Loss of power under acceleration

I have a P38 dse with the M51 engine

I have an intermittant fault and thought I would ask the forum for any help/ideas, it can be harder to start when warm. The power can be fine and then just drop off, it can drop off at below 30 or at 50+ but at times we can get full power. If I do it slowly I get power up to 70+ without any issue but then I can have it fail completly.
Tonight on the motorway it failed and I could not get above 50 and slight hills dropped down even more.

Things I have done to date that has not sorted the problem

Replaced the in tank fuel pump

Changed the turbo pipes (all 3)

Cleaned the intercooler

Changed the fuel filter

The turbo does not have any play in the shaft

Revs well when not in drive but fails when driving

Checked the pipe from the fuel filter to the inlet manifold (not changed it)

Checked all the connections from the air filter to the turbo but not inspected for small cracks or holes

Changed the relay for the fuel pump (it improved right away after coming home tonight) but then started to fail on a test run, not as bad but still failing, the relay gets very very hot) possible cause but not sure why

If I have missed anything I appologise

If anyone can suggest a cause of the relay overheating or a possible reason for the loss of power that I have not yet covered

Thanks

MAP sensor or pipe from map to inlet manifold. Unplug pipe and see what happens

Thanks, I didn't think of that and I should have
What do you think will happen?

I suspect that you would get no power if the pipe is removed but the MAP sensor could be breaking down and have an intermittant fault causing the issue

Is this what you are thinking or have I missed something

Thanks
Dave

What mileage?

Does it die if you lift off the throttle after a run, like when you stop at lights/roundabout after motorway speeds?

You may want to look up ‘limp mode’ with the gearbox in the search bar, see if it sounds similar to your symptoms

Get it on diagnostics is best solution if it’s an option.

Just taken the pipe from the map sensor to the inlet manifold, give it a suck and blow and it is clear

Went for a drive with it off and the car drives and goes through the gears but does not have the boost (that the turbo would give) I then put the pipe back on the map sensor and unplugged the map and checked for dirt etc and put it back on and took another test drive, she pulls like a train.

To reply to Rangerover dt - The tickover is great, I get no drop in revs or cutting out at any time, the mileage is 173000 but that is not anything that should be considered as she runs fine when the fault is not there, I had driven from Preston to York and back without a problem then up to Lancaster from Preston again no problem, coming back from Lancaster the problem presented itself.

I would think is could be the MAP sensor but does anyone know how to test the resistance (what pins) and what the readings should be?

Ofcourse if it is not showing the fault it won't give bad readings but need to know what it should be when the fault comes back

If you could let me know the pins and readings on the sensor and the plug I would be grateful, I can then hopefully get this issue fixed

Cheers

If you unplug sensor and it works fine - sensors shot.
If as you say it now works with connections cleaned - problem solved - thank Rubberknees

The issue is intermittant but I will see what happens when I unplug the map sensor and report back but I can't do this until the problem comes back

I think for the cost just replacing the map sensor or buy one in just to be ready

Fingers crossed with your help I have sorted the problem. The plug and sensor were not dirty when I checked but the pulling off the hose and the plug may have altered something in the sensor to fix it short term

Now to buy a new sensor

Thanks

Wait!
Be sure it’s the sensor first they are pricey. They can get sticky

Diagnostic will tell you exactly. Check LZ map for someone near you with nanocom06 - they may come and find out for sure for the price of tea/cake/beer

dubloman said:

The issue is intermittant but I will see what happens when I unplug the map sensor and report back but I can't do this until the problem comes back

I think for the cost just replacing the map sensor or buy one in just to be ready

Fingers crossed with your help I have sorted the problem. The plug and sensor were not dirty when I checked but the pulling off the hose and the plug may have altered something in the sensor to fix it short term

Now to buy a new sensor

Thanks

Click to expand...

Original only on MAP sensors or it causes issues. Think they are Bosch?

dubloman said:

The issue is intermittant but I will see what happens when I unplug the map sensor and report back but I can't do this until the problem comes back

I think for the cost just replacing the map sensor or buy one in just to be ready

Fingers crossed with your help I have sorted the problem. The plug and sensor were not dirty when I checked but the pulling off the hose and the plug may have altered something in the sensor to fix it short term

Now to buy a new sensor

Thanks

Click to expand...

The function of the MAP sensor can be seen in live data on diagnostics.
With the MAP sensor unplugged, the car will lack power.
Check the spigot in the manifold that the pipe connects to is clear.

Should have said pipe can clog up especially at manifold end. Hopefully was MAP and you are ok. If you can put it on diagnostics as data says you can soon find out.

When I took the pipe off from the MAP sensor I sucked and blew down the pipe and it was clear (as I didn't feel any resistance at first)

It only cleared after I messed with the sensor

when I drove it without the pipe attached to see how it ran, it did run better but not the boost, it didn't bog out as it had been.

I then stopped half way to put the pipe back on the map sensor, removed the plug to check for dirt but it was very clean

Then I had the boost and it was much more responsive and drove as it should.

This is why I think it must be the map sensor

I will check the LZ map and see if anyone can help but having a MAP sensor in stock can't hurt if it is the map sensor I can change it out when it next presents the fault and if it sorts it great job

If I can get someone to come and check the live data on diagnostics but if it is not showing a fault or is not acting up the reading would not show

Thanks for all your help

dubloman said:

When I took the pipe off from the MAP sensor I sucked and blew down the pipe and it was clear (as I didn't feel any resistance at first)

It only cleared after I messed with the sensor

when I drove it without the pipe attached to see how it ran, it did run better but not the boost, it didn't bog out as it had been.

I then stopped half way to put the pipe back on the map sensor, removed the plug to check for dirt but it was very clean

Then I had the boost and it was much more responsive and drove as it should.

This is why I think it must be the map sensor

I will check the LZ map and see if anyone can help but having a MAP sensor in stock can't hurt if it is the map sensor I can change it out when it next presents the fault and if it sorts it great job

If I can get someone to come and check the live data on diagnostics but if it is not showing a fault or is not acting up the reading would not show

Thanks for all your help

Click to expand...

Corrosion of contacts is a common problem on the P38, simply unplugging and re-plugging the connector may have cleared the problem. The MAP sensor seems to be very reliable.