500. Never let it get to the rev limiter I don't think. I'm really starting to second guess my recollection of getting 5500 rpms out of it when I first got it last year. Maybe I just trimmed it too high. Compression is right on spec on all 4 cylinders. It only has 150 hrs on it. Hopefully I can find a 13 pitch prop to try this week. It currently has a 17 pitch 3 blade SS prop on it. From everything I've read and folks I've talked to a 22' pontoon with a 70 hp should be more around 13 pitch.

[Moonlighter]

22ft pontoon…. 70hp engine…… making that engine work very hard!

Try the lower pitch prop. you probably want to be able to hit around 5500rpm at wot trimmed out to optimum, but check the operating range for your engine year and aim somewhere close to the top of that range, within a couple hundred rpm.

Remember that Suzukis run different final ratios to most other brands so direct comparisons are not applicable.

Have a look on the Suzuki UsA website where they show the current model engines and have boat tests with various boats.

I found this one where even with a 90 on a 22’ pontoon they ran a 14x 13P prop.
http://www.suzukimarine.com/Product%20Lines/Outboard%20Motors/Products/DF90/2012/~/media/Marine/BoatBuilders/TestResults/P/Premier/Premier%20225%20Sunstation%20DF90A

And this one for a 70 on a 20’er

http://www.suzukimarine.com/Product%...202080%20DF70A

[selfel]

Those are great links, thanks so much! Hoping for an easy fix here.