OM642 error 2020-1 Fuel Pressure High

[clarknova]

2007 GL 320 CDI
~295,000 km

Recently my check engine light has been coming on, at which point the car loses power. It feels to me like there is no turbo boost, like the wastegate is being held open. I guess it's a limp mode of sorts. This has happened dozens or maybe a hundred times in the past month, and always while coasting with my foot off the accelerator. It's particularly common and pesky while descending a valley, because then I have to ascend the other side with insufficient power unless I can quickly clear the code, at which point full power is restored. I have noticed no other symptoms than the CEL and the lack of power that follows.

The error code that accompanies these incidents is "2020-1: rail pressure monitoring via pressure control valve: The rail pressure is too high for the closed pressure regulator valve." I have found very little information about this error on the web or through Identifix.

I did find the attached document GF07.10-P-1014OHG that states that the CDI control unit is supposed to shut off fuel to the injectors and reduce rail pressure through the quantity control valve (Y94) and pressure regulator valve (Y74). The wording of the error suggests to me that the controller believes the PRV to be closed, and that the rail pressure is higher than expected with the PRV closed.

I connected the iCarsoft and started monitoring rail pressure, PRV and QCV while crossing the valley multiple times. Unfortunately the CEL did not light once during all this, so I will have to continue to investigate. However I did see some values that didn't make sense to me.

Rail pressure. At idle, this typically flatlined around 260 bar IIRC and increase with throttle to a maximum of ~1350 bar while climbing the hill. While descending the hill and coasting, rail pressure was usually in the 1100 - 1300 bar range, which I did not expect. As soon as I got back on the accelerator it would drop to expected values relative to load.

PRV. Typically around 18% at idle and higher while coasting down hill. Values fluctuated during normal driving. I don't think I ever saw it drop below about 18%.

QCV. Around 32% at idle with some change during driving. No obvious correlation with engine speed or load.

Although I haven't found anything that points firmly toward any specific diagnosis, everything I've read and seen seems to implicate a problem with the PRV, QCV, rail pressure sensor, fuel filter, injector pump or injectors. Unfortunately it's a long list and only the fuel filter and pressure sensor are cheap enough to try without a more serious investigation.

I will continue to monitor the PRV, QCV And pressure values and hope to catch them when the CEL comes on again. I'd like to read any insights or suggestions from others on the forum as to what else to check for.

 

[Steve@Avantgarde]

Usually its caused by a sensor giving a spurious value as opposed to the fuel pressure actually being too high. The fuel pressure is goverened by the high pressure pump, which is driven off the engine. From there the quantity control and rail pressure sensors chatter to the ECU to provide the necessary running values.

I've had both be faulty causing that fault code before. I would look at the live data of both the QCV and RPS, look at the wiring pins to make sure there is no loose pin grab that can cause indifferent resistance readings.

 

[clarknova]

Thanks. I will continue to monitor.

 

[supernoodle]

I'm new to the Mercedes, but understand the HP system, so a little background. The 2 actuators, QCV and PCV allow three different strategies to control the rail pressure. First is QCV only. PCV remains closed, QCV is controlled to regulate fuel into the pump thereby controlling rail pressure. This is most efficient as the HP pump only has to pressurise the required amount of fuel. This is generally used at higher loads or where efficiency is important.
Second is PCV only. Here the QCV is open, so HP pump pressurises the full fuel flow. The PCV controls the pressure by regulating the fuel passed back via the return. This is good for heating the fuel on a cold engine.
Third is a combination of these where they are both controlled. It offers the advantage of a dynamic response to changes in pressure demand, particularly pressure decay during an overrun. This I expect to be used in light to mid loads.

Icarsoft live view shows the method used under "Rail Pressure Control". Yes it shows the rail pressure sensor, QCV, PCV values but no rail pressure demand value. That's not very helpful. I notice that the update rate on live data on my icarsoft sucks, way too slow for anything useful on rail pressure. May be the freeze frame has something useful?

I don't see it can be injectors, problems there would reduce pressure.
Could be electrical/sensor, but would expect that to be rather random.
Could be a return line restriction.
Worst case could be pump. They have something called a zero delivery throttle inside. Its there to ensure even when QCV is closed there is fuel flow through the pump for lubrication. If that gets blocked more fuel than expected gets passed through the high pressure path of the pump and into the rail. I doubt this is the cause, but should mention it.

 

[clarknova]

Thanks, I had not read anything that explained the interplay between these components, but your post helps to clear up those functions. With icarsoft reporting QCV and PCV as percentages, I'm guessing those are PWM values. Does a higher number indicate more open time or more closed time? IE, would 0% indicate a fully open valve or fully closed?

And what would I expect to see while coasting ("0 fuel")? Based on your explanation, I guess PCV would be doing most of the restricting if fuel is cold, or QCV when fuel is warm. Maybe I should be watching fuel temperature as well as CV values.

If the PCV is controlling return flow does that mean it is operating post-rail? If this is the case, then a closed PCV would result in a higher rail pressure, all else being equal, right?

This morning on the way to work the CEL did not come on and the rail pressure was ~450 bars while coasting down the hill.

 

[clarknova]

I just realised I put a typo in the thread subject (OM642), but I can't seem to edit that now.

 

[Blobcat]

I just realised I put a typo in the thread subject (OM642), but I can't seem to edit that now.

Looks fine to me…

 

[supernoodle]

No idea what units the values in icarsoft are. On mine QCV was reading 270%, PCV was 175%. QCV setpoint is calculated as a volume, PCV as a pressure. The output is ultimately a duty cycle, so that can only be in the range 0-100. The best bet is just to graph it out on icarsoft to see see the pattern rather than worry about the absolute numbers.

Yes, PCV is on the end of the rail, QCV is on the inlet of the pump. So closing PCV or opening QCV increases rail pressure.

You can see here, system is in PCV mode. QCV is stable, PCV is moving to control pressure.

 

[clarknova]

Interesting. My icarsoft screen looks a lot different from that (dark text on white background) and I don't think it's able to graph more than one value at a time, although it can show multiple values instantaneously, like in your first capture. Mine's an iCarsoft MB v2.0.

 

[mersum1es]

At some point, type of FQV checged (ie. no voltage opern ot closed). I have no indicatinoo when this happened, I just read if from local forum, not checked myself. SDS would provide ecu pressure demands, and individual tests for FQV and PCV.

Funny thing is, that actually fuel starvation CAN be seen as a high pressure fault code. When system is stuggling to rise pressure due to lack of fuel or excessive leak, and suddenly there is full conditions for fuel delivery, control system cannot follow fast enough and prssure overshoots. If pressure demand is not very high at the time, it triggers a fault code. 1000 bar at pedal up sounds jamming valve, if that can be repeated.

 

[supernoodle]

I agree over pressure faults can occur as a result of a previous starvation, but I've always seen both under and over pressure errors in such situations. Maybe not exactly the same time but at least some of the time.

For info I checked on a Delphi tool, PCV and QCV values are still in % but were about one tenth of those on icarsoft. They have a much better update rate too, so you can really see what is happening. You can also graph any available parameter, not just those in the groups icarsoft defines.

Some other vehicle brands make available the QCV and PCV current demand /actual and the rail pressure demand/actual PIDs available for the view. I would expect Mercs do too but not sure what tool supports this. For now you'll have persevere with what's on icarsoft and hope there's something useful in the freeze frame next time it sets.

 

[Masterlee]

I have 07 gl320 with 210k miles. I have experienced the same issue. Vehicle shut off while driving. Took to Mercedes Benz Dealer. Pulled the code 2021-001. Fuel rail pressure too low. They recommended to replace the fuel rail and some other part (maybe the fuel pressure control) due to the restrictions build up in the fuel rail. Quoted me 3100 see attached picture.
The problem here is I am afraid that replacing the fuel rail is not going to solve the problem. Same dealer quoted me 1750 for labor on R&R the starter which I did myself in 4 hours.
Another thing is it indicate the rail pressure is low. I am not sure it is the same code. Maybe they share the same code.
Some mechanic told me start with the low pressure fuel pump and sender pump.

Masterlee

 

[mersum1es]

I would start with injector spill off leak test...

 

[Uncle Benz]

I would start with injector spill off leak test...

Absolutely this ^

 

[alexanderfoti]

+3

 

[kepa75]

Hello,

I'm new here and this is my first post. I'm from northern Italy and since last year I'm driving a w461 with the OM642 engine. I also have problems with the injection system.
Whenever I step of the gas pedal and I get into deceleration, the rail pressure rises to approx. 1000 - 1500 bar (and I get a ticking noise). Once the motor gets below approx. 1200 rpm, the pressure drops to approx. 300 bar (and the noise quits).
I get no errors from the system, but still thinking it is not normal, so I'm wondering what could be the malfunction. If I'm correct under deceleration the PCV should be closed and therefor the pressure only regulated trough the QCV? From my live-data (Carly app over OBD dongle) still it seems the PCV is active.
What can be the problem? QCV not able to reduce quantity?

Thanks,

Peter

 

[supernoodle]

QCV is on the input to pump.
PCV is on the end of the rail.
So during a decel or overrun when there is no injection the best way of dropping pressure in the rail is to spill some fuel by opening the PCV.
Closing the QCV prevents further fuel entering the rail but if you're already over pressure you need to get rid of some of that fuel. If you don't do that when you go back on the pedal chances are pressure is much higher than demand and you'd get awful combustion noise.

As the actual pressure gets closer to demand you have open QCV again otherwise when injection resumes you'd get undershoot.

Some systems have a further back up safety mechanism so that when there is a fuel system overpressure the injectors are pulsed for a very short duration such that the control valve opens and fuel gets split via the leak off rail. The duration is so short no fuel actually gets injected. When this is happening you'd hear a buzzing noise. Not sure if this is used on Om642 though.

 

[kepa75]

Thanks for this input, so most likely my PCV is not operating correctly to "evacuate" the pressure? In the live data I see that the PCV gets triggered, but never more than 45 - 48 %. On the other side the QCV moves even less under deceleration, I would say it barely changes, stays around 30 - 40 %.
Is it normal that PCV and QCV have just such short working range? In my case I would say they go from 20 to 50 % only, the QCV probably even only to 40 %.
The noise I hear could definitely be a buzzing noise of valves opening rapidly...

 

[supernoodle]

The values in % you see for those actuators are the duty cycles of the PWM used to control the solenoid. Closed is usually around 50% and it doesn't have to drop much to open. 20% to 50% doesnt sound unreasonable. I don't see much different on mine. I don't know how good the live data is on Carly either, iCarsoft for example is rubbish, 1 sec sample rate. You need to be logging at 10ms to really monitor rail pressure. When I look at it on icarsoft it just aliases all the detail out.

I don't know if Carly shows it, but some tools will show you whether the fuel system is operating in PCV mode, QCV mode or both. Generally PCV is used on start and when fuel temp is low, so don't know if you'll see that in Italy right now. When cold you'd know if PCV wasn't working. A dealer tool like Star will have the ability to switch pressure control modes to you can test it properly though.

As I say I don't know if Mercs use that blankshot (injector control valve buzzing), but if they did it should be as a failsafe and thought they would have flagged an error first. Rail pressure decay after pedal decay should be quick with the PCV, so does sound suspicious.

 

[kepa75]

Hello, the Carly System has also quite a lag in sending information, so it is surely not real-time (would say 1-3 sec lag).
The PCV on my om642 should be spring closed in a deenergized state, so I guess with low current (and low %-value) it will be open and again be forced close when % is around 50 %? Is it the same for QCV?
I definitely have a pressure augmentation (no decay) after pedal decay (and then the buzzing noise).
And there is though one strange sentence in the Mercedes document (GF07.10-P-1014OGX) which explains the overrun mode fuel shutoff, function:
"Deceleration fuel shutoff, function sequence
If the accelerator pedal is not actuated (zero quantity delivery), deceleration mode is triggered. The CDI control unit switches off the
fuel injectors (Y76) in deceleration mode dependent on the coolant temperature, the engaged gear and at an engine speed >1600 rpm.
The CDI control unit also lowers the fuel pressure in the rails over the pressure regulating valve (Y74). Upon operation of the accelerator
pedal or a drop in the engine rpm to < 1600/min, the CDI control unit again actuates the fuel injectors and increases the fuel pressure in the
rails over the quantity control valve (Y94) or the pressure regulating valve, dependent on the Model of regulation.
If the conditions for teaching in the injector zero quantities are fulfilled, however, the fuel pressure in the rails can be increased in deceleration
mode to up to 1000 bar."
There is this last sentence which I don't get and I also get values higher than 1000 bar.
I think I need to find a work-shop that has Star-diagnose and is willing to check accurately!