Fueling and misfiring issues under heavy load

[maddogslayer1]

Ok so to start off I bought a 2006 B7 A4 last year with 127k miles and got it stage 2 tuned by an authorized Unitronic dealer. I went from stage 1+ to stage 2 and all these issues started happening and have been on going for quite some time now. I’ve been trying to track down the problem bit by bit but I’m just sick and tired of guessing and thought I would finally come on here for some help. Anyways I’ll try to explain the problem in as much detail as I can. So my car runs great with low speeds. It can rip through the gears like no problem (manual trans btw). But when in 6th gear under heavy load let’s say starting at 80mph if I floor it my car does not like it and starts to have slight misses here and there which progressively get worse the closer to 100mph I get, but then by the time I’m going 100mph almost every time exactly at 100mph the misfires will get so bad that the car decides it needs to go into limp mode. Now most of the time it doesn’t throw a code (usually when it’s really abrupt and disorienting misfires) but sometimes it does and it’s codes like p0089, p2293 and a few other ones in the past (which I don’t remember anymore off the top of my head) but these are the current codes it throws. I’ve got an upgraded GFB diverter valve I’ve replaced the hpfp and the cam follower which was absolutely worn through. I replaced the fuel pressure regulator to a higher bar rated one for tuned or more power cars (I think it was something like going from 30 bar to 35 bar or something like that) I’ve replaced the fuel filter, air filter, and spark plugs (ngk bkr7eix with .030 gap) today and replaced coils a bit ago. I have a lpfp that I snagged off a parts car a bit ago and that’s the last thing I need to try but before I go through that hassle is there anything that I might be missing here or is there a sensor somewhere that could be causing this. I took it to Audi at some point in this process and they said I needed a new hpfp but that didn’t change a thing everything is still the same as far as the fueling issue. On another note I wish I could do data logging to see what the fuel trims and pressures are under load but I don’t have access to that. So if anyone has any pointers before I go ahead and put the lpfp in lmk. Thanks! Btw car is now at 157k miles.


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[EvolutionArmory]

A lot of stage 2 cars really need the HPFP upgrade even though the tuner might say it doesn’t.

You really need to run logs to see what is going on or otherwise you’re just guessing.

We need to see what your low pressure fuel pump is doing at that speed and load and we need to see the high pressure readings too.

If I was to guess I’d say you need an upgrade kit for your HPFP. You said you replaced yours but I’m assuming you meant with another stock one. You also need to check the status/duty cycle of your low pressure fuel pump at idle and at WOT. All fuel issues need to start with low pressure diagnostics first in my experience because the high side can’t work right if the low side doesn’t.

[jason96r]

What are your modifications? Do you have the HFC/test pipe they require for the tune?

Have a catch can or stock PCV? For whatever reason mine has fueling issues with a catch can. I can't figure that out.

I run unitronic too. I would upgrade the HPFP as mentioned then change the tune. My car didn't like their stage 2 either.

[maddogslayer1]

A lot of stage 2 cars really need the HPFP upgrade even though the tuner might say it doesn’t.

You really need to run logs to see what is going on or otherwise you’re just guessing.

We need to see what your low pressure fuel pump is doing at that speed and load and we need to see the high pressure readings too.

If I was to guess I’d say you need an upgrade kit for your HPFP. You said you replaced yours but I’m assuming you meant with another stock one. You also need to check the status/duty cycle of your low pressure fuel pump at idle and at WOT. All fuel issues need to start with low pressure diagnostics first in my experience because the high side can’t work right if the low side doesn’t.

I did replace it with a stock one. I have no way of running data logging because I don’t have the software. Any recommendations that can be affordable? Maybe just take it to the shop that did my tune?


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[maddogslayer1]

What are your modifications? Do you have the HFC/test pipe they require for the tune?

Have a catch can or stock PCV? For whatever reason mine has fueling issues with a catch can. I can't figure that out.

I run unitronic too. I would upgrade the HPFP as mentioned then change the tune. My car didn't like their stage 2 either.

Yeah my car was fine on stage 1+ but as soon as I went to stage 2 I’ve been dealing with this nightmare. Replaced the lpfp last night and the dang thing is leaking now after I filled it back up so now I have to take it off and clean it again and make sure it’s good and sealed. I have a HFC that they wanted for the tune no catch can just oem pcv which has been failing I’ve already replaced 2 of them in the matter of a year.


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[jason96r]

Europa has vcds cable for $199. Shops charge about $100/hr now definitely worth having.

Ecstuning has their scan tool for about $170. Has vcds can log but the real cable is better and has cheaper option now.

[jason96r]

Unitronic has a downpipe as required for stage 2. Not sure if factory restriction would cause your problems though.

[EvolutionArmory]

I did replace it with a stock one. I have no way of running data logging because I don’t have the software. Any recommendations that can be affordable? Maybe just take it to the shop that did my tune?


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That depends on your definition of affordable. To me, 200 bucks for the basic VCDS package is affordable. If you break it down like this, VCDS pays for itself after like 2 hours of shop diagnostic time. Not owning it is actually costing you money if you use that logic 😀

[maddogslayer1]

Unitronic has a downpipe as required for stage 2. Not sure if factory restriction would cause your problems though.

I have the free flow cat Jason


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[maddogslayer1]

That depends on your definition of affordable. To me, 200 bucks for the basic VCDS package is affordable. If you break it down like this, VCDS pays for itself after like 2 hours of shop diagnostic time. Not owning it is actually costing you money if you use that logic [emoji3]

Yeah you are right there but I have no idea how to use it. Also don’t have a pc. Only Apple laptops. I saw a code reading tool at my local auto parts store that can do data logging. I may try that.


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[maddogslayer1]

I ordered the high and low pressure sensors going to replace those. After that I will have no idea what to do from there other than data log with something but I still won’t know what I’m doing with the numbers the log will give me.


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[EvolutionArmory]

You never know how to do something until you learn. It isn’t hard.

Listen, you could just keep throwing parts at the car until you eventually fix it or you can learn how to diagnose things.

If you want to keep trying the things to throw at it approach, let me recommend a high pressure fuel pump upgrade.

You know the car runs on stage 1 but not on stage 2. What is different with stage 2? The car is asking for more boost and fuel. You’re getting fuel codes. The logical guess says you need an upgraded HPFP so it can supply the right fuel pressure under heavy load. If your low pressure fuel pump was bad, you’d probably have codes when you were stage 1 as well.

[maddogslayer1]

You never know how to do something until you learn. It isn’t hard.

Listen, you could just keep throwing parts at the car until you eventually fix it or you can learn how to diagnose things.

If you want to keep trying the things to throw at it approach, let me recommend a high pressure fuel pump upgrade.

You know the car runs on stage 1 but not on stage 2. What is different with stage 2? The car is asking for more boost and fuel. You’re getting fuel codes. The logical guess says you need an upgraded HPFP so it can supply the right fuel pressure under heavy load. If your low pressure fuel pump was bad, you’d probably have codes when you were stage 1 as well.

Makes sense. I’ll do some data logging and come back to this thread if I’m completely lost again. I will also consider getting the hpfp upgrade if need be. I appreciate all the help!


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[maddogslayer1]

So I put the hp and lp sensors in. At this point I’ve replaced everything in the fueling system with oem parts. Still have the problem. Went out today and bought a code reader that can do data logging. I have no idea what all these figures and numbers mean anybody have any idea what “normal” or acceptable numbers are for the stuff I need to know. Also what should I pay attention to. Like what category and what number should it be so I can do some comparing. Thanks!


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[EvolutionArmory]

To log fuel pressure you log block 230 and 231 if it’s anything like VCDS.

You’ll see requested and actual fuel pressure. Normal is requested fuel pressure. This is dictated by the ECU tune. If actual doesn’t meet requested, you have an issue.
Here’s an example of a high pressure log I put into graph form. You’ll see it matches very closely all the way through. This is full throttle in 3rd gear from 1500 all the way til I hit the rev limiter. This is how you log.
http://i59.photobucket.com/albums/g309/zeddirte/52D174D3-E7F8-4402-A9F0-AC34F02744E7.jpg (http://s59.photobucket.com/user/zeddirte/media/52D174D3-E7F8-4402-A9F0-AC34F02744E7.jpg.html)

This is a low pressure log. Same thing. 1500 all the way to rev limiter.
http://i59.photobucket.com/albums/g309/zeddirte/22BAF635-748F-4E53-A476-32A8D1749735.jpg (http://s59.photobucket.com/user/zeddirte/media/22BAF635-748F-4E53-A476-32A8D1749735.jpg.html)

You can see it starts to fall off at 5k. This is ok because I’m still close to 4 bar. If it was below 3bar close to redline I’d be concerned with my set up. Anything under 2.5 bar at redline with the stock fueling set up would concern me.

[EvolutionArmory]

Stage 2 tunes could ask for anywhere from 110-130 bar depending on how aggressive they are. If you log high pressure fuel and it requests 130 and you can’t meet it or if it’s bouncing all over the place, chances are you need a HPFP upgrade.

[maddogslayer1]

Ok thanks evolution! I’ll do some logs tomorrow and see what I get. Thanks so much for the tips!


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[rowanta]

You never know how to do something until you learn. It isn’t hard.

Listen, you could just keep throwing parts at the car until you eventually fix it or you can learn how to diagnose things.

If you want to keep trying the things to throw at it approach, let me recommend a high pressure fuel pump upgrade.

You know the car runs on stage 1 but not on stage 2. What is different with stage 2? The car is asking for more boost and fuel. You’re getting fuel codes. The logical guess says you need an upgraded HPFP so it can supply the right fuel pressure under heavy load. If your low pressure fuel pump was bad, you’d probably have codes when you were stage 1 as well.I had my 06 manual transmission with hfc añd s4 exhaust tuned to stage 2 unitronic and also had issues. The car would go in limp mode about 90 to 100 mph. Bought a jhm hpfp internal upgrade, installed it and that problem went away. Haven't gone for the 2+ upgrade yet

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[maddogslayer1]

I had my 06 manual transmission with hfc añd s4 exhaust tuned to stage 2 unitronic and also had issues. The car would go in limp mode about 90 to 100 mph. Bought a jhm hpfp internal upgrade, installed it and that problem went away. Haven't gone for the 2+ upgrade yet

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Sounds like I need the hpfp upgrade...


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[EvolutionArmory]

You very well could. Logs will help figure that out.

[maddogslayer1]

Last night ended up with code p2096 post catalytic fuel trim too lean bank 1


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[EvolutionArmory]

Find a way to run logs. You need to find out what your tune is asking for high pressure fuel. You won’t get anywhere except with maybe a little luck without them.

You probably need a HPFP upgrade with the tune you’re running but this is only a guess. Logs buddy. That’s how you diagnose a tuned car.