Fuel Pressure Issues

[ParkerV2]

Need some geniuses to help me figure out an issue with my car before I give up and sell it.

Two months ago I was having a fuel cut when I would go WOT above 4k ish. I was running a datalog while testing it and my fuel pump completely shit the bed. Voltage went to 0 and HPFP PSI also went to 0. The log is here:

https://docs.google.com/spreadsheets...t#gid=12737430

After replacing the relief valve and a brand new HPFP With internals, my fuel psi now fluctuates with rpm but won't go above 1000. MY HPFP Voltage is still at 0. After taking it to 4 different shops including a Mazda dealership these are the things I have replaced, and still have 0 HPFP Voltage and car runs like shit,
-HPFP with internals
-Relief Valve
-Fuel Rail Pressure Sensor
-In tank Fuel Pump
-Bought a used ECU and had Mazda program the immobilizer to let the car start
- Been through two batteries while the car has been down because of mechanics leaving my AP on and draining the battery
-I've also tested the spark plugs by unplugging one at a time while the car running and they all seem to working fine.

Currently, the car idles, but won't build boost or drive good because my fuel pressure never goes above 1000.
A guy named Justin Henry who works on speeds all day said he checked my wiring and it seemed to be good and said I was getting an error between my PCM and fuel pump, that is when I replaced my ECU.
Any ideas on any tests I can do would be much appreciated.

[Solarsurge]

Posting old logs is great and all, and we can see the failure, but posting a current log would be more helpful so we can actually see what it's doing now. There are a few things I can see in your post that don't make sense...

1. I have left my AP on in my car for like 2 weeks. I HIGHLY doubt that's going to drain your battery very quickly.
2. I see no mention of fuses or relays being checked.

Power to the in tank pump/regulator flows like this:
Battery+ => 25A Fuel Pump Fuse => Fuel Pump Relay (CIRCUIT) ==> Fuel Pump Ballast Resistor => Fuel Pump Speed Control Relay (FUEL PUMP) ==> In Tank Pump

To test the resistor ballast, disconnect the battery - terminal and remove the ballast from the car. Check for continuity with multimeter by touching test leads to the resistor pins. According to the manual, resistance should be .304-.336 ohms at 68 deg F. Now, I can tell you from personal experience that literally any one I have ever tested has been between 1.2-1.6 ohms, so I think the manual is wrong or the meter I use just sucks at measuring resistances that low. Either way, if you're in the ballpark, you're fine.

To test relays, the relays are the 2 blue relays next to each other in the fuse box. On the relays, there are 4 pins. With the short sides of the rectangle being top and bottom, there 2 are vertical brass pins next to each other at the top and 2 horizontal copper pins on top of each other at the bottom like this:

| | <--Brass Pins
__
__ <--Copper Pins

The brass pins are the leads you want to test with a multimeter. Touch positive and negative leads from the multimeter to those pins (doesn't matter which) and they should read around 70-80 ohms. Next, just take wires from the battery + terminal to the left pin and battery - terminal to the right pin. It should click. If it doesn't you've found your problem.

Fuses, I'm pretty sure you don't need instruction for. If you do, please sell the car lol

[Ms3Silver]

Originally Posted by Solarsurge Posting old logs is great and all, and we can see the failure, but posting a current log would be more helpful so we can actually see what it's doing now. There are a few things I can see in your post that don't make sense... 1. I have left my AP on in my car for like 2 weeks. I HIGHLY doubt that's going to drain your battery very quickly. 2. I see no mention of fuses or relays being checked. Power to the in tank pump/regulator flows like this: Battery+ => 25A Fuel Pump Fuse => Fuel Pump Relay (CIRCUIT) ==> Fuel Pump Ballast Resistor => Fuel Pump Speed Control Relay (FUEL PUMP) ==> In Tank Pump To test the resistor ballast, disconnect the battery - terminal and remove the ballast from the car. Check for continuity with multimeter by touching test leads to the resistor pins. According to the manual, resistance should be .304-.336 ohms at 68 deg F. Now, I can tell you from personal experience that literally any one I have ever tested has been between 1.2-1.6 ohms, so I think the manual is wrong or the meter I use just sucks at measuring resistances that low. Either way, if you're in the ballpark, you're fine.

Hate reviving old threads but I'm having a pretty similar issue and I don't see much else related to the 1000~psi problem. My relays and fuses are fine but my resistor ballast is measuring .8~ ohms. I'm thinking this is my issue and currently looking into finding one that costs less than the $150 EdgeAuto wants, but wanted to see if this had either been solved or if I could just get a confirmation my resistor needs replacing.
I've already replaced:
HPFP(with upgraded internals)
HPFP O-Rings/seals
Relief Valve
Pressure Sensor
Different Relays/fuses(didn't have a voltmeter at the time)

[Solarsurge]

Originally Posted by Ms3Silver Hate reviving old threads but I'm having a pretty similar issue and I don't see much else related to the 1000~psi problem. My relays and fuses are fine but my resistor ballast is measuring .8~ ohms. I'm thinking this is my issue and currently looking into finding one that costs less than the $150 EdgeAuto wants, but wanted to see if this had either been solved or if I could just get a confirmation my resistor needs replacing. I've already replaced: HPFP(with upgraded internals) HPFP O-Rings/seals Relief Valve Pressure Sensor Different Relays/fuses(didn't have a voltmeter at the time)

The ballast only affects the in tank pump, which is electrical. If your car was sputtering, not starting, or not getting enough gas TO the HPFP that would be a potential issue. Easy way to test is to simply check your fuel pressure with your engine off. Should be at least 60 psi. If it is, your problem is either in the rail or the HPFP itself. The HPFP is a mechanical pump that’s cam driven. It only builds pressure when the engine is on and that pressure obviously increases as the engine revs higher. Did you check the cam follower bucket the HPFP piston goes into for any damage?


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[Ms3Silver]

Originally Posted by Solarsurge The ballast only affects the in tank pump, which is electrical. If your car was sputtering, not starting, or not getting enough gas TO the HPFP that would be a potential issue. Easy way to test is to simply check your fuel pressure with your engine off. Should be at least 60 psi. If it is, your problem is either in the rail or the HPFP itself. The HPFP is a mechanical pump that’s cam driven. It only builds pressure when the engine is on and that pressure obviously increases as the engine revs higher. Did you check the cam follower bucket the HPFP piston goes into for any damage? Sent from my iPhone using Tapatalk

Yeah I’ve checked the whole housing(internals, spill valve, whatever portion is just covered by a bolted in plate). No damage as far as I could see. However, in the ON position I only see about 30-36psi. I have a new fuel filter, I’m just trying whatever I can before either dropping my tank or cutting the back seat hole wider to pull the ITFP.

[Solarsurge]

Originally Posted by Ms3Silver Yeah I’ve checked the whole housing. No damage as far as I could see. However, in the ON position I only see about 30-36psi. I have a new fuel filter, I’m just trying whatever I can before either dropping my tank or cutting the back seat hole wider to pull the ITFP.

I’m confused. The fuel filter is in the tank. How did you replace it without doing that to begin with? It’s very unlikely the ballast. If the in tank pump is failing it would probably be whining a bit, but 35psi sounds like a clogged filter or something not done right if you messed around in there. I knew the stock pump would give me issues at my power level so I just got one of the Deatschwerks kits on Edge and upgraded it for like $150. It was cheap enough that I replaced everything in one shot and didn’t have to worry about doing any troubleshooting.

Fuel pressure will drop off a bit once the EVAP system kicks in, but off a fresh prime (turn key to on without cranking over) it should be 60+ psi.


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[MSMS3]

I'm not sure a WOT log is a good idea right now. If rail pressure is only 1000 psi, it is not safe to do a full log. The above suggestion regarding resistor ballast and relay function is a wise one. Do that and see if it passes those tests.

As to the new pump, did it come with upgraded internals or did you install them yourself? If you did the install you might want to retrace your steps just in case. You must do the assembly under super clean conditions to avoid contamination. Be sure to carefully inspect the o-ring. Be sure you didn't damage it when installing the piston assembly, and be sure it is well-lubed with engine oil when you reassemble the pump.

[Solarsurge]

I have no idea what my actual power is right now but it’s detuned and I’m still in the 400+ club. Fully built, big turbo, intake and exhaust manifolds, with head ported and upgraded valve springs. My setup just needed more fuel to begin with.

Yours on the other hand is probably just getting old. Fuel pumps don’t last forever and god knows what is in those underground tanks at the gas station. Your filter may just be clogged. Either way, it’s like $25 for a new filter or $150 for a whole new kit with a brand new, better pump and a filter. My time is worth the extra money just so I know I’m not back in there doing the same shit over again in 6 months.


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[Ms3Silver]

Originally Posted by Solarsurge I have no idea what my actual power is right now but it’s detuned and I’m still in the 400+ club. Fully built, big turbo, intake and exhaust manifolds, with head ported and upgraded valve springs. My setup just needed more fuel to begin with. Yours on the other hand is probably just getting old. Fuel pumps don’t last forever and god knows what is in those underground tanks at the gas station. Your filter may just be clogged. Either way, it’s like $25 for a new filter or $150 for a whole new kit with a brand new, better pump and a filter. My time is worth the extra money just so I know I’m not back in there doing the same shit over again in 6 months. Sent from my iPhone using Tapatalk

Sounds good. I’ll get in there and swap out the filter and if needed, the pump itself. I appreciate the help!

[ParkerV2]

I spent around $1500 on the car trying to fix it before I decided to give and not waste any more money. I took it to multiple specialists around my area and none could figure it out. I went through a new, AP, ECU, HPFP, In tank Fuel Pump, Pressure relief valve, and nothing could be figured out. Was really bummed to get rid of it and I hope anyone else facing this issue can get it solved.

[Solarsurge]

Originally Posted by ParkerV2 I spent around $1500 on the car trying to fix it before I decided to give and not waste any more money. I took it to multiple specialists around my area and none could figure it out. I went through a new, AP, ECU, HPFP, In tank Fuel Pump, Pressure relief valve, and nothing could be figured out. Was really bummed to get rid of it and I hope anyone else facing this issue can get it solved.

Well, to anyone who may read this: I can tell you there are very few “specialists” on this platform and you’ll pay a fortune at Mazda. Their mechanics are instructed to replace an entire $750 fuel rail over a $50 sensor because they deem it a “structural issue” to replace just the sensor. I’d highly suggest reading repair manuals, getting your hands dirty, learning how it all works, and doing your own work. Otherwise, you’ll get extremely frustrated or broke. These cars can be a pain in the ass when you don’t know what you’re doing, but trust me... they’re not that complicated and pretty easy to troubleshoot. I am to the point I can break down the entire front end of the car, swap an entire engine, and put it all back together again in a day or two (including goofing off and taking breaks). Hell, I can build the damn engine in a few hours as long as I have the parts.


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[Ms3Silver]

Update to anyone that cares or might have any other ideas.

Still chasing the issue, though it seems to have gotten slightly better.. I replaced the pressure sensor with a brand new one from the recommendation of another forum user and that, for whatever reason increased my fuel pressure readings. Now I read 41-44psi with the key turned to the ON position and can reach pressure levels of around 1400~ psi. Still not enough, but progress is being made.

Things I’ve done since are check the continuity and resistance across all relevant harness connectors, teed a gauge to my itfp(holds at 60psi), replaced my hpfp unit(no change), KOEO test reaches pressure levels of 1350-1400~psi before starting to drop off.

I’m leaning towards my pressure sensor since that seems to have the biggest effect on everything. My original sensor reads a constant 2000~psi, one I bought from a part out reads a constant 0psi and 0v to the pump, cheap $15 eBay part only gets readings of 30~ at ON and 1000~ while running, and brand new from AutoZone sees 41~ at ON and 1400 while running. I’m just out of ideas as the original sensors part number cannot be found anywhere online.

[Solarsurge]

There is no part number because Mazda calls for replacing the entire fuel rail, which comes with the sensor pre installed. But I think you just answered your own question. Lowest common denominator is the sensor if you’re getting 3 different readings from 3 different sensors. NORMAL fuel pressure readings are as follows:

KOEO (Key On Engine Off) : 55-70 psi
Idle : 400-500 warmed up to normal operating temps (can be slightly lower or higher, varies with conditions)
WOT : ALWAYS, ALWAYS, ALWAYS above 1600

Keep in mind fuel pressure at KOEO WILL taper off once the evap system kicks on. It should be 60 psi from a fresh prime COLD and it should hold fairly steady for a few minutes.

Edit: On a side note... NEVER trust eBay parts for critical components of your fuel system! You may be the lucky one and it may work out great and you get to brag that you saved a few bucks. OR you can sit and watch your car roast in flames because a cheap ass part failed and fuel sprayed all over a hot engine bay. That sucker is holding 1800+ psi at WOT. That requires quality materials, precision machining, and “higher than eBay” testing and quality control.

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