Fuel Rail

[Dean Fletcher]

Yesterday I picked the car up from airport a mile down the road it starts jumping and stalled at the lights. I thought I’d stalled it so I set off again then the reg counter starts going up and down.
Read the codes it comes up with
The rail pressure sensor has a short circuit to battery?
Any one had a similar issue? Due to having kid in the back I pulled over called good old AA. He calls ahead of time and asks the issue; I tell him what codes I have read and the issue.
By the time he comes (30 minutes) iv had the car on and off and give it some revs and all seems to be normal again.
He scans it comes up with fuel rail pressure again. Then the engine light goes off.
I went for a test drive with him all seems normal. She said I can get it recovered but now all the values seem fine and can’t see any issues it was my choice. So I decided to go for it and travel up north.
Got through a busy M60 and onto M6 no problem all the way home no issues then soon as I stop outside the house and reverse into the parking place the car cuts out and I eventually get it into the parking place with higher revs.
I turned the car over last night sounds like a bag of spanner’s.
So……. The scanner is pointing at rail pressure sensor short circuit to battery but also but also power consumption of component y74 (pressure regulator valve) and component y94 ( quality control valve) is flashing red. Y74 at 728mA and Y94 at 812mA.
Today I’ll be looking wiring for all these components, connections and fuses.
I originally thought a bad fuel filter because it’s been 2 to 3 years since I changed it roughly 7000 miles. Iv got one on order now.
Any other pointers?
Thanks

 

[Dean Fletcher]

Ps the 7 years younger E400 is looking ever more appealing but I’m trying to stick with the old girl

 

[ajlsl600]

Stick with older. Less tech involved. Less hassle less expense I like the interior toys but all the hassle with modern tech has me preferring "good", older stuff and keeping more of my cash in my pocket . And maybe making my own decisions on how I spend my money as opposed to being led by maker to expense

 

[Dean Fletcher]

Stick with older. Less tech involved. Less hassle less expense I like the interior toys but all the hassle with modern tech has me preferring "good", older stuff and keeping more of my cash in my pocket . And maybe making my own decisions on how I spend my money as opposed to being led by maker to expense

im 100% with you on this but the less hassle part isn't coming true these days.

 

[Doug1234]

Do they all share the same power supply ?.
The rail pressure sensor is shorted internally as per the code so is it affecting Y74 and Y94 through that shared power supply forcing codes up for them also

 

[mioba]

What code reader are you using. Years ago i used a blue tooth plug in cheap thing off ebay. Was only good for the bin in hindsight.
A better code reader will be more conclusive.
I had engine light on and EPC error on my W220 last year. Plugs in my icarsoft - points directly at the fuel rail sensor. Ordered a new one, unclip wire, unbolt sensor, new one in. Been perfect ever since. On that alone the icarsoft paid for itself.

 

[supernoodle]

Rail pressure sensor is on a 5v supply. The quantity and pressure control valve normally have a power from vbatt, the ECU is the low side driver for those circuits, ie switches the ground.

When it can't trust the rail pressure sensor it would have to assume a safe position for the pressure and quantity conttrol valve, so don't read into those current draws until you've fixed the rail pressure sensor issue.

A short to battery fault means the voltage at the ECU pin is at the 5v (it can't actually detect any higher voltage).
All ECU sense pins will be pulled up to 5v or pulled down to ground. This is so that they don't float when open circuit. I expect that this is pulled down to be honest, but you can check that by measuring at the plug, sensor disconnected. 2x5v and 1 ground is pulled up, 1x5v and 2 ground is pulled down.
Assuming pulled down, a SCB fault it is either short in wiring or dodgy sensor.
If it is in fact pulled up internally, SCB implies wiring fault making it go open circuit or dodgy sensor.

 

[Dean Fletcher]

Using a Autel maxicom

What code reader are you using. Years ago i used a blue tooth plug in cheap thing off ebay. Was only good for the bin in hindsight.
A better code reader will be more conclusive.
I had engine light on and EPC error on my W220 last year. Plugs in my icarsoft - points directly at the fuel rail sensor. Ordered a new one, unclip wire, unbolt sensor, new one in. Been perfect ever since. On that alone the icarsoft paid for itself.

 

[mioba]

not a cheap bit of kit.
Check the wiring then go from there. MB looms are pretty damn solid though and usually well placed with good measures to prevent vibrations etc

 

[Dean Fletcher]

UPDATE…..possible solution
So after tinkering around testing wires etc it looks like it’s pointing to the connector it’s self and not the sensor.
I had the injector seals done a few months ago and looks like the clowns have put the loom back in a dodgy position which is always pulling on the sensor that plus I think they have broke the connector as it pulls on and off without having to unclip the little grey clip first that’s and the vibration of the engine.
I started the car up with sensor unplugged engine light on with same code.
Plugged sensor back in engine light on / cleared codes engine light stays off.
Took it for a 65 mile journey and no problems.
Only time will tell, now I need to find a solution to stopping the connector vibrating off over time

 

[supernoodle]

Good, so that circuit must be pulled up internally, so open circuit gives the SCB fault.

 

[ajlsl600]

Often you can buy a, repair plug with tails and solder n shrink wrap .. deutz connectors may do, but mb will likely be able to supply. Looks like clowns got at it...

 

[Dean Fletcher]

Just done another 30 mile trip and all seems ok. Anxiety does set in when coming to a round about and traffic light

 

[mioba]

I effing hate ham fisted mechanics. Best bet to wrap some insulation/gaffa round it to hold the sensor in the housing for the time being

 

[Dean Fletcher]

I effing hate ham fisted mechanics. Best bet to wrap some insulation/gaffa round it to hold the sensor in the housing for the time being

There’s so many things iv found while working on my own car that garages have done to cut corners. For instance few weeks ago I changed the callipers disks and pads. The retaining bolt for the disk had been drilled to tighten back up for the sake of a pound why not put a new one on. Also the plate on the front calliper had been stuck back on with sealant. Boils my pi$$ with these cap handed s0ds

 

[mioba]

Many garages are the same to be fair, its all about turn around time for them. They dont want a car sitting on a lift while they wait a day for a disk retaining bolt.

I agree I have seen so many hash ups on my sisters car - zip ties, jubilee clips instead on fuel clamps, etc

lack of pride in what they do

 

[Dean Fletcher]

Many garages are the same to be fair, its all about turn around time for them. They dont want a car sitting on a lift while they wait a day for a disk retaining bolt.

I agree I have seen so many hash ups on my sisters car - zip ties, jubilee clips instead on fuel clamps,

It’s a joke like really. With every set of brembo disks iv bought come with 2 new bolts. Going to look at buying a new rail pressure sensor depending on price this is due to the clip that broke.
Took car for another 70 miles after fitting fuel filter seems smoother and didn’t miss a beat.
New oil and filter is the next job. Both air filters fine for a while. Possible oil cooler change but need to check underneath for the leak, sure I seen it last time I was under there.