P38A Down on power when warmed up

enjoi said:

I just tried this and interestingly enough, unplugging the MAF seemed to make no difference. The idle was the same, and from my best judgement, the performance from a quick drive seemed the same.
I would have expected a super rough idle with an unplugged MAF? Do I have a dud MAF then?

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With MAF unplugged the engine resorts to preset values in the ECU and so if MAF duff the engine will run OK. When driving under load ie up a hill is there any difference between having MAF plugged in and MAF unplugged If struggles with MAF plugged in but no struggle with MAF unplugged would point to faulty MAF. I have found it is safe to drive with MAF unplugged until I have replaced it.

Rubberknees said:

With MAF unplugged the engine resorts to preset values in the ECU and so if MAF duff the engine will run OK. When driving under load ie up a hill is there any difference between having MAF plugged in and MAF unplugged If struggles with MAF plugged in but no struggle with MAF unplugged would point to faulty MAF. I have found it is safe to drive with MAF unplugged until I have replaced it.

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As said above^^^^ on the diesel the engine runs on default fueling maps with the MAF unplugged. The only differences I noticed on testing with the MAF unplugged were slight smoke on hard acceleration and slightly increased fuel consumption.

With all due respect, as per my previous I would swap out the ECU temp sensor (which only costs a tenner) first:-

ETC8496 BLUE sensor/ black/brown connector ECU

Range Rover 4.0 P38 | '95 - '99 | Gems engine
Range Rover 4.6 P38 | '95 - '99 | Gems engine


There is a second sensor that only feeds the gauge AMR5929 so don't confuse them.

The car has classic temp sensor fail symptoms - running an over-rich start-up/cold mixture.

Good luck.

Moosekeeper said:

With all due respect, as per my previous I would swap out the ECU temp sensor (which only costs a tenner) first:-

ETC8496 BLUE sensor/ black/brown connector ECU

Range Rover 4.0 P38 | '95 - '99 | Gems engine
Range Rover 4.6 P38 | '95 - '99 | Gems engine

Coolant Temperature Sensor SNB802 Lucas Sender Transmitter DBC3728 ETC8496 New | eBay

Coolant Temperature Sensor SNB802 Lucas. Part Number SNB802. LUCAS CAV 73170, 73198, 73335, 73355A, 8TT, 8TT73355A, SNB1164, SNB802. JAGUAR DBC3728. LAND ROVER ETC8496. ROVER ETC8496. Type Sensor, coolant temperature.

www.ebay.co.uk

There is a second sensor that only feeds the gauge AMR5929 so don't confuse them.

The car has classic temp sensor fail symptoms - running an over-rich start-up/cold mixture.

Good luck.

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+1 ^^^^^^^

The OP already said engine ECU was reporting 91deg, so unless the actual temp is vastly different to the sensor reading that seems to be ok.

The gauge sensor value appears to be available in Nanocom BECM Inputs menus. Will compare the two on mine later.

Moosekeeper said:

With all due respect, as per my previous I would swap out the ECU temp sensor (which only costs a tenner) first:-

ETC8496 BLUE sensor/ black/brown connector ECU

Range Rover 4.0 P38 | '95 - '99 | Gems engine
Range Rover 4.6 P38 | '95 - '99 | Gems engine

Coolant Temperature Sensor SNB802 Lucas Sender Transmitter DBC3728 ETC8496 New | eBay

Coolant Temperature Sensor SNB802 Lucas. Part Number SNB802. LUCAS CAV 73170, 73198, 73335, 73355A, 8TT, 8TT73355A, SNB1164, SNB802. JAGUAR DBC3728. LAND ROVER ETC8496. ROVER ETC8496. Type Sensor, coolant temperature.

www.ebay.co.uk

There is a second sensor that only feeds the gauge AMR5929 so don't confuse them.

The car has classic temp sensor fail symptoms - running an over-rich start-up/cold mixture.

Good luck.

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I've got the Thor engine. I think this is the one I want? https://www.4wdindustries.com.au/range-rover-p38-discovery-2-v8-water-coolant-tempe

I'd be surprised if my coolant temp sensor was busted, it seems to return fairly sensible readings on my OBD reader. But for $40 I'm happy to give it a whirl.

It's also probably worth mentioning that I don't think this down-on-power issue is actually related to the engine temperature as I first assumed. I think it ran well when cold because I also happened to change a dead battery when I changed the O2 sensors. So perhaps it wasn't becoming sluggish again as it got warm, but rather, became sluggish as the adaptive values (Which were probably reset with the battery change) settled in.

The temp sensor looks right for a Thor. ( I had a RR Classic "Softdash" actually.) Not as cheap as I thought so maybe hold off changing it. But having a fresh sensor in stock could be wise as they are out of production and getting scarce - example:-
https://www.ebay.co.uk/itm/223906343909
You might get more reliable values and better running anyway with a fresh new one.
Hope that helps,
Clive

enjoi said:

It's also probably worth mentioning that I don't think this down-on-power issue is actually related to the engine temperature as I first assumed. I think it ran well when cold because I also happened to change a dead battery when I changed the O2 sensors. So perhaps it wasn't becoming sluggish again as it got warm, but rather, became sluggish as the adaptive values (Which were probably reset with the battery change) settled in.

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Bad earths can certainly kill the power.

Thought I'd provide an update of the on-going issue. Battery was dead for a couple of days before I recharged it and towed my boat to the ramp to perform some trailer repairs.
On the way to the ramp, the Rover towed like an absolute champ, no dramas at all. However, once it warmed up, it felt like I was towing a fully packed horse float. The drive home was a bit of a slog.

One thing I've noted when it's down on power is the unmistakable lack of V8 rumble when I put my foot down. I can put my foot to the floor and there's lots of engine noise but no grunt, and there's no extra power.
When the car is cold and fresh start, I can put my foot down and it's very spiritedly. It has that distinct low end grunt sound

I've got some data for the trip to and from the boat ramp.

This is to the ramp


I would say from the second half of that above trip you could start to notice the Rover struggle under load.

And from the ramp:



The entire journey home was very sluggish under load.

Any other data from that trip that could be worth sharing?

How are the O2 sensors behaving?

O2 sensors look okay!