Pump or Rail Pressure while cranking?

Simple question, maybe not a simple answer, can't find it anywhere.
I've done the work to start and drive my failed 2013 JSW HPFP to the dealer for buyback, the pump cratered a week before the set date, and only 34k miles. Skipping the details, it didn't start, and I'm trying to figure out why. Specifically, I'm not sure the replacement pump is actually making the pressure and charging up the rail to proper pressures, and I want to verify, but don't know how. I got VCDS for this job, and it showed me a P0087 code, but not sure how significant since this is a non-running car, just cranking. Can I use VCDS to legitimately test this, or ???
I used Measuring Blocks and graphing to observe pressure during cranking, but nothing. Yes, the system is all primed.
I'm hoping there is a "clever" way to validate that the pump is actually doing what it should be, so that I can see my next move. VCDS or otherwise.
Thanks.

You should be seeing fuel pressure over 150 bar for a car to start.
Lower than that you can't expect it to start.

Did you replace the injectors?

I actually pulled the injectors apart (2micron helped me), cleaned and tested them. Nice spray patterns out of all the nozzles. I'm not 100% sure nevertheless that I don't need new injectors, but before I go that extra expense, I want to ensure that the pressure is being produced, which is why I'm trying to verify the rail pressure while cranking.

Henrick 150 bar sound reasonable, but how can I use vcds then to monitor this? When I used the measuring block and put in 20, it shows, supposedly, the high pressure. But I get no result while cranking. The RPM's show and graph during cranking. I'm new to vcds, so I don't know fully what it will and won't show, but it seems like it should be showing results in real time while cranking...???

The rail pressure will build pretty quickly once you start cranking... maybe within 5 seconds you'll see it ramp up pretty quickly.

If any of the injectors' upper chamber is leaking, they will bypass and not allow any rail pressure to build.

I've found this out from doing the first HPFP failure I got to replace. I tried just the pump(s) first, cleaned everything thoroughly... would not build rail pressure. Checked and tried everything I could think to do. Went ahead and put 4 new injectors in, started up 10 seconds later.

You also need to take the rail apart, and clean or replace both the rail pressure sensor and the rail pressure regulator.

So in closing: bad injector (even one), will cause rail pressure to bypass to the return side, and thus no rail pressure, so no start.

Sounds like good advice. Is there a way to test if the upper chamber of the injector is bypassing?

Thanks Oilhammer, you said:
"I tried just the pump(s) first, cleaned everything thoroughly... would not build rail pressure. Checked and tried everything I could think to do. Went ahead and put 4 new injectors in, started up 10 seconds later.
You also need to take the rail apart, and clean or replace both the rail pressure sensor and the rail pressure regulator."
Very good info, thanks. 1st question: HOW DID YOU KNOW "would not build rail pressure..." ??? How did you test it?? I'm dying to do this, but nobody has told me how. I tried with vcds as I already explained. Maybe I just don't know how to use it correctly.
Also, 2micron (Andrew) is directing me to pull apart the injectors (again) to completely eliminate the leaking while seated. First time I flushed and blasted them with air, and hole spray pattern great (with 125 psi air pressure), but 125 psi causes a wetness at tip after about 20 sec. I think you also would tell me that needs to be fixed from what you said. Moreover, I busted my retention valve on the injector return line, which was easy to do by the way, and replaced it with an aluminum rod I drilled a small hole through and stuffed with cotton. I understand it needs to hold back 145 psi from the injectors? As is, when I run lift/auxiliary, diesel bleeds back TOWARD the injector return line. I pulled a return connector at the injector to verify this. I have a new valve on order.
I pulled the pressure sensor, but not sure what can be done to it, though I would like to test it (???). As far as the pressure regulator, I believe I adequately tested that it is good, and I made a video of that (linked below), and drew the conclusion that it needs the 9.2 V signal NORMALLY to CLOSE the valve, and under overpressure conditions that signal would disappear and open the valve to release pressure from the rail. What I'm confused about is that the "negative" side of the connector does not appear grounded with ignition on, but maybe it gets grounded after the car is running (shown in the vid). After all, it makes sense to me to ignore closing the valve at least until conditions exist that are normal for a running engine. That is, if it's not running, why send the (9V) signal to close the valve, since the car is not running and pressure conditions are irrelevant at that point. Hopefully that makes sense. Actually, writing this just made me realize that the valve should close while cranking in order to build pressure, and that is something I CAN check! I can monitor the positive side of the regulator connector while cranking. If the other side gets grounded, the high side drops to about 8.5 volts from 9.2 when the solenoid is activated. With just the ignition on and not running or even cranking, it drops to approximately zero, not driving the solenoid.
Anyways, you are affirming the info from 2micron that I need to pay attention to the injectors, and I also think I need to pay attention to the injector return line, so these are tasks for tomorrow, er, later today.
In the meantime, I would still love to know how to test rail pressure!
Pressure Regulator test:
https://youtu.be/EfCLyiNWNDA

No need to throw money at all 4 injectors before you confirm the failure.
You can install bearing balls to injector lines to prevent any fuel getting to them.
Then crank and monitor the pressure (once you find out how). Ensure it stays high enough.
Then remove the bearing ball from each line one by one, followed by crank and pressure reading confirmation.
This way you will nail down the injector (or two) which might be leaking pressure to return.

The pressure reading is somewhere there in VCDS measurings. You just need to sit, search and find it.

There is a labeled measuring block in VCDS for actual and requested rail pressure, I forget where, and I do not have a CR car here right now to check.

The rail pressure is VERY high... over 100 bar, so checking it with a measly 125 psi of air pressure will not tell you squat.

KermaTDI said he can properly test and repair them, and so I sent him the second bad set I had, because I found this out after the fact but still had them in the scrap barrel.

I would contact him for more information.

I had already sat down and went through all the measuring block groups. There are 254 groups. Groups 1, 4, 18, 19, 20, 21 have high pressure fields. 10 fields total. 4 of these are "actual", 3 are "specified", 1 is "control status", 1 is "control deviation", and 1 is "control valve". The "actual" is what I was watching, which sits there at 0 bar or 640 bar, cranking or not. I was able to see "specified" consistently go to 144 bar while cranking, but then confirmed it not actual when it reported the same when I unplugged the pressure sensor on the rail. Once I saw the actual go to 8 bar. But only once.

So I don't know how useful any of this info is. Nothing is convincing here to me... like showing 640 bar actual while it's really 0.

And I also verified that the pressure regulator remains open while cranking. I verified my regulator works, and that it remains open with ignition on as in my previous post/vid. I was sure that when cranking it would close, otherwise how else could rail pressure build? But, no. It stays open. That is very baffling to me. So, I forced it closed while cranking with a 9V battery, but vcds still showed 0 bar, even though I don't know how to interpret that reported 0 bar. And I know the pump is outputting something since I attached a tube to the high pressure line from pump to rail and it squirts out when clamped off (lift/aux pressure sealed).

So ugghh, I sense I'm creating confusion here. I know I'm confused! I think I will focus on the injectors at this point as is suggested and ignore the seeming illogic of the regulator and the uncertainty of the vcds info. But, if anyone has a suggestion on the vcds, or anything else, please offer!

The ECU only holds rail pressure when it needs to, the rail does not remain under pressure after the engine is turned off.

There is a downloadable (or online viewable) .pdf out there, just google "Volkswagen 2.0L Common Rail Engine Self Study Guide" or something of the sort, and you can read the specifics of how the fuel system works. It has been helpful to me.

I have it on another computer. It is posted on this site somewhere too.

Here is one:

http://www.jameshalderman.com/images/vw/2_liter_tdi_common_rail.pdf

The pdf is awesome Oilhammer, thanks a ton, I'll definitely be spending some time with that! In the meantime, I'm going to pull apart those injectors again and try to completely stop the leaking.

Your statement about the ECU only holding pressure when needed certainly makes sense, my befuddlement is that when cranking, it should decide it needs rail pressure! But there is something else going on that makes this logical, and hopefully I'll either figure that out or at least overcome it. And now those injectors...

I am surprised they didn't offer warranty with only 34k miles.

Mine same year is coming up to 100k miles. Due to some expensive components possibly coming up in its future I think I am going for the buy back. Belt and pump for sure, but HPFP and turbo also come to mind. I guess the $5k they would give me might cover those items but probably it is easier to just get another one. I am going to miss this one.

Mine was in a wreck in a different state before I bought it, thus salvage status is still attached to it and nothing I can do about that, VW thus won't warranty.

Hate to revive an old thread, but as the original poster asked, how does one test the fuel pressure (and what should the values be) on a 2012 TDI? I've been searching for hours and cannot find the info. Trying to diagnose a hard cold start condition.

You will need VCDS to read the rail pressure sensor, but if you have low fuel pressure you will get a code, and likely will have more issues than a hard start. have you checked your inter cooler pipe for water?

ihatespeed said:

You will need VCDS to read the rail pressure sensor, but if you have low fuel pressure you will get a code, and likely will have more issues than a hard start. have you checked your inter cooler pipe for water?

Click to expand...

I have VCDS - not sure where to even start to find the fuel pressure and what values they should read.


As for the intercooler pipes, I've never had an issue with icing up. The car does lots of 5 hr trips, with plenty of hard acceleration, so I wouldn't think it would be an issue now, especially in the summertime.

You need 400-500 bar rail pressure during cranking.Measuring blocks 19-21 have actual rail pressure I believe. Or at least one or two of them do. I'd log requested and actual.