[SOLVED] Fuel Pressure Issue... Need diag help

Cameron Keyte

Cameron Keyte

Greenie N00B Member
Greenie Member
Car: 2008 Speed3; 3.5" intake, CS turbo back, AT internals, Reyes Wiretuck, AP v3, (Same tune for years), Damond PCV plate with dual CCs. 180 compression all cylinders, last checked 07/10/2020.

Issue: KOEO fuel pressure won't go above 36psi. HPFP pressure won't go above 1060psi after the car is running. AP reads 0 HPFP Sensor Voltage. Sometimes will pop code P0091. *Attached, see a log of idle with some revs.

Parts replaced: MAF, MAP (CS 3.5bar} Crank Position Sensor, Cam Position Sensor, Fuel Pressure sensor in the rail, FPRV, In-tank pump (1st tried stock from junkyard, currently has new DW 65c), fuel filter sock, low pressure fuel lines (Off tank and to the HPFP), injector solenoid and fuel pump solenoid, injector resistor (used unit), harness coil, and of course spark plugs.

Things I've tried; HPFP ORing kit and cleaning, multiple HPFP housings and internals; jumping the injector resistor, cleaning and swapping spill valves; continuity tests from spill valve to ECU; replaced the ECU, 'hot wiring spill valve buy running the red wire directly to battery, added grounds to HPFP housing.

Short of going to the dealer and having them scope it, I'm out of ideas. Willing to try just about anything at this point.
 

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Throttle position is not increasing at all. Perhaps the sensor is bad?

Who tuned you and what changed after that tune?
 
Raider said:
Throttle position is not increasing at all. Perhaps the sensor is bad?

Who tuned you and what changed after that tune?
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TPS and APP were both fluctuating with the three little blips I did during the log.

And I tuned me. Same tune for four years. Hybrid tune based on Cobb OTS.

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Put a fuel pressure gauge on at the HPFP inlet to see what your pump is actually putting out. Stop throwing parts trying to fix it.

Verify actual fuel pressure then begin checking wiring between all sensors and the ECU including load testing them to verify they can carry current.
 
L337TurboZ said:
Put a fuel pressure gauge on at the HPFP inlet to see what your pump is actually putting out. Stop throwing parts trying to fix it.

Verify actual fuel pressure then begin checking wiring between all sensors and the ECU including load testing them to verify they can carry current.
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Just lost light here in Texas. I'll do it first thing in the morning.

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First koeo of day. What AP says vs. fuel pressure gauge.
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Here's some video:

After first startup:

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After a minute, I unplugged the spill valve to see what the AP pressure would show, it dropped down to 38psi, car still ran at idle. Plugged the spill valve back in, and the lowside pressure starting doing this:

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The pressure is off like that possibly because the ECU saw spill valve unplugged, then was trying to control fuel pressure to the HPFP. Shut down, unplug battery for 2 minutes and reconnect the repeat the KOEO test. You have decent fuel pressure going to the HPFP but you shouldn't condemn the spill valve yet or the fuel pressure sensor.

Check for corrosion, moisture, or poor terminal tension at the ECU and the connectors for the spill valve, intake manifold connector, then the 2 above the HPFP.
 
Ensure ground on hpfp is tight, probably not it but always worth checking.

Seems to me like it could be the PRV, new OEM only tasca is probably the cheapest but slow to ship
 
Awafrican said:
Ensure ground on hpfp is tight, probably not it but always worth checking.

Seems to me like it could be the PRV, new OEM only tasca is probably the cheapest but slow to ship
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I actually added a ground, in addition to the little one in the coil harness. 8awg directly from the stock point on the fender. Using a multimeter, battery positive to HPFP housing, it's reading B+.

L337TurboZ said:
The pressure is off like that possibly because the ECU saw spill valve unplugged, then was trying to control fuel pressure to the HPFP. Shut down, unplug battery for 2 minutes and reconnect the repeat the KOEO test. You have decent fuel pressure going to the HPFP but you shouldn't condemn the spill valve yet or the fuel pressure sensor.

Check for corrosion, moisture, or poor terminal tension at the ECU and the connectors for the spill valve, intake manifold connector, then the 2 above the HPFP.
Click to expand...

Guess it's time to completely rip apart the harness... Thanks for the suggestion
 
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jsmith said:
What is B+ on a multimeter?
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B+ refers to the voltage before any drops in the system. In the case of a normal passenger car, that's 12 volts.

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It's pissing unburnt fuel out the tailpipe at idle now. Plugs aren't fouled, luckily.
 
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Couple of Workshop Manual tests:

No short to ground from Spill Valve Terminal B to PCM 2F
No short to ground from Spill Valve Terminal A to PCM 2G

Key On: Continuity from B to 2F & 2G ; Continuity from A to 2F & 2G.. Same with Key Off


Ohms across the spill valve; 2 ohms key off, .1 to .2 with Key On
 
You cant measure resistance of a circuit with power going through it.
 
Terminal B (red wire) voltage when running, 9.7
Terminal A (blue wire) voltage when running, 9.0

*** IGNORE: Just reflashed a tune, STFT were in the positive 11s, AFRs were 17+, and smells like a ton of unburnt fuel
 
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Do you have a big vacuum leak? A vacuum leak with cause lean fuel trims and the ECU can dump fuel to compensate to try to bring them back down
 
L337TurboZ said:
Do you have a big vacuum leak? A vacuum leak with cause lean fuel trims and the ECU can dump fuel to compensate to try to bring them back down
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Scratch that the tune I flashed was on old version that didn't have the sensor cal values for the CS MAF sensor...

Flashed again to the correct tune and it ran much better. Attached is a log at idle, then a hold of around 3200 rpms, then 5000ish

Still 0 HPFP Sensor Volts, STFTs are super negative

Also, Fuel pressure from the tank still bounces like crazy at idle, but stays at a consistent 60psi when you give it throttle
 

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since the hpfp pressure sensor is reading 0v i'm a little at a loss as to where the HPFP pressure readings are actually coming from (a gen1 thing maybe?). In any case I'd suggest checking the wiring/connector to the hpfp sensor that's connected to the fuel rail. Also did you get an oem replacement sensor for it?
 
nekret said:
since the hpfp pressure sensor is reading 0v i'm a little at a loss as to where the HPFP pressure readings are actually coming from (a gen1 thing maybe?). In any case I'd suggest checking the wiring/connector to the hpfp sensor that's connected to the fuel rail. Also did you get an oem replacement sensor for it?
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Spill valve wiring seems to checkout. I'll be doing a deep dive into the wiring harness in the next couple days. I rebuilt and installed the Auto transmission in my Mazda 5 this last weekend. Need a break from cars... Haha

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