Let's talk about fuel issues -- Fuel Pressure Drop under Acceleration

[petersonb]

Okay, so this has been an ongoing issue for about 2 months now.
All online research has shown many people with similar symptoms, but I have yet to find anyone with the exact symptoms. Thus, I turn to the great people of s197forum

ISSUE SUMMARY AT THE BOTTOM, if you don't want to endure the long read.

The problem first presented itself while driving up a hill:
1. no feel in the throttle
2. No power
3. Rpm dropping, regardless of throttle action

At this time, my fuel pressure gauge wasn't connected. I was on the side of the highway, I pulled CEL codes, said fuel pressure at the rail. I went under the hood and pulled the regulator body from the rail and noted air in the line. Put it back on and turned the car over. It took a while to refill the lines, but then the car started and I babied it home 25mi through the mountains.

I ordered a new fuel pump (replacing the already-installed Aeromotive Stealth 340lph). It took a few days to arrive. Once it arrived, I took the car for another test spin, did a few WOT pulls.... And NO problems. I had reconnected my fuel pressure gauge, and saw ~50-52psi, like normal.

I sent the fuel pump back and drove the car fine for 2 weeks or so.
The same problem occurs again, so I order another fuel pump. The car drives fine for a week or so, but I keep the Pump in the trunk just in case.

I have made two 1200mi trips in the mustang in the last week and a half. The first one, the problem occurred about 30mi in under hard acceleration. I pulled over and replaced the fuel pump. Pulled onto the highway, gave her some throttle, and sure enough: fuel pressure STILL dropping to about 20psi (from 50ish). I continue my (necessary) trip, making 4 more stops total.

Each time, the pressure drops more and more until its at zero, the car stalls, and I'm on the side of the road. I pop the hood, remove the regulator, let all the pressure/fuel out of the lines, reconnect, and keep driving.

I return from the first trip, replace the pressure regulator, problem seems to go away. Car runs fine for a day or so, then I make a ~200 mi trip and the problem is present again. Acceleration, fuel pressure drop.

I pull the fuel filter, everything is in check there. I disconnect (what I think is) the hose for PCV (from valve cover to intake, just before throttle body). Checked via carb cleaner for vacuum leaks -- nothing noticeable.

I put everything together, and hot rod around town for the night. Hot rods just fine around town.

Problem occurs again the next day. I have a Kenne Bell Boost A Pump. There are two wires that go to a dial which either increases or decreases the fuel "boosting." If there is no dial present, one should simply connect these two wires together....in effect, this is the same as the dial being set to "full ON"

I try driving with the wires completely connected, and completely disconnected.

Issue is present under both conditions, but seems less severe with them disconnected (meaning dial would be full OFF -- I.e. no "boosting")

Second 1200mi trip. I make it about 300mi without issue. Then, same exact problem; same exact repair. This time I completely disconnect the boost a pump. This time I reset the trip meter to see how far I can go without incident. (Sneak peek: 640mi)

Car drives fine for the rest of the 300mi to destination (Nashville, TN). Doesn't drive perfect, but drives as expected. Without the boost a pump, I expected it would be fine until there was a large fuel demand, then would run lean. I kind of test it on the highway and exactly as expected.

I drive 600+ miles like this. Reliable, but not high performance, as I expected.

Thinking I had found the problem (the boost a pump), I drive home happy, thinking I've solved the problem after months of ripping out my hair.

Fast forward 300mi. Driving on flat ground, cruising at 80mph, loss of power, fuel pressure *slowly* decreases until it gets below 10psi and engine sputters to a stop.

The usual repair (remove pressure regulator, replace, turn over motor, drive) gets me going for the remaining 300mi home.

I haven't driven the car since, until today (trip was last week). Drove to the mechanic shop (where I am now) with no noticeable issues. Then again, it's just low speed city driving.

SUMMARY:

Loss of fuel pressure under acceleration (usually) and normal driving (occasionally). Started with incidents few and far between, now consistently messing up.

I've replaced fuel pump, pressure regulator on the rail, checked for vacuum leaks, checked fuel filter, disconnected the aftermarket Boost A Pump.

The remedy so far has been opening the fuel lines (by way of removing the pressure regulator from the rail), then reconnecting. This remedy has been successful for about 100-300 highway miles at a time.

ABOUT THE CAR:
2006 Mustang GT
Stock motor/internals (4.6L)
GT500 52lb injectors
91 octane fuel
M112 Supercharger at 12psi
Aeromotive Stealth 340lph fuel pump
Autometer A/F ratio gauge
Autometer Fuel Pressure gauge at rail
465hp/455tq at wheels with tune from Racers Edge Tuning in CA
------
Thanks for reading, and THANK YOU in advance for any help that fixes this issue. It's been a miserable journey.

 

[muztangman93]

Just had a similar issue have you datalogged it while its doing this. My fuel pump volts were crazy. Ended up being a hose that connected to the pump had a cut in it so it was dumping fuel back into the tank.

 

[muztangman93]

Check your spark plugs when you get it figured out. I went wot when I got home and it was missing in higher rpms pulled plugs and they were all white from getting real hot with the low fuel pressure and 1 was really bad.

 

[86GT351]

I would datalog for sure to watch Fuel Pump Voltage. Have you spoken to your tuner about the problem?

 

[petersonb]

It's difficult to suck air through the top of the carrier, where the main line connects (outside of the tank), and it's difficult to blow air through the T connector which receives fuel from the pump.

I'm not sure, but I feel like pulling air through that top connector should be like pulling on a cigarette ... But this is like sucking a super thick milkshake through a coffee stirring straw.

Possibly the check valve? It's the white thing on the hose in the picture.

 

[Fullboogie]

You said you "checked" the filter - did you replace it?

I would also check:

Sock filter at the bottom of the basket
Crossover tube
Pickup tube
Fuel pressure sensor

 

[petersonb]

You said you "checked" the filter - did you replace it?

I would also check:

Sock filter at the bottom of the basket
Crossover tube
Pickup tube
Fuel pressure sensor

I didn't replace the filter. It's fairly new.

Sock at the bottom is clear (less than a week old).

I don't know which is the pickup tube. There's a lot of hoses here.

I've replaced the thing that ford calls the "Fuel Injection Pressure Sensor" that bolts to the top of the fuel rail on the passenger side.

 

[petersonb]

You said you "checked" the filter - did you replace it?

Also, air pulled through the filter like a cigarette or easier.

Air doesn't pull easily through the check valve on the pump.

My question is, is air supposed to flow easily through this valve? Because online research shows that aftermarket fuel check valves open at 3psi.

 

[muztangman93]

datalog that's what you need to do

 

[petersonb]

datalog that's what you need to do

Roger that.

I will, and then I will be back here with results. Also, I'm going to replace the check valve.

Thanks so far, guys!

 

[petersonb]

Only update so far is that the Fuel Pump duty cycle is now at about a 22-23 at idle, and used to be at about 15-17.

And only goes up to 50, but I think that's a Ford thing (so i've read).

Check valve ordered, as well as 1ft of submersible hose. Will update then, too.

 

[muztangman93]

What is the fuel pump voltage and the fuel pump act voltage

 

[reddsled]

I have head that with a boost a pump and larger fuel pump you need to replace the factory wire harness with a larger wire awg. The problem could be as simple as you are drawing more current than the wire will allow and once that wire get hot from being overworked your voltage at the pump drops. Next time it happens touch the wires to the pump and see if they are hot.

 

[reddsled]

Like doing construction if you run a high power saw pluged into a skinny extension cord that cord gets hot and kills your saw.

 

[Makdaddy]

Sounds like a line collapsing when you release the pressure it expands, untill it collapses again

 

[petersonb]

Like doing construction if you run a high power saw pluged into a skinny extension cord that cord gets hot and kills your saw.

I can understand this theory. I will check wires next time.

Sounds like a line collapsing when you release the pressure it expands, untill it collapses again

Perhaps the line is "normally" (i.e. under "low" pressure condition) collapsed, or "normally" not collapsed?

I guess that, when thinking of a garden hose, I could imagine scenarios in which the hose collapses, or expands under high pressure, depending on how it's bent.


And to be honest, I've considered the hoses being the culprit. I guess I will keep that on the list.

It definitely seems as though something is clogging the line.

So onward in the search I go. Thanks again, guys!

 

[muztangman93]

I honestly think if you log the voltage you will find your problem. If a hose is collapsing or has a cut in it you will see the voltage spike where its trying to get fuel to the rails but cant. Same as if your wiring is not sufficient. You will see a voltage issue. Take you only a short period of time to do it.

 

[petersonb]

I honestly think if you log the voltage you will find your problem. If a hose is collapsing or has a cut in it you will see the voltage spike where its trying to get fuel to the rails but cant. Same as if your wiring is not sufficient. You will see a voltage issue. Take you only a short period of time to do it.

Okay, so I'm not sure which value is pump voltage. I'm using an SCT tuner for datalog, and I'm not even sure if its capable of doing that. I don't have much experience using it.

 

[muztangman93]

Are you using a computer as well. Download livelink and then you can choose what pid you want. You need fuel pump actual voltage and fuel pump voltage. You could also talk to lito on here he would be able to tell you what to log as well.

 

[petersonb]

Are you using a computer as well. Download livelink and then you can choose what pid you want. You need fuel pump actual voltage and fuel pump voltage. You could also talk to lito on here he would be able to tell you what to log as well.

My mind is blown. I had no idea about livelink.

I'll be back this afternoon with good info. Thanks!