The engine cranks just fine, but it is very hesitant to start?

OZ1991

MEMBER
2015 FORD TAURUS
3.5L
6 CYL
2WD
AUTOMATIC
93,000 MILES

I purchased this car a while ago and I've done a major service.

1- Changed brake + engine oil and filter.
2- Drained and refilled coolant.
3- Replaced air filter.
4- Cleaned all 6 injectors.
5- Fixed a brand-new fuel pump along with its module (FPDM).
6- Cleaned my Cats + O2 Sensors.
7- Spark plugs are clean (replaced recently by previous owner).
8- Vacuum leak test in the engine bay conducted (smoke machine test) no leaks at all.

All this has been done to no avail, the problem is still persistent, and the car acts up when I try to crank it up.
I've approached a data logger who had claimed the engine is running lean and the intervention of the PCM is helping the car stay alive by increasing the fuel to the mix.
Short fuel trim values are off.
and it's also worth mentioning there are no engine codes popping up whatsoever.
Help!

Video (Click to make bigger)

7 Replies

JACOBANDNICKOLAS

MECHANIC
109,901 POSTS

Hi,

My first thought based on what you have already done is the engine coolant temperature sensor (ECT) may be sending a faulty signal to the PCM. If that happens, it causes the air/fuel mixture off and can cause this to happen.

Do me a favor. If you have a live data scan tool, connect it and check the ECT signal before starting the engine. It should be very close to the ambient temperature. If it is far off, the sensor is the likely cause.

Also, once the vehicle is at operating temperature, check the short-term fuel trims and let me know what they are.

Let me know what you find. If you don't have a live data scan tool, let me know.

Take care,

joe

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Thursday, January 4th, 2024 AT 9:18 PM

OZ1991

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14 POSTS

Hello Joe,

Appreciative of your prompt response and apologies for the delay in responding.

So basically, upon hooking up my SCT device in the car I've gotten to notice the Cylinder head temperature & Engine Coolant temperature were just fine as they read the current ambient temperature of 33 Celsius and gradually ascended as I cranked up the engine.

The Cylinder head Voltage had dropped down from 2.5 Volts prior to ignition to an absolute minimum of 1.29 upon the engine warming up.

My short trims (bank 1 and 2) had shown 1.00 (assuming 100%?) Prior to ignition and eventually fluctuated between a max value of 1.13 and a min value of 0.7 upon cranking the engine but they do tend to stick around 1.05 @ operating temperature for the most part.

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Saturday, January 6th, 2024 AT 3:49 AM

OZ1991

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I was trying to send you the log file for you to review but couldn't figure out a way. I have also noticed that my STF in bank 1 is relatively slacking behind bank 2 most of the time wherein B1 = 0.86 and B2 = 0.93 at one point in time.

Of course, as you are aware these values cannot be looked at one instant and has got to be relatively reviewed over the course of the log. I have already ordered the ECT sensor and going to get it fixed tomorrow in an attempt to get this done and over with since it literally has driven me nuts :)

Why have you not suspected the crankshaft position sensor at all though.
The car runs fine beyond the point of starting, shifts are smooth and it definitely has power upon slamming down the throttle.

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Saturday, January 6th, 2024 AT 4:09 AM

OZ1991

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14 POSTS

Here is another engine bay footage showing how vigorously the engine shakes on start up.

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Saturday, January 6th, 2024 AT 8:56 AM

JACOBANDNICKOLAS

MECHANIC
109,901 POSTS

Hi,

The trims look good. As far as the crankshaft position sensor is concerned, it is more likely to cause problems when the engine is at operating temperature.

Let me know.

Joe