Tamdem pump pressure testing

[resto1975]

I have a PD150 that seems to be suffering from lack of fueling, lift pump pressure is fine and the car starts on the button and idles well but the throttle response is terrible and will hardly pull itself along.
So far i have checked:
Cam timing,
lift pump,
MAF,
MAP,
Filter,
Turbo,
Exhaust system,
Injector settings,
Camshaft.

The spec for the tandem pump is 7.5 bar at 4000 rpm which the pump will produce but at low rpm the needle on the gauge bounces around so much it bent the needle on my very expensive Sykes pressure gauge.
Has anyone tested pump pressure and what did you see or is there anything i am over looking.

Any suggestions gratefully recieved as i am running out of ideas !!!

 

[ryanp]

maybe use a dampened gauge, Glycol filled maybe, I use one of those for EMP measurements!

 

[DanG144]

It sounds to me as if you have a LUK pump, the vane style, and one vane is not working. These have been known to break the vane springs. At least two guys have fixed theirs with substitute generic springs from a hardware store.

Most of the tandem pumps easily provide much more pressure than the ratings. I don't even bother pressure testing, just flow.

If you have a LUK pump, put the return flow line into a bottle at idle. You should get about 1.2 lpm or more. If you get significantly less, then replace the pump, or repair it.

Verify that your lift pump is providing more than 3 lpm out of the fuel filter to the engine.

 

[resto1975]

Hopefully will have some time tomorrow for some more testing will post the results if all goes to plan.

 

[rshelor]

It sounds to me as if you have a LUK pump, the vane style, and one vane is not working. These have been known to break the vane springs. At least two guys have fixed theirs with substitute generic springs from a hardware store.

Most of the tandem pumps easily provide much more pressure than the ratings. I don't even bother pressure testing, just flow.

If you have a LUK pump, put the return flow line into a bottle at idle. You should get about 1.2 lpm or more. If you get significantly less, then replace the pump, or repair it.

Verify that your lift pump is providing more than 3 lpm out of the fuel filter to the engine.

So how does one check the flow rate out of the filter? Do you jumper a relay? If so which one and where is it on a 2005 Jetta w/BEW PD engine? Thanks.

 

[DanG144]

I do not jumper a relay to test lift pump flow.
I just pull up the rear seat and put a 12v supply to the pump, with the filter inlet line into a jug.
If you want to test through the filter, clamp closed the fuel return line from the filter, then put the line to the top of the tandem pump into a jug.

http://forums.tdiclub.com/showthread.php?t=225672

 

[rshelor]

Thanks, I'll give it a shot. I checked the flow rate on my tandem pump (unknown to me who made it) and got exactly one liter per minute at idle. Does this sound too low? You suggested in another post that it should be 1.2 L/min. My engine stumbles at light throttle under load like going up a hill intermittently so I can't really determine flow rates when it does falter. Also, the flow rate was of course through the filter and I think I got a bad tank of fuel....or else something went south after the fill up. I await UPS w/a new filter to replace the one w/about 2,000 miles on it.

 

[DanG144]

With a good lift pump and a good tandem pump, I did get 1.2 lpm repeatedly.

With your problem I would certainly look at your lift pump performance, after you get your new filter in place.

 

[rshelor]

Thanks, will do. BTW, the lift pump has about 20,000 miles on it. It seems strange to me that a clogged filter would cause intermittent problems, seems like a clog would be a clog at all times, not just sometimes.

 

[JPDiesel]

I had a 2004 with a bad tandem pump.
Symptoms were stumble from off idle to ~ 2000rpm.

Jason TDI suggested a Diesel purge.

He set it up to feed from a bottle hanging from the open hood (gravity feed) with a return line back to the bottle.

When running at idle this way, it would not return any fuel back to the bottle from the return line and it only ran on 3 cylinders.

When the rpms were raised the idle smoothed out and fuel started to return to the bottle.

This turned out to be a good way to test the tandem pump.

Changing the pump cured the problem.

 

[resto1975]

My problems turned out to be injectors, still not sure why but a secondhand set sorted the problem, tandem pump pressure held at above 4 bar maxed at 7 bar under all conditions on road test.

 

[rshelor]

I would like to pressure test the tandem pump, but don't know what fittings, nor where to buy them. I have an excellent gauge, but I think the nipple I would need would not have pipe threads, be metric, and probably not available. Bentley shows a banjo bolt setup, but I haven't a clue where to find that set-up. Any help there?

In the meantime the filters haven't arrived to test output of the lift pump. The "no fuel being returned from the tandem pump" observation is an interesting one that I wil look into. I assume since the purge bottle was gravity fed that one should do the same with the diesel fuel supply if doing a similar check as the lift pump would introduce fuel pressure that would skew the outcome.

 

[rshelor]

My problems turned out to be injectors, still not sure why but a secondhand set sorted the problem, tandem pump pressure held at above 4 bar maxed at 7 bar under all conditions on road test.

And how does one determine if injectors are to blame?

 

[jimbote]

I would like to pressure test the tandem pump, but don't know what fittings, nor where to buy them. I have an excellent gauge, but I think the nipple I would need would not have pipe threads, be metric, and probably not available. Bentley shows a banjo bolt setup, but I haven't a clue where to find that set-up. Any help there?

In the meantime the filters haven't arrived to test output of the lift pump. The "no fuel being returned from the tandem pump" observation is an interesting one that I wil look into. I assume since the purge bottle was gravity fed that one should do the same with the diesel fuel supply if doing a similar check as the lift pump would introduce fuel pressure that would skew the outcome.

I used an old broken turbo feed line (oil filter housing end) and feed line banjo bolt for my fitting, attached to a hose and gauge...it's 12x1.5 iirc ....

 

[rshelor]

I used an old broken turbo feed line (oil filter housing end) and feed line banjo bolt for my fitting, attached to a hose and gauge...it's 12x1.5 iirc ....

Believe it or not, but I salvaged my oil feed line when replacing the turbo, but that sounds like a good idea. The threads are the same? Thanks for info...want to rent out your set-up?

 

[jsrmonster]

And how does one determine if injectors are to blame?

PD injectors will clog internally with bioD and veggie fuels. The tiny return holes clog up and can't return fuel. Seen many like this already. Cleaned a few sets with success. (note: you can't R&R pd injectors w/o special fixture or you will break anti-rotation/alignment pins).

Tandem pump pressure test: http://www.youtube.com/watch?v=-FHfTOrWS88

Jeff

 

[jimbote]

Jeff, I was under the impression the tiny holes were the feed to the injector and the small single hole above was the return

 

[jsrmonster]

Jeff, I was under the impression the tiny holes were the feed to the injector and the small single hole above was the return

Have you ever seen the crap inside the removed injector cap when they are clogged? Those holes are smaller than the injector tip holes. It is returning, since its clogged on the inside. you can scrape out the crud with a knife, use a torch and compressed air to finish cleaning. lots of carb cleaner helps too.

Jeff

 

[jimbote]

I know what holes your referring to....from the tip it's the area between the first and second oring....no I have never had a PD injector apart ...I'm not qualified

 

[jimbote]

looking at the VW self study guide it clearly shows the "nut" area of the injector with the small holes as the fuel supply....maybe some gets returned through this area too?....I'm a novice @ PD's for sure so let the lessons begin ....EDIT...maybe the bio/veg deposits form on the inside because the fuel slows or the inside of the unit is so hot it cooks....like the goo on the outside of the fryers @ stanley's fish house

 

[jsrmonster]

orange is supply, tan area is return port.

 

[jimbote]

a little off subject...but between the Luk and Bosch tandem pumps which is the preferred unit?

 

[rshelor]

With a good lift pump and a good tandem pump, I did get 1.2 lpm repeatedly.

With your problem I would certainly look at your lift pump performance, after you get your new filter in place.

Well, I finally got a filter in and it helped, but still missing intermittently. So I checked flow of lift pump and when I did I got a flow of exactly one liter per minute. Not the three liters per minute as reported in this forum somewhere. Interestingly, I reversed the polarity to the pump and evidently back flushed the pump (or it was Juju). Still one liter per minute, but it ran like a top. That is, until it died at an interstate exit fifty miles from home and wouldn't restart. I'm hoping the lift pump, a no-name replacement from Canada/China(?), is to blame. I have read that if the non-VDO lift pump dies, so does the vehicle. Stay tuned for results.

 

[DanG144]

Did you replace the whole assembly or just the pump/motor inside?

Some of the replacement pump/motors have too long a discharge nozzle, the tube buts up against the filter, and allows only a tiny portion of the fuel pickup filter to be used, about the size of your finger tip. It can quickly plug up.

If this is the case, cut about 3 mm off the pump discharge nozzle, clean the screen, and you are back in business.

 

[rshelor]

Well I opened the wallet and bought a new lift pump after being left dead at the interstate exit and that fixed it. Still a little surging when going up a steepish hill w/moderate accelerator pedal. I'm looking to check the tandem pump. So do tandem pumps die at a certain point, or are they fairly robust? I have 310,000 miles on the vehicle.

 

[slamhouse]

Haven't had any personal encounters with a tandem pump failure, from what I know and hear, they are fairly robust and hardly ever fail.

Do you have VCDS? Or do you know anyone nearby with VCDS?

A good thing to check with all those miles is injector deviation. Might be time for some injector seals and rebuilds.

 

[DanG144]

The tandem pump does fail, especially the LUK vane type pump.
The pumps can last a long time, though.
I think that running without the lift pump can cause them to wear faster.
I would prefer the Bosch gear type for a replacement.

 

[Bobby Singh]

With 783's or 100% nozzles can't be sure now:

http://img.photobucket.com/albums/0903/cossie_power/Golf mods/FuelPressure.mp4

 

[Ohnoitsthexops]

I don't have a pd but I had lots of algae in my tank tha caused a problem just like this. **** was clogging the in tank pickup before it even made it to the fuel filter.

 

[Losha]

Well I opened the wallet and bought a new lift pump after being left dead at the interstate exit and that fixed it. Still a little surging when going up a steepish hill w/moderate accelerator pedal. I'm looking to check the tandem pump. So do tandem pumps die at a certain point, or are they fairly robust? I have 310,000 miles on the vehicle.

Have you replaced turbo in this car? if not I would strongly suggest you pull intake hose off and check shaft play in turbo, side to side and axial play. Some side to side play is normal, but if you have axial movement then its the signs of turbo failure soon. That as well will cause low RPM's surges and light/moderate acceleration hesitations. I haven't seen this on BEW engine to verify, but on BRM I had few cars this summer with exact symptoms and all ended up needing new turbo. One for fact was still drivable except was making screeching noise under boost, after replaced turbo car drove like brand new, no more surging in low rpms and hesitation to accelerate also customers clamed that mpg's went up quite a bit.

So pull intake hose off check shaft play and post results here what you findout.