Do I just throw parts at it?

So my wife's Ecoboost 1.6 Escape is have a stalling issue. After it has gotten to temp and then parked, if you then get back into after about 15-20 minutes and start it it will stall after running for a minute or two. I can restart it right away and it may stall one more time or not. I had a shop look at it and they replaced the fuel injection pressure sensor. That did not fix it. I then replaced the high pressure fuel pump on the motor which also didn't fix it. I took it to another shop and they said they couldn't recreate problem (even though I can every time) which makes me think they didn't really try and just charged me for it. 

I have been watching when it stalls on OBDLink and the fuel pressure drops from around 600-800 psi at idle to around 100psi. I don't see anything else obvious going wrong which makes me think it is something in the fuel system. Do I just buy a bunch of parts off Rockauto and throw them and hope it fixes it? Cause given the amount it costs to get a shop to look at it, I can quite a few parts.

Fuel pump check valve failure here. I don't know if it is a seperately serviceable part or integrated into the pump.

TurnerX19 said:

Fuel pump check valve failure here. I don't know if it is a seperately serviceable part or integrated into the pump.

Is that on the in-tank pump or high pressure pump? I have already replaced the high pressure pump.

In reply to 93EXCivic :

That would be on the low pressure pump. 
No codes? Which fp sensor did they replace? There are two. 

Saron81 said:

In reply to 93EXCivic :

That would be on the low pressure pump. 
No codes? Which fp sensor did they replace? There are two. 

No codes. The one on motor.

Just to cover all the bases, are you absolutely certain the pressure drop preceded the rpm drop, or is it possible the pressure fall after/while rpm fell?

Can you see the pressure setpoint on OBD? Maybe the engine sees something that causes it to request less pressure, and that something is the root cause. 

I believe that engine uses a Bosch pump (please correct me if I am wrong) and those use an interesting valve timing to control pressure. So rather than demanding a 0-100%, the ECU requests a certain angle, and that results in a different fluid volume being pumped. If the cam timing is even a little off, fuel pressure can go haywire, so is there any indication the cam timing may be suspect? Given the lack of codes, I'd just look for a sporadic cam phase relative to demanded position on the OBD app.  

if you poke the gas, can you keep it running or will it die?   

We've had a similar issue with my wife's 2.0 EB fusion.  It was especially bad after putting gas in, which turned out to be caused by a bad purge valve allowing fuel into the intake via the evap system.  It would cause the o2 signal to stick full rich and eventually trip the CEL.   

the purge valve was cheap but a pain in the ass to swap out

Strizzo said:

if you poke the gas, can you keep it running or will it die?   

We've had a similar issue with my wife's 2.0 EB fusion.  It was especially bad after putting gas in, which turned out to be caused by a bad purge valve allowing fuel into the intake via the evap system.  It would cause the o2 signal to stick full rich and eventually trip the CEL.   

 

the purge valve was cheap but a pain in the ass to swap out

No if you poke the gas it still dies. There doesn't seem to be any difference between full tank or almost empty.

cyow5 said:

Just to cover all the bases, are you absolutely certain the pressure drop preceded the rpm drop, or is it possible the pressure fall after/while rpm fell?

Can you see the pressure setpoint on OBD? Maybe the engine sees something that causes it to request less pressure, and that something is the root cause. 

I believe that engine uses a Bosch pump (please correct me if I am wrong) and those use an interesting valve timing to control pressure. So rather than demanding a 0-100%, the ECU requests a certain angle, and that results in a different fluid volume being pumped. If the cam timing is even a little off, fuel pressure can go haywire, so is there any indication the cam timing may be suspect? Given the lack of codes, I'd just look for a sporadic cam phase relative to demanded position on the OBD app.  

I am fairly sure the fuel pressure drops first but I will try to check again. I'll also look cam phase. I'll have to look for the pressure setup point. I am not sure tbh.

For some reason, Fords tend to go through fuel pump relays like candy.  They'll work great, but fail intermittently when hot.

I chased that exact issue you describe for almost a year in my Mazda B4000

In reply to 93EXCivic :

I'd put the low pressure sensor on it if you're throwing parts at it... it's cheap and easy to get to. 

I believe the low pressure pump delivers fuel to the high pressure pump, if it is failing then it can have similar symptoms.  A shop should have a reader than can simulate the running of the car when it is off and tell whether the relays are working or not, or if the pump is working or not.  On my BMW there is a seperate DME that controls the pump, I had that fail on mine.

93EXCivic said:

cyow5 said:

Just to cover all the bases, are you absolutely certain the pressure drop preceded the rpm drop, or is it possible the pressure fall after/while rpm fell?

Can you see the pressure setpoint on OBD? Maybe the engine sees something that causes it to request less pressure, and that something is the root cause. 

I believe that engine uses a Bosch pump (please correct me if I am wrong) and those use an interesting valve timing to control pressure. So rather than demanding a 0-100%, the ECU requests a certain angle, and that results in a different fluid volume being pumped. If the cam timing is even a little off, fuel pressure can go haywire, so is there any indication the cam timing may be suspect? Given the lack of codes, I'd just look for a sporadic cam phase relative to demanded position on the OBD app.  

I am fairly sure the fuel pressure drops first but I will try to check again. I'll also look cam phase. I'll have to look for the pressure setup point. I am not sure tbh.

Pressure setpoint is a very dynamic parameter with HP, so you'll only get a consistent number once the engine has warmed up and is idling smooth (ie no throttle inputs). Since that's usually when it dies, it might be easier said than done, especially with the low sample rate of OBD. But to answer your original question, I would NOT just throw parts at it until gathering all the data I can. If data alone doesn't tell you anything, only then would I start with turning wrenches. Heck "I changed htis part and nothing happened" is technically also data, but I prefer the free kind first. 

I won't say it isn't the low pressure pump, but I will say that the HP pump can draw gas in with no assist at idle, but it'll start cavitating at higher loads without the assist. Just doesn't seem likely since you only have the problem at idle unless the LP pump is causing the closed-loop controls on the HP pump to go unstable. You've got a new HP pump in there anyways, so I really would like to disprove the idea that it is something else perturbing the system before anything else. 

I've seen a few of these with intermittent stalling issues relates to fuel pressure sensors, both high and low pressure. I'd replace whichever one hasn't been replaced already, if it fails within operating range it won't set a code.

Alright well I am going to start with the other fuel pressure sensor then try the relay then the low pressure pump in the back.