Commonrail: Need more fuel

[Rub87]

sure. but even with an extra pump the speculation is that it has to be timed. otherwise the 4.2 would have worked fine for the guys.

what you say about the cavitation makes sense. at 3000 rpm one can run about 100 mg per stroke. at 4500 I get railpress undershoot with only 90mg.

 

[ryanp]

From testing increasing the feed flow and pressure makes no difference at all on 2.0 and 3.0 engines.

Under driving sounds good but on 2.0s a little harder unless you play with TB rollers to make a little more room on the belt

 

[Rub87]

sure but then there for chance to keep te pump timed..

 

[ryanp]

Yeah I guess CP3 would care less but CP4 needs to stay at 1:1 for sure. Slight timing tweek on pump could help

 

[TDIMeister]

Does anyone know if the pump in the CRs have a single or multi-nose cam?

Edit: I mean the ones specific to the VAG CRs.

 

[2micron]

anyone has some ideas to get a but more out of it instead of changing to cp4.2 or cp3

You can try a couple of simple mods. Meister's case pressure increase allows a slight increase, maybe a few hundred RPM more, before the pump drops pressure. You have to modify the "overflow" or "cascade" valve to give more internal case pressure within the pump. Simply increasing the feed pressure (stronger auxiliary pump) does nothing as Ryan mentioned as the cascade valve will still maintain 62psi.
The cascade valve is a simple spring and plunger relief valve, factory set at 62 psi.

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An modified and adjustable cascade valve to increase the pressure will allow a few hundred RPM more stable rail pressure, but is not the only mod for this pump.

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Further increases can be had by increasing the metering valve flow. All the injector fuel passes through these triangular ports in the piston within the metering valve:

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Triangular ports x 3
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You can see the difference in the larger CP4.2 metering valve ports:

Sure, swap metering valves or carefully open up the larger, lower end of the triangle.
These mods together will offer slightly more stable output and rail pressure at higher RPM's, together with Rub's increased duty cycle on the metering valve.
Rub, please share your pump part number. Our American Passat has a slightly longer stroke eccentric shaft, which you may already have?
Meister, all CP4 series pumps have a dual lobe eccentric shaft, offering two strokes per shaft revolution, if that helps answer your question?
All the best!
Andrew

 

[TDIMeister]

Thanks very much Andrew. Your suggestions all agree with my "open up the HPFP and look for anything that might be restricting/throttling the flow."

The HPFP does not "need" to be timed with the engine (waiting for Drivbiwire to swoop in to tell me - again - I'm wrong...), so it can be over/underdriven. The pressure compensation is mainly due to emissions reasons to minimize cycle-to-cycle variations.

Emphases added:

Through a series of rigorous tests, it was demonstrated that control of the indexed torque in each cylinder through the combustion control significantly reduced dispersions of the injected overall fuel mass in the observed mapping areas and that utilising cylinder pressure-based combustion control significantly reduces the range of emissions as compared to conventional diesel engine control units, concerning particulate and NOx emissions.

http://forums.tdiclub.com/showthread.php?p=3207565&highlight=MTZ#post3207565

So, the *absolute* universal law that some hang on to that holds that the HPFP must be timed is, IMNSHO, a bunch of hooey. After all, concerns about emissions went out the window with the first performance mod done to the engine.

 

[Drivbiwire]

Yes Dave I would have to disagree in a performance application...

Follow the pressure pulse and you will see why it should be timed.

Peak performance is limited only by the quantity of fuel you can deliver in a specified ideal window of time.

As you commence injection, the rail pressure will begin to drop at the exact moment that you need to sustain the peak pressure to insure you don't suffer a delivery rate reduction at the back end of the injection window.

Ideally if you can sustain the peak pressure later in the injection event power in terms of sustained torque at high rpm's will not suffer.

Oversupply of fuel early on (injection advance) can buy you additional time for injection, however these gains are almost always lost to the over-pressure of the initial combustion pulse that works against you in terms of power. Sustaining peak rail pressure thru timed pumping will give you the pressure needed to deliver the quantity at the needed rate.

Shaping the injection window so that you net a more uniform combustion pressure pulse by sustaining peak rail pressure later in the injection would be key.

Not timing the pump to the injection event will cause a loss of peak pressure at the latter end of the injection event, thus power will suffer.

 

[ryanp]

A larger capacity rail would help to reduce the drop in pressure and subsequent spike from the HPFP.

I could make a test on my own car with CP4 and rail pressure issues, swing the pump 1/2 and then 1/4 .

I have a CP3 fitted to another car, along with 2260, this has no rail pressure issues any longer, smokes much less but power and torque are almost exactly the same as before with CP4 but no limp.

I'm convinced we need larger injectors at the same time as a pump upgrade. Anyone know of upgrades? It's like a 1hr test for me! I have lots of possible choices but someone will know!

I also have a larger CP4 on order

 

[TDIMeister]

So what? You're losing pressure anyway at high RPM and getting an under pressure deviation. (responding to DB)

 

[2micron]

So, the *absolute* universal law that some hang on to that holds that the HPFP must be timed is, IMNSHO, a bunch of hooey. After all, concerns about emissions went out the window with the first performance mod done to the engine.

Yes!! Agreed. Thank you Meister!! I thought we busted the Myth about timing years ago, but I understand its hard to shift away from the "Distributor Pump" injection timing we are all used to!!
Remember running the common rail remotely from the old Lawnmower??? Watch the video below!!!

Vibration testing on the Rail to Measure The Pump "Pulses"
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Here's a video showing the car running with the CP3 pump, driven by a 1950's Gravely Lawnmower!!
http://s1059.photobucket.com/albums/t428/2micron/?action=view&current=DSCI0496.mp4
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Just an update, My car has over 12K hard miles running an "un-timed" CP3 pump.
All the best!!
Andrew

 

[Rub87]

Dave,

CP4.1 has 3 lobes on the cam.

here a log from this car I talked about. what the controller is exactly doing is still a bit of a mystery for me. Ive looked in the SW and there is not much more than 2 PID controllers with feedforward map.

in the beginning of the log it goes in limp mode. then cycled the ignition and then afterwards its fine for some reason. here and there some interaction from T3 limit. bigger injectors would be good.

do you know what pump is on the 2l 240hp biturbo tdi?

 

[nate0031]

Dave,
CP4.1 has 3 lobes on the cam.

They were correct before, it does indeed have two lobes on the cam.

Edit: Not my photo BTW. I think it was originally posted by OilHammer.

Another Edit: Better picture for this posted by 2004LB7

 

[nate0031]

A larger capacity rail would help to reduce the drop in pressure and subsequent spike from the HPFP.

I could make a test on my own car with CP4 and rail pressure issues, swing the pump 1/2 and then 1/4 .

I have a CP3 fitted to another car, along with 2260, this has no rail pressure issues any longer, smokes much less but power and torque are almost exactly the same as before with CP4 but no limp.

I'd love to see tests with the pump timed out.

Might I ask what the CP3/2260 car is putting down?

 

[Rub87]

They were correct before, it does indeed have two lobes on the cam.

Edit: Not my photo BTW. I think it was originally posted by OilHammer.

Another Edit: Better picture for this posted by 2004LB7

my mistake, its offcourse the cp3 that has 3 lobes.

 

[ryanp]

I'd love to see tests with the pump timed out.
Might I ask what the CP3/2260 car is putting down?

When we get chance i'll do it.

My dyno is know to be conservative, it makes 245bhp last time we checked, 255hp is the most a CR with 2260 has made on my dyno before rail pressure issues.

 

[Rub87]

Seems to match the one I made. This is with stock exh and almost railpress issues (only very now and then with not fully warm engine)

Now I added some fuel after 3k5 where there was more room due to less backpressure and railpress issue was there

 

[ryanp]

Ruben, did you manipulate metering valve maps?

 

[Rub87]

tried it yesterday, didnt seem to make any difference

 

[ryanp]

same here! will try a larger metering valve!

 

[storx]

I tried a different metering valve and all it did was adapt it seemed.. first few runs it ran better and then it went back to fuel cut..

 

[Rub87]

in this car its opposite. when mdium warm engine it goes quicker in limp, I guess it corrects the full load for cold engine to overcome higher friction?

 

[storx]

i am not sure, i was sent a different metering valve to test and it really made no difference after about 40 miles of driving.. to me

 

[ATR]

Subscribed!
read through this thread today and I'm really looking forward to seeing how the cp3 works out.

Les, I may have missed it but why did the cp4.2 not work out for you?

 

[Dirtracr95]

Subscribed!
read through this thread today and I'm really looking forward to seeing how the cp3 works out.
Les, I may have missed it but why did the cp4.2 not work out for you?

It has to do with the timing of the pump and the fact that the pistons are 90° apart from each other. A bit difficult to explain but we were able to prove through extensive testing that the engine was running on only one of the two pistons at any given time.

This is what your after

 

[ATR]

This is what your after

Okay that makes sense.

Thanks!

 

[Terry270]

Just found this thread, am I reading correct that swapping in a cp3 pump will give us a pump that is much less likely to grenade itself and flow more fuel?

 

[Dirtracr95]

Just found this thread, am I reading correct that swapping in a cp3 pump will give us a pump that is much less likely to grenade itself and flow more fuel?

In short yes but no one has publicly pushed the pump past the cp4.1 limits

 

[Terry270]

In short yes but no one has publicly pushed the pump past the cp4.1 limits

So for now its just in the "making sure it runs correctly" phase?

Also I know from owning an 08 ram 3500 that there's many options for 50%-120% over cp3's. Does having a cp3 open us up to those options?

 

[storx]

In short yes but no one has publicly pushed the pump past the cp4.1 limits

What are you talking about, i was forced to scale back fueling on my tune to allow my car to be drivable without constantly going into limp mode from fuel rail pressure drop... so i would say i along with a handful of others have pushed it past its limits.