2008 150 txrg starts and shuts off constantly

[arctic 1]

that's right I cant start it only with intake cleaner which I would rater not do and yes I do have a yds

[twirk_twirk]

Okay, YDIS is a great tool to have.

When you have a chance, hook up the YDIS software and take readings of the intake pressure and atmospheric pressure while the engine is off.

These two readings should be the same (approx. 30inHg at sea level).

If they are not, it indicates that you might have a faulty atmospheric pressure sensor and this can cause your engine to NOT start, even though as you state, you have fuel, fire and compression.

This is another option for you to look at. Again, I am speaking from experience

[arctic 1]

ok will do is this the other sensor on the intake
also do you think the isc should be so hot that I can barely touch

[arctic 1]

give me 5 mins I will run out and plug her in and see if the numbers are the same

[twirk_twirk]

Yes, the atmospheric pressure sensor is the sensor sitting next to the Idle Speed Control and looks like this:

I don't have advice on the ISC heating up. Someone else with experience there might chime in hopefully.

[arctic 1]

I am not at sea level about 100 feet about and I have a intake press at 4 and atmosphere at 19

[twirk_twirk]

Okay this is very good info.

No matter where you are at, these two numbers should be the same when engine is off.

With engine off, if intake pressure = 4 and atmospheric pressure = 19 something is wrong. (However, neither of those two numbers are correct if you are at 100feet above sea level, perhaps someone else will chime in here)

I would venture to say that your atmospheric pressure sensor is shot and needs replacing. ALSO, however this strengthens my first point about checking your battery specs. Just look at it and make sure it's got the correct Ah rating for the F150. If it doesn't and you replace the atmos pressure sensor without replacing the battery, for sure you'll be buying another atmos pressure sensor sooner than later, you'll see other weird symptoms pop up as well.

[arctic 1]

okay I will try to grab that sensor tomorrow also and will indeed check the battery with all this being said I wonder is it possible that the ISC has something to do with these numbers being wrong

[arctic 1]

ya looks prob more like 4 to 5 hundred above sea level

[twirk_twirk]

Just as a side note, with engine running, the intake pressure should be approx. half of the atmospheric pressure.

just as reference here is a screenshot of my F115 pressure sensors with engine OFF (at sea level) and with engine ON, running at idle. Notice how at idle the intake pressure sensor is about half the value of the atmospheric pressure sensor (this was after I had replaced the faulty atmospheric pressure sensor)

[twirk_twirk]

Let us know what you find out tomorrow.

Hopefully rodbolt will have some info for you on the ISC valve.

[arctic 1]

got it ya I def have something going on great to have some help

hopefully rodbolt will cut back in with some ISC info

will try these sensors tomorrow and hope for the best

will keep u posted

[arctic 1]

where are you guys located just curious

I am in Canada's high arctic Iqaluit ,Nunavut

[greasyshaft]

The isc will get warm, electronics tend to that

[rodbolt17]

usually most anything over 200*F means the ISC is sticking mechanically and is over currenting the ECU.
THINK mon THINK.
wher does the 12V + power supply come from to operate the ISC?
where does the GROUND path go during operation?
the ISC is NOT monitored by the ECU.
the ECU sends the request and ASSUMES the ISC physically moved.
if it cannot move then the request(ground path) is continuously repeated.
its a stepper motor and not a continuos run motor.
it controls idle air.
the engine will run with the ISC unplugged and removed from the intake.
will most likely idle about 1800 RPM or so but you can use your thumb over the hole to lower idle speed.
the MAP sensor can be tested with an ohm meter,the 5V reference can be tested both loaded and unloaded.
remember garbage in equals garbage out.
but if the ECU is overheating due to excessive current draw it can do stupid things.
5 v is standard digital electronics protocol.
the 5v is generated inside the ECU and fed to all the engine sensors requiring a 5Vreferance.
its always possible that the sensor that throws the code is NOT the sensor that failed due to the common use of the 5Vreference.
and 19" of mercury is about 22,000 ft.
the F250 will run with a baro of 19" but runs very lean about 2800 RPM.
dunno why Yamaha mapped the F250 to be able to run at 22,000 ft as most water is rather solid at that altitude.
but it never threw a code.

I have seen sticking ISC valves light ign coils on fire and take out the ECU on the F225, and burn up ECU's on the F115.
never saw it on an F150, yet.

so if I looked at a key on engine off baro reading below about 30"Hg I would either assume a hurricane was coming or suspect either the 5V ref failed or is loaded down, the ground or feed back path failed or the sensor itself failed.
now is where a bit of testing and a bit of understanding can save a lot of time money and frustration.
easy test.
simply use paper clips slipped inside the back of the connector.
gor from orange to black.
turn on the key.
should have 5V.
if not unplug the sensor and recheck.
if it stays low or high start unplugging any other sensor with a 5Vref.
typically the weather channel in your area has baro pressure.
simply check to see if your baro pressure and the weather channel are close.
unlike automobiles the baro pressure is locked into the ECU at key on and wont change until the next key cycle.
boats,unlike cars, typically wont change altitudes enough to alter fuel ratios during a key cycle.