TheSamba.com :: View topic - m-TDI (Landy pump) lift pump needed?

Sun Jul 21, 2013 1:21 pm

I had this problem last year and thought I solved it. When the engine is hot and I do a lot of stop'n'go, the engine will be difficult to start. Last year I found that the fuel solenoid was working better with a feeder relay in the engine compartment, then I found a suspect joint on the fuel line and fixed that too.
The problem is less often nowadays but now when we have really hot summer days, the trouble comes back. It is specially annoying when I need to start and stop on the road ferry that goes to my island...

It is a 1Z with a Landy Discovery pump. Fresh injectors and no leaky lines.
When it occurs the engine turns well on the starter but nothing happens.
Wait five to ten seconds, try again and the engine starts right away with no hesitation.
Sometimes I have to wait longer, but when it starts it's instant.

Either it has something to do with the temp or the fuel pump starves. As far as I know there's no way to compensate for hot fuel on the mechanical pumps but it could be the fuel shutoff valve that is wonky. The Land Rover's have a lift pump, I haven't.

I've seen a few threads on this thing Internet with Rover's having the same issue but none really comes with an answer.

Andrew, what do you think? :)

Sun Jul 21, 2013 1:38 pm

Different injection pump I know, but with a lift pump on my AHU and ALH they both start virtually instantly, without the lift pump they would turn a revolution or so before they fired.

It sounds like you are getting no fuel though with your first attempt, maybe hook up an LED to the fuel solenoid so you would know if it is getting power when this problem arises?

Sun Jul 21, 2013 1:43 pm

Hello!

check out the rubber cone under the solenoid too ;-)

wat kind of set up do you have internally??

Bye!

Sun Jul 21, 2013 1:45 pm

If you add a fuel pump make sure its the correct type and not one designed for a gas fuel injection aplication as the fuel pressure will be too high and you'll blow the seals and /or damage your inj. pump.

Sun Jul 21, 2013 1:58 pm

Everything seems to be OK with the valve but I'll hook something up and make a clean operation.

I think I'm testing the lift pump just to do something, I have a spare parts shop pretty close and they have cheap universal pumps that should do it. 120 l/h and 0,10 Bar (works with diesel, yes).

Sun Jul 21, 2013 2:18 pm

svenakela wrote: 120 l/h and 0,10 Bar (works with diesel, yes).

I know that a 43 gallon per hour pump (6 psi, .4 bar) was tried with ALH Jettas and at high engine RPM the fuel pressure from the lift pump dropped to zero, the IP really returns a lot of fuel to the tank.

If that 120 L/h pump is positive displacement and does not allow fuel to flow through it at a higher rate than it can pump then you will likely end up with fuel starvation issues at higher RPM.

Sun Jul 21, 2013 3:00 pm

jackbombay wrote: svenakela wrote: 120 l/h and 0,10 Bar (works with diesel, yes).

I know that a 43 gallon per hour pump (6 psi, .4 bar) was tried with ALH Jettas and at high engine RPM the fuel pressure from the lift pump dropped to zero, the IP really returns a lot of fuel to the tank.

If that 120 L/h pump is positive displacement and does not allow fuel to flow through it at a higher rate than it can pump then you will likely end up with fuel starvation issues at higher RPM.

Good point. It's a sucking pump made for the engine compartment (or close to) and I think it allows pass through if the flow is higher. I'll test it.
There is another one with less flow but higher pressure but I think flow is preferred though.

Sun Jul 21, 2013 3:01 pm

Perhaps 6psi is too high and it was pumping fuel THROUGH the IP and not TO the IP. The IP's internal feed pump is designed to have vacuum at the inlet.

Sun Jul 21, 2013 5:11 pm

Don't think so, IDI's can act weird with lift pumps but not TDI's. I found some good info over at tdiclub.com and they run all types of pumps, PD lift pumps, Walbro's and Bosch 044. I actually think I might get a 044 copy instead (from the same shop), it flows a lot more.
We'll see tomorrow! :)

Sun Jul 21, 2013 5:41 pm

Yeah, but if your pump+the built in supply pumps pressure excides the IP's pressure relief valve pressure then its just going to bypass. I suspect lots of those people that see improvement have worn supply pumps to start with.The volume is what you're after.

Sun Jul 21, 2013 6:50 pm

I have a LR pump on an ALH in a vanagon. It does not have a lift pump and always starts instantly. I don't think one is necessary if everything is working right, but they can certainly be helpful. 6psi is not going to hurt anything. One of the moderators on vwdiesel.net did some testing on how different pressures of feed pumps affect the internal pump pressure and found that any pressure at the inlet is added to the internal pressure. Issues only seem to arise if the combined pressure of the lift pump and what is developed by the vane pump exceeds what the pump seals can handle.

kgold, the pump's pressure regulator is affected by the pressure difference of the fuel before and after the vane pump. If there is an added 6psi before the vane pump, there will also be an added 6psi after the vane pump and so the difference will be the same and the regulator will not be affected.

Sun Jul 21, 2013 6:52 pm

I have had a 6 PSI walbro (43 GPH) in my ALH Jetta for about 8 years now, I know it doesn't do anything at 4000 RPM, but it makes starts happen "right now" and the torque at idle is nuts, it'll hold 1st gear from a stop light up a %20+ grade (San Francisco) at idle with 4 people in the car, casually move foot to gas pedal from brake, increase RPM, ease off clutch and move up the hill.

EDIT- GPH instead of GPM

Sun Jul 21, 2013 7:58 pm

Mr. Libby, so if I understand you correctly increasing the supply pressure effectively increases the plunger stroke due to the fact that the injector pop pressure is fixed? 8)

Jack, all mechanically injected diesel engines should be able to go to full or near full fuel condition to maintain idle speed if yours couldn't prior to adding an extra pump then I would suspect the internal vane pump was worn. There is a funny self fulfilling profecy in these conditions IMO. By the time you realise an extra pump will help power output you've already been starving your pump of fuel and lubrication thus causing the need for the pump. Unless someone added a pump to a stock vehicle before increasing power output. :wink:

Sun Jul 21, 2013 8:02 pm

kgold708 wrote: Jack, all mechanically injected diesel engines should be able to go to full or near full fuel condition to maintain idle speed...

My Jetta is a 2003, and is an E-TDI. I added the lift pump at ~40,000 miles, the injection pump really should not have been worn with such low mileage, the car has 196,000 miles on it now...

Sun Jul 21, 2013 8:28 pm

You're e-tdi still has a VE injection pump. I'm sure that the fine gentilemen at bosch built plenty of excess capacity into the vane pump to allow for any and all operating conditions the pump was capable of serving plus a significant excess volume to allow for proper cooling and lubrication thus they added the spill port to return excess fuel to the tank.

Your external pump not helping at 4000rpm is because of the fuel map, timing advance, or internal mechanical governor not fuel flow FWIW.

Sun Jul 21, 2013 8:40 pm

kgold708 wrote: Your external pump not helping at 4000rpm is because of the fuel map, timing advance, or internal mechanical governor not fuel flow FWIW.

On TDIclub it was shown many years ago that a PD lift pump helped maintain requested timing advance at high RPM where without a lift pump the actual injection timing lagged behind the requested injection timing, and a lift pump "fixed" this, thus maximizing power. The Walbro pump does not move enough fuel at high RPM though so it does not have this benefit like the PD lift pump does.

EDIT- this was all back in the mid 2000s...

Sun Jul 21, 2013 8:50 pm

43gpm wasn't enough?

I'm guessing those fine people were requesting timing advance above base timing that was far beyond factory spec, there's a lot of ways to skin a cat is all. Like I said to Drew increasing the pumps internal pressure advances injection timing because the injector pop pressure is fixed. These are two stage pumps.

Sun Jul 21, 2013 8:50 pm

kgold708 wrote: Mr. Libby, so if I understand you correctly increasing the supply pressure effectively increases the plunger stroke due to the fact that the injector pop pressure is fixed? 8)

Well, I wasn't trying to say that but it would follow. Then again, the difference would not be anywhere near significant. A 6psi increase in pressure doesn't get you to 3,000 psi very much sooner.

Sun Jul 21, 2013 9:15 pm

Well actually, if the stock internal pressure is 3psi and the plunger is capable of a 1kpsi pressure rise then you're getting 3k earlier in its stroke which gives you more advance and duration. In a E-tdi application the ecm can match requested timing and volume it couldn't before, this was the point I'm trying to make.

Sun Jul 21, 2013 9:20 pm

EDIT- You posted while I was typing....

kgold708 wrote: 43gpm wasn't enough?

I'm guessing those fine people were requesting timing advance above base timing that was far beyond factory spec, there's a lot of ways to skin a cat is all.

That was a mistake, it was supposed to read GPH, and it wasn't enough flow as at high RPM fuel pressure pre IP dropped to zero.

That was with modified programming, was it far beyond factory spec? Well, some M-TDI proponents believe that E-TDIs are not capable of changing injection timing notably, in which case its not possible to adjust the timing well beyond factory spec...

I do feel that the addition of a lift pump helped my TDIs, if I were Sven and had a low cost lift pump around I would try it, but I would also look at my fuel cut solenoid circuit as well.