P38 DSE loss of power when driving

RangeRoller dt · 2024-10-31T17:48:04+0000

@Craig P38D
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Craig P38D · 2024-10-31T17:54:55+0000

Hello everyone, I am having a sort of similar issue with my 2.5 DSE auto recently. The top speed seems almost limited to 70 MPH and the speed drops steadily to about 57 MPH on long steep hills. Before the problem started, I was able to accelerate uphill without an issue. So far I have changed the oil and filter, air and fuel filter. I've changed the MAP sensor and checked the MAP pipe is clean, with no cracks and is securely fitted. I found during investigation that the turbo hoses were a bit soft and replaced those. The acceleration is now really good and the engine revs smoothly up to 3000 RPM ish when pushed, before changing up. However the problem persists on the motorway and I'm still stuck at about 72 MPH at about 2500 RPM. I don't normally drive faster than 65 MPH, but like to have a little in reserve which is now lacking.

At some point a tuning box was installed, which used to flash when the engine was running, but no longer does so. I'm wondering if this might be the cause, although it seems odd that the performance is there at lower speeds.

I read elswhere that changing the fuel pump relay might help and I plan to do that tomorrow.

Has anyone had a similar experience? Any advice greatly appreciated.

Grrrrrr · 2024-10-31T18:03:04+0000

I would certainly take the tuning box out before I did anything else.

Datatek · 2024-10-31T19:38:48+0000

Craig P38D said:
Hello everyone, I am having a sort of similar issue with my 2.5 DSE auto recently. The top speed seems almost limited to 70 MPH and the speed drops steadily to about 57 MPH on long steep hills. Before the problem started, I was able to accelerate uphill without an issue. So far I have changed the oil and filter, air and fuel filter. I've changed the MAP sensor and checked the MAP pipe is clean, with no cracks and is securely fitted. I found during investigation that the turbo hoses were a bit soft and replaced those. The acceleration is now really good and the engine revs smoothly up to 3000 RPM ish when pushed, before changing up. However the problem persists on the motorway and I'm still stuck at about 72 MPH at about 2500 RPM. I don't normally drive faster than 65 MPH, but like to have a little in reserve which is now lacking.

At some point a tuning box was installed, which used to flash when the engine was running, but no longer does so. I'm wondering if this might be the cause, although it seems odd that the performance is there at lower speeds.

I read elswhere that changing the fuel pump relay might help and I plan to do that tomorrow.

Has anyone had a similar experience? Any advice greatly appreciated.

A failed power box may well limit performance. Also, you don't say what year your car is, but if it has a MAF sensor and EGR, failure of the MAF will affect performance. You can check this by running with the MAF unplugged.

Craig P38D · 2024-10-31T20:42:56+0000

Datatek said:
A failed power box may well limit performance. Also, you don't say what year your car is, but if it has a MAF sensor and EGR, failure of the MAF will affect performance. You can check this by running with the MAF unplugged.

Hello and many thanks for your reply. My car is a P plate 1996 with 235K on the clock. I suspect that the engine may not be the original.
I am wondering if gear box might be a factor, as the car goes really well in first to third gears, but then runs out of steam when it shifts to 4th. Box was serviced 4 years and 20 K ago and has been topped up once. Perhaps it needs topped up, I will need to check. I am rubbish with electrics so was a bit scared to tackle the tuning box myself. There aren't any warning lights on the dash.

I will take your advice and that of Grrrrrr and report on results. Thanks again for your help.

RangeRoller dt · 2024-10-31T22:21:54+0000

Check the fuel flow rate from the lift pump in the tank. Should be 180ml in 10 seconds when you bridge the relay. How to in tech archive (top of RR section).

P38 DSE loss of power when driving

RangeRoller dt

Well-Sprung Member

Craig P38D

New Member

Grrrrrr

Technician, Bodgit & Scarper Ltd

Datatek

Well-Known Member

Craig P38D

New Member

RangeRoller dt

Well-Sprung Member

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