[iqraceworks]

I was on the way home from work today...just cruising on the highway at 70mph. I just barely rolled into the throttle a little bit to get in front of a car before I changed lanes, and it instantly felt like the car started shaking and running rough. No check engine light, but something felt off. I ended up clicking it down into 5th to get the vibration to calm down a bit. I figured my center bearing on the driveshaft failed, or a u-joint. I limped the car home as easy as I could. I did notice that when I rolled onto the throttle the motor had no power at all.

When I pulled in the driveway....the car was idling like it was only running on 4 or 5 cylinders. I shut the car off, and then fired it back up....instantly, everything was back to normal. I scanned for codes and have a 29DC injection cutout, 2C77 O2 sensor after cat, and 2C78 O2 sensor 2 after cat). LPFP was right at 72psi at idle, and HPFP was around 700 at idle.




So.....did I have an injector die, and then come back to life after I restarted the car? Since the O2 sensors triggered a fault...may there was a rich or lean mixture? Could an injector have gotten stuck open? Faulty LPFP sensor?

I'm running a Walbro 450 LPFP, and when I did a log a few weeks ago, the HPFP looked to be in great shape. My plugs and coils are new with only around 8,000 miles on them.


I went out this morning after the car sat all night and fired it up. It idled so rough that it only ran a couple of seconds before it died. I tried starting it a couple more times.....same result. Then I hooked up MHD to see what the LPFP and HPFP pressures were.....this time it fired up and ran smooth as can be!!...and all fuel pressures look fine.

I'm at a loss....

[_N54]

Found this online:

The cylinder injection switch-off code indicates the N54 is not flowing enough fuel. These codes are common with HPFP issues – a well documented problem on the N54. Data-logging is extremely helpful if you are getting this code. LPFP issues may also cause 29DC codes. Data-logs would help track down the issue as you can read fuel pressures and determine whether the high pressure or low pressure pump is to blame.

How is your fuel pressure on the low and high side? I know you're on the process of getting the RB's dialed in.

[iqraceworks]

The issue I'm running into is that I never seem to catch it at the right time. And then when I hook up MHD to monitor the pressures...the car then fires up and runs fine. Very odd.

The RB TWO's are great! Just got my 93 tune revision back yesterday.... Just need to get this fueling issue figured out first.

Can HPFP's just die like that? A couple of weeks ago when I was doing my E40.tune logs....it's was flowing plenty of fuel with no signs it was weak.

[Saif2018]

Originally Posted by iqraceworks

The issue I'm running into is that I never seem to catch it at the right time. And then when I hook up MHD to monitor the pressures...the car then fires up and runs fine. Very odd.

The RB TWO's are great! Just got my 93 tune revision back yesterday.... Just need to get this fueling issue figured out first.

Can HPFP's just die like that? A couple of weeks ago when I was doing my E40.tune logs....it's was flowing plenty of fuel with no signs it was weak.

You might have to keep running a Datalog frequently, without catching it on a Datalog, it would be difficult to say, HPFP aren't cheap and throwing money at it and finding out it's something else is gonna be a pain in the butt. Could be HPFP, LPFP and or injectors.

[iqraceworks]

Well, I was able to get a log! I fired up the car this morning while I had MHD running and was able to log everything. As you can see, LPFP and HPFP pressures look fine, but as I went for a drive, as soon as I start rolling onto the throttle....and the HPFP pressure starts to climb up to around 2,600psi.....and then just falls on it's face.....down to 422psi. Then it triggered the 29DC injector cutout faults again, and I had to limp it home. Once home I shut if off, started it back up...and all was morning again.

When a HPFP goes bad.....is that how they act? They build pressure just fine....and then just crash?

Here is the log...sorry, it's kind of long...

https://datazap.me/u/iqraceworks/log...12-20-21-24-27

[Saif2018]

Originally Posted by iqraceworks

Well, I was able to get a log! I fired up the car this morning while I had MHD running and was able to log everything. As you can see, LPFP and HPFP pressures look fine, but as I went for a drive, as soon as I start rolling onto the throttle....and the HPFP pressure starts to climb up to around 2,600psi.....and then just falls on it's face.....down to 422psi. Then it triggered the 29DC injector cutout faults again, and I had to limp it home. Once home I shut if off, started it back up...and all was morning again.

When a HPFP goes bad.....is that how they act? They build pressure just fine....and then just crash?

Here is the log...sorry, it's kind of long...

https://datazap.me/u/iqraceworks/log...12-20-21-24-27

Could be early signs of failure. I assume you have index 12 Injectors already?

Does the HPFP take a nose dive on a less aggressive map?

Would suggest you send the log to V8Bait for his advice,

[iqraceworks]

The first time it did it...I was cruising on the highway at 70mph....almost no load. As far as injectors, I have a mix of index 1's and 12's. If it was an injector problem though, why would the high pressure fuel pump pressure take a dive like that?

[Saif2018]

Originally Posted by iqraceworks

The first time it did it...I was cruising on the highway at 70mph....almost no load. As far as injectors, I have a mix of index 1's and 12's. If it was an injector problem though, why would the high pressure fuel pump pressure take a dive like that?

Doubt it was your injectors, probably the HPFP but get v8bait advice before buying it.

[_N54]

Originally Posted by iqraceworks

The first time it did it...I was cruising on the highway at 70mph....almost no load. As far as injectors, I have a mix of index 1's and 12's. If it was an injector problem though, why would the high pressure fuel pump pressure take a dive like that?

Apparently the Index 1's were the greatest N54 injectors

[iqraceworks]

I've got an email out to Justin asking for some advice. At least the problem is repeatable......as soon as you roll into the gas, the HPFP tanks, and the car goes into that injector cutoff/rough running mode.

I'm a little surprised that there isn't a hole lot of good info I can find regarding typical HPFP symptoms when they fail. The fact that mine builds pressure to 2,600psi or so and then just takes a dive to 400psi sure makes it look like it's bad. Is there some sort of pressure bypass inside those HPFP's that could be weak?

[iqraceworks]

So...I went out tonight after work and tried to get a nice clean log showing what's going on. I slowly rolled onto the throttle in 3rd gear.

As I'm rolling into the gas in 3rd gear, at around 3,000rpms with only 4psi of boost the HPDP pressure just tanked...it dropped from around 1,200psi down to 215psi. As soon as I let off the throttle, it bounced back up to 2,800rpms.

Both banks STFT jumped up to 34% (trying to correct a lean condition). If this was a stuck injector, I don't think both banks would be equal...one would be way rich or way lean....right?

At this point........I'm pretty sure it's a HPFP issue. What am I missing here?

https://datazap.me/u/iqraceworks/3rd...-24&zoom=59-83

[iqraceworks]

Well....I gave it one more shot before I ordered a new HPFP. First, I checked all the plugs after the car sat all day...all dry and look fine (no leaky injectors). Then I hooked up MHD, got a log running, and fired up the car.

This time the HPFP never got above 50psi...the motor sputtered and coughed as it attempted to idle. After doing that for around 10 seconds, the HPFP came to life and the pressure sprung up to around 2,600psi and the motor started to idle normal.

At this point....I'm 110% sure it's a HPFP problem. I think something is jacked up with the built in fuel pressure regulator. I'm going to order a new one off of FCP Euro tonight, along with a new rail pressure sensor.

I will report back after the parts show up and I get to take the car for a test drive.

https://datazap.me/u/iqraceworks/no-...12-20-21-22-23

[z335g]

Originally Posted by iqraceworks

Well....I gave it one more shot before I ordered a new HPFP. First, I checked all the plugs after the car sat all day...all dry and look fine (no leaky injectors). Then I hooked up MHD, got a log running, and fired up the car.

This time the HPFP never got above 50psi...the motor sputtered and coughed as it attempted to idle. After doing that for around 10 seconds, the HPFP came to life and the pressure sprung up to around 2,600psi and the motor started to idle normal.

At this point....I'm 110% sure it's a HPFP problem. I think something is jacked up with the built in fuel pressure regulator. I'm going to order a new one off of FCP Euro tonight, along with a new rail pressure sensor.

I will report back after the parts show up and I get to take the car for a test drive.

https://datazap.me/u/iqraceworks/no-...12-20-21-22-23

any update on this? I am chasing the same issue and havent changed hpfp with no avail

[iqraceworks]

Originally Posted by z335g

any update on this? I am chasing the same issue and havent changed hpfp with no avail

Yep....it was the HPFP. Installed a new one, problem is gone.

[titan.n54]

Originally Posted by iqraceworks

Yep....it was the HPFP. Installed a new one, problem is gone.

Do you replace the rail pressure sensor too? HPFP error confirmed?

[iqraceworks]

Originally Posted by rsalazart

Do you replace the rail pressure sensor too? HPFP error confirmed?

Nope...didn't replace the rail sensor. Just the HPFP. Been running great ever since

[iceMuffin]

Having same issues with my '07 335. car kinda starts but then dies. Error 29DC. It appears that the computer is deactivating the HPFP to protect the engine. I understand the computers' concerns, but I really need to move the car up the driveway.

If clearing the codes doesn't cause the car to start, can I unplug/send 12v to the solenoid on the HPFP to force the car to start?

The condition is one cylinder isn't running right so the computer deactivates all cylinders to protect the engine. How do i override this?

I understand that the HPFP may be running at lower pressures, but I refuse to believe that it went from running great to running at LPFP pressures in a matter of seconds. assuming the issue is lower pressures do to the pump being the original pump. The failure mode of the pump isnt catastrophic failure, just gradual loss of pressure over decades.