Intermittent stall

[MEgearhead]

I have been fighting an intermittent stall on a 05 BHW for over 5 years. Nothing ever shows up on VCDS. It will not immediately restart. It has stalled under power, coasting, and idling.

It seems to be a fuel supply problem as I have to cycle the ignition switch at least 30 times and even then it takes about 4 times of cranking for 5 seconds. On 4 occasions I had to have it towed home, the last time I towed it, after using VCDS to run the lift pump 3 times and around 15 - 20 seconds of cranking it started up and ran fine.

At first I thought it was a lift pump problem, but have never been able reproduce a lift pump failure. I did notice some pitting on the fuel pump relay contacts, so I replaced it with a new relay. I've removed the lift pump from the tank twice and run it in a 5 gal bucket of fuel. It works perfectly, and the venturi siphon gizmo keeps the cup full and overflowing.

I thought it might only happen at 1/4 tank or less, but it happened today at over 1/2 a tank. The first two incidents were around a year apart, but now it's down to nearly every week.

Once I thought it might be a fuel filter, but it has happened after less than one tank on a new filter. I change the fuel filter at each oil change, cut every old filter open, and have never seen any sediment or water.

Any suggestions are greatly appreciated. Thanks!

 

[dtrvler]

Crank/engine speed sensor.
Doesnt always set a code.
Cheap. Causes random stalling often getting worse over time. Pretty quick to replace. My car did the same thing. Of course could be something else.
Or.
Cam sensor. Ck wiring for both for chafing. Engine computer needs to know how fast its turning and the relationship of cam and crank position. Or it freaks out and kills itself.

Air may be in fuel system from the filter changes. You can bleed the tandem pump at the test port on the pump to see if there is air. (Less likely.)

It would be good to test the tandem pump fuel side. There is a test port. Alot of times cars will run with good tank pump, bad tandem pump but car will start hard.

 

[MEgearhead]

Thanks! I think I'll try to check the tandem pump first, as that seems most likely based on the symptoms and checks I've done.

I have not been able to get VCDS on it promptly every time, but all the instances I have been able to, I get an rpm indication and injection quantity while cranking. So, I'm less inclined to suspect the crank/cam sensor. However, it might be worth ruling that out.

Thanks again! I didn't realize that it would run with a failing tandem pump.

 

[MEgearhead]

While waiting for a banjo fitting to be shipped to check the tandem pump pressure, I decided to see if the car would run without the lift pump operating. Removed the lift pump relay. It started, but only made it about a block. Behaved the same as every other time it has stalled. Re-installed the relay then ran the lift pump with VCDS 3 times and it took 3 attempts of cranking 5 sec each to get it started. Ran rough for about 20 seconds and then was fine.

I pulled the relay again, opened it up and looked at the contacts. The new (1 yr old) relay contacts were pitted. Might it be a sign of a lift pump failure in the near future?

When I ordered a new relay a year ago the original part number 8D0 951 253A was superceded by part number 4H0 951 253A. Does anyone know if that is correct?

I have read that it should run without the lift pump operating. Has anyone proved this to be true in practice? It could be a couple issues working together to cause the problem.

 

[MEgearhead]

Finally got the fittings I needed to test the tandem pump. At idle it's 40 psi and at 1500 rpm it would be over 100 psi. It hits 100 psi at 1400 rpm. Guess I need to study the fuel system a bit. Any suggestions are greatly appreciated!

 

[BuckeyeMan71]

I had that problem and it was the crank positioning sensor. It doesn’t throw a code most of the time but it will kill the engine and you have to wait awhile for it to re-start. It’s only $30 and takes about 15min to replace. How many miles are on it

 

[MEgearhead]

Thanks! It has 220k miles. It started doing this around 5 years ago at around 170k. The way it acts it sure seems fuel related. When it finally starts it stumbles then gradually clears up exactly the same as after running out of fuel.
Since this is the second suggestion to replace the cps maybe I'll just go ahead and do that. Thanks again!

 

[MEgearhead]

No joy on the CPS. It clearly seems to be a fuel delivery issue. It is still very intermittent (once every one to three weeks). The last time it cut out turning onto our street so I was able to coast home. The solution is always the same: cycle the ignition switch 20+ times or use VCDS to run the lift pump 3 times. It will then start on the 3rd 5 sec cranking attempt, and run rough for a few seconds then smooth out and run fine for a few weeks.

I know for a fact the car will not run without the lift pump operating even with a full tank. I was under the impression that the tandem pump could still draw fuel from the tank with a lift pump inop.

I checked the tandem pump output pressure: 40psi at idle and pegs the 100 psi gauge at 1400 which seems high.

 

[MEgearhead]

I am at my wit's end. Actually somewhat have given up and bought another car, but I would like to get this car going again for my son. Does anyone know what the flow output of the lift pump should be? I checked it today and get about 0.7 lpm.

 

[zzdiesel]

When you had the pump out did you inspect the tank? Just thinking something could be in ther that periodically blocks the pump inlet.

 

[MEgearhead]

Turns out it was the lift pump. Installed a VDO lift pump and tested it's output. It overfilled a 1 L bottle in less than 30 s. VDO was the manufacturer of the original lift pump. In fact the replacement pump was identical except the VW, four circles, and part number were ground off. No stalls since. Now we may have lost reverse on the transmission, but that's another subject. Thanks to all that provided input.