steveball
Member Since: 09 Jun 2011
Location: Corsham, UK
Posts: 208
 
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| Restricted performance following work on fuel pump | |
Some information on a problem I have had and resolved this week, in the hope that it helps someone else in the future.
Like many others, I've had trouble with the fuel gauge reading intermittently on my 2010 3.6 TDV8. It's a very common problem, caused by two poor connectors in the wires to the pair of senders, which are mounted on the fuel lift pump in the tank.
It's a bit fiddly, but that problem is fairly easily solved. I removed the fuel pump through the access panels underneath the rear seat, cut out the offending connectors and soldered the wires together. I used some heat-shrink tubing to protect the new joints. Refitting the pump is a bit fiddly, there are two parts to the pump, one behind the driver's seat and the other behind the passenger seat. They sit in place and are fixed by spring loaded plastic locators, which fit into recesses in the roof the tank.
Because the fuel tank was quite full, I pumped about 40l of fuel out of the tank, into two 20l fuel cans. It's still a smelly job, definitely for your oldest clothes, but it can be done and I hope it won't be needed again.
Having put all the fuel back in and put everything back together, I confidently switched on the ignition to look at the fuel gauge. Great - reading exactly as I would have expected..... and then the problems start.
On starting the engine, I got a Restricted Performance message about 6 seconds after starting. The engine would continue to run, but be completely gutless. Almost impossible to pull away. There were also assorted other dashboard error messages, including Gearbox Fault.
I had a look at the fault codes to try to understand what was going on and got quite a few DTCs. Some are probably because of low voltage - I was reading the codes without the engine running and without a battery charger connected.
Because there were several DTCs, I needed to choose what to focus on. After a couple of false starts, I focused on the DTC P0088-00 (Fuel rail/system pressure - too high). My reasoning was that this was then triggering U0401-81 (Invalid data received from PCM).
I monitored the fuel rail pressure during starting and for the few seconds afterwards, until the Restricted Performance message came up.
What I saw was fuel rail pressure rising rapidly on cranking, peaking at c.400 bar, before dropping off to around 300 bar at tickover. After a few seconds, coinciding with the Restricted Performance message, pressure dropped further to around 240 bar and then rose and fell slightly in a cycle. The readings weren't terribly far out from that described in the Workshop Manual. They weren't terribly clearly described there, though, because there are ranges for high- and low-boost pressure.
I discovered at this point that I could drive the vehicle, if I could get it up to operating temperature. I could prevent the restricted performance appearing if I could keep the revs above tickover. Once it was fully warm, I could allow the revs to drop to tickover with no message (most times, anyway). I could reset the message by stopping and starting the engine. It drove OK, but made for some interesting driving! OK on main roads and country lanes, where I could manage to keep above tickover easily, but very tricky in traffic, requiring some left-foot braking and knocking into neutral.
I read up on how the fuel rail pressure is controlled. There is a pressure control valve, driven by the Powertrain Control Module, which releases (the very high) fuel rail pressure back into the (relatively low pressure) supply line. One of the investigative approaches suggested was to make sure that this return line wasn't kinked because that would prevent effective PCV operation. I was pretty confident on this because all the work I'd done was as the fuel tank, not the engine compartment.
It got me thinking, though, about whether a clogged fuel filter could cause these symptoms. Might I have disturbed some muck in the fuel tank (or even introduced some from the old fuel cans that I'd used)? The LR service schedule appears to suggest that the fuel filter only needs to be replaced every 10 years, but mine has done 130k miles in the last 8 years and its a very fine (2 micron) filter, so easily clogged. Running out of ideas now, but a filter is cheap enough and looks as though it might be original - so surely no harm in replacing it.
So I managed to pick up a filter locally at Euro Car Parts and fitted in this morning. In comparison to the work I'd done on the lift pump, an easy job. I chose to disconnect the fuel lines and remove the filter and housing together. No more than 15 minutes work and it allowed me to drain it and swap the filter easily on the bench.
Refitted the filter and all the fuel lines. Purged air from the system by switching on the ignition without starting, leaving for 30 secs or so, then switching off. Repeating this 3 or 4 times.
Started the engine and waited for Restricted Performance. Previously it would appear, when cold, at about 6 seconds from starting. Two minutes later, no error messages 
Re-ran the capture of fuel rail pressure on starting for comparison with before. Now peaks about 320 bar on cranking and very quickly drops to 220 bar at tickover. Then remains rock solid at this level.
Quick test drive confirms that, not only is the problem solved, but the drive is absolutely transformed. I don't think it's my imagination - there is definitely significantly more power on acceleration. Makes me wonder how badly clogged the fuel filter must have been. Can't believe that a 10 year, unlimited mileage service interval for this makes sense. It's a fairly quick and simple job and the replacement filter was only £20. Probably cheaper if you can wait a few days, too.
So glad to have got to the bottom of this. I was panicking a bit. If this didn't solve it, I felt I was going to try to troubleshoot the 'failed to communicate' DTCs and not sure I have the kit or skill to do that.
I'm not entirely clear why it drove OK when warm, except that the weather is pretty chilly this week (often low single-figures Celsius) and there is a system that pumps warmed fuel back into the filter once the engine is warm. Presumably cold diesel is marginally thicker than warm diesel and that was just enough to trigger the message. Current: 2010 Range Rover L322
Vogue SE, TDV8 3.6, Bournville
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Now gone: 2002 Range Rover L322
Vogue, TD6, Giverney Green
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30th Oct 2018 2:55pm
