P38 DSE Auto intermittent lack of power after vehicle has been hot

Hi All again,

Recently the P38 has intermittently losing power when it has got hot(up near the red) I have done datateks fan mod so have no viscous fitted. The fans come on fine and bring the temp back down when required.

The issue I’m having is more and more often I end with no power once it got up near the red. I know the ecu limits power one car is HOT and I can deal with this. Todays problem was temp had settled back to half way on guage but I lost power for a few miles intermittently which I believe could be a faulty or intermittently faulty ecu coolant stat.

Does that sound like a plausible explanation? I also think there is a coolant temp sensor on fip but I’m unsure of the symptoms of this.

Apart from this car drives well with recent water pump and upgraded radiator And uses no coolant.

Any one any ideas?

Many thanks,

Jacob

JT_spark said:

Hi All again,

Recently the P38 has intermittently losing power when it has got hot(up near the red) I have done datateks fan mod so have no viscous fitted. The fans come on fine and bring the temp back down when required.

The issue I’m having is more and more often I end with no power once it got up near the red. I know the ecu limits power one car is HOT and I can deal with this. Todays problem was temp had settled back to half way on guage but I lost power for a few miles intermittently which I believe could be a faulty or intermittently faulty ecu coolant stat.

Does that sound like a plausible explanation? I also think there is a coolant temp sensor on fip but I’m unsure of the symptoms of this.

Apart from this car drives well with recent water pump and upgraded radiator And uses no coolant.

Any one any ideas?

Many thanks,

Jacob

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If the stat is correctly set per the instructions, the temperature should never get near the red zone. If it does, the power will be reduced. The EDC coolant temperature sensor will not cause loss of power if it's faulty as far as I'm aware unless it is signalling over temperature. There is a fuel temperature sensor and a fuel heater but I doubt they will be the cause. It needs to go on diagnostics first to check for recorded fault codes and then look at the coolant sensor on live data.

Datatek said:

If the stat is correctly set per the instructions, the temperature should never get near the red zone. If it does, the power will be reduced. The EDC coolant temperature sensor will not cause loss of power if it's faulty as far as I'm aware unless it is signalling over temperature. There is a fuel temperature sensor and a fuel heater but I doubt they will be the cause. It needs to go on diagnostics first to check for recorded fault codes and then look at the coolant sensor on live data.

Click to expand...

Thanks Datatek, when I purchased the thermocouple for the fan mod I purchased one off eBay which wasn’t the best quality as it has a wide range of on off so if I set it maybe a bit to high to stop fans being on for to long. I’ll try cranking it down a bit (fans on more) and see if that helps. I’ve got a few code readers that can let me see live data not RR specific so I’ll see if they shed any light on the situation. Hope your well and thanks for the reply.

Jacob

JT_spark said:

Thanks Datatek, when I purchased the thermocouple for the fan mod I purchased one off eBay which wasn’t the best quality as it has a wide range of on off so if I set it maybe a bit to high to stop fans being on for to long. I’ll try cranking it down a bit (fans on more) and see if that helps. I’ve got a few code readers that can let me see live data not RR specific so I’ll see if they shed any light on the situation. Hope your well and thanks for the reply.

Jacob

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The fans should come on at 98C, if the stat is any good they should go off at between 90 & 92 C. I hope you removed the fan cowl to maximise airflow.
When set up correctly, the gauge should never get above the 12 o'clock position. If you are running up to the red zone, expect a cracked head.

Thanks I’ll recheck all of that, fan cowl has been previously removed, car generally sits at halfway on guage unless idling for a long time or doing lots of low speed work or I have foot down for a while up very long hills Mile or so in length. Don’t like the sound of the cracked head problem, I had heard about it. Best get it set up a bit better by the sounds of it!

Thanks again

JT_spark said:

Thanks I’ll recheck all of that, fan cowl has been previously removed, car generally sits at halfway on guage unless idling for a long time or doing lots of low speed work or I have foot down for a while up very long hills Mile or so in length. Don’t like the sound of the cracked head problem, I had heard about it. Best get it set up a bit better by the sounds of it!

Thanks again

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I’ll reply my own thread incase it helps anyone, intermittent problem that gradually got worse.

Car passed the Mot recently with no advisory’s yippee I thought. I decided to pick my son up from school and on the way home getting stuck in traffic approaching an extremely busy roundabout where theres no where to stop it happens again. Keep idling but the accelerator does nothing. Roundabout is on a hill so managed to coast down for a bit with hazards on into a close. Then it was struggling to idle and finally cut out and would not restart. I then had to push it to not block the close. Moved it out of the way. Gave it a few mins and it started back up and drove fine, as I was quite near home I thought I’d chance it. Made it to the end of my road and it happened again! Got it home after a bit of faffing.

I’ve now fixed the problem, The green ECU coolant sensor was intermittently failing. I purchased a new one only to find the cutting out problem was fixed but now the auto box would only charge up at really high revs like 3750rpm at 30mph. It never done that before so thought I’ve only changed the faulty sensor. I put a multi meter on it and it was open circuit so that was faulty as well just in another way. I left the connector off for a few days and car still ran ok (bit lumpy) still changing gears at high rpm. Got another (different make) tested with multimeter first to check around 2.0 kohms. Fitted and now all is well again. Drives and changes great once again. Hopefully that may help someone one day. My logic was the original sender was over reading the temp cutting engine power to save itself and when no signal was detected from the second faulty sender the ecu would default to a cold engine, hence the high rpm gear changes to warm the engine up. Now to sort leaning suspension! Tho I’ll start a new thread when I get time to look into that.

Cheers all

Well done that guy

Thanks for posting the result

Nice one and a cheaper fix to boot