Independent Renault Forums banner

Renault Scenix RX4 1.9 DCI low fuel pressure

5K views 37 replies 7 participants last post by  GB86 
#1 · (Edited)
Just rebuilt the cylinder head on a customers 2001 scenic RX4 with 98k on the clock after the auxiliary belt failed and threw the cambelt off around 6-7 months ago (been parked up ever since), she was originally intended to scrap the vehicle but with winter fast approaching and the need for a 4x4 deceided to have it repaired.

The head works been carried out by ourselves, new timing belt fitted and turbo replaced with a new item whilst we had the cylinder head off, valve clearances adjusted with shimmed tappets sourced from the main dealer.

We've got the lost compression back and the vehicle cranks healthy but will only run on brake cleaner / easy start when sprayed into the intake. After checking the live data on our snapon diagnostics (not the best on French cars at the best of times) we've got low rail pressure which is fluctuating from 1.8 - 3.6 bar (hence non start). The low pressure pump is priming soon as the keys turned on and is running for 30 seconds or so before shutting off. We've checked the supply to the high pressure pump which is plentiful although there appears to be no or very little fuel getting to the rail itself. We've removed the pressure regulator from the rear of the high pressure pump and we're getting a low reading of 3OHMS so have swopped it for a used regulator from another car with same engine, with a reading of just over 5OHMS. Yet we still have the same fuel rail pressure of 1.8-3.6 bar.

The stop light and red engine management light are illuminated on the binnacle and from memory the code was 1802 (will double check this afternoon)

Has anyone got any suggestions/checks before we start swapping the HP pump out for another unit?
 
See less See more
#2 ·
Is cam shaft sensor ok, not got damaged...
Row of smaller relays in the engine bay fusebox,
Next to the row of fuses ,,, the two nearest the fuses, not got a dirty connection one closest is fuel pump relay, next to that engine management, ..
Injectors were put back in the same cylinder. ....
Known these engines needing dragging in to get pressure up, enough to get running, then every turn of the key it will start....
Diesel no contaminated with standing,,,,,,
 
#5 ·
See if you can pull up that code, will try and convert to Renault code, and will look, and see if anything is mentioned.. Always seem to get a low fuel pressure reading,,, Have had to drag these engines in, dont think the injectors like standing empty...
 
#8 ·
This thread is here because the rules clearly state that a business name CANNOT be used as a user name. Please contact Admin to either register as a site Sponsor OR Have your user name changed to something suitable. Thanks
 
  • Like
Reactions: madnoel10
#9 ·
2001 Scenic 1.9 RX4 Low Rail Pressure Non start

We've just repaired a customers 2001 scenic RX4 1.9 DCI (F9Q) after the aux belt failed and threw the cam belt off around 6-7 months ago (vehicle had been parked up since this happend.) Her original plan was to scrap the vehicle but with winter fast approaching and the need for a 4x4 we got the job.

The head work has been completed and valves replaced / reseated and valve clearances reset with new shimmed tappets from the dealer, as well as a new timing belt and tensioner, we also replaced the turbo for a new unit whilst we had the head off.

We've now got the compression back on all cylinders and the vehicle cranks healthy but will only fire and run on brake cleaner / easy start. After hooking up our snapon diagnostics (which isn't the best on French vehicles as most will know) we've got low rail pressure which is fluctuating from 1.8 - 3.6 bar (hence the non start). And the code "1809" stored which reads "Fuel Rail Pressure Sensor Circuit" and "1802".

We've swopped out the pressure regulator for a known good one from a 52 reg Laguna with the same engine and part number, and tested this before fitting and got a reading of just over 5 Ohms which we believe to be good. Although we still have a low and fluctuating rail pressure of just 1.8 -3.6 bar.

The low pressure pump is priming for 30-35 seconds every time the key is turned in the ignition and the supply to the HP pump is plentiful although there appears to be very very little or no diesel leaving the HP pump and entering the rail

Can any of you Renault experts suggest anything else to check before dropping out the HP pump? (Much appreciated)
 
#12 ·
You will find it all back, Unfortunately with the interventions. I trust I Can now ban AutoClinic as a member.
 
#23 ·
What have you tried to bleed the system?
Electric lift pump and you say it runs for 30? secs on ignition on ?

Wandering if it is worth disconnecting, giving it a permanent 12v feed and cracking a few pipes to get any air pockets out?

Can't remember without going back if you had swapped pressure rail sensor for a known good un?
Or checked supply to it.?
 
#24 ·
Yeh the LP pump runs for a minimum of 30 seconds every time ignitions switched on, in regards to bleeding we simply cycled the key several times prior to trying to start it.

The sensor on the rail looks pretty new to be honest but we haven't changed it or tested it as such.
 
#25 ·
Can't remember the connections on the rail sensor but from memory, 5v feed, ground and return.
Return needs to be 1v plus for injectors to open.
Normally higher then that on cranking
Think pin 2 is the return?

Question is whether pump is raising pressure but sensor fubar or whether pump is not getting fuel and hence no pressure.

I'd guess the second but tis a guess.
However, if there is air in the system, the main pump cannot self prime and with the work you've done, air got in there.
 
#26 ·
Rail sensor connected / ignition on:

Pin 1 (Green) no reading
Pin 2 (Pink) .4V
Pin 3 (Green) 5V

Rail sensor disconnected / ignition on:

Pin 1 (Green) 10-11 OHMS
Pin 2 (Pink) 4.9 V
Pin 3 (Green) 5V

There appears to be no fuel at all on the rail, I've cracked injectors off cycled the pump and cranked and there doesn't appear to be the faintest hint of diesel
 
#28 · (Edited)
Yeh loads of fuel coming from filter to HP pump but that's as far as it gets?

I've just removed all injector pipes from the rail and can confirm there's no diesel at all leaving the HP pump although live data is still showing the rail pressure fluctuating between 1.8-3.6 bar even with all pipe work removed?
 
#29 ·
By removing the pipe from HP pump to Rail and cranking were getting a small squirt of diesel although I'd imagine it would take several fully charged battery's to actually pressurise the rail itself to a pressure where it would even attempt to fire.

How quick should the HP pump fill the rail on these?
 
#30 ·
Should fill the rail relatively quickly.

That is assuming the pump has fuel where it should and nowt sticking from sitting about.

The ideal is that the lift pump should prime till air is out of system, then when cranked, the HP pump has summat to grab and it should all work.

Obviously that ain't happening.

With a manual primer in these situations, someone priming while the engine cranks can help it catch.

12v feed to lift pump bypassing the system while cranking?
 
#31 ·
Have you recoded injectors back to the ecu, or were they put back in their respective cylinders...
Have you squirted easy start down the injectors, not the cylinders, but the injectors where the pipes fit.....

connected
1 & earth 0 ***937;
3 & earth Ignition ON 5 V
2 & earth Ignition ON 0,5 V
Fuel pressure sensor
 
#32 ·
On your rx4 the fuel rail pressure sensor disconnect multi plug 3 terminal.
Terminal 1 earth wire colour green goes to ecu pin no's b3c with plug disconnected bridge out terminals 1 & 3 to check earth
Terminal 2 pink wire at key on should show approx. o.5 plug connected back probed at plug goes to ecu pin no's bd1
Terminal 3 green wire at key on 5v's ecu pin no bh2. if this side of things is not right then you cannot get any rail pressure this has to be sorted out first. The very most likely causes interference from other circuits Check the insulation on the terminal plug
for insulation between terminals high resistance in wiring ecu earths needs to be checked.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top