First, thanks to everyone for the useful posts, this site has been very helpful for all of my mods.

I'm having an issue that started recently, where sometimes I can only get around 6psi of boost, and the car has no power after 4k rpm.

Leading up to this, my gas mileage dropped from 28mpg to 23.5 mpg. This was before the intercooler and tune were installed.

After the tune, mileage is about 20mpg.

I make two 25 mile trips a day in the car. The problem usually shows up on at least one of the drives. The car is fine after startup, has full power, 18psi of boost. During the trip it will get into a state where it has max of around 6psi boost, and no guts over 4k rpm.

If I turn the car off, remove the key, count to 30 and restart it, it resets and runs with full power.

I have some OBD info. I'm not sure what these O2 values are telling me... this is with the accelerator down and it trying it's hardest, on the freeway... this is the max boost it will achieve in this state.

Any ideas? I'm wondering if it may be a sensor issue. I wanted to get your opinions if it was anything obvious before dealing w/ RENNtech etc...

Vehicle speed (MPH)
54.68066
Fuel rail pressure (psi)
1506.942
Fuel rate (gal/hr)
5.314451
O2 voltage (Bank 1 Sensor 2) (V)
0.9
O2 sensor lambda wide range (current probe) (Bank 1 Sensor 1)
0.835212
O2 sensor current wide range (Bank 1 Sensor 1) (mA)
-0.7851563
Boost (psi)
6.236623


Here is a full OBD Log. The drive starts with full power, and Row 4155 is one where it is in this low power state.
https://docs.google.com/spreadsheets...it?usp=sharing


I've copied the info for the log where the problem is occurring here also.

All Log Info
Time (sec)
2078.87
Vehicle speed (MPH)
54.68066
Fuel rate (gal/hr)
5.314451
Fuel system 1 status
2
Calculated load value (%)
58.82353
Engine coolant temperature (F)
221
Short term fuel % trim - Bank 1 (%)
5.46875
Long term fuel % trim - Bank 1 (%)
3.90625
Intake manifold absolute pressure (inHg)
41.93274
Engine RPM (RPM)
4138
Ignition timing advance for #1 cylinder (deg)
15.5
Intake air temperature (F)
109.4
Mass air flow rate (lb/min)
9.407853
Absolute throttle position (%)
78.43137
O2 voltage (Bank 1 Sensor 1) (V)
0
Short term fuel trim (Bank 1 Sensor 1) (%
0
O2 voltage (Bank 1 Sensor 2) (V)
0.9
Short term fuel trim (Bank 1 Sensor 2) (%)
99.21875
Time since engine start (sec)
2083
Fuel rail pressure (psi)
1506.942
Commanded evaporative purge (%)
0
Fuel level input (%)
80
Number of warm-ups since DTCs cleared
8
Distance traveled since DTCs cleared (miles)
164.6634
Evap system vapor pressure (inH2O)
0
Barometric pressure (inHg)
29.2348
O2 sensor lambda wide range (current probe) (Bank 1 Sensor 1)
0.835212
O2 sensor lambda wide range (current probe) (Bank 1 Sensor 2)
0
O2 sensor current wide range (Bank 1 Sensor 1) (mA)
-0.7851563
O2 sensor current wide range (Bank 1 Sensor 2) (mA)
0
Catalyst temperature (Bank 1 Sensor 1) (F)
1279.22
Control module voltage (V)
13.923
Absolute load value (%)
102.3529
Fuel/Air commanded equivalence ratio
0.848388
Relative throttle position (%)
67.05882
Ambient air temperature (F)
98.6
Absolute throttle position B (%)
78.43137
Accelerator pedal position D (%)
80.78432
Accelerator pedal position E (%)
40
Commanded throttle actuator control (%)
89.80392
Engine run time run while MIL is activated (min)
0
Engine run time since DTCs cleared (min)
0
Input voltage read by the scan tool (V)
13.6
Mass air flow rate (lb/min)
6.847845
Intake manifold absolute pressure (inHg)
57.60894
Boost (psi)
6.236623
Acceleration (ft/s²)
5.368474
Instant fuel economy (MPG)
10.28905
Total fuel economy (MPG)
21.77086
Distance traveled while MIL is activated (miles)
0
EGR error (%)
0
Latitude
32.92947
Longitude
-96.75933
Altitude (m)
152
Bearing (deg)
223.7
GPS Speed (m/s)
23.96
GPS Accuracy (m)
3

 

A quick follow up question on O2 Sensor values.

Are these the correct OBD sensor readings to look at for O2 sensor, and if so what are normal ranges of values to expect? I'm trying to figure out if I have a bad sensor.

O2 voltage (Bank 1 Sensor 2) (V)
0.9
O2 sensor lambda wide range (current probe) (Bank 1 Sensor 1)
0.835212
O2 sensor current wide range (Bank 1 Sensor 1) (mA)
-0.7851563

 

What's the mileage on the car? Any CELs or half-filled engine lights coming on when you go into the low-boost situation?

 

Thanks. It's got 94k miles on it.

There are no half filled engine lights or codes when it goes into low boost mode (or otherwise).

 

I would look at the possibility your HPFP is on its way out (if it hasn't been replaced already) or look at the vacuum lines under the intake manifold that are connected to the pressure converter. It's possible the lines are swelling and slipping off the connectors, causing a lack of boost.

 

Thanks.. the fuel rail pressure (psi) is showing 1506.942 while this is happening. Does that mean anything as far as the health of the HPFP?

I'll check those lines also.

 

I honestly am not sure if that's a healthy PSI or not.

 

Timing and lambda are fine. A lambda of .835 equates to an AFR of 12.2 which is fine at 6 lbs of boost. Bank 1 sensor two voltage is a null value as it is used by the ECU only to verify catalytic efficiency. HPFP pressure should be at 1700+ psi. Renntech tunes do not alter the factory HPFP pressures. Throttle position appears to be WOT however absolute load is at 102 and should be at 180 minimum. It not unusual to see just over 200% WOT in over boost. My guess is the ECU is sensing lower fuel pressure and limiting boost via load to protect the engine from running overly lean.

 

Eric what program did you use to log all of this sensor data?

Much appreciated!

 

I would suggest one additional step. Turn the ignition on but do not start the car and record your FRP. What your actually reading at that point is the low pressure fuel pump output. It should approx 70 psi or better. Then start the car and FRP at idle.

 

Eric I'm assuming your using Dash Command with ScanXL Pro, I'm wonder could you provide the PIDs for the Fuel Rate (gal/hr) as I can't locate these PIDs in Dash Command. I'm new at this spent half my day sifting through Dash Command and am slower at learning when compared to Torque Pro App, Torque Pro App is much simpler to set up but doesn't off the extensive logging options that can be viewed in ScanXL Pro. I will be logging in Dash Command and transferring those log files to my home computer via ScanXL Pro.

It's impossible to get all those PIDs in the first post on one Dashboard, as I understand it I can only log what's on the current dashboard. This Dash Command logging is a ***** to understand even given the primitive cave man instructions!

If you prefer to PM me as so not to clutter your thread, of course anyone else that may be able to help out is welcome to.

Any assistance would be greatly appreciated!

 

Thanks for all of the specific info, that is very helpful. So when the HPFP goes, it's kind of intermittent I guess? I do stall sometimes after startup, and this is intermittent also. This morning was doing the same thing, 1500psi max.

 

I'm using an Android app called TouchScan. It's pretty nice. In the settings you can specify all the PIDs to log, and it's independent of what is on the Dashboard. So that is very cool. Then you can share the csv.... I send mine to gmail and save to google docs, then open with google sheets. Works pretty well.

 

I tried to connect with the car on but not started, and none of my OBD apps would connect. They would fail on setting up the protocol.

Idle FRP is 680-715. Max achieved today was 1500. This weekend was hitting 1700. I guess the HPFP slowly fails, intermittently? I do have stalls after startup from time to time, that is another symptom of HPFP right?

So with this tune, I wonder how to approach the dealer on the HPFP replacement? I understand they have a 120k warranty on them, but don't want to get sidetracked because the car has a tune. It was stalling after startup before the tune, so maybe start there.

 

Yes one of the symptoms is stalling/rough starts. You have to press the start button twice to energize the can-bus for communications with the adapter. Then you should be able to see the LPFP pressure on the HPFP PID. Since the connection has already been established you can also then observe any fluctuations in HPFP output during startup.

 

Try cleaning your MAF sensor.

 

OK, thanks for the help ya'll.

The LPFP pressure is 98psi. It's pretty consistent.

I cleaned the MAF sensor this morning.

It idles much more smoothly.

I did one run and was getting 18psi. I'll see how it does on the commute this week. If it can go a week and maintain full boost, it's good. We'll see.

 

Does this little LPFP trick work with (DashCommand) other apps that monitor HPFP fuel rail presure?

 

Yep, anything that reads the HPFP will read the LPFP when the engine isn't running. I found this out one the last build when my ecu wouldn't control the Bosch pump. The car would start and run on the LPFP output, but just barely. Rough start, poor idle and anything beyond mild acceleration would cause it to stumble. Once we hooked up the autologic and saw what was going on, I was amazed it ran at all.

 

OK, I think it's good! Been running well. Here's everything I did:

- New O2 Sensor in bank 1.
Improved gas mileage by 4mpg, but did not fix the boost issue.

- Low Pressure Fuel Pressure seems ok at 78-98 psi

- HPFP is a bit suspect, topping out at 1500psi instead of 1700's, in some cases.

- Gapped plugs at 0.25 Seemed to run smoother but still no boost fix.

- Cleaned MAF sensor. Used a whole can of cleaner on it, what a mess.
Idle was immediately smoother.

After these changes, my mileage is back to normal, and the exhaust tone has changed a bit since it's not running so rich. Throttle response and performance seem good.

Thanks for all the tips everyone, it's been a huge help and so much easier than putting the car in the shop.

 

1500 psi for the HPFP is a bit low considering you have a tune. Compared to my 07 MCS, I consistently see 1700+ on moderate boost (6-8 psi) and 1800+ on WOT on stock tune. Tunes place more demand on everything, HPFP's included. I think Tigger2011 said it best,