Loss of power when warm?

[gt0336]

Hi, fairly new here. I own a 1995 P38 HSE, love the car but she has developed an intermittent problem that neither myself nor my mechanic have been able to fix. (in fairness to my mechanic, the problem didn't seem to happen while he had the car.)

What is happening is, after a while driving (I'd say about an hour or so) the engine starts losing power, the further I push on the excelarater the more power I loose. The problem started a couple of weeks ago while I was towing an empty box trailer for about an hour, the car started loosing power to the point it would stop, so I pulled over and shut it off. It would start again with no problem, but loose power again after a few minutes of driving.

So I had it towed to my mechanic, he had the car for a week but couldn't find a problem, no fault codes etc. I had the fuel pump replaced a few weeks ago as the old one failed, this has been tested and is working fine, I also run the car on premium fuel. I've had the car back for a week and it has been running fine, until yesterday when I took it for a longer drive, after about an hour it started loosing power again although this time if I backed off the excelarater it would come good, until the next hill or if I push the excelarater a little harder. Has anyone else had this problem, any idea's? Thank you.

[PaulP38a]

Crank Position Sensor is probably faulty. Maybe the fuel filter, located on the chassis rail towards the rear on drivers side on pre-99 models.
Cheers, Paul.

[bee utey]

Your fuel tank venting may not be working, loosen the cap when it happens and see if you get a major air inflow. A new cap may cure it.

[sawtooth4x4]

Crank Position Sensor. Pretty common issue. Pretty easy to fix. Just wish my hands were smaller to get to that thing.

[poleonpom]

Sounds like it could be both, but my money would be on the fuel filter.

Try the fuel filter first, as a clogged one will suck power from your car. Also, I found that when I replaced my fuel pump, I must have stirred up 16 years of muck as I had lack-of-power issues directly after the fuel pump change. Fue filter is often overlooked and cheap and easy to replace.

The CPS will give the same sort of issues, but the car tends to stall rather than loose power. It won't register on your system as it's an intermittent fault, however it's easy to check; when the car stalls or looses power, open the bonnet and poor water on the CPS to cool it down. If the car performs without issue, then its the CPS (until it gets warms and dies again). Another easy to fix problem.

Let us know how you get on

[DT-P38]

...the engine starts losing power, the further I push on the excelarater the more power I loose...

It would start again with no problem, but loose power again after a few minutes of driving...

towed to my mechanic, but couldn't find a problem...

back for a week and it has been running fine, until yesterday...

it started loosing power again although this time if I backed off the excelarater it would come good, until the next hill or if I push the excelarater a little harder.

This could just about be de-ja-vu (how is that supposed to be spelt?) of my situation when my Crank Position (thought it was Angle) Sensor went silly. Apparently, they can become misaligned and chew themselves up?!? Mine got "cleaned up" and re-installed and has been good ever since.

[poleonpom]

This could just about be de-ja-vu (how is that supposed to be spelt?) of my situation when my Crank Position (thought it was Angle) Sensor went silly. Apparently, they can become misaligned and chew themselves up?!? Mine got "cleaned up" and re-installed and has been good ever since.

The screws that hold he CPS are not torqued up. I was surprised how loose they were when I replaced mine (easy job and happy to talk you through it)

[gt0336]

Thanks for all the advise, I am fitting a new fuel filter tomorrow. Can someone advise on the location of the crank position sensor? Can seem to find anything in Rave. The problem came back again today after a while driving in the heat (about 34 here today). Took a long drive yesterday (much cooler day) and it went fine apart from a very brief loss of power on the way home.

[wayneg]

Look again at Rave, Page 408 under fuel system. Its there.

[gt0336]

Cheers mate, found it. Can anyone direct me to any photos or diagrams of the crank position sensor? The diagram in rave isn't the best.

[benji]

Imagine bolting a starter motor to the wrong side of the motor, thats where it is.

[gt0336]

Changed the fuel filter this morning (old one was very fould up). Took her for a test drive, but doesn't seem to have fixed it, put my foot right down and started loosing power. The more throttle I gave the worse it got. Even less power if I push sport mode. Although smaller amounts of throttle it seemed ok.

[Hoges]

If the crank position sensor is faulty then surely the engine should exhibit problems as soon as you try and start it...?

Secondly, since it seems OK for an hour or so when starting from "cold" then progressively loses power...am wondering about a temperature-related issue...

There is a fuel temperature sensor which is critical to proper functioning of the fuel injection system... there is also a fuel pressure regulator.... I suggest you get these checked...

I'm thinking fuel starvation ...

Have you tried bee utey's suggestion re loosening the fuel cap?

EDIT: another thought: how long is it since you have checked out the relays ( in the fusebox beside the battery) esp. the one controlling the fuel pump... look for brown burn marks on the yellow ones especially...

[gt0336]

Thanks for the reply hoges, she starts up fine and even if it stalls after power loss it's starts again after a minute no problem. I did try the fuel cap, but no change. I did look at the relays a few weeks ago as I needed to change the relay for the a/c and I do remember the fuel pump reply having some burn marks on it, but as the pump was working I didn't think much of it.

[gt0336]

Another update, swapped the fuel pump relaywith one of the good ones and went around the block. Still no change, drives ok at low to medium throttle but when I put my foot down she looses rev's/power for a few seconds the kicks back in for a second then looses power again and so on.

[wayneg]

Did you try the cold water on the CPS trick yet? I must admit I have never tried it on a p38 Range Rover however on my Merc its the first test when loss of power or stalling symptoms occur.
The CPS goes bad when hot so cooling it gets it working again.
It could also be the Maf sensor. You can clean the Maf but I doubt a dirty maf would cause your Symptoms. A new Maf can be had for less than $60 on e-bay and wouldnot be a bad thing to change anyway if its the original. search for part 0280 218 010 . I would try and find someone close by who was willing to put their maf into your car for a quick test. Its only two screws if you have the right screw head bit. ( I always change mine to std cross head as I clean mine every 6 months)
Have you tried a generic OBD2 reader to see if there are any clues?

[gt0336]

Did you try the cold water on the CPS trick yet? I must admit I have never tried it on a p38 Range Rover however on my Merc its the first test when loss of power or stalling symptoms occur.
The CPS goes bad when hot so cooling it gets it working again.
It could also be the Maf sensor.
Have you tried a generic OBD2 reader to see if there are any clues?

Haven't tryed the cold water yet, still having trouble locating the CPS, although when I put my foot down in it today it was right after pulling out of the drive way so the car wasn't hot yet, but still had power loss. (only when giving a lot of throttle.) I have plugged the OBD scanner in and she's not Showing any fault codes. Idid clean the MAF sensor at te last service a couple of months ago while changing the air filter.

[Scouse]

Can you borrow a fuel pressure guage to see what's happening under load?

I wonder if the fuel pressure regulator is weak...disconnect the vac hose or clamp off the return hose.

[gt0336]

Can you borrow a fuel pressure guage to see what's happening under load?

I wonder if the fuel pressure regulator is weak...disconnect the vac hose or clamp off the return hose.

Thanks Scouse, my mechanic did test fuel pressures when I took it in to him and he says they are fine.

[zhoey]

I'd be looking at the intake air temperature sensor or the MAF.

[gt0336]

I'd be looking at the intake air temperature sensor or the MAF.

Will give the MAF a clean tomorrow, could the Catalytic converter's be causing this problem at all?

[Hoges]

Will give the MAF a clean tomorrow, could the Catalytic converter's be causing this problem at all?

Not unless they are blocked...

Also, how did you clean the MAF? They are quite fragile.

Have a reread of Scouse's comment, I think he was referring to a "dynamic" fuel pressure measurement...i.e. connecting a pressure gauge to the fuel rail then driving the vehicle for a distance to see what pressures were obtained when it lost power....a static test doesn't tell the whole story. There's no hint that the mechanic did a 'dynamic 'test

[wayneg]

https://www.aulro.com/afvb/images/imported/2012/03/1152.jpg
..

Also, how did you clean the MAF? They are quite fragile.



Cleaning the Maf is not the issue here, The Maf can go faulty and give intermittent bad running and stalling hence my suggestion to try a known good one.

If anyone wants to clean the Maf it is simple if you have the right tamper proof bit to remove it. ( once off refit with normal screws for next time )



Remove the two screws holding the insert into the Maf housing. Remove the insert and electrical connector. Spray Maf Cleaner or contact cleaner into the "air Flow" orifice onto the inner wires. Repeat a couple of times. Done

[gt0336]

Not unless they are blocked...

Also, how did you clean the MAF? They are quite fragile.

Have a reread of Scouse's comment, I think he was referring to a "dynamic" fuel pressure measurement...i.e. connecting a pressure gauge to the fuel rail then driving the vehicle for a distance to see what pressures were obtained when it lost power....a static test doesn't tell the whole story. There's no hint that the mechanic did a 'dynamic 'test

Cleaned it with a spray, I'll check with my mechanic but he told me he tested the fuel pressure while driving. Cheers.

[DT-P38]

Did you put another/new cps into it?

[gt0336]

Did you put another/new cps into it?

Hi mate, no not yet. Would like to try and be and sure as I can it needs replacing before I buy a new one. Cheers.

[zhoey]

I'd be looking at the intake air temperature sensor or the MAF.

......or even an air leak somewhere along the air intake since you are complaining that you lose power on acceleration.

[DT-P38]

Hi mate, no not yet. Would like to try and be and sure as I can it needs replacing before I buy a new one. Cheers.

Getting de-ja-vu again!

[gt0336]

Was under the bonnet this morning and noticed that both screw heads holding the throttle position sensor are broken off. The sensor seems to be still attached fairly tight, although giving it a jiggle the engine seems to rev higher. Could this be the cause of my problems? Cheers.

[Hoges]

Could very well be...the TPS is critical for injection timing, ignition timing, feeds into autotrans ecu etc ...good find!!

[MACA0007]

Hi, having the same problem with my GEMS p38. I beleive the CPS's are at the back of the engine with the reluctor located on the flywheel. Currently looking for new ones around Brisbane. Cheers.

[Keithy P38]

Wish I could help mate. Good luck.

On a cold motor it's a 5min job to replace.

[TheTree]

If it is the CPS then pouring cold water over the rear of the engine when it is playing up should fix it temporarily

Steve

[garybrook]

Unless I misunderstood, wasn't he said about him finding the TPS bolts or screws broken, or at least loose, at the top-rear end of the engine near the induction area. If they were broken and the sensor was floating around then the symptoms would be about right, but this was originally a 2012 thread.

If the loose TPS isn't your current issue, I have recently installed a new CPS in my 150K 2000MY P38 HSE 4.6, which is a Bosch sensor and may not fit on your GEMS engine. My Bosch original sensor was just fine but I've kept it as a spare as some fail early and others later.

If you want to you're welcome try it on yours for the price of shipping both ways, which I don't know at the moment. It's a bit of a fiddle replacing at the back of the passenger side of the head, and I broke part of the plastic clip the locks the cable to the loom (but NOT the loom bit - thank goodness), but I'm sure it's working well to test yours. Let me know.

[Keithy P38]

CPS' are not interchangeable between bosch and gems engines.

Cheers
Keithy

[TheTree]

I believe there are three different types, two GEMS ones and a Thor version

Steve