DF 140 idle slows down with cover.

[gildas]

Hi all

All I posted this on several boat/engine forums.
I will put the answer/solution on all of them at the end.
So don’t be surprise and don’t «*waste*» your time to answer on all of them :-)

I have a quite old Suzuki DF 140 more than 10 years, 1000 h.
I changed the IAC valve recently.
I tuned the idle speed with the screw (not the «*electronic*» way..it may be important). Idle speed around 800 rpm. Just ok.
All seems ok when the cover is out.
With the cover after 1 or 2 secondes, it is slowing down, and may stall…

So it is like if the air was not flowing inside with cover…but what , how ? And especially at low speed when it is not needing much air.

After that it runs perfect, but I had to put in gear, then put the cover and all was ok from slow gear to full throttle.

Thanks a lot for your advises.

Regards Gildas

[Moonlighter]

Ok, we are really not into guessing games here on this forum.

If you are saying that you know what the problem was/is, please put it up here along with the solution.

If you dont, and you actually want some help, let us know.

[gildas]

Hi moonlighter

sorry if my post is not clear,
english is not my native language I may not have explain correctly.

no I don't know the answer.
I asked the question on several forums.
If I get the answer on another forum, I will post here to share what I learned.

please let me know if I have to explain more cleary my issue

thanks for your help
regards
Gildas

[Moonlighter]

Ok, thats fine.

Check the engine just below the flush hose connection point on the port side. You should take the lower covers off as well as the cowl to get a good look at this area.

Look for corrosion and holes in the engine holder near a casting plug at that location.

This is a known problem with earlier model 140's before 2008. The engine holder casting was changed to eliminate it in later years.

As a result, hot exhaust gases escape from the corroded hole and choke the engine, symptoms very much like what you have described - when the engine is running and the main cowl is removed, the engine gets clean air and runs fine, but when the cowl is put back on, the exhaust gas is trapped under the cowl and gets sucked into the engine, causing it to run badly and stall.

The heat escaping from this area can also damage nearby wiring.

Let us know what you find. There are some options to address the issue if you find this is the problem.

[redlowrey]

That as my first thought too, but I think the check engine light would have come on with a map sensor code, plus at wide open throttle it would have been down on power with all that exhaust gas being consumed.

Adjusting the idle speed without the ecu holding the duty cycle at 15% is a wast of time, as you screw the air bypass screw out, the ecu will drop the duty cycle on the iac to try and keep the rpm at 700rpm.

[Greg Moore]

Redlowry, check what Moonlighter suggested. You don't run O2 and knock sensors like newer 140's, your ECU will have no idea it's breathing crappy air! The leak will typically be the same or worse at idle (harder to push exhaust down to prop at idle). At higher speeds, the leak won't have increased much but the engine air intake is much higher so the percentage of exhaust in the air is very low.

[Moonlighter]

Lets wait and see what he finds.

If he does find that the plug has corroded out, if he posts some photos, then everyone can suggest options.

[redlowrey]

Redlowry, check what Moonlighter suggested. You don't run O2 and knock sensors like newer 140's, your ECU will have no idea it's breathing crappy air! The leak will typically be the same or worse at idle (harder to push exhaust down to prop at idle). At higher speeds, the leak won't have increased much but the engine air intake is much higher so the percentage of exhaust in the air is very low.

''''''''''''''That is right the ecu has no idea that the combustion chamber is full of exhaust gas, and it still injects the same amount of fuel for a chamber full of air and fuel.

The engine starts to run rich, manifold vacuum drops and map sensor signal voltage increases, fuel injector pulse width increases engine floods and stalls, and usually the check engine light comes on with a map sensor code.

[gildas]

hi all,

thanks for all the hints and excuses for no reply.
I did not have time so far to test again.

Be sure that I will reply with the results.

regards
Gildas

[pniksnut]

if you're at the boat also check the flame arrester located just before the throttle body. i had a custumer with an power issue and no error code's. in the end we found a dirty flame arrester.



https://photos.app.goo.gl/YvORosRS8yZYm4tq1

[gildas]

I will check that also.

whoo that is great hints so far.
can't wait to test all that.
I am learning a lot of new words as well ;-) . (english not my native langage)

[Hoosmatroos]

I had to look-up where New Caledonia was

You guys must have the most beautiful water in the world

[gildas]

Hi all
some videos to show exactly how it goes.
I did not have time to open but I changed the 4 block anode I did not see any corrosion.
In case the videos can help. thanks
https://photos.app.goo.gl/a8MU1gdIznAMnrt23
https://photos.app.goo.gl/T9M8Gwtxksg5D5ZN2

[pniksnut]

looks great to me. i only hear the ref limiter because its in neutral.
dont understand what your problem is

[gildas]

I totally missed the point with my video...
at least we can more or less that it is running fine.
but we don't see/hear when it is slowing down when I put the main cowl.

thanks