[jonathanpatt]

Hello,

I have been working to diagnose a recurring intermittent issue in my girlfriend's 2007 Ford Escape with the 3.0L V6 engine.

It's been to several shops for intermittent stalling issues over the past years across two owners. The primary drivability symptom is intermittent hard starting that may require multiple attempts to crank before it will start, as well as intermittent rough idle, and within the first few minutes of driving it will sometimes stall when coming to a stop and returning to an idle. It's also set a variety of codes, mostly relating to the fuel rail pressure sensor, including P0191, P0192, and P0193. It has also set P0606 occasionally.

Before I began working on, the shops that looked at it previously replaced the fuel rail pressure sensor 3 times, the fuel pump and fuel filter twice, the fuel pump driver module once, and the PCM once. Nothing has resolved the issue and it continues to persist.

I started looking at it more recently and while I am not a professional mechanic I have a decent understanding of automotive function. When watching the fuel rail pressure PID on my scan tool while the stall condition shows up, I can see the pressure spike to the maximum of the fuel pressure range and then dive to 0 before restabilizing. Sometimes it just runs rough and comes back, sometimes it stalls completely. I've put up the fuel pump duty cycle PID as well and graphed it at the same time as the FRP PID and observed the duty cycle dropping AFTER the FRP sensor is showing reduced pressure. This makes sense to me since it's a returnless system with the PCM adjusting fuel pressure based on the signal from the FRP sensor.

I have gone through Ford's Pinpoint Test DD for addressing the P0191, P0192 and P0193 codes. When I got to DD21:

DD21 CHECK THE FRP CIRCUIT FOR A SHORT TO VREF AND FRT IN THE HARNESS

- Measure the resistance between:

FRP PCM Connector Harness Side - VREF PCM Connector Harness Side

Is the resistance greater than 10K Ohms?

No — Repair the short circuit

The resistance between those two pins was 3,600 Ohms. Trying to figure out where the short circuit was, I backtracked to a connector between the PCM and sensor and still got a similar number. Then I backprobed at the sensor and saw similar still. Finally, I unplugged the wiring harness altogether and tested between the two pins of the FRP sensor and got about 5,400 ohms there.

Since this seemed to fail the diagnostic test from Ford, I purchased a replacement sensor. I tested the same pins with my multimeter on the new sensor and got infinite resistance between them there. It passed all the remaining tests in the diagnostic flowchart. Took it out for a test drive, same drivability issue and stalling.

Does anyone have any thoughts or suggestions on where to continue from here? Since it's intermittent, I'm leaning towards there being a short to ground or voltage somewhere on the sensor circuit which only occurs intermittently while driving. But why only while early in the drive cycle? You can drive around for an extended period of time with no issue sometimes and then stop the engine for less than a minute and it can have an issue shortly after that. So it's not just a cold/hot engine issue. I've done a visual inspection of what I can see but have not found anything obvious.

 

[Mountain Escape]

Hello,

I have been working to diagnose a recurring intermittent issue in my girlfriend's 2007 Ford Escape with the 3.0L V6 engine.

It's been to several shops for intermittent stalling issues over the past years across two owners. The primary drivability symptom is intermittent hard starting that may require multiple attempts to crank before it will start, as well as intermittent rough idle, and within the first few minutes of driving it will sometimes stall when coming to a stop and returning to an idle. It's also set a variety of codes, mostly relating to the fuel rail pressure sensor, including P0191, P0192, and P0193. It has also set P0606 occasionally.

Before I began working on, the shops that looked at it previously replaced the fuel rail pressure sensor 3 times, the fuel pump and fuel filter twice, the fuel pump driver module once, and the PCM once. Nothing has resolved the issue and it continues to persist.

I started looking at it more recently and while I am not a professional mechanic I have a decent understanding of automotive function. When watching the fuel rail pressure PID on my scan tool while the stall condition shows up, I can see the pressure spike to the maximum of the fuel pressure range and then dive to 0 before restabilizing. Sometimes it just runs rough and comes back, sometimes it stalls completely. I've put up the fuel pump duty cycle PID as well and graphed it at the same time as the FRP PID and observed the duty cycle dropping AFTER the FRP sensor is showing reduced pressure. This makes sense to me since it's a returnless system with the PCM adjusting fuel pressure based on the signal from the FRP sensor.

I have gone through Ford's Pinpoint Test DD for addressing the P0191, P0192 and P0193 codes. When I got to DD21:

DD21 CHECK THE FRP CIRCUIT FOR A SHORT TO VREF AND FRT IN THE HARNESS

- Measure the resistance between:

FRP PCM Connector Harness Side - VREF PCM Connector Harness Side

Is the resistance greater than 10K Ohms?

No — Repair the short circuit

The resistance between those two pins was 3,600 Ohms. Trying to figure out where the short circuit was, I backtracked to a connector between the PCM and sensor and still got a similar number. Then I backprobed at the sensor and saw similar still. Finally, I unplugged the wiring harness altogether and tested between the two pins of the FRP sensor and got about 5,400 ohms there.

Since this seemed to fail the diagnostic test from Ford, I purchased a replacement sensor. I tested the same pins with my multimeter on the new sensor and got infinite resistance between them there. It passed all the remaining tests in the diagnostic flowchart. Took it out for a test drive, same drivability issue and stalling.

Does anyone have any thoughts or suggestions on where to continue from here? Since it's intermittent, I'm leaning towards there being a short to ground or voltage somewhere on the sensor circuit which only occurs intermittently while driving. But why only while early in the drive cycle? You can drive around for an extended period of time with no issue sometimes and then stop the engine for less than a minute and it can have an issue shortly after that. So it's not just a cold/hot engine issue. I've done a visual inspection of what I can see but have not found anything obvious.

Welcome to the city, Jon
I think you were on the right track about hunting down your grounds, and cleaning them up
Chasing wiring can be a nightmare, but it definitely sounds like you've possibly got a chewed, or broken wire

Have you checked your air intake? That is the only thing I have not seen you talk about besides your plugs/coil packs

cars only need fuel air and spark… Being hard to start, it's not getting one of those three.

I almost wonder if you've got a pinch in your fuel line or something
With multiple codes, I would suggest clearing them, and see which one comes back first. You can often get a cascade effect which will mislead you from the actual problem.

 

[tomw]

Would a summary be that the indicated pressure spikes, and the pump is essentially shut down(zero psi) and then you have the stall?
I think you more or less feel the pressure sensor shorts, and the driver kills pump juice, and pressure drops. All that being caused by the low Ohms somewhere in the circuit.
Given the top of the tank is accessible and you can inspect the connectors & wiring that are so hard to reach on other vehicles, I would take a look there. I would disconnect all connectors and inspect for evidence of corrosion or damage.
An alternative if you don't want to chase down a short circuit is to run a parallel wire. You could de-pin the connectors and
use a separate wire to connect as needed. If that cured the problem you know you have a short. Question then is does it make sense to run down a short in a vehicle that is 15 years old. Will it be on the road for any length of time? I don't know the condition so have no view on that. If you lived in a salt state, where corrosion was a common cause to send a vehicle to the boneyard, it may not make sense to fix the wire, and a jump is just fine. If you do leave a jumper, be sure it is protected from corrosion & water intrusion.
Given the sensor is on the fuel line on top of the engine.... and ... the ECM is about two feet away... mounted in the firewall, running a jumper should not be difficult. Finding a proper pin to fit would be.
I would want to look at the ECM connectors. I think there are 3 large bundles/connectors that are accessible without removing anything. I would remove them and look for corrosion in there. Corrosion or bent pins are possibles... I think
tom

 

[dwightbresemann]

I research the codes using Ford's service information. One thing common with all the codes, to include P0606, voltage. High, or too low. This leads me to a poor ground somewhere.

Are you familiar with voltage drop testing a DC circuit? If not, recommend searching YouTube. This type of testing is important.

Or, you can jump right in and clean every ground you can get your hands on. Start with testing, fulling charging and cleaning the battery terminals. There should be a body ground under the battery. The body to engine ground and grounds to PCM.

Nothing wrong with adding your own extra grounds all the way around. My own vehicle, I made a ground from the negative terminal to the PCM case, with others along the way.

All circuit testing is performed with the circuit active or working.

Focus on the grounds.

 

[jonathanpatt]

Would a summary be that the indicated pressure spikes, and the pump is essentially shut down(zero psi) and then you have the stall?

That's correct, the pressure sensor's indicated pressure spikes to 5V and then dives to 0V, and with a short lag after that the fuel pump shuts off and then starts up again at full duty cycle before restabilizing. From reading the Ford specs, the actual expected range of the fuel pressure sensor is 0.5V for 0 PSI and 4.5V for the maximum end of its range. 0V and 5V are out of range and trigger the code because they indicate something wrong with the sensor or circuit generally.

I think you more or less feel the pressure sensor shorts, and the driver kills pump juice, and pressure drops. All that being caused by the low Ohms somewhere in the circuit.
Given the top of the tank is accessible and you can inspect the connectors & wiring that are so hard to reach on other vehicles, I would take a look there. I would disconnect all connectors and inspect for evidence of corrosion or damage.

I've inspected all the connectors between the PCM and the sensor and inspected the wiring harness as much as I can reach including with a mirror and light behind the engine, but it's very hard to get down behind so that could be a point I've missed. I've also done a lot of wiggle testing around contact points but haven't been able to recreate the issue while at idle when doing so. I may just have not found the exact spot yet.

An alternative if you don't want to chase down a short circuit is to run a parallel wire. You could de-pin the connectors and use a separate wire to connect as needed. If that cured the problem you know you have a short. Question then is does it make sense to run down a short in a vehicle that is 15 years old. Will it be on the road for any length of time? I don't know the condition so have no view on that. If you lived in a salt state, where corrosion was a common cause to send a vehicle to the boneyard, it may not make sense to fix the wire, and a jump is just fine. If you do leave a jumper, be sure it is protected from corrosion & water intrusion.
Given the sensor is on the fuel line on top of the engine.... and ... the ECM is about two feet away... mounted in the firewall, running a jumper should not be difficult. Finding a proper pin to fit would be.

I haven't tried this yet but it sounds like it could be worthwhile to depin the FRP wire from the PCM connector and run a parellell wire. I do have some replacement pins but I don't think they're the right ones, so I'd need to find the correct pins to use for that.

The vehicle has been in the southwest all its life and is rust-free and in good condition overall despite its age, and this seems to have been the primary issue. It has definitely had some mouse damage to wiring elsewhere in other circuits, so that may well be the issue here too and I just haven't found it.

I would want to look at the ECM connectors. I think there are 3 large bundles/connectors that are accessible without removing anything. I would remove them and look for corrosion in there. Corrosion or bent pins are possibles... I think
tom

These all look good with clean connections, no bent pins, and good pin fitment from what I've tested so far.

 

[jonathanpatt]

I research the codes using Ford's service information. One thing common with all the codes, to include P0606, voltage. High, or too low. This leads me to a poor ground somewhere.

Are you familiar with voltage drop testing a DC circuit? If not, recommend searching YouTube. This type of testing is important.

I have done voltage drop testing on at least some of the circuits involved but I'm not sure if I've systematically tested all the FRP-related circuits yet and that will be something I try the next time I get access to the vehicle (next weekend now).

Or, you can jump right in and clean every ground you can get your hands on. Start with testing, fulling charging and cleaning the battery terminals. There should be a body ground under the battery. The body to engine ground and grounds to PCM.

I've inspected and cleaned the PCM grounds and a few other body grounds that I've seen so far. I haven't seen any evidence of corrosion or damaged ground wires yet. And there are no other sensor issues or other codes, which I feel would be more likely to show up if the PCM as a whole or the 5V circuit were having ground issues.

 

[jonathanpatt]

I wanted to add that before looking at any of the electrical aspects of this, I also inspected the vacuum system which connects to the fuel rail pressure sensor and replaced multiple cracked lines and fixed all vacuum leaks I was able to find. There had been a broken line coming to it, and while replacing it improved the idle to some extent, it did not fix this intermittent issue.

 

[tomw]

I don't know if OBD-II scan tools will show the Fuel Pump Driver output, but a possibility is that the driver is not working properly and is sending a 'Give all she's got, Scotty' to the pump, and thus the indicated pressure reported by the sensor has actually jumped to the max pressure. Have you looked at the driver and its 'command' to the pump (%?)?
One check that trumps in a way is an actual fuel pressure gauge on the fuel rail. It should indicate if there is an overpressure condition. Unless you are sure the engine is being starved when it is running poorly, it could be a too-rich condition. Given the area of operation, odds of a corrosion problem are small. OTOH, because of same, familiarity with corrosion problems and bad grounds is not common and something that would be looked for, so it could happen. If the sensor that is wigging out is connected to the ECM as I think, it does not have a long run of wire, and goes from the sensor, across to the other side, and then up to the ECM on the firewall. Likely 5 feet or less. What are the odds that a wire in that loom has gotten damaged insulation and is not crossing to a 5V source? Or possibly crossing to a good grounded conductor, and causing the voltage to spike given such a good ground(sensor indicates low resistance).?
tom

 

[jonathanpatt]

I don't know if OBD-II scan tools will show the Fuel Pump Driver output, but a possibility is that the driver is not working properly and is sending a 'Give all she's got, Scotty' to the pump, and thus the indicated pressure reported by the sensor has actually jumped to the max pressure. Have you looked at the driver and its 'command' to the pump (%?)?

My scan tool will show expected fuel pressure (what the PCM wants), actual fuel pressure (what the sensor is reporting), and % duty cycle of the fuel pump. At the same time that the fuel pressure PID spikes to maximum (which is outside the range of what the sensor is capable of reporting in normal operation), the fuel pump duty cycle is still the same as it had been before the spike and after a short lag time, drops to 0% in response to the sensor reporting higher than maximum pressure. This suggests to me that the issue is on the sensor circuit rather than the driver module/fuel pump circuit.

One check that trumps in a way is an actual fuel pressure gauge on the fuel rail. It should indicate if there is an overpressure condition. Unless you are sure the engine is being starved when it is running poorly, it could be a too-rich condition.

If the fuel pump is shutting off, it seems it's being starved.

Given the area of operation, odds of a corrosion problem are small. OTOH, because of same, familiarity with corrosion problems and bad grounds is not common and something that would be looked for, so it could happen. If the sensor that is wigging out is connected to the ECM as I think, it does not have a long run of wire, and goes from the sensor, across to the other side, and then up to the ECM on the firewall. Likely 5 feet or less. What are the odds that a wire in that loom has gotten damaged insulation and is not crossing to a 5V source? Or possibly crossing to a good grounded conductor, and causing the voltage to spike given such a good ground(sensor indicates low resistance).?
tom

Visual inspection between the sensor and PCM has not revealed a problem so far, though it drops behind the engine and is not very accessible in that area, and wiggle testing hasn't been able to reproduce anything yet. If there is a loose connection or worn through insulation it's likely very small thus the apparent intermittent short. There was a new pigtail for the sensor connector poorly installed with exposed wires which I cut back and reinstalled properly but that did not change the behavior.

 

[tomw]

Given the vintage, it may be that you could find a used harness from the engine to the ECM, including the suspected area for not too much money. A u-pull or u-pick-it could have exactly what you need for a low cost. If that fixed the problem, I would be satisfied, likely then taking the harness apart to find an actual chafing of the insulation, or a damaged spot.
tom

 

[jonathanpatt]

I backprobed the sensor wire, 5V ref wire, and sensor ground wire and jumpered them between the PCM connector and sensor, which didn't fix the issue. However, I presume this would only eliminate an intermittent open and not an intermittent short, since I didn't depin the connectors and eliminate the existing harness wiring from those pins (I can't really do that for the 5V ref and sensor ground since those are shared circuits, but since they don't affect other sensors that I can tell, I also presume they aren't the issue).

I ordered some terminal ends for the PCM connector and will try fully depinning and bypassing the FRP signal wire with my own when I next get a chance.

I also noted that the temperature signal does not fluctuate when the pressure signal does, which suggests to me there is no issue with the 5V/ground circuits themselves, only potentially in relation to the pressure signal wire.