Merc 115 (Yamaha) 4 Stroke stalling issue, do not believe it is fuel related

[mattboeppler]

I am a long time reader and first time poster.

I have a 2002 Mercury 115 four stroke and I am having an issue with stalling when giving it some fuel. I have the Yamaha YDS system and have been using that often. It will run at all RPM ranges without spitting at all when I get it there. If I bump the gas fast it will not stall. If I slowly get the rpms up it stalls often. The fuel system has been cleaned (VST, VST Filter, Injectors, etc.) New spark plugs and firing on all 4 cylinders.

I have looked at the voltage on the TPS with the YDS and with the engine off the values range from 0.7 (throttle closed)- 3.9 (throttle open all the way).

I do not know much about setting the TPS or anything about the ISC. I know there are a few setting on the YDS about the ISC but I am a little lost with that. Is that the thing located above the VST tank with hoses coming off of it or is it somewhere else?

Any ideas would be great. Engine is serviced and I am very mechanically inclined but always learning. Below is a copy of my data logger. Thanks, Matt

Save date February 26 2014
ECM No.: 68V8591A10

Diagnosis
Code Item Result Condition
13 Pulser coil Normal
15 Water temp sensor Normal
17 Knock sensor Normal
18 Throttle position sensor Normal
19 Battery voltage Normal
23 Intake temp sensor Normal
28 Shift position switch Normal
29 Intake press sensor Normal
37 Intake air passage Normal
44 Engine stop lanyard switch Off
49 Over cooling Normal

Diagnosis Record
Total hours of operation 210
Code Item Occurred
Diagnosis Record is unavailable.

Engine Monitor
Monitor Item Result Unit
Engine speed 0 r/min
Intake pressure 98.55 kPa
Intake pressure 29.17 inHg
Atmospheric pressure 985.5 hPa
Atmospheric pressure 29.2 inHg
Ignition timing - deg
Battery voltage (12-16) 12.2 V
TPS voltage (0.5-4.5) 0.699 V
Throttle valve opening (0-90) 0 deg
ISC valve opening 65 %
Fuel injection duration 0 ms
Water temperature (below 90) 21 °C
Water temperature (below 194) 69.8 °F
Intake temperature (below 70) 21 °C
Intake temperature (below 158) 69.8 °F
Engine stop lanyard switch OFF
Shift position switch ON
Oil press switch ON
Dual engine system switch OFF

Data Logger[Engine operating hours according to engine speed]
Engine speed Time[h]
- 1000 r/min 13.8
1000 - 2000 r/min 13.7
2000 - 3000 r/min 6.7
3000 - 4000 r/min 40.4
4000 - 5000 r/min 40.1
5000 - 6000 r/min 4.1
6000 - 7000 r/min 0.1
Engine hours 210

Data Logger[Data comparison graph]
Engine speed[r/min] Battery voltage (12-16)[V] TPS voltage (0.5-4.5)[V] Water temperature (below 90)[°C] Intake pressure[kPa] Oil press switch[0:OFF 1:ON]
950 14.72 0.72 22 44.4 0
950 14.79 0.72 22.4 45.9 0
900 14.58 0.72 31.2 53.8 1
900 14.65 0.72 32.9 52.8 1
800 14.58 0.72 33.7 48.4 1
850 14.36 0.72 34.6 46.9 1
900 13.92 0.7 25.4 50.8 0
850 14.36 0.7 28 47.4 0
850 14.06 0.7 30 47.9 0
3800 14.36 0.94 30.8 55.3 0
800 14.58 0.7 31.2 45.4 0
800 14.65 0.7 31.2 45.4 0
800 14.58 0.7 28 46.4 0

[rodbolt17]

my guess is an incorrect link and sync or a sticky ISC valve.

[mattboeppler]

my guess is an incorrect link and sync or a sticky ISC valve.

When you say incorrect link and sync what do you mean?

Also, where is the ISC valve located?

Thanks for the reply, Matt

[rodbolt17]

means its possible that the throttle plates and plate position is no longer correct in relation to the TPS.
The ISC is located on the intake manifold.
it controls idle air and sometimes 65% open at idle is simply to much.
always is on an F150.
what typically happens is as your slowly moving the throttle the ISC and the ECU cant react correctly and it leans out and stalls.
if you accelerate rapidly guess what?
the ECU not only stays with sychroneous injection it adds group injection AND the sudden drop in intake vacuum adds about 5 PSI to the fuel rail.

its how EFI mimicks the accelerator pump on an old carbed motor.
so see, even with all the dodads bells and whistlers that motor has to react just like they did in the late 1800's.
open the throttle on a gasoline motor and you MUST add fuel or it goes blah.

so what your describing is an inadequate A/F in the intake manifold.

its why I keep harping, its suck squeeze bang and blow.
everything else simply helps it go.

[mattboeppler]

What do you think I should do to set the correct relation to the TPS? I have not done this before. Also, how should I clean the ISC? Thanks a ton!

means its possible that the throttle plates and plate position is no longer correct in relation to the TPS.
The ISC is located on the intake manifold.
it controls idle air and sometimes 65% open at idle is simply to much.
always is on an F150.
what typically happens is as your slowly moving the throttle the ISC and the ECU cant react correctly and it leans out and stalls.
if you accelerate rapidly guess what?
the ECU not only stays with sychroneous injection it adds group injection AND the sudden drop in intake vacuum adds about 5 PSI to the fuel rail.

its how EFI mimicks the accelerator pump on an old carbed motor.
so see, even with all the dodads bells and whistlers that motor has to react just like they did in the late 1800's.
open the throttle on a gasoline motor and you MUST add fuel or it goes blah.

so what your describing is an inadequate A/F in the intake manifold.

its why I keep harping, its suck squeeze bang and blow.
everything else simply helps it go.

[mattboeppler]

Could it be the shift cut out switch not adjusted correctly or faulty?

[ausnoelm]

I guess it COULD be lots of things, the best Yamaha guy in the known world has given you his opinion and a place to start but you choose to ignore that and ask "could it be?"

[mattboeppler]

I didn't ignore anything, read both posts

[aussiemarkc]

Suck,squeeze,bang and blow... Sounds like the quintessential woman !!!

[mattboeppler]

Suck,squeeze,bang and blow... Sounds like the quintessential woman !!!

That's great!

Update on where I am at.

It seems the ISC valve is working properly. I pulled it and sprayed it and it is working fine. I test it with the key and also with the YDS and it opens 100 percent when tested and 55%-65% when idling.

When I bring up the rpms and try to hold it there the engine wants to surge down. I cleaned the fuel system once again and it looks nice and clean. I have 40-45 PSI of fuel pressure at key on. Fuel pump seems to be working correctly.

I now have a throttle position sensor code that I did not have before so I am starting to think that my be the problem along with adjustment. I have a new one on order and should be here within a few days.

What are your thoughts rodbolt? I appreciate the help. What is the best way to adjust the throttle position sensor?

Thanks, Matt

[rodbolt17]

I am thinking your going to own a spare TPS.
do you have the service manual ?
if you have an actual failed TPS it will be the first one I have seen.
unless its been sunk.

[mattboeppler]

I have found the service manual online.

What do you suggest I do next? Once again, thanks for the help.

[rodbolt17]

I suggest you use the manual to properly test the TPS and do the link and sync.
remember that % number you see on YDIS is only a REQUEST.
its what the ecu is asking.
as the ECU does not and cannot monitor the physical position of the ISC it assumes its correct.
65% is a tad higher than I shoot for.

[mattboeppler]

I suggest you use the manual to properly test the TPS and do the link and sync.
remember that % number you see on YDIS is only a REQUEST.
its what the ecu is asking.
as the ECU does not and cannot monitor the physical position of the ISC it assumes its correct.
65% is a tad higher than I shoot for.

Holding the ISC in my hand I can see it move in and out and rattle when I do the request. When I open it 100 percent on the YDIS the RPMS go up to about 1400 for the 2 second test and then idles back down.

I will do the TPS test and link and sync. The engine has not been sunk, just sat for a while but all the fuel system has been cleaned twice now.
Thanks, Matt

[rodbolt17]

ok, it moves. and your point?

that valve controls idle air, sometimes at 65% and a slow moving throttle opening you end up with to much air and the motor goes blaauugh.

by moving the throttle rapidly the rapid voltage feed back by the TPS alerts the ECU that the accelerator is opening rapidly.
the ECU responds by firing the injectors in a group mode as well as the synchroneous mode this adds fuel.
now as the throttle is rapidly moved intake vacuums falls rapidly as well.
the vacuum line in the pressure regulator is brought into play now.
with that sudden vacuum drop the regulator will actually tighten a bit and add about 5 PSI on the rail that the ECU cant monitor.
more pressure for the same injector ON time means what ?