Fuel Pressure Issue

M

Mike117

Greenie N00B Member
Greenie Member
I have a 2008 speed3 with around 94k miles. At around 65k miles, corksport short ram intake/TIP, and HPFP internals were installed. Have just run the Cobb OTS Stage 1+ tune since then for these last 3 years on these mods. Recently started getting misfires on startup, then slowly the car started to stutter on acceleration. Occasionally get the P0300 random misfire code. Hooked up Accessport and saw fuel pressure was low, and here is the issue and scenario that has occurred over the last few weeks:

When I would start the car, pressure would show only the low in tank pressure of around 60 psi but sometimes bump up to 2-300psi and back down. The odd thing now is that while trying to solve this issue, I am driving the car with the fuel pressure showing around the low in tank pump pressure of around 60 and the car accelerates fairly well with normal AFRs, unless I get on the gas harder it will stutter and AFRs will flash up to 15-16s momentarily. It seems like after the car is warmed up it will occasionally go up to the normal fuel pressure and at those times I am still able to hit around 1800 psi but havent been into much boost as i'm driving it very cautiously. Short and Long term fuel trims have also been okay, from -10 to 0. I replaced the fuel pressure relief valve and that was not the issue.

Has anyone had an issue like this? What should I look into next? I have searched and watched videos and cannot seem to find someone with a problem like this that wasn't just the relieve valve. I cannot find much info on the spill valve and if it's function/misfunction could cause this. I have not seen any videos or info on cleaning it or issues with it.

What would cause the pressure to stay at that low in tank pressure of around 60 psi and how is that even enough for the car to drive/accelerate? I have not run any ethanol specific fuel/tune. Any help on what to try next would be greatly appreciated. Thanks, Mike
 
When it comes to ltft 10 or more you have a leak 5 or less is ideal and 7 you should probably look into it.

Sounds like you probably have an issue with the spill valve or pressure relief valve (prv) if the PRV valve is the issue replacing it with a new OEM part is the only way to go.

Spill valve can be cleaned here's a link to a hpfp tear down so you can clean and get to the spill valve https://www.mazdaspeeds.org/index.php?threads/hpfp-o-ring-rebuild-michael-rey-facebook-kit.8069/

Ground issues can also cause weird fueling on the speeds check the grounds especially the ones near the hpfp if they're loose at all I've heard of issue
 
Thanks for the reply and your time. I did just replace the relief valve with a new OEM one. I had some doubt that it was the issue since I occasionally still get 1800 psi, but even more so because everytime i start the car it is now only at around 60psi. I didnt think that made sense that it would be the relief valve because i figured the pressure at startup would vary and be higher than 60 at times. I think first i will take the spill valve out and check it aince it can be done without even taking the pump out of the car.
I have heard that if there if a grounding issue that it almost always immediately throws a code. I'm hoping it is not an electric issue. Thanks again
 
Thanks again for the help. The reason I had doubt that it was the relief valve is that even on acceleration, the pressure stayed low around 60. Even if the relief valve is bad, it would still act as a bottle neck and the pressure should go up when you are on the gas. I also didn't see how the car could even run with such a low pressure.
After replacing the relief valve and finding that was not the issue $150 later, I found it was the spill valve causing my low pressure issue. I removed the spill valve from the hpfp (very easy since its accessible on top without removing hpfp) and it must have been stuck. There was gunk inside so I cleaned it up. (Even though the car has never run an ethanol specific tune/fuel. Very easy. Wish i tried that before spending the money on a relief valve, especially with how easy it is to access and clean. I just didnt see much of any info on the spill valve or its functions or any posts of it being a culprit (when not ever running ethanol) after searching all over the internet. Simple clean, put it back in, started car and pressure right up to 1700+ on cold start instead of the 60-70psi previously.
I still dont really understand how the car ran so well and accelerated decent with 60psi of fuel pressure, nor the exact function of the spill valve. My take is that its as if the valve being stuck open is as if the fuel bypasses the hp fuel pump and goes right to the fuel rail as the pressure I had was the in tank pressure, yet always had a constant supply of that low pressure and it would never drop below about 60psi, and the car ran okay. Seems very odd.
 
Awafrican said:
When it comes to ltft 10 or more you have a leak 5 or less is ideal and 7 you should probably look into it.

Sounds like you probably have an issue with the spill valve or pressure relief valve (prv) if the PRV valve is the issue replacing it with a new OEM part is the only way to go.

Spill valve can be cleaned here's a link to a hpfp tear down so you can clean and get to the spill valve https://www.mazdaspeeds.org/index.php?threads/hpfp-o-ring-rebuild-michael-rey-facebook-kit.8069/

Ground issues can also cause weird fueling on the speeds check the grounds especially the ones near the hpfp if they're loose at all I've heard of issue
Click to expand...
The issue of the low fuel pressure was temporarily resolved by taking the spill valve off and cleaning as described in that cleaning thread. The fuel pressure went back to normal for a few weeks but then the issue came back. I'm curious what specifically in the spill valve causes this issue and can it/how can it be further taken apart if neccessary? What is causing it to seize closed or open? As the issue came back, sometimes after starting the car I will have the 55-70psi in tank fuel pump pressue, but then it seems after i'm driving for a while and things get warmed up it will then begin to function correctly. I haven't been able to find any info on how the spill valve actually works, just what its purpose is.
When I take the spill valve off, is the bottom part supposed to be hard to get off (work both sides evenly until it is free)? By taking the spill valve off and cleaning it and this seeming to help briefly, it seems to point to the spill valve being the issue, but I haven't been able to keep this issue at bay. I'm not sure how it functions...do I possibly need a new (tiny) spring? Thanks for any help/thoughts on this.
 
Since you mentioned that cleaning and messing with the spill valve helps the issue for a while have you looked at the connector and pins for the valve itself? If there is corrosion or expanded/bent pins then maybe when you disconnect it, clean the valve itself and reconnect it the connection becomes ok for a little while before it goes back to being an issue again.

The car was showing 60 psi of pressure because that's what the FPS was reporting back to the ECU. Direct injection won't run well with pressures that low because it can't force the fuel into the engine with pressures inside the cylinder being so high. If your car is running ok then most likely the actual pressure in the high side of the fuel system is ok and it's a sensor error which is why you see the reading so low.

Check your fuel pressure sensor as well as it's wiring to make sure there isn't any problems on that end. If possible take a few data logs then use virtual Dyno to graph the data. Look for any irregular drop outs of information on your fuel pressure reading. It should be a smooth curve.
 
L337TurboZ said:
Since you mentioned that cleaning and messing with the spill valve helps the issue for a while have you looked at the connector and pins for the valve itself? If there is corrosion or expanded/bent pins then maybe when you disconnect it, clean the valve itself and reconnect it the connection becomes ok for a little while before it goes back to being an issue again.

The car was showing 60 psi of pressure because that's what the FPS was reporting back to the ECU. Direct injection won't run well with pressures that low because it can't force the fuel into the engine with pressures inside the cylinder being so high. If your car is running ok then most likely the actual pressure in the high side of the fuel system is ok and it's a sensor error which is why you see the reading so low.

Check your fuel pressure sensor as well as it's wiring to make sure there isn't any problems on that end. If possible take a few data logs then use virtual Dyno to graph the data. Look for any irregular drop outs of information on your fuel pressure reading. It should be a smooth curve.
Click to expand...
Thanks much for your time. I had checked the connector and it was in good shape but I did make sure it was clean and add a little bit of di-electric grease to protect it. I couldn't understand why the car would run 'decent' with the pressure showing that low. When it is that low I make sure to monitor the AFRs and I go easy on it. I can't give it too much throttle as the car just feels limited while the pressure reading shows this low. I have to accelerate slower than normal and going up hills I get a little nervous. I had replaced the pressure relief valve but that made no difference.
I'm not sure if the fuel pressure readings affect other parameters / if the ECU getting these low readings puts the car into any kind of safe mode but when the pressures read that low the car sure does run poorly. I will look into the connections and try to get to the fuel pressure sensor.
 
The odd part though is that the low reading of 55-70 is the pressure of the in tank fuel pump. So maybe that's just a coincidence since the car should not be able to run/accelerate with that low of a pressure.
 
Was there any follow up to this? It seems to be identical to the issue that I'm having.
 
Brado said:
Was there any follow up to this? It seems to be identical to the issue that I'm having.
Click to expand...
did you figure out your issue? just had these same symptoms come up. did a hpfp cleaning and about to replace my fuel rail fuel sensor. but seeing if im missing something before doing so.
 
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