Check Engine Light / Diagnostic Challenge

Rod Owner Cameron Park, California Posted   Latest   Edited   Bounty  
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2003 Ford Thunderbird 3.9L (A) 5-spd (5R55S)—1FAHP60AX3Y104551
P0193 - Fuel Rail Pressure Sensor Circuit High Bank 1

I have been dealing with this 2003 Ford Thunderbird that has a 3.9 V8 engine and 115,000 miles on it. It came to me initially for a check engine light and no associated drivability issues. It had a P0193 fuel rail pressure A circuit high input. I checked fuel pressure and it was normal, checked the power and ground at the fuel rail pressure sensor, all normal. I replaced the fuel rail pressure sensor with a factory Motorcraft part thinking this could be an intermittent problem. 

The vehicle returned about three months later with the check engine light on with the same P0193 fault code. No other faults were in the system, again no drivability issues. I installed my fuel pressure gauge and fuel pressure was normal, spec. for this vehicle is 30 to 65 psi. I drove the car with the gauge installed and could not identify any problems with fuel pressure. At cruising speed the the fuel pressure would very between 45 and 55 psi. The car runs great and has absolutely no drivability issues. This fuel system is a single line return less system. The fuel pump is a variable speed unit that is pulse width modulated by the rear electronic module. There are two fuel pumps as the fuel tank is a saddle mount configuration. By accident I discovered an unusual event. During a long deceleration at highway speed I noticed that the fuel pressure would very gradually rise and could reach 80 to 85 psi. This was the only time it would occur. I also noticed that this is when it would set a pending P0193 fault. If I continued to do this the check engine light would come on and the P0193 would be a current fault. There were no other faults set in any modules. During this event I also monitored the voltage at the fuel rail pressure sensor "A" circuit which confirmed that there was a higher than normal voltage. I also monitored the duty cycle during this event going to the fuel pump and it was low the whole time fuel pressure would be rising. 

The following is what I have done: 

  • Replaced both fuel pumps with O.E.M factory pumps.
  • Replaced the rear electronic module and latest programming.
  • Replaced the fuel filter.
  • Tried another P.C.M. Current P.C.M. has the latest programming.
  • Performed a voltage drop test on the wires from the fuel rail pressure sensor and the P.C.M. all good.
  • I tried removing the purge line during this event and fuel pressure would still rise.
  • I removed the vent line at the canister vent solenoid, pressure would still rise.

By now I had effected the way this event occurred during deceleration and it was substantially better to the point that I was unable to get the P0193 to set at all. Do I know what fixed it....NO. At this point I released the car to the customer as I could no longer duplicate this event. I was uncomfortable about this and told the customer to let me know if the light should come back on. So fast forward to today six months later and the car is back with the same P0193 fault and doing the same thing during a long down hill deceleration. I really need some help on this one as I have exhausted all my resources. My local Ford dealers do not even want to see this car. Any help, thoughts, suggestions or ideas would be very much appreciated.

***UPDATE-5-2-2019: This problem is still unresolved, I had to release the car back to the customer as they needed it. They will be returning it at a later date as to try and resolve this issue. I want to thank everyone for all the feed back, help and reply's. In my career I think this has been my most challenging vehicle problem. When the car returns I will repost and provide any additional information at that time. Over and out. 

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Keith Diagnostician
Collinsville, Oklahoma
Keith Default
 

What does your Freeze Frame data look like when the code sets? Pay attention to environmental evidence, such as the intake air temperature coolant temperature, as this may give you a clue on how to replicate the concern more often so we can determine the cause of the fault.

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

Hello Rod Have you check your your noise suppressors capacitors I believe there are three of them on this vehicle. This information was stated By Allied Auto Repair had experienced the code p0191 let me know if it helps any.

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Keith Diagnostician
Fayetteville, North Carolina
Keith Default
   

I would monitor the fuel pump circuit With a scope on both sides. Even though the duty cycle maybe low that’s no indication that one side or the other is not shorted during a decel event. Maybe there is enough chasis flex that a wire pinch issue is occurring somewhere during that time frame. If so a scope will show it and it could be causing full command on the pump. The only way for the

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Rod Owner
Cameron Park, California
Rod Default
 

Thanks Keith I will check that out.

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Keith Diagnostician
Fayetteville, North Carolina
Keith Default
 

Anytime bud. Hope that helps

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

This is a great advice! One thing to note is that scoping voltages at the control wires will not rule out 100% the REM going crazy and grounding the wire(s) (even while showing low duty cycle on the scantool). Unlikely, but still... However, putting the amp-clamp on the control wire by the REM will show where the current goes. Also, moving the amp-clamp along the wire might help to pinpoint the

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Rod Owner
Cameron Park, California
Rod Default
 

Dmitriy, What I did was had my Fluke meter hooked right into the wires coming out of the REM and watching the duty cycle percentage. The scan tool and the Fluke meter were very close in their readings when this event would happen. If there was a short to power or ground on either wire there should have been a noticeable change on my Fluke meter.

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Keith Diagnostician
Fayetteville, North Carolina
Keith Default
   

If that is indeed the case then there has to be a command issue or a restriction. I'm assuming that when you said the fuel pressure rose you where actually monitoring with the gauge. I guess from that point I would try to find what duty cycle should be during fuel cut. If its within specs then this would lend its self to an actual restriction or poor feed back from rail sensor. I do like the

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Rod Owner
Cameron Park, California
Rod Default
 

Keith, Yes I am monitoring the fuel pressure with a gauge on the fuel rail. That is a great question as to what the duty cycle should be during deceleration. I could not find that spec. anywhere. That was also one of my questions early on. I will put an amp probe on the pump wire and try to see what the rpm is. Since this is a return less system my question is even if the duty cycle is correct

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Keith Diagnostician
Fayetteville, North Carolina
Keith Default
 

I would think that it should be entirely controlled by the duty cycle. That’s why I’m kind of thinking it might be a feed back issue from the rail pressure sender. Could have the same issue as I stated with pump (chassis flex) but with the rail pressure sensor. It should be shutting duty cycle all the way down if it sees the pressure that high I would think. Modern systems do. Maybe monitor the

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
   

Rod, it looks you have checked the operation of the fuel supply system thoroughly enough. So, here is a wild idea. [EDIT -- skip it; a more relevant idea has been found].

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

Rod, I have noticed a few patents from that era describing a pressure relief valve: patents​.​google​.​com/patent/US54778… patents​.​google​.​com/patent/US66227… Could you check if your system has one (possibly inside the fuel tank?)

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Rod Owner
Cameron Park, California
Rod Default
 

Dmitriy, No pressure relief valve at all. There is just a check valve to maintain fuel pressure when shut off.

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Michael Mobile Technician
Clinton, Utah
Michael Default
 

Rod, I am wondering if there is a problem with O2 sensors demanding higher fuel pressure. I would watch the O2 sensors and see there are any problems.

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Rod Owner
Cameron Park, California
Rod Default
 

Thanks Michael I will check that out also.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Rod: Unless I am misunderstanding you, Ford disagrees with your interpretation of "normal spec". Take a look at Page 61. Please note the failure time required before a code flags. Eight seconds is a lifetime. Also, note the difference between PSIA vs. PSIG. Granted, these don't fix the vehicle but it does tell you what the module cares

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Rod Owner
Cameron Park, California
Rod Default
 

Anthony, Thank you for the information, this all helps. I am working on gathering more data and will post on the site. Based on the information you provided and if I am understanding it correctly, the REM module should be able to control the fuel pressure within the normal range under any given circumstance, I.E. down hill deceleration. I wish I knew what the minimum percentage or duty cycle

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
   

Hi Rod: I'll offer you some unsolicited advice. Don't live and die by Freeze Frame. Contrary to popular belief, there is no requirement on when it is collected. Some may be collected now. Some, a little later on. I'm not saying to blow it off. I'm saying that if makes sense, great. If it doesn't make sense, kick it to the curb. While it is more useful on CAN vehicles because you can possibly

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Rod Owner
Cameron Park, California
Rod Default
 

Anthony, Yes I am with you on the freeze frame data. Thanks again for the feed back.

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Caleb Technician
Mishawaka, Indiana
Caleb Default
 

So lots if great input here I have just one idea. I have noticed on newer GDI engines that on long decel events the rail pressure rises. I always attributed this to heat soak in the rail until you hit the gas again. In fact heat soak rising rail pressure KOEO is how I check for direct injected leaks. So anyway is it possible the rail pressure is actually rising on long decel events because of

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Rod Owner
Cameron Park, California
Rod Default
 

Caleb, This system does have a fuel rail temperature sensor that does monitor the fuel temperature in the rail and there is a PID for it. As I understand it this is done to prevent vaporization of the fuel the fuel rail. I am not sure how much effect this has on the fuel pressure but I am going to check this again.

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Rod Owner
Cameron Park, California
Rod Update
 

Here is an update, something that is rather unusual that I stumbled on is when the car is going down a long hill in decel. mode and the fuel pressure begins to rise if you engage the cruise control the fuel pressure will drop immediately. There is no increase in speed as the set speed is less than the speed of the car. If I go down the long hill with the cruise control engaged there will be no

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

Interesting info, Rod! Now that you have a “known not bad”, you can compare it with the “known bad”. I would try to compare fuel pump duty cycles, injector pulsing, and other drivability parameters shown on the scan tool (TPS, MAF/MAP, fuel trims, etc). May be something will stick out...

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Chris Technical Support Specialist
Commack, New York
Chris Default
 

Are there any rogue networking DTC's? The FPDM functions of the REM are network communicated. If there is a loss of messages, the REM may stay at the last commanded state for the Fuel pump output. These particular vehicles were known for networking issues.

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Rod Owner
Cameron Park, California
Rod Default
 

Chris, No there are no other faults in any of the modules and no network communication faults. Thanks for the reply.

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