VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: Alcaid on October 05, 2011, 04:18:16 am
-
Hi,
Is there a reason not to use a lift pump on our VE pumps as they do on the TDI engines? (VE, PD, CR) Will it affect timing and advance it too early in any way? Timing is controlled mechanically in our pumps and not electronic as on the TDIs so there might be an effect with higher input pressures?
-
It will have no effect on advance. Just make sure you don't use too high of a PSI lift pumpand blow out your pump seals.
-
Hi,
Is there a reason not to use a lift pump on our VE pumps as they do on the TDI engines? (VE, PD, CR) Will it affect timing and advance it too early in any way? Timing is controlled mechanically in our pumps and not electronic as on the TDIs so there might be an effect with higher input pressures?
I thought the lift pump would alter the pressure diff across the advance system.
Why not cure the pump's pump, after al it's only a vane pump, and I bet the vanes can be reversed if damaged, just like the vac pump.
-
I thought the lift pump would alter the pressure diff across the advance system.
Why not cure the pump's pump, after al it's only a vane pump, and I bet the vanes can be reversed if damaged, just like the vac pump.
Fixing something that isn't broke will not solve anything...
I was thinking of adding a lift pump to help the pump maintaining the proper advance up to 6000rpm. I've seen VP pumps failing to do this even up to measly 4500rpm without a lift pump and I feel the VE pump on my 1.6TD is failing to maintain advance at high revs (governor main spring shimmed solid) but haven't been able to check it (Vag-Com logging sure is useful, but not an option on our 1.6TD... :P)
-
I have a 6psi electric pump feeding my 1.6 n/a and 5500 rpm's are no problem.. Obviously with a non-turbo there isnt a ton of power up there.. but with my straight pipe exhaust it sounds AWESOME.
-
i got a small lift pump, and i could tell the difference in the top end after i installed it.. its alot better than just having a suction feed, and it makes your filters last longer..
-
I thought the lift pump would alter the pressure diff across the advance system.
Why not cure the pump's pump, after al it's only a vane pump, and I bet the vanes can be reversed if damaged, just like the vac pump.
Fixing something that isn't broke will not solve anything...
I was thinking of adding a lift pump to help the pump maintaining the proper advance up to 6000rpm. I've seen VP pumps failing to do this even up to measly 4500rpm without a lift pump and I feel the VE pump on my 1.6TD is failing to maintain advance at high revs (governor main spring shimmed solid) but haven't been able to check it (Vag-Com logging sure is useful, but not an option on our 1.6TD... :P)
Why not install a weaker advance spring, then the pump doesn't need to be overloaded with high internal pressures, to get the same advance?
We are lucky over here as we don't get water in the diesel. ;D and so filters last.
-
Weaker spring would be my fix. There is a line of them that are color coded and the green one is the weakest therefore it gives the top end advance sooner or at lower pressures. You really have to gauge the IP to see what the pressures are at all cycles of the system before you can fix a lack in the advance at higher pressures. There are shims in that cover of the advance, have you played with that mod?
There is also only a certain amount of advance you can get. I think it is stated someplace here either 24 degrees or 12 not sure on that number. If you have good top end pressure and still lack advance I would be looking at the pump rebuild. Something is worn out and not moving the cam plate as it should to advance the injection time.
-
I've wondered this too.
The low pressure side of the timing advance piston is connected to the front of the pump,..
so if the internal pressure is 6 psi higher,
and the pressure at the front of the pump (and other end of timing piston) are 6 psi higher too, then nothing would change.
-
I really don't think a low pressure pump pushing fuel into the inlet is going to change the timing much. Ever notice that it takes a pretty good change from idle to get the little bit of advance the cold start lever gives? I remember that the few degrees you get from pulling on the start lever is negated as soon as you get somewhere beyond 1200 RPM. Don't quote me on that but it is low. Now if the normal pressure in the IP at idle is supposed to be 43 psi and at 2000 RPM it is 74.5 then in the middle at about 58 PSI you are already advancing like the start lever.
I run a gauge and I can tell you that it is pretty quick to jump to 55 PSI as you upshift. Keeping more fuel coming into the pump under pressure instead of relying on a pull from the pump may help that jump happen sooner but I don't think you will even notice it. I doubt that once the internal pressure at idle is produced that there is an additive effect going on. It overrides the inlet pressure from that low pressure pump.
In the fire business we rely on pumps a lot and staging pumps in line allows us to move water long distances or produce high pressures. Depending on how and with what pumps. Some are built for volume others pressure. I am thinking this adding a low pressure pump to the front side of the IP is similar to how we would try to combine pumps to keep up with a high demand on the system down the line. You can starve a pump if the pressure is to low from the first but I don't think that is the situation here. Having the first pump producing more pressure didn't add to the final output either. It was/is limited by the rotation of the second pump. In our IP that is the vane pump.
-
The reason why I want to add a lift pump is not the get the timing advance sooner as some of you write about, but rather maintaining it at the top rpm range were these pumps tends to starve and internal pressure drops.
-
The reason why I want to add a lift pump is not the get the timing advance sooner as some of you write about, but rather maintaining it at the top rpm range were these pumps tends to starve and internal pressure drops.
Sounds reasonable, but I thought the govenor limited the max rpm.
As pump operates under an excess of fuel, would the late mk2 fuel bypass back to the filter rather than back to the tank not help that?
Then there is my belief that dropping the internal pressure of the pump coupled with a weaker advance spring, would get you all the advance needed, and less bursting pressure on the pump seals, less loading on the internal lift pump etc.
Check 'my' graph to see that the internal pressure of pump v rpm is linear over a large range of idle pressures...
-
Have you logged case pressure doing a WOT run from 1500-2000rpm to ungoverned redline? Thats' when you see it dropping. I've seen it on several TDI pumps without lift pump and I don't see a reason why the VE pumps would act differently.
-
Have you logged case pressure doing a WOT run from 1500-2000rpm to ungoverned redline? Thats' when you see it dropping. I've seen it on several TDI pumps without lift pump and I don't see a reason why the VE pumps would act differently.
Er nope ;D
I don't do wide open throttle stuff ;)
My testing was confined to gauge readings upto 3500 ish under no load, as I have my head under the bonnet[hood] to read the gauge on a 9" length pipe with one eye whilst the other eye logs the digital readout on my strobe box, so you could be right :)
-
why do the dodge guys use lift pumps instead of weaker springs?
im still gonna say that a lift pump is better than a weak spring. the pump is being PRESSURE FED fuel, it doesnt have to make suction on its own.. that allows my stiff spring to advance sooner than a weak spring. because if the vane pump doesnt have an available excess of fuel, then it cant start advancing till it has enough fuel present to raise the internal pressure..
-
When I worked with Giles we tested this on a test bench. I forget the exact numbers so I am just going to make them up. We fed the pump with 6 psi at idle and the internal pump pressure was 36. We increased the lift pump pressure to 46 PSI and the internal pump pressure went up to 76 psi. The advance gauge did not move in the slightest. We tested it at 1500 RPM pump (3000 engine), feeding with 6 psi the internal pressure was 106 psi. We then fed it with 36 psi and the internal pressure was 136 and the advance did not change.
-
because the advance works on the principle of pressure differentials..
the regulator keeps the internal pressure XXpsi higher than the inlet pressure..
-
Thanks guys! Lift pump it is then! :)
-
if you run your engine up to the upper RPM range much, thats where you will notice the lift pump most..
my lift pump made my car have quite a bit more up top..
-
What kind of lift pump do you have? What psi and gph? From what I can tell, with the small orifice in the return bolt, not much fuel is returned to the tank at idle. Do you know the return rate at 5,000 rpm? Probably not that much so the demand on your elec lift pump isn't that great and you do not have to worry about fuel starvation at high power/rpm situations. That VE vane pump is a powerful pump, much more so than your elec lift pump. I wonder if you can get the same results (better top end) by changing to bigger diameter fuel lines (from tank to IP for both supply and return).
-
Haven't bought a pump yet, this one seems pretty optimal: http://forums.tdiclub.com/showthread.php?t=309596
-
What kind of lift pump do you have? What psi and gph? From what I can tell, with the small orifice in the return bolt, not much fuel is returned to the tank at idle. Do you know the return rate at 5,000 rpm? Probably not that much so the demand on your elec lift pump isn't that great and you do not have to worry about fuel starvation at high power/rpm situations. That VE vane pump is a powerful pump, much more so than your elec lift pump. I wonder if you can get the same results (better top end) by changing to bigger diameter fuel lines (from tank to IP for both supply and return).
i know 1/2" is pretty standard on a hopped up cummins.. and the feed line needs upgrading worst. the return line not soo much.
-
The return line for the size of it roughly 1/8" to the ip, I'm sure it's a metric size is pretty steady at anything above idle, this adds up quickly and the return from the out of the ip is a small hole, but at pressures over 50 psi also moves a lot of fuel. If there's any restriction in return you will have problems with leaky return lines off your injectors. I had a gasser and the return line in the tank is long so it puts the return fuel under slight pressure from the weight of the fuel in the tank. I had to open the tank and cut this off so it just dumps the return fuel into the tank; otherwise I have leaky injector returns. I kept the throttle body pump that was in the tank as my (mk3) lift pump and used a cheap holley pressure regulator to regulate the fuel down to about 4 psi.
-
Whatever lift pump you go with make sure you install a gauge so you can see if it is able to supply enough fuel throughout the RPM range. The return moves quite a bit of fuel as it also is used to cool the pump.
I read a very interesting article about fuel line sizing recently with all sorts of math but I can't find it now. This one kind of covers the topic
http://sbmar.com/main/articles/understanding_fuel_line_sizes_vs._fuel_supply_restriction/
-
Whatever lift pump you go with make sure you install a gauge so you can see if it is able to supply enough fuel throughout the RPM range. The return moves quite a bit of fuel as it also is used to cool the pump.
That's why I'm considering the Fuelab lift pump because that seems like one of the few options that actually has a high enough flow to not run out of steam on top.
-
ill rig up a pressure/vac gauge this weekend, right before my pump.. i dont think its ever going to read vacuum, even with the crappy cheap shaker fuel pump..
you can pump a 5 gallon can of gas in about 8-10 mins with the small shaker pumps..
-
I put one of those pressure/vac gauges in before the IP and after the filter on a suggestion by Mark I think it was. I noticed that I was pulling a few lbs of vac then as it went up I would get air in the line. Once I smoothed the copper washers and fire them to a blue color they worked fine after that. I think he mentioned he used the vac reading as sort of a way to tell when the fuel filter was plugged up.
So you can and may indeed see a vac reading on that gauge once you get it in.
I have also seen some of those gauges that show actual flow. Liters/min or gallons/min, I wonder if hooking one of those to the outlet side of the IP and measuring the amount of fuel returning to the tank would be a means of gauging if you were shorting the delivery to the IP?
I also wonder if hooking one on both sides of the pump and getting a differential would allow us to determine the actual amount of fuel used. I know the ScanGauge I have gives me all kinds of numbers about that stuff but I think that comes from sensors that are part of the Electric Brain From Detroit, Japan, or other.
All we would need is a differential between in and out and miles driven to get to MPG. Time to go talk to my computer programmer son.