Irregular Fuel Pressure - Spiking/Dropping

[Pmbrown]

probably a long shot, but wondering if anyone has any ideas or experiences with irregular fuel pressure. I’ve searched everywhere for an answer but am at a dead end. Today while driving my Cobra I had fuel cut when barely hitting the throttle. I limped it Home and noticed that my fuel pressure (even at idle) fluctuates from 15-40 constantly (sometimes jumps to 60). (The needle literally bounces around everywhere). At one point the car wouldn’t start, but eventually starts and idles completely fine (but fuel pressure still is bouncing all over the place while ideling normal). If I drive the car, it’ll eventually sputter/die out because there isn’t enough pressure in the system. Any ideas or should I just start with replacing my FPRS and Fuel Filter. Hopefully I missed something while seaching this forum and can be pointed in the right direction, but if not any ideas really do help

 

[01yellercobra]

My first guess would be the FRPS. From there a dying fuel pump. What are the specs on the fuel system?

 

[Pmbrown]

My first guess too. I was wondering if it could be a fuel filter, but Im not sure if that would fluctuate the fuel pressure more than just reduce it. I got the car a year ago and it was mainly stock other than I believe a smaller pulley and tune. Therefore I believe the fuel system is stock. It ran great until this issue and now it barely runs!

 

[gt347mustang]

Frps

 

[Pmbrown]

Update: Unfortunately I’m a little concerned now. I believe it’s a failed FRPS, and although it’s an easy fix, to me it smells like fuel at my oil dip stick. Then again my dip stick doesn’t ignite at all when I put a lighter to it, so maybe not. I’ll replace the FRPS and do a full oil change but if fuel got it the oil I’m not sure if it’s a too late kind of thing...

 

[01yellercobra]

The dip stick not lighting doesn't mean anything. Pull the vacuum line from the FRPS and smell it. If it's wet or smells like fuel the FRPS is bad. If your oil smells like gas plan on changing it. And I'd change the fuel filter just to be safe and so you know when it was done last.

 

[Pmbrown]

Yeah I swapped the FRPS and oil today. Car seems to run fine and pressure is around 35psi. The only strange thing is the FRPS Sensor I got has a much smaller vacuum hole than what was in there. I have the LMR one which clearly has a much smaller vacuum hole. So... Solved other than that annoying detail.

 

[Pmbrown]

Well.. I guess this is still unresolved. I’m stumped. Changed the FRPS but fuel pressure is still all over the place and the car cuts out. I’m actually surprised it wasn’t the FRPS with the symptoms I have.

 

[MackDombles]

Well.. I guess this is still unresolved. I’m stumped. Changed the FRPS but fuel pressure is still all over the place and the car cuts out. I’m actually surprised it wasn’t the FRPS with the symptoms I have.

Although my car is different, I have the same drive train as you. And I battled the fluctuating fuel problem for months. It turned out to be the line in the tank at the fuel pump was split. Caused fluctuating pressure at idle and part throttle. Might not be it but it sure was on mine.

Sent from my [device_name] using the svtperformance.com mobile app

 

[Pmbrown]

Thanks! Honestly anything helps. I have a feeling the issue is something very simple but difficult to find. Electrical, Bad Ground, etc. I didn't think about this before, but about the same time this happened my back left speaker started cracking like crazy. Even with the volume down. It seems to be picking up interference (possibly from a loose ground or something on the fuel pump). I'll keep everyone posted if anyone is interested

 

[aarons04cobra]

Thanks! Honestly anything helps. I have a feeling the issue is something very simple but difficult to find. Electrical, Bad Ground, etc. I didn't think about this before, but about the same time this happened my back left speaker started cracking like crazy. Even with the volume down. It seems to be picking up interference (possibly from a loose ground or something on the fuel pump). I'll keep everyone posted if anyone is interested

I would start by getting access to a scan tool and do a mode 6 to watch the fuel trims and see whats going on. That should at least give you a good starting point.

 

[Pmbrown]

I think a "bad ground" issue is the front runner. I replaced the FRPS which didn't work, and was about to back the car on ramps to do the fuel filter. When i tried to crank it, i had ZERO fuel pressure and an unbelievably loud buzzing from my CCRM. If i had to guess, there has been a loose ground wire bouncing around causing the fuel pump to spike etc during normal driving. Sounds like the ground completely came off, causing the CCRM to buzz. Sounds like it's time to look for loose wires.... SO ANNOYING

 

[94 Cobra R]

Past week, been having a problem with Fuel Pressure surging under any type of boost, even partial load. Got worse over the week, to the point that I had to be careful to not get into any boost at all. Went to the junkyard today and bought a used FPDM (ordered a modified one from Black308 in the meantime) and popped it into the car. Runs like a champ. No codes before, ran fine besides boost, but leading me to believe these could go bad...just a thought.

 

[Pmbrown]

Solved. Well 90% sure I got it. Honestly it was stupid. I replaced a few parts and it turned out to be a half assed ground near the battery. Basically upgraded the negative terminal to a multi port rather than shoving all the calbles in. Sounds like my CCRM was tripping out and surging the fuel pump. Fooled me

 

[persico]

Solved. Well 90% sure I got it. Honestly it was stupid. I replaced a few parts and it turned out to be a half assed ground near the battery. Basically upgraded the negative terminal to a multi port rather than shoving all the calbles in. Sounds like my CCRM was tripping out and surging the fuel pump. Fooled me

Just curious, did this fix the problem for good?

 

[Pmbrown]

It was a bad ground. I ended up having (2) bad grounds (black connector behind the battery and the actual (3) copper cables connecting right to the battery). Wasted tons of time checking into the fuel pump PCCM Board, FPRS, Fuel Fulter, etc. There are a few places Ford is notorious for bad grounds. If you have a bad ground it'll pulse your PCCM Board which controls your fuel pump.

 

[persico]

Great thanks. Having a similar problem. It comes and goes. Got the car with a trunk mounted battery. I'll take a closer look at the grounds. Any chance you could post a picture. Thanks again!

 

[Pmbrown]

No problem. If your PCCM Board ever starts buzzing really loud the ground got really bad. Otherwise your next option should be your FRPS Sensor. Almost identical symptoms. That sensor goes bad all the time, especially if you ever hit close to redline. It's just as likely it's the FRPS.

 

[persico]

Yeah my FRPS was pouring fuel out of it so I replaced it and changed the oil. The car runs pretty good but it seems like after it warms up the fuel gauge will start to jump all over the place. If you can post a picture of the ground locations that would be a great help. Oh yeah I put the kenne bell disk in the FRPS so it shouldn't blow again. Thanks much!