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This one has the local mechanics stumped. Not willing to pay dealer rates for diagnosis yet, so I'm looking for some help here.

The car died sitting at a light one day - would crank but not start. Police pushed it off to the side of the road. Waited for a tow. By the time the tow arrived, it magically started up and they drove it on and off the flatbed. Started once in the driveway but then not again. After a lot of troubleshooting, and verification that the fuel pump was not running, we replaced the fuel pump. Still wouldn't start, stored a P0191 code.

Bypassed the intertia switch and it fired right up. But there is still a problem but the symptoms are slightly different, persistent P0191 code and now a P0174 (lean) code.

There's a hesitation off idle and it's a bit lethargic at random. After driving for a period of time, it will not restart unless you let it sit for at least a few hours. We replaced the fuel pressure/temp sensor to no avail. The car does have a fuel pump driver module mounted to the RH C-pillar, though few parts sites list one for this car. We were thinking of replacing that next, but there is one odd symptom that we can't figure out. When it's cranking and not starting the pump is definitely running. If we crack open a line we'll get a blast of air, then fuel, and then it will run. It does this when it's cold so it's not vapor lock.

Where could it be getting air from? There are no EVAP codes, though the EVAP monitor may not have run yet given the fact that we haven't been able to drive it much because of these fuel issues.

Any advice would be greatly appreciated!
 

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Discussion Starter #3
Thanks for the reply Sheila.

No, we haven't checked that since the codes and symptoms are pointing to fuel delivery. Not that the ckp isn't involved in all that, but it's the air in the lines that really have us stumped. I'll take a look at it though.
 

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My middle son had the exact same symptoms on his '06 500 several years ago. His was intermittent though. Took it to a reputable local shop that kept it for several days to a week trying to diagnose but couldn't. They apologized and told him to come and pick up the car. No charge. Car's been running fine since he brought it home??? Keep us (me) updated please.
 

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My middle son had the exact same symptoms on his '06 500 several years ago. His was intermittent though. Took it to a reputable local shop that kept it for several days to a week trying to diagnose but couldn't. They apologized and told him to come and pick up the car. No charge. Car's been running fine since he brought it home??? Keep us (me) updated please.
The problem is that it's intermittent so not only do we have a hard time duplicating it, there's no set pattern that would point to anything specific. At first we thought it was doing it when it was hot, then it started doing it cold. Then we thought we had to wait a few hours, but then this morning it wouldn't start after sitting overnight. There's no rhyme or reason.

We're going to replace the inertia switch anyway - the date code is on the "bad" list according to a TSB on the matter. But it still misbehaves with it completely bypassed so I doubt that's the problem. Like I said before, the air in the line is puzzling. The only thing I can think of is that maybe the original problem was the intertia switch, but we replaced the fuel pump not knowing any better. Maybe we goofed that up somehow? There are two internal and 2 external connections on the pump. Pretty straightforward push-n-lock fittings. Kind of tough to mess up.

I'll let you know if/when we figure it out.
 

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I think you probably know more about this than I do, but sometimes a nudge from a noob helps...

P0191 - Fuel Rail Pressure Sensor Circuit Range/Performance

Maybe you purchased a defective replacement fuel pressure/temp sensor? (My gut says you were on the right track with this part.)

Could a cut/defective o-ring on this part explain air getting back into the fuel system? You would think you'd notice a fuel leak around this, though.

Also, was wondering if perhaps the fuel pump you installed could account for the same. Maybe it is bypassing/leaking internally in the fuel tank?

I think you effectively ruled out the inertia switch, but a new one couldn't hurt if it is on the TSB suspect list.
 

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Discussion Starter #7
I think you probably know more about this than I do, but sometimes a nudge from a noob helps...

P0191 - Fuel Rail Pressure Sensor Circuit Range/Performance

Maybe you purchased a defective replacement fuel pressure/temp sensor? (My gut says you were on the right track with this part.)

Could a cut/defective o-ring on this part explain air getting back into the fuel system? You would think you'd notice a fuel leak around this, though.

Also, was wondering if perhaps the fuel pump you installed could account for the same. Maybe it is bypassing/leaking internally in the fuel tank?

I think you effectively ruled out the inertia switch, but a new one couldn't hurt if it is on the TSB suspect list.
We thought maybe the new pressure sensor might be bad so we swapped it with the old one. Didn't fix it.

I think we've ruled out the intertia switch, too, but my dad is hell bent on replacing it anyway.

My dad took it to another mechanic yesterday who was kind enough to offer some free advice. He said to put a hair dryer up to the fuel pump driver module while it's running to see if it quits. It did. The theory now is that the fuel pump driver module intermittently isn't commanding the pump to run fast enough to properly pressurize the system, and quits completely when it gets hot. The very first failure was on a very hot day. For some reason my nephew (it's his car) doesn't use air conditioning and the car has a black interior. Gets very hot inside. Despite this, my dad is going with the intertia switch first. If I were a betting man, I'd say that we'll be ordering a fuel pump driver module in a couple of days after we realize the intertia switch didn't fix it.

Or...like you say it could be a bad, new pump module. I installed it and it looked correct and in tact but you never know.
 

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Discussion Starter #9
I think you found the problem. Let your dad do what he wants. He's just trying to help.
I know he's trying to help. I just hate to see him waste his money on replacing good parts.

So, he replaced the inertia switch today. Started it up, put it in drive and it stalled and wouldn't start. He bypassed and it's fine again (fine as in it runs, but still has the prior symptoms). Ordered the fuel pump driver module from Ford. We'll see how that goes...
 

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So the fuel pump driver module didn't fix it. Everything has been replaced now except the fuel tank pressure sensor. I guess we're going to do that next.
 

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So the fuel pump driver module didn't fix it. Everything has been replaced now except the fuel tank pressure sensor. I guess we're going to do that next.
Man, you're going through the wringer on this one. Please let us know what does fix it.

I've been working with a guy with a problem like this on a Mercedes for months. It's out of warranty and the dealer says don't bring it back. Heard today he has a buyer for it.
 

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Fuel tank pressure sensor is only related to monitoring air pressure in the tank for the EVAP system. You can take the sensor out, throw it in the garbage, and it will have no effect on pump or engine performance, other than a CEL for the EVAP system.
 

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Fuel tank pressure sensor is only related to monitoring air pressure in the tank for the EVAP system. You can take the sensor out, throw it in the garbage, and it will have no effect on pump or engine performance, other than a CEL for the EVAP system.
I know. Try telling that to my dad :) The P0191 persists. He put the original fuel pressure/temp sensor back in and it wouldn't run at all. I don't know if that's a clue or not.

I don't know where the air is coming from but it's definitely what's killing it. When it dies you have to let it sit for a few hours before it will restart. But if you open up the fuel rail to bleed the air out it will start and run again for a while until enough air gets in there for it to quit again. Sometimes it's only a few minutes, other times you can drive it for miles and miles. It only happens when it's idling, which is exactly when it quit the first time - idling at a light. It's like vapor lock but it's not from getting too hot. It's behaving exactly like it did the day it was towed so I don't think it's related to our work in replacing the pump module. We're going to pull it back out and check it anyway.
 

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I'm a GM mechanic, so I may be talking out my backside. But I would be checking the fuel pressure regulator.

But the other thing that has me curious is the fuel rail having air in it. These fuel systems should have a return fuel line going to the tank. This fuel return is what stops air from getting trapped in the fuel rail.

For me, it sounds like either the return fuel line is clogged, or the regulator is stuck, not allowing fuel to return.

Just my 2 cents
 

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It's looking like it was the alternator. We didn't have a low battery light or any voltage related codes, but my dad noticed that the lights would flicker occasionally and my nephew (it's his car) said sometimes his cell phone wouldn't charge. My dad checked the voltage at idle and it was basically just battery - 12.2V. At 2k RPM it would go up to 14 volts. This might explain why it had a rough idle.

Our theory is that the pump wasn't maintaining enough pressure to prevent vapor lock - hence the air in the system that would stall it and keep it from restarting. While low voltage isn't in the list of things to check with the P0191 code it could theoretically cause the code if the pump isn't delivering the expected pressure.

It's only been a couple of days since he replaced the alternator (based on is description I'm glad I wasn't part of that job - doesn't sound like fun) but the car is running much better overall.
 

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Several years ago the wifes 04 Tec spit out a P0191. To make a long story short, the solution was a new fuel pump.
 

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I'm a GM mechanic, so I may be talking out my backside. But I would be checking the fuel pressure regulator.

But the other thing that has me curious is the fuel rail having air in it. These fuel systems should have a return fuel line going to the tank. This fuel return is what stops air from getting trapped in the fuel rail.

For me, it sounds like either the return fuel line is clogged, or the regulator is stuck, not allowing fuel to return.

Just my 2 cents
It's a return-less system. I'm a GM guy too and had never seen one before. There is no regulator per se. There's a pressure/temp sensor that feeds info to the PCM. The PCM decides the optimal fuel pressure given load, temperature, etc. and maintains that pressure by varying voltage to the fuel pump. There's no return. The air, we think, is from vapor lock. If fuel pressure is too low it will vapor lock causing the "air" which is actually fuel vapor. The issues started during some really hot days in August. The P0191 code is a generic no/too-little/too-much fuel code so we replaced everything fuel-related to no avail.


Several years ago the wifes 04 Tec spit out a P0191. To make a long story short, the solution was a new fuel pump.
That was the first thing we did. Seemed logical but didn't fix it.

I think the new alternator fixed it. Fingers crossed. Maybe we were overlooking the obvious, but it would have been nice if the P0191 troubleshooting mentioned checking battery voltage at idle.
 

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^ Let us know if it "stays" fixed.
I haven't posted in a while but it didn't stay fixed. Any day we get that's above around 50 degrees it will still vapor lock. It's driving us insane. We're going to take it to the dealer along with the list of everything we've replaced to see what they can do. We don't want them to throw a bunch of parts at it like we did.
 
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