Problem with rail pressure

kiwilml

kiwilml

Member
Nov 4, 2015
454
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Alright I'm starting this thread for my brother. He has a '14 lml that he just recently took to a professional shop that works on these a lot.

Had a stroker cp3 conversion done with their s475/stocker kit. He has new tuning by PPEI and it runs really good, but with that being said, it loses rail pressure at high rpms. It'll shift into next gear and go right back up to 29k and then slowly start falling off.

They deleted fuel filter under hood so lift pump goes directly to cp3. We changed filters and checked pressure on lift pump and it's all good.

He called exergy and they didn't think it would be a pump issue and said something about the FPRV. I guess on these models it's electronic? Has anybody had any experience with them or think that could possibly be our problem or what?

And help or ideas appreciated.
 
Ne-max

Ne-max

I like turtles
Nov 15, 2011
3,361
64
48
Lincoln, Ne
Have them data log it. Watch commanded rail pressure, actual rail presure and fpr %. Also need to see what lift pump pressure is at WOT. Idle dont mean much.
 
D

Digmax

Member
Jan 23, 2016
289
2
18
Hi to all, just got signed up, been lurkin though ha, this is actually my truck we talking about here, Just had kiwi start this thread. I have no idea what the pulse is, its prob a 625 horse tune. It is very clean and wont get over 1200 degrees wot. How does the electric regulator work on front of drivers rail?

Sent from my C811 4G
 
kiwilml

kiwilml

Member
Nov 4, 2015
454
0
16
Ok yeah we did log it the other day and he sent it to PPEI but hadn't heard anything back yet.. And not sure on pulse width but it does it on the street tune and can't really run the max tune yet so not sure if that tune does it or not..

And yes we watched desired rail pressure and it stays on 29k

I agree on watching lift pump pressure under WOT but hadn't had a way to yet.. We turned pressure up from 10 to 14 and it made no difference when we went back out and tried it, so we kinda was thinking wasn't lift pump problem..
 
juddski88

juddski88

Freedom Diesel
Jul 1, 2008
4,657
120
63
Chesterfield, Mass.
Digmax said:
Hi to all, just got signed up, been lurkin though ha, this is actually my truck we talking about here, Just had kiwi start this thread. I have no idea what the pulse is, its prob a 625 horse tune. It is very clean and wont get over 1200 degrees wot. How does the electric regulator work on front of drivers rail?

Sent from my C811 4G
Click to expand...

This is some info taken from GM's public release statement on new tech related to the 2011+ duramax:

The fuel system high pressure side uses a two-chamber pump that generates 200 megaPascals (mPa) of pressure (29,000 psi). Two high pressure lines feed the right fuel rail. A transfer tube carries fuel to the left fuel rail. A Fuel Rail Pressure sensor (FRP) is located on the rear of the left fuel rail.

The high pressure pump is timed so the peak pressure pulses match the injection events. Matching the pressure pulses results in a more constant pressure within the fuel rails. If the pump is removed, it must be retimed when it is installed. There are timing marks on the pump gear and camshaft gear that must be aligned, following SI procedures.

Two Fuel Rail Pressure Regulators (FRPR) are used. FRPR1 is still located on the injection pump as on previous Duramax engines. FRPR2 is located on the front of the left fuel rail. This solenoid is normally open. The ECM supplies pulse width modulation to change the duty cycle of FRPR2 to control the amount of fuel returned to the fuel tank.

The new Duramax engines are equipped with Bosch piezoelectric fuel injectors. These injectors operate a high voltage, indicated by the orange color of the injector harness.

IMPORTANT: Do not make contact with the fuel injector harness, ECM or fuel injectors while the ignition is in the On or Run position. Use certified insulated gloves EL-48286. These Class 0 gloves are rated at 1000 v. Check for functionality and check the expiration date of the gloves.

The ECM supplies high voltage and provides a ground. Voltage is supplied up to 160v at 20 amps, and can peak up to 240 v. This causes the injector to open. The capacitor discharges through an injector for initial opening and holds open with 12 v.

Injectors are grouped into four pairs: 1-4, 6-7, 2-5, and 3-8. If a condition is detected in a group, that group is disabled and a DTC is set.

On the fuel system return side, the return lines are now equipped with snap-in connections. The return side is under pressure.

A pressure retention valve maintains 0.4 to 1.1 mPa of pressure within the return lines to provide proper fuel injector operation.

TIP: Improper injector return line pressure may cause a no-start or performance concern.

If the engine runs out of fuel, or if the fuel system is serviced, the system must be primed. After priming, a feed line from the low pressure side of the pump backfills the injector return lines. The feed line will also backfill if pressure falls below 0.3 mPa in the injector return lines.
 
D

Digmax

Member
Jan 23, 2016
289
2
18
I got a new electronic RPRV gonna put it on Monday, just a stab in the dark!

Sent from my C811 4G
 
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