2008 Landrover LR2

Hello Folks,

Working on a friends vehicle.

-P0088 Fuel Rail Pressure too High
-P0175,72 System too Rich

Scan Data

-LTFT Neg 22.5 at idle, improves a little at higher rpm until engine dies
-Fuel Rail Pressure 380Kpa at 2.5 volts from sensor signal (with DVOM), when engine is dying volts drop to 0.31v and scan data is 0 KPA.
Volts drop very nicely with the PCMS KPA interpretation, very smoothly. I don't suspect the sensor yet.

-Tailpipe strong odour of unburnt fuel. O2 sensors reporting very rich.

-Waiting for the proper adapter to put a guage on the fuel rail.

I suspect high fuel pressure.

In the meantime, decided to voltage drop the feed and ground to the Fuel Pump. It was easy access under the seat!

Used a Booster cable from battery (-) to pump (-) got 4.5v of drop.

Used a Booster cable from battery(+) to pump (+) got 0.750v.

I repeated this test with the other booster cable and got the same numbers.

So, until I get that adapter to test the pressure, can I be confident that these voltage drops condemn the pump or the wiring?

I used t-pins at the pump.

I'm thinking those numbers are telling me I'm dealing with a bad pump.

Next week I'll have the adapter, and also plan to scope the current and voltage on the Fuel Pump. The Fuel Pump is PWM and this is an Electronic Returnless style Fuel System.

I told my friend not to replace the sensor first, because of the high Fuel Pressure so as not to damage a new sensor. I jumper the 5v signal to ground and scan tool read 0v. placed a 1.5v batt in series between the two and read ~200 which tells me the wiring is good.

Tried unplugging the MAF when it was running and it got worse.

Id appreciate some advice on the voltage drop numbers I produced.

Thanks

Paul

What engine type are you actually dealing with?

As you talk of 380Kpa and the O2 sensor/fuel correction values it sounds like you're talking of multiport sequential fuel injection system, obiously two banks....so i asume you are working on a gasoline engine.

If so you might want to look at the spark plugs until you get your hands on a fuel pressure gauge. The plugs could tell you something about the condition the engine is running under.

You might be dealing with a skewed O2 sensor as well. Try disconnecting the front O2 sensor and look if the raw gasoline smell in the exhaust diminishes.

What are the bank 1 fuel trims/O2 readings, considering that a bad fuel pressure sensor reading most likely was to affect both banks in a similar way.

Your voltage drop results do not condem the pump yet, it all dependes on the circuit design....

Imagine the pump was ground side controled , pwm as you stated. What would be the measured voltage drop with a 66% ON duty cycle. (one third of the suplly voltage, and nothing wrong with it!)

The voltage drop on the positive side seems quite high, but if there is a dedicated fuel pump driver module -which again I assume -the voltage drop on the positive circuit leg should be measured from fuel pump module to fuel pump, not from battery positive.

Thanks for your reply,

Inline Straight Gasoline6, 2 Banks, both Neg 22 LTFT, P0175 and P0172

Have Not Checked the plugs yet( great idea though!)... will be revisiting this vehicle next week when the fuel rail adapter arrives. At that point if the fuel pressure is good, I'm likely to suspect the sensor, although I'm happy withe the sensors wiring integrity. I'll have to revisit that and get more serious about the O2 sensors, at the moment I don't believe them to be lying.

Thank-you for mentioning about the Duty Cycle, I completely didn't consider that! However, the fuel module is in the tank, so the only wire I could really drop is the power feed from the ECM to the Module according to the diagram.

But I was quipped for time and the fastest easiest drop was the one I did, funny part is, is that those voltage drops never fluctuated with Engine RPM ( on ground or power side)

SO, I definitely will post back sometime next week with my findings. Thank-you for some very helpfull ideas.

It should be worth to mention, if the vehicle is left overnight, starts up right away just like it should, negative fuel trims, goes to closed loop, and the longer you run it, or rev it, the pressure on scanner and volts on the sensor drop smoothly down to 0, 0.31v respectively then it dies. Then it will not restart until you wait about 10 mins. So I gather its just full off fuel. I hate to run it to much in this condition so as not to damage the catalyst.

My friend is planning on changing the FPump and sensor regardless. I just want to confirm either or, or both. For costs sake were hoping it is just the sensor.

I also plan on scoping the current and volts on the feed as well next. Ill post back with my findings.

Thanks

To all who replied, thank-you.

Confirmed fuel P.S.I. 56 lbs, Good. Pump is OK

Fuel Pressure Signal Erratic and all over the place. Bad Sensor, Confirmed signal wire integriy, hi/low volts...good!

Replaced Fuel Pressure Sensor LTFT -22, STFT +22, Confirmed Fix!

Took vehicle for a 20 min in town drive with scanner hooked up, all FTrims hovering +/-3-5%

Thanks

Paul