P38 4.0 GEMS - hesitation from idle

[poohbear]

Hi all,

Slowly working through the various niggles the truck came with but I have a new problem to diagnose.

It starts and idles fine 90% of the time but recently it occasionally starts, revs leap up to around 1500 as normal but then will stall. It has also developed a nasty habit of when you put your foot on the gas it practically dies before picking up. It will do this if just pullung off or when accelerating hard between gears.

I have recently changed the MAF, Centre exhaust (cat section) including both O2 sensors, ignition leads. Though can't tie it down to any individual component change.

Can anyone point me in the right direction to start looking for faults?

Thanks in advance.

Dave.

[Ally V8]

From very distant memory Gems will do this if the stored closed throttle position voltage is too low.It need to be about .55-.72v and can be reset on Testbook.

[elbekko]

Have the adaptive values reset and see if that helps.

[poohbear]

Thanks for the replies - hope to be the owner of a nanocom-evo in the next couple of weeks, so will have a look at resetting those values - along with resetting the SRS, coding new remote fobs etc, etc............

Dave.

[Ally V8]

You cant code up P38 fobs - they are set to the Lockset barcode at the factory.If you can just reset the stored closed throttle position voltage.You may make matters worse by resetting all the adaptions,for instance if the Maf is down on its output the fuel trims wont cope and it will be flat in performance.Looking at live data values should be the first thing to do along with fault codes as a guide.

[poohbear]

Oh bummer, guess my only option for a working fob is the main stealer then!?!

Understood re. adaptive values - will start as suggested and go from there.

Thanks,

Dave

[poohbear]

OK - so evo in hand have managed to reset SRS fault, that's a good start!

looking at the stored closed throttle position voltage is 0.575 - I can edit this value but don't know what value I'm looking for? Does it have to relate to anything else - any other stored values?

Thanks,

Dave.

[Ally V8]

That value should work fine,just make sure the TPS voltage goes down to that value or less when you operate the throttle.Some more info here;

http://www.rangerovers.net/forum/7-range-rover-mark-ii-p38/31338-throttle-position-sensor-replacement.html

Take a look at the oxygen sensors as live data when coming off idle - until you really start to push it the sensors should both be switching between 0 and 5v. 0v is rich,5v is lean,they should both be switching around once a second.Also look at the short term fuel trims on both banks - see where they are heading.

[poohbear]

Hi AllyV8,

thanks for the pointers - values read today are as follows:

Started from cold on Petrol switching to LPG after a couple of minutes.

Bank 1 -

O2 sensor switching fine

LTFT = -152.5

STFT = 3.75

Bank 2 -

O2 sensor not switching

LTFT = -152.5

STFT = 38.75

There is also a fault reported on the Bank 2 O2 sensor so I guess the first step is to replace that. Can anyone tell me which side is bank 2 before I start trawling through rave?

Have also read through a number of your posts on rangerovers.net - there is some really useful information there, so thanks again.

As an aside I now have a Nanocom Evolution which is unlocked for the P38 - I'm based in Northampton, so if anyone needs codes reading/reset then I would be happy to help out for a beer token or two!

Dave.

[Ally V8]

Bank 1 is LH bank from the drivers seat looking forward.It may be worth swopping the sensors side to side - this will prove it is actually the sensor.That short term trim at 38 on the rh side is causing a very rich mixture on that bank,which is choking the engine - cause of hesitation...

The sensors are available for a sensible sum on a direct fit part number from any good factor who is an NGK/NTK stockist.Remember they are 5-0v Titania sensors so the exact one is important.After you fit it,just check the air flow reading is at least 22kg/hr at idle and more than 90kg at 3000 rpm engine running free all loads off.This being the case it will then benefit from an adaptive reset.

If swopping the sensors does not swop the fault to the lh bank then you need to do more legwork with wiring diagram and multimeter.

[poohbear]

OK - fault follows O2 sensor when swapped between banks, new one arriving tomorrow.

Air flows match rave specs - so looking good so far!

D.

[poohbear]

I've been running the truck for a while now, so thought I'd check back in. I swapped the knackered lambda for a new one and that solved the 'bank 2 02 Sensor' fault. It turns out the MAF was only reading about 18 at idle but I reset adaptive values anyway (to be honest it was an accident - I thought it was another menu layer on the EVO but it turned out to be the 'reset' button!?!).

Have run it for a few weeks now and the cold start hesitation is almost gone - What is annoying is that when booting it hard (joining motorways from slip road etc.) it still has a horrible moment between gears where it dies momentarily then comes back. There are no logged codes anywhere but there is an intermittent gearbox fault which comes up on the message centre sometimes either when ignition is turned on or engine turned off. I have tried to read this fault with the EVO but it doesn't find anything logged?

Any ideas anyone?

On the plus side MPG is now around 13/14 in town, it was doing 9 when I got it - unfortunately LPG has gone up 4ppl!

Dave.