A4 B7 fuel cutout shortly after start

[bcr10]

Hello, lurking for awhile as I've been trying to figure out this issue. Here is the scenario:

2007 A4 2.0t

When the engine is cold, it starts up just fine and runs perfectly. Let's say I drive for 20 minutes, stop and run into a store, and come back out. I start the car and it seems to start normally. Then after 5-10 seconds it just dies. I'll crank it again and it sputters at 400-500 RPM and dies after a couple seconds like it's starving for fuel. Repeat 10(ish) times and suddenly it starts and runs again with no issues at all. No performance issues at all while driving.

You know the sequence of the engine starting at a slightly higher RPM and then gradually stepping down to normal idle? It seems like right when it would normally be starting that step down is when it cuts and dies. It makes it seem like something electronic or a bad sensor. Here's what I've replaced so far based on other threads: LPFP, fuel filter, N80 valve, crank position sensor, coolant temp sensor, low pressure fuel sensor.

The only code I'm getting right now is P0089 (fuel pressure regulator). I just bought a fuel pressure regulator that is next on my list of parts to swamp out, but at this point I'm not sure it's the issue, especially since P0089 seems to be a phantom code that alot of people just end up living with. There's no electronic component of the fuel pressure regulator, and it just seems to me like something is getting or sending an incorrect signal under oddly specific circumstances.

Any input appreciated!

[texadelphia]

This sounds like exactly what mine did a couple weeks ago. It only happened once but leading up to that incident it would sometimes stall when I would start to move after a warm start. But typically it would start right back up. I was getting no MIL or codes during scans. I took it into the dealership shop after I had trouble getting it to restart and they recommended a new hpfp because they said it was dropping pressure. I just got it installed this past weekend and have driven it a couple times. It hasn't happened since but it was intermittent to begin with. Might be something worth looking into.

Here's the thread on my issue: https://www.audizine.com/forum/showt...tarting-issues

[Jeevan]

go to harbor freight and buy a cheap fuel pressure testing kit and do testing at both low pressure and high high pressure side. Let us know the results

[Acomat05]

Just as an FYI make sure the LPFP lines inside the tank are not caught up in the fuel sending unit as if they are pinch in a way the fuel going out will reduce your pressure. I had that happened to me before and taught was the pump and ended been a kinked line.

If you dont have a zip tie holding the 2 lines together to prevent them from getting tangle with the FSU get one in. If you need a picture I will share one just have to dig the old pump. I upgreaded to new HPFP internals and a RS8 FCM but before I did all that I ad the low pressire issue and hate it.

[texadelphia]

Just as an FYI make sure the LPFP lines inside the tank are not caught up in the fuel sending unit as if they are pinch in a way the fuel going out will reduce your pressure. I had that happened to me before and taught was the pump and ended been a kinked line.

If you dont have a zip tie holding the 2 lines together to prevent them from getting tangle with the FSU get one in. If you need a picture I will share one just have to dig the old pump. I upgreaded to new HPFP internals and a RS8 FCM but before I did all that I ad the low pressire issue and hate it.

I'd be interested in a picture of what you're talking about as I'm probably going to be replacing my LPFP soon.

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go to harbor freight and buy a cheap fuel pressure testing kit and do testing at both low pressure and high high pressure side. Let us know the results

Doesn't the high side go to like 1500 psi? The gauges I'm seeing only go up to 100 psi.

[Acomat05]

Texadelphia send me you email via PM, I cant get the stupid pics to upload

[Jeevan]

I'd be interested in a picture of what you're talking about as I'm probably going to be replacing my LPFP soon.

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Doesn't the high side go to like 1500 psi? The gauges I'm seeing only go up to 100 psi.

https://www.youtube.com/watch?v=IKGK9FlvXmI

[Acomat05]

Should be on my gallery now

[texadelphia]

Should be on my gallery now

Awesome. Thanks.

[Acomat05]

[IMG][/IMG]

that line is connected to another line in the tak that is coming form the passenger side without the zip tie will tangle down as the fuel drop and gets pinch reducing fuel flow. This is somethiong I noticed that original pumops came in with but replacements/aftermarket dont.

Hope it helps and let me know if you have questions!

[texadelphia]

https://www.youtube.com/watch?v=IKGK9FlvXmI

This is interesting. So the gauge is between the pump output and the feed to the fuel filter and the other line is between the return from the filter and the return inlet on the pump?

Back to the OP's problem, wouldn't he have a hard crank on cold start ups AND warm starts if this was his problem? Might still be interesting to see if the lpfp is getting up to pressure and holding.

My pump is only getting up to 4 bar according to the shop that checked it. Anyone know the spec on our lpfps?

- - - Updated - - -

[IMG][/IMG]

that line is connected to another line in the tak that is coming form the passenger side without the zip tie will tangle down as the fuel drop and gets pinch reducing fuel flow. This is somethiong I noticed that original pumops came in with but replacements/aftermarket dont.

Hope it helps and let me know if you have questions!

Makes sense.

[Jeevan]

This is interesting. So the gauge is between the pump output and the feed to the fuel filter and the other line is between the return from the filter and the return inlet on the pump?

Back to the OP's problem, wouldn't he have a hard crank on cold start ups AND warm starts if this was his problem? Might still be interesting to see if the lpfp is getting up to pressure and holding.

My pump is only getting up to 4 bar according to the shop that checked it. Anyone know the spec on our lpfps?

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Makes sense.

the video link for youtube is just to provide reference on how to test lpfp and hpfp, answer your question about the pressure on high side.

[texadelphia]

the video link for youtube is just to provide reference on how to test lpfp and hpfp, answer your question about the pressure on high side.

Gotcha. But he's only testing the low pressure side right? When he's in the engine bay, the gauge is hooked up between the filter and the hpfp and when he's in the car his gauge is between the lpfp and the filter. I guess if you wanted to check the high pressure side you could look at block 106 on vagcom or odbeleven.

[Charles.waite]

go to harbor freight and buy a cheap fuel pressure testing kit and do testing at both low pressure and high high pressure side. Let us know the results

Don't do this, come on man... Our high sides go up to 120+ bar, thats close to 2000 psi. Any harbor freight gauge isn't going to read that high. Besides, all the fuel pressure info is able to be logged in VCDS. Getting a manual gauge is pointless, find/buy/borrow a VCDS cable and just run some quick logs on low pressure pump duty cycle, LP-side fuel pressure, and Hi-side Rail pressure.

OP, I bet this is a Crank Position Sensor issue, not fueling. The fact that it works fine until its warm, then presents issues is pretty classic Crank sensor symptoms. You might want to consider replacing the N80 (just in case) too. But log LPFP duty first.

[texadelphia]

Don't do this, come on man... Our high sides go up to 120+ bar, thats close to 2000 psi. Any harbor freight gauge isn't going to read that high. Besides, all the fuel pressure info is able to be logged in VCDS. Getting a manual gauge is pointless, find/buy/borrow a VCDS cable and just run some quick logs on low pressure pump duty cycle, LP-side fuel pressure, and Hi-side Rail pressure.

OP, I bet this is a Crank Position Sensor issue, not fueling. The fact that it works fine until its warm, then presents issues is pretty classic Crank sensor symptoms.

Another CPS infant death? Is there a bad batch of these floating around?

Sent from my moto x4 using Audizine mobile app

[Charles.waite]

Could be. Depends where the Crank sensor came from. Parts store? very likely. Dealer? unlikely.

OP what do you mean when you say " I just bought a fuel pressure regulator that is next on my list of parts to swamp out" Our FPR is inside the fuel filter. Be a bit more specific when you list replaced parts (links to products and part numbers would be awesome), it helps us help you because there are certain brands that are widely known to be garbage.

Particularly, what brand Crank sensor and what brand fuel filter. And did you get the correct fuel sensors for your VIN/Engine? BWT cars use different parts than the BPG cars (same fitment, electrically different, and using the wrong one will cause issues running.

[bcr10]

This is the fuel pressure regulator I was referring to that I have not replaced yet: https://www.ecstuning.com/b-genuine-...or/06d130757c/

This is the crank sensor I used to replace the original: https://www.ecstuning.com/b-delphi-p...6a906433g~dlp/

Fuel filter was Mahle. I had considered changing the N80 as well but I feel like I'm just throwing darts at this point.

Agreed a VCDS cable would help, was trying to avoid shelling out the money for one but might have to bite the bullet. Would I be able to see real-time pressures for low and high side?

[Charles.waite]

Yea you’re throwing darts. That isn’t a fuel pressure regulator (despite ECS’s description). It’s an over pressure dump valve for the rail. It only opens above 120bar and just dumps pressure until it’s no longer above spec then closes. Again, something super easy to diagnose a failure on in VCDS in about 2 minutes by logging rail pressure.

I’ve never read heard anything good about Delphi. I know they’re a large Donestic supplier, but I have no idea if their Audi parts are good or bad.

Mahle is fine for a fuel filter. Personally, I tend to go with Mann for filter-type stuff as they’re usually OE but I don’t think there’s any reason to double Mahle’s quality.

Now don’t feel too badly since some of these parts are going to need replacement due to age eventually anyway. Yea you’re playing darts but it could be worse.

However you could have bought a VCDS cable done logging and ruled out most of the parts you bought (and possibly even have been able to diagnose the actual issue here), and likely spent less money doing so. And yea, VCDS shows you real time pressures on both the high and low side and well as fuel pump duty cycle (how hard it’s working, basically), and you can output that data then graph it against rpm and see the data visually. There’s tons of stuff VCDS is useful for.

You can also get ODBEleven, I believe it has those capabilities, though in general it’s more limited. And Android only.

[texadelphia]

However you could have bought a VCDS cable done logging and ruled out most of the parts you bought (and possibly even have been able to diagnose the actual issue here), and likely spent less money doing so. And yea, VCDS shows you real time pressures on both the high and low side and well as fuel pump duty cycle (how hard it’s working, basically), and you can output that data then graph it against rpm and see the data visually. There’s tons of stuff VCDS is useful for.

You can also get ODBEleven, I believe it has those capabilities, though in general it’s more limited. And Android only.

Do you know which measuring block shows low side pressure? My research showed that it was Group 103 but on ODBEleven the description is something about rail pressure. Although the value it's giving is only about 4-5 bar so it can't be rail pressure.

The only disadvantage I've found with measuring pressure with a vag-com is that the key has to be on. So if you want to cycle the key off and see if your system is holding pressure, you can't. But I guess the low side pump isn't constantly running until you actually start the car so I guess it doesn't really matter.

[Charles.waite]

The system isn’t really designed to hold tons of pressure though. The rail will bleed off down to 5bar or so after a while. The low side should more or less maintain 4-5bar though. If you want to measure resting low side pressure you just need to pull the fuel pump fuse and let the car sit for however long you want. The reason you need to pull the fuse is because the pump primes when you open the drivers door AND on key on so the low pressure side will be pretty pumped up by the time you get VCDS logging. The rail won’t raise however, it’ll still be more or less on par with the low side.

[BloodnGuts]

Anything new on this


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[bcr10]

Yes, sort of. I broke down and bought a VCDS cable, but only got to fool with it for a little bit yesterday...still learning. I managed to get the fuel rail pressure pulled up. I had driven the car for awhile and then let it sit for 15 minutes, my typical scenario where I see the problem, and it stalled out as normal. The fuel rail pressure was like 3.5bar, so obviously a problem there. I kept trying to start it per usual, and finally rail pressure went up to a normal level (50-75 bar? I can't quite remember), and everything ran normal.

So the question is why the low fuel rail pressure...why no issues when it's cold or has been sitting overnight? I don't know if the rail pressure started that low or if it was higher when it first started and ran, and then dropped, so that's something I need to check again. One thing that is tricky for logging is that between each stall, I have to turn the key to off and back to on, which interrupts logging and causes it to freeze up momentarily.

So for next steps...any advice on what data I should be looking at? There were so many fuel fields, I wasn't sure which was low/high, which was duty cycle, etc. Any advice on keeping logging going during these stalls? And of course, any thoughts on what I've seen so far?

[Okedokey]

Checking Fuel Pressure
Prerequisites:
Ignition ON
Engine ON (Idle)
System voltage at least 11.0 V.
Coolant Temperature at least 80 °C

[Select]
[01 - Engine]
[Meas. Blocks - 08]
Group 103
[Go!]
Field 1: Fuel Pressure (Low), Specification: 2800...7200 mbar
Field 2: Fuel Pump Adaptation, Specification: -1000...+1000 %
Note:

Timing chain driven engines such as the CCTA, CBFA and CCTA were phased in during model year 2008. Those engines do not use a G410 (Low) Fuel Pressure Sensor so Measuring Blocks group 103 is not applicable.

Group 106
[Go!]
Field 2: Fuel Rail,Pressure (actual): (A value ≈ 35 to 55% is considered normal at idle)
A value ≈ 55% to 60% could be considered as an indication of a low fuel pressure concern
A value above ≈ 60% to 70% usually indicates there is a failure or restriction
A value fluctuating ≈ 35% to 95% may indicate an intake fuel pump failing
Causes of low pressure can include:
Damaged/restricted fuel lines
Fuel filter issues including restricted/clogged or incorrect part number (wrong pressure relief value)
Faulty in-tank fuel pump and/or in-tank fuel pump controller.

Group 140
[Go!]
Field 3: Fuel Rail Pressure (High), Specification: 25.0...110.0 bar
Increase the Engine Speed while checking this value, the Pressure has to rise with the Engine Speed.
Group 230
[Go!]
Field 1: Specified Fuel Rail Pressure (High)
Field 2: Actual Fuel Rail Pressure (High), Specification: 25.0...110.0 bar
Field 3: Deviation between specified and actual fuel pressure, Specification: max. 5.0 bar