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2015 Audi A8 4.0T P008B

  • Tutti57
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29 Jan 2019 16:51 #26667 by Tutti57
2015 Audi A8 4.0T P008B was created by Tutti57
This one barely runs and the code is low pressure fuel pressure too high. These have high and low pressure pumps.

Fuel trims are totaling -25 to -30 on both banks, running super rich. There were also both bank rich codes, multiple cylinder misfires, and an injector shut off code for cat protection.

Fuel trims get better with a little throttle but it's not perfect. Could be due to foiled plugs but the main issue seems to be the high fuel pressure.

Not much info out there on this. Mitchel directs you to the low pressure sensor to see if there is "about 5v" between pin 1 and 2 with the sensor unplugged. I have 5.7v. Is that about 5?

I figured it was, so it then wants you to pull the engine module and do some resistance tests, to either find a bad wire, pressure sensor, or control module.

The ecm is not easily accessible and I didn't see any harnesses near it to get to. Im hoping to find a pic for voltage at that sensor. If i get a pid change in voltage with it unplugged, I think I can assume the wires to the ecm are good. How do I condemn this nice, easy to get to sensor or am I off here?


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29 Jan 2019 17:47 #26670 by chief eaglebear
Replied by chief eaglebear on topic 2015 Audi A8 4.0T P008B
might wanna look at all the tsbs on that bugger

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30 Jan 2019 15:35 - 30 Jan 2019 15:36 #26694 by chief eaglebear
Replied by chief eaglebear on topic 2015 Audi A8 4.0T P008B
I could not access diagrams on bbb I need information
Last edit: 30 Jan 2019 15:36 by chief eaglebear.

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30 Jan 2019 17:39 #26698 by Tutti57
Replied by Tutti57 on topic 2015 Audi A8 4.0T P008B
No bulletin help on this one. It's a three wire sensor. 5v, ground, signal to ecm.

Another code came up stating a circuit issue with the signal wire being over 4.7v for x period of time. Possible causes are the sensor itself or a short to power or open. The signal wire had like 3v on it koeo, so it doesn't sound open or shorted to power.



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30 Jan 2019 23:45 #26704 by Rev Scott
Replied by Rev Scott on topic 2015 Audi A8 4.0T P008B
Backprobe the 5 volt reference and return wires at the sensor, if both are higher than 5v, disconnect sensor. Measure again at the same spot. If they’re still high, check all other sensors that are receiving 5v reference voltage on that circuit. You’ll need a good set of wiring diagrams for this one.
If you determine that all sensors and wiring on reference circuit are not causing the issue, don’t forget to check ALL ECM power and grounds. The computer can’t give a clean 5v reference if it’s getting shoddy power or ground.

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01 Feb 2019 17:04 #26743 by Tutti57
Replied by Tutti57 on topic 2015 Audi A8 4.0T P008B
I'll add that it is making an AWFUL metallic metallic sound from the left turbo. Can of marbles sound.

My boss had me put in new plugs because they were all fouled, and a new low pressure sensor. It started, made it's terrible noises, then the noise went away and it idled great. So well that I thought it stalled. I turned it off and back on and it sucked again.

Tried looking at fuel trims data but didn't want to run it long running like that and noticed it didn't come out of open loop watching in global obd2. I ran it for probably a good minute. I think I saw the coolant yep was at 110*? Don't heated O2 sensors start reaponding pretty quickly? No codes we're set at this time.

I mistyped/spoke earlier, the 5v ref actually read 5.07v.


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04 Feb 2019 18:24 #26787 by Tutti57
Replied by Tutti57 on topic 2015 Audi A8 4.0T P008B
Two codes right now are both banks rich. The car barely runs or starts. I'm not really sure where to go with this one. The o2s are all black and I'd assume that the plugs are again too. How do you get data with a car that won't run well?

Could fouled O2 sensors cause it to run pig rich?

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06 Feb 2019 06:32 #26822 by Tutti57
Replied by Tutti57 on topic 2015 Audi A8 4.0T P008B
Trying to go back to the basics here. What could cause both banks to be pig rich?

High fuel pressure - no more code for that

Regulator - PCM controlled on this car

Bad O2 sensors - they are black but are very expensive on this car. I could pull the brake booster hose but you have to hold the thing at like 3k to keep it on, so I don't know if the induced vacuum leak will lean the O2 out at that rpm.

Stuck open purge valve - can't find it to test!

MAF - doesn't have one apparently?

MAP - I could test this

Mechanical - it definitely has the can of marbles sound but it also did run great for about a minute at one point. Still won't rule this out.

Am I missing anything?




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06 Feb 2019 06:54 #26823 by Monde
Replied by Monde on topic 2015 Audi A8 4.0T P008B
ECT, IAT and TPS sensors. Also, stuck open injector, and pcm itself. There should be more.

Vouloir, c'est pouvoir.
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07 Feb 2019 05:40 #26844 by Tutti57
Replied by Tutti57 on topic 2015 Audi A8 4.0T P008B
Whelp, this one went to the dealership. I didn't see it in Mitchell when I looked but saw one in identifix that addressed what seems to be our issue. Bad turbos.

My boss contacted the dealership that turned the customer away, on a car with 32k miles, who has gotten everything serviced there, and they agreed to good-will the repair. Lucky him. The turbos are like 10 hours and the about $7k a piece.

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07 Feb 2019 06:28 #26847 by Monde
Replied by Monde on topic 2015 Audi A8 4.0T P008B
Thank you for the update. We all will learn from that.

Vouloir, c'est pouvoir.
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07 Feb 2019 20:36 #26867 by Tutti57
Replied by Tutti57 on topic 2015 Audi A8 4.0T P008B
No problem. I wish I could've saw that one through to the end, but that's the way it goes!

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08 Feb 2019 11:11 #26877 by Tyler
Replied by Tyler on topic 2015 Audi A8 4.0T P008B
Been following along, sorry to hear you had to let this one go. Best for the customer in the end, given the goodwill repair. $7,000 per turbo is a tough call to make (for me, anyway). :(

Your updates are genuinely appreciated!
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