Fuel pump bad ?

[jamaicanmecrazy]

Hello All. I have 08 S6 with some low pressure fuel system codes.
Few details for ya. Since I got the car this April it always had a lethargic cold start and then fire up afterwards.
Late October I messed up and got back into town dangerously low on gas probably had single digit range when I got to a pump. Light came on maybe three weeks later. I've never had the cel come on till this issue. Fuel pump always primes when ignition is on.
I have so far replaced the low pressure fuel sensor which are know to fail, the fuel filter which houses the regulator was replaced as well. I obtained a scanner which allowed me to get some information I hope can help you help me.
One last thing besides the slow cold starts I have no misfires no stalling or cutting of power under acceleration. Car has like 136xxx miles.
Probably original pump. I'm second owner.
Thanks so much and happy holidays.

[Avantly]

It says upper limit exceeded, are you sure the sensor is ok? Have you measured the fuel pressure with a test gauge?

[jamaicanmecrazy]

Hi. Are you referring to the low pressure sensor? If so I did replace the sensor. I have not checked the pressure yet. I’m replacing the pump this Sunday.

[Avantly]

Always good to diagnose before repairing. It looks like you have 3 possible failures: 1) There is an issue with the fuel pressure sensor circuit; 2) There is an issue with the fuel pressure sensor; 3) There is an issue with the fuel pump.
Looks like you have eliminated 2) leaving 1) and 3).

[jamaicanmecrazy]

I really appreciate you pitching in to help. I can borrow a pressure gauge from my local auto zone. I will do the test prior to installing the pump tomorrow. I found instructions on how to perform it. Wish you a great weekend

[jamaicanmecrazy]

By the way I did another scan yesterday and it was showing the fuel pump 1/2 load at 80 at idle. I believe it should be around 47-50.

[Avantly]

I took a quick peek at the SSP for the 5.2 V10 and it looks like low pressure is measured by sensor G410. It appears that low pressure is regulated solely by the low pressure pump control module in conjunction with the G410 sensor. If this is correct, then it would seem that if it was unable to regulate, and regulation pressure was actually high, then fault might lie in the pump control module, or communication between the ECM and the control module. Are you able to communicate with the low pressure pump control module?
IF the G410 sensor reading of 80psi is wrong, i.e. something is wrong with the G410 wiring, or the sensor itself (which seems unlikely since you have replaced it), then the ECM would likely be regulating the low pressure side to minimum, and a measurement gauge would show a much lower pressure than 80.
If a gauge shows 80psi or higher, i.e. the G410 sensor is reading correctly, then it seems that something must be wrong with control of the low pressure pump itself, i.e. with the low pressure control module or associated wiring.

I am basing all of this on looking at the SSP as I have not done much work at all on the 5.2 cars.

If you had a low pressure issue with the low pressure side, I would be suspecting the fuel pump, but with pressure too high... I think something else is probably going on.

One interesting thing I noted in the fuel system diagram is that excess pressure in the high pressure fuel system is bled off back into the low pressure lines via pressure limiting valves in each high pressure fuel rail. If pressure ends up actually measuring high with a gauge, I wonder if one of these could have something to do with it...

[jamaicanmecrazy]

Howdy Avantly. I still haven’t got the fuel pressure tested but I replaced the low pressure pump on Sunday. I am getting a code for low pressure ,p310b I believe. I was normally getting 2-3 codes prior. I will do a log when I drive in to work today and post the results. Good theory on the limiting valves. 1 thing to let you be aware of, 1 car has an ecu tune , should I install the stock tune and see if that’s contributing? Wish you a great day

[jamaicanmecrazy]

This is what I found today.

[jamaicanmecrazy]

Also ecm # 2 said misfire in cylinders 5 and 8. As far as The check dtc memory of ecm#2 code goes , I disconnected the battery before swapping the fuel pump and that code was a first for me prior doing the pump. Really debating flashing the car back to stock for now.

[Avantly]

That P310b code appears to imply that your low fuel pressure system is exceeding the upper limit, i.e. it is too high.

For diagnosis of problems like this I would definitely diagnose on stock maps, who knows what the tuner did without actually looking at their file... For all you know they've deleted some DTC's that you might need in order to diagnose the problem.

[jamaicanmecrazy]

Installed stock tune at work then drove home. Took a quick drive round the neighborhood and got light and scan showed just the p310. I really need to get fuel pressure tested I gues. I’ll call around tomorrow and see if someone can help me with that.

[jamaicanmecrazy]

The low pressure sensor I installed was purchased was from a Napa auto. I’m wondering if I should look into an oem from dealer or maybe something from ecs tuning? Were these updated over time ?

[Avantly]

As a rule of thumb, literally all the stuff sold at the box stores, unless it has an OEM brand on the box, is the same exact thing as the bottom of the barrel cheapest chinese junk you will find on Rock Auto, Amazon, Ebay, etc. Think brands like "WVE" or "SKP" etc - The box stores put this junk in their branded box and slap a warranty on it to trick you into buying it. Duralast doesn't = built to last, it = built to make an extra dollar for investors who care nothing for you or anyone else. I haven't bought an auto part at a box store in almost 10 years because of this. Highly recommend you source OE/OEM parts for your car from the likes of FCP Euro, Deutsch (ShopDAP dot com), Rock Auto. Those are my 3 primary sources other than the dealer here and there.

The car thinks your pressure is high, but it doesn't say whether this could be a circuit fault, or an actual pressure fault, i.e. if the circuit is shorted or open, will you get a pressure related code, or a voltage related code? I don't know for the 5.2.
Here is something you could try in the mean time: Unplug the low pressure fuel sensor. What codes does that cause?

[jamaicanmecrazy]

Cleared codes then unplugged sensor then drove to work. Car drove well ,nothing to cause notice. I pulled code p2539. Low pressure fuel system sensor circuit: upper limit exceeded. Code labeled Active/static. Plugged sensor back in and cleared codes and did a drive and pulled same code plus the 310b. This time the p2539 was labeled Passive/Sporatic and the P310b was labeled ActiveStatic

[Avantly]

It really sounds to me like you have an intermittent open circuit in the sensor signal wire.

How does the connector look? Do the pins inside the connector look ok? Is the wire at the back of the connector in good shape/not excessively bent or kinked? I haven't had any major harness issues on C6 yet, most of my C6 electrical problems have just be connector or pin issues.

[jamaicanmecrazy]

Avantly when installed that cheaper non oem sensor the cel went away when I started the car , it stayed off for over a week before it came back. I ordered an oem sensor from ecs tuning yesterday and I will have it Thursday. I’ll check the connector this weekend and post if I find anything. Otherwise I’ll let you know how the new sensor works. Merry Christmas

[Avantly]

It honestly won't surprise me if the off brand sensor failed that fast... I once bought those same off-brand china VVT solenoids for a 3.2 TFSI... Half of them threw codes right out of the box (the old ones were just leaking oil). I ended up prying the old ones apart, installing new O-rings and crimping them back together xD

[jamaicanmecrazy]

https://www.facebook.com/share/r/1F5...ibextid=wwXIfr

[jamaicanmecrazy]

Hi Avanty. Installed the oem sensor after work and cleared codes. Went for a few drives nothing yet. I’ll see what happens on the drive to work tomorrow. Did notice oem sensor has silicone around the seam where both ends are joined and I noticed some corrosion in the old sensor which is barely 2 months old.

[Avantly]

That is great! Hope the codes never come back! The chinesium electrical parts are so bad, lmao. It's a shame that a lot of the ~2010 and on vehicles are using these parts from the factory. The electrical problems appearing on late 2010s and 2020s vehicles are downright insane.

[jamaicanmecrazy]

That is great! Hope the codes never come back! The chinesium electrical parts are so bad, lmao. It's a shame that a lot of the ~2010 and on vehicles are using these parts from the factory. The electrical problems appearing on late 2010s and 2020s vehicles are downright insane.

Insane indeed. I help my wife run an ebike shop here in our town and a few times I’ve had to replace sensors and control units on brand new bikes out the box or they fail after a few rides , doesn’t matter if it’s a $1600 bike or a $8000 bike.
Anyway I just scanned the car haven’t driven since last night and no codes are present in both exam’s. I didn’t trust not seeing the cel so scanned it. I gave it the beans with bacon last night before I put it away. I also was impatient and reflashed the tune on the ecu. Going for a nice Sunday drive later and we’ll see what happens.

[Avantly]

Beans and bacon, I lol'd

[jamaicanmecrazy]

Drove a lot yesterday and no codes and everything is feeling great.