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  #1  
Old 07-12-2023, 11:31 PM
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N55 apparent loss of boost no codes

So the other day after a few hot runs of 70-100 ish preforming flawlessly, in stop for fuel and drive away and have what seems to be no boost before 2000 rpm.

I thought maybe I accidentally got 87 fuel or something.

Put in a can of octane boost and some injector cleaner and engine runs perfectly fine over 1800 RPM but to have any acceleration I need to use sport shift to get a lower gear.

Symptoms of a boost leak except no codes. Vacuum pump? Boost solenoid?

Sadly I left my smoke machine home and I'm out of town for 3-4 weeks. Gah.

I do have most of my car tools with. Including my manometer.

Looking on the interwebs for similar problems almost everybody with similar symptoms also has codes.

I drove 700 miles including a lot of mountain roads no problem other than having to downshift a lot.

So; vacuum leaks also can be a cause and I seem to have found one inside the valve cover. Where the vacuum comes from the pump, it's got oil in it meaning there's an internal crack.

I need to replace the VC anyhow but I have little confidence that's my whole problem. I also don't think that it's the boost solenoid because it works high RPM without the burping symptoms.

I'm betting a leak in the charge/boost pipes or the IC.

I'm hoping somebody else has similar symptoms. Mostly the no torque low rpm. At 1200 RPM might as well be in neutral I cannot accelerate at all! When going up hill 100% pedal literally did not even change rpm or downshift unless I went to 105% with the kickdown.

I'm expecting that I'll find a leak in the boost pipes or IC but I don't have a compressor or my smoke machine.

I'm planning to make a boost leak tester with some PVC caps and my motive pressure bleeder as soon as tomorrow.

Any feedback appreciated. This is my second turbo car and never had any turbo related problems on my first one.
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Old 07-25-2023, 05:22 PM
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Sorry to hear you’re dealing with this. It almost sounds like the lower RPM exaust side of the turbo is blocked. Or maybe a failing bearing on the turbo making it hard to spin? These turbos are new to me so I’ll be excited to hear what this turns out to be.
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Old 07-25-2023, 05:29 PM
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Thanks for reply.

I finally did get an error with high demand (passing on a mountain). Led to two things:

1) internal fault in the vacuum tank in the convey head cover (what everybody besides bmw calls a valve cover)

3) crack in the boost solenoid.

I found articles and YouTube video that matched some of the symptom but most solenoid fault caused high not low rpm problems.

I took out the VC last night and today installed new.

I pulled vacuum on the VC tank and it does not hold vac (I knew that would be the case due to oil in the vac tank).

I bought a boost solenoid in case that also was bad and sure enough when I pull vac on the inlet it just leaks like a sieve.

I have a couple hours of putting all the electrics, fuel and air parts back on but should have satisfaction of full power tonight!

Will be interesting trying to get it started with the air in the HP fuel lines.
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Old 07-25-2023, 05:50 PM
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Wow. Have you finally made it home or are you doing all that on the road? I hadn’t even thought about trying to bleed the fuel system with a HPFP in line. I wonder if ISTA has a procedure / “special BMW tool” for that. Will the electric low pressure pump not pass pressure past the HPFP to let you bleed it?

I have started a Benz M272 engine with an un-bled fuel line after a head replacement.
It was pretty herky jerky for about 15 seconds then smoothed out fine, and has had no long term problems.
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Old 07-25-2023, 05:56 PM
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I pulled the fuse and started the car. Ran for about 6 seconds and starved.

I had a rag to catch the no pressure fuel in the lines when removing them. Then I burn the rag in the middle of the driveway. There's no better way to dispose of gas soaked rag than controlled burn.

I brought many off my mechanic tools with mei was planning to change the brake fluid.

What I didn't bring was my smoke machine :-(

I thought I had a boost leak but turned out it's mostly boost solenoid and vacuum tank slowly filling with oil.
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Old 07-25-2023, 05:58 PM
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That's an interesting thought about low press bleed but I didn't see anything about bleed procedure.

I don't use laptop I use foxwell nt710 and did discover it had a function to prime the oil lubrication so maybe it has similar for prime injectors.
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Old 07-25-2023, 11:10 PM
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Got it buttoned up and full power is restored!

the car started with a bit of a long crank no need to do anything special with bleeding fuel lines

After about 40 minutes of pretty spirited driving I got an error 29d8: intake air comparison too high.

Prob one of the sensors in the intake path not agreeing with the others. It cleared and did not come back. I'm well over the curve!
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