My continuing fuel supply saga

After testing the lift pump in place, i.e., in the tank, with constant, direct battery power, and not getting any fuel at the fuel filter intake, I took the pump out and "table-tested" it, again with direct battery power, and got a fountain of fuel; I don't have any way to measure the pressure, but it seems like it should be enough (but I'm certainly not positive; but it wasn't zero, which is what I was expecting from the in-place test). So I went back to testing the supply of power to the pump. After confirming that all the (dash-side) fuses are intact, suspicion fell on a driver-side-below-dash relay that's been hanging loose long enough that I forget how/why it's been hanging loose. I can't figure out where it goes (surely contributing to the "why"), and it not being connected didn't noticeably affect car performance/operation, except it now dawned on me that if it's the supply to the lift pump and the tandem pump has been doing the work of the lift pump for a while... Anyway, that led me to more carefully check the voltage at the female side of the pump power supply plug. The result: when I turn the ignition to "on" (not start) I get a split-second spike of 10.7 V, then nothing. Conclusion: the dangling relay is not the (only) power pathway to the pump--the pump power supply plug is getting some voltage--but that voltage is less than the 12V I've been told the pump should be getting, and it's lasting less than a second.
Thoughts?
Thanks.

Do you have VCDS?

The fuel pump only runs for a second when you turn the key on but don’t start the engine. Then when you start the engine it runs continuously. If you have VCDS you can command the pump on and check the voltage at the plug. I do not believe the are 2 paths for power to get to the fuel pump so I suspect that isn’t your issue.


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I have a Ross Tech VAG-COM (which I haven't used since switching to Mac when Windows switched to 8); I do have access to a PC, but I vaguely recall something about Ross Tech also not updating to Win 8; can I do what you describe w/ the the Ross Tech VAG-COM, and does Ross Tech run on Windows 8?

Yeah, it runs on Windows 8 I think.

VAG-COM and VCDS is the same thing.




[Select]
[01 - Engine]
[Basic Settings - 04]
Set Group to "035" if Available
[Go!]
[ON/OFF/Next]



http://wiki.ross-tech.com/wiki/index.php/Fuel_Pump_Basic_Settings_for_PD,_PPD,_and_CR_TDI_Engines



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Also lift pump failure isn’t uncommon on these cars so I wouldn’t rule that out. Maybe when moving the the bench you jostled it around enough to free it up temporarily,


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I didn't literally test it on a bench: I put it in a plastic container on the ground and supplied 12V directly from the battery to the power supply spades. I'll try to command the power to the plug to stay on using the VCDS technique.

Let me know what you find. I’ll bet power is getting to the plug though.


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But: before when I tested the pump in the tank and looked for flow at the fuel filter input, I supplied the pump w/ direct battery power and let it run twice, once for only about 10 sec. but the second time for about a minute: should I have let it run even longer, e.g., if the supply line between the pump and the filter was completely empty?

That should be plenty of time. Could you hear the pump running?


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I think if you supplied the power from the battery backwards the pump would run in reverse. Could that have happened?


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Is it possible that, if air is getting into the line somehow, then the supply line isn't staying full, i.e., fuel is draining back into the tank, when the pump is off; in other words, is the line supposed to remain full even when the car is off, and if it isn't, then air is getting in the line and this is causing my problems?

What is the issue you are trying to solve?

First I would take a step back and put everything back to normal. Then I would empty the fuel filter housing and put it back together empty. Then I would use VCDS to command the pump on 6 times in a row so that will be a total of 3 minutes and then check if fuel filter housing is filled back up.


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kdawg89 said:

That should be plenty of time. Could you hear the pump running?

Click to expand...

Yes.

kdawg89 said:

I think if you supplied the power from the battery backwards the pump would run in reverse. Could that have happened?

Click to expand...

Most definitely, b/c someone else here said polarity didn't matter.

Polarity definitely matters!


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kdawg89 said:

What is the issue you are trying to solve?

Click to expand...

Progressively worsening stalling, both upon starting (car starts then immediately stops) and at speed (car momentarily stalls while driving but immediately "roll-starts" back up; feels like/initially interpreted as the engine "missing" cycles). Problem started back at the beginning of July, temporally corollated to a "fur bomb" "exploding" in and filling my engine bay with fur. Professional mechanic wasn't able to fix; various things I've done since then (see my previous threads between then and now), including replacing the fuel filter (which was notably damaged) and checking the recently changed air filter, appeared to have/temporarily fixed the problem, but it kept creeping back, most recently to the point where I can't keep the stationary car running for more than about 30 seconds.

First I would take a step back and put everything back to normal. Then I would empty the fuel filter housing and put it back together empty. Then I would use VCDS to command the pump on 6 times in a row so that will be a total of 3 minutes and then check if fuel filter housing is filled back up.

Click to expand...

OK, if I can get the VCDS system running, I'll try that.

"Put things back to normal": I'm embarrassed to say, I've lost track of whether the blue line goes on the output ("V") tap or the input ("R") tap.

Why are there taps? Where does the blue line go? I don’t have one of these cars anymore and I don’t remember what it looks like where the pump electrical connection is.


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"Taps": I don't know what things are called: nipples? The tubes protruding from the top of the pump from/to which fuel is taken/delivered: the hose going to one is blue, the other is black. Anyway, I guessed blue=out, which I guess must've been right, b/c then I VCDS-ran the pump four times (but I was lazy and left the fuel filter in/fuel system intact), then tried to start the car. It started fine, i.e., didn't stall, and idled fine, without having to rev it, for at least a minute, so then I risked a test drive, which, from my place, starts w/ a steep climb of about 300 ft, and then drove it maybe a half-mile round trip: it stalled only once, at a stop sign. So, I think the lift pump is physically capable of delivering fuel; and I'm back to not knowing what the problem is. (However, since I had the VCDS in, I ran an auto-scan, cleared the codes, and ran it again; I'm going to review the results during commercials while watching baseball.)

The two seemingly relevant VCDS-reported faults:

Engine Speed Sensor (which--I'll have to double check--is what the mechanic who failed to fix the problem replaced, at having detected the fault code, so I suspect this one just may never have been cleared before I got the car back) Implausible Signal - Intermittent

Fuel Level Sensor "Open or Short to Plus - Intermittent" (might this cause the pump to stop running, for its own "safety," if it thinks there's no fuel in the tank? Or does this merely feed the dash fuel meter?)

Here is a pretty comprehensive document for checking PD fuel systems. The is written for BEW but the BRM is basically the same fuel system. I would check this stuff. You could also tee into the output from the tandem pump and run a fuel pressure gauge to where you can see it while you drive and see if your fuel pressure is dropping out and causing the stall.


http://pics.tdiclub.com/data/517/PD_fuel_delivery_check.pdf


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Is there a specific reason you think fuel delivery is what is causing your stall?


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Thanks, I've already been referred to that and done the things I have the tools to do. I guess I'm just going to have to bite the bullet, cash in some savings, and risk taking it to another mechanic, maybe a dealer.

kdawg89 said:

Is there a specific reason you think fuel delivery is what is causing your stall?


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Click to expand...

Just what I've been told here on other threads: my air supply seems to be OK--what else could it be?

I would lean towards something electrical, harness chafing is quite common on the BRM, I think under/around the air box and battery tray is common, loose/corroded ground is common I think one of the most common is maybe under the battery tray. That engine speed sensor code is suspect, I wonder if you have a chafed wire, someone might have replaced a sensor but if the wiring is chafed the original sensor wasn’t the actual problem.

I would google BRM harness chafing and check some of the more common locations, if I had to bet on something to cause random stalling on a BRM that would be it.


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I found another thread on the web with similar sounding issues, there issue ended up being the ground under the cowling by the vin tag. I would check that, and all the other grounds. I think a ground issue is more likely to cause a stall than a chafed harness, harness damage causes all kinds of weirdness but not usually stalling.


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Ok, sounds plausible (any problem having to do with something in the engine bay has always been my biggest suspect, since the stalling started when my engine bay became immersed in fur). Oh, and BTW: that dangling "relay": not a relay, it's the VCDS plug (I remembered: dislodged it and then didn't put it back to make and keep it more accessible).

How did your engine bay become immersed in fur?


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Is it hard to start or does it start well but randomly stall/lose power?


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kdawg89 said:

I found another thread on the web with similar sounding issues, there issue ended up being the ground under the cowling by the vin tag. I would check that, and all the other grounds. I think a ground issue is more likely to cause a stall than a chafed harness, harness damage causes all kinds of weirdness but not usually stalling.

Click to expand...

If I understand this hypothesis correctly, basically that would intermittently "starve" a circuit of its required voltage, right? Which circuits--besides the main battery circuit, of course--need to be closed for the engine to run? (Note: I see no evidence of "brown-outs" in any other electrical system, though I do have, chronically, a plethora of electrical problems, incl., most recently, with the tire pressure sensors.) And do you know of a "real-view" (i.e., not a circuit diagram) guide to where "all grounds" are?
PS: thank you very much for staying on this and doing additional digging (what exactly did you search for, i.e., terms and search engine/site?)--I greatly, greatly appreciate it!

Yeah, so if the ground drops or there is a weak ground the voltage cuts out or drops to an unusable level. For example if your fuel injector circuit loses its ground connection your fuel injectors won’t fire anymore and you will stall, or if the voltage drops you will lose power/stall.

I think this is all of them, I know some of those descriptions aren’t great but it’s the best I’ve found so far. I believe right/left is as if you were sitting in the driver seat.

1. engine compartment, top of right front chassis member, underneath headlight
2. passenger compartment, base of A-pillar, behind trim
3. connection at right end of cylinder head
4. battery to chassis, under engine hood, near battery
5.right side of trunk, on inner wheel housing, behind trim
6. left side trunk on C-pillar, behind trim
7. left side trunk,on inner wheel housing, behind trim
8.engine/transmission ground, on top of left front chassis member
9.in plenum chamber, next to right strut tower
10.engine compartment, on top of left front chassis member
11.in plenum chamber, next to left strut tower


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