XDi engine - intermitant power loss

[Eightpot]

Been havinga few problems with the FL which I initially thought were to do with brakes or VCU etc causing the car to slow down abruptly, but after intensive testing it appears it's actually the engine losing power when pulling away.

Haven't had chance to have a thorough drains up yet, and I'll be checking things like fuel filter/IC hoses/loose wires etc, but as I don't have any history with freelanders, just wondering if this is something that has come up before or if there are any likely suspects I should check first.

The symptoms are, if I hold the accelerator down partially and let the engine rev, the revs will suddenly drop off and for a second or so I can floor the throttle and nothing happens, then it will pick back up again. Any issues with throttle potentiometers or sensors on these??

ta

[EggNChips]

Been havinga few problems with the FL which I initially thought were to do with brakes or VCU etc causing the car to slow down abruptly, but after intensive testing it appears it's actually the engine losing power when pulling away.

Haven't had chance to have a thorough drains up yet, and I'll be checking things like fuel filter/IC hoses/loose wires etc, but as I don't have any history with freelanders, just wondering if this is something that has come up before or if there are any likely suspects I should check first.

The symptoms are, if I hold the accelerator down partially and let the engine rev, the revs will suddenly drop off and for a second or so I can floor the throttle and nothing happens, then it will pick back up again. Any issues with throttle potentiometers or sensors on these??

ta

It's not clear from your post if you're suffering a misfire or if the engine is returning to idle. Does the engine management light come on when you have a problem?

Yes, a common problem is the needle lift sensor on the no1 injector. Check for chafed or broken wires. This can be unplugged and the engine will run with reduced power, but it will eliminate / confirm if it has a problem. Wiring into FIP can become corroded and MAF sensor has a finite life.

Always check the obvious first, Fuel filter and air filter. If in doubt change them, they only cost a few quid and it's amazing how much trouble they can cause if they are blocked.

TPS sensor going is pretty uncommon I think, but can happen. Other thing is brake light switch as this is used for plausibility with TPS.

[Eightpot]

Thanks - there's no misfire, it's just returning to idle. When driving from standstill the car accelerates then power drops off leaving the car crawling along at 4mph , and will gradually pick up again after a couple of seconds.

No warning lights - funny you mentioned brake light switch though as this has only started happening immediately after I replaced the brake servo - was thinking I may have knocked something off when doing the work but couldn't see anything obvious.

presuming brake light switch is operated off the pedal under the dash? It's not unlikely I may have knocked a wire off while fiddling about under there, do you reckon this could affect engine management then? (It's raining cats & dogs outside otherwise I'd run straight out and have a look!)

Thanks -

[EggNChips]

Thanks - there's no misfire, it's just returning to idle. When driving from standstill the car accelerates then power drops off leaving the car crawling along at 4mph , and will gradually pick up again after a couple of seconds.

No warning lights - funny you mentioned brake light switch though as this has only started happening immediately after I replaced the brake servo - was thinking I may have knocked something off when doing the work but couldn't see anything obvious.

presuming brake light switch is operated off the pedal under the dash? It's not unlikely I may have knocked a wire off while fiddling about under there, do you reckon this could affect engine management then? (It's raining cats & dogs outside otherwise I'd run straight out and have a look!)

Thanks -

Yes it definitely will affect the egine management. The system uses the brake light switch as a plusibilty check against the Throttle position sensor, just in case the TPS went short circuit. You therefore couldn't use left foot braking with this system as the activation of the brake would override the throttle sensor.

There are reports that putting in the wrong bulb into the taillight/stoplight can cause the throttle to stop working as current feeds back to the ECU fooling it into thinking that the brake is pressed.

[Eightpot]

Ok -

thanks for the pointers, but I've checked the brake switch and unfortunately it all seems ok, or certainly it's all there and intact and wired up. I ws hoping I'd knocked a wire off.

I have now isolated the problem, but need to identify the cause next -

If when parked I hold the throttle open lightly, enough to hold the revs at around 2500rpm, and keep my foot totally still, after a couple of seconds the revs drop down to 1000 rpm.

I can then push my foot flat to the floor and nothing happens - revs stay the same! It can be held down indefinately with no change whatsoever.

lifting off and pressing back down on the accelerator cancels everything and it can be revved again.

If I rev harder and hold it, no problem, just seems to be on a light throttle.

I've had a shufty round the engine and everything looks fine - no loose wires or anything hanging off. It's a low mileage engine, so wouldn't suspect anything to be worn in a major way (68k miles)

any ideas?

[EggNChips]

Ok -

thanks for the pointers, but I've checked the brake switch and unfortunately it all seems ok, or certainly it's all there and intact and wired up. I ws hoping I'd knocked a wire off.

I have now isolated the problem, but need to identify the cause next -

If when parked I hold the throttle open lightly, enough to hold the revs at around 2500rpm, and keep my foot totally still, after a couple of seconds the revs drop down to 1000 rpm.

I can then push my foot flat to the floor and nothing happens - revs stay the same! It can be held down indefinately with no change whatsoever.

lifting off and pressing back down on the accelerator cancels everything and it can be revved again.

If I rev harder and hold it, no problem, just seems to be on a light throttle.

I've had a shufty round the engine and everything looks fine - no loose wires or anything hanging off. It's a low mileage engine, so wouldn't suspect anything to be worn in a major way (68k miles)

any ideas?

Definitely won't be anything serious, but none the less annoying Mines got 180k and is still sweat as a nut. My best guess is that it is the TPS or ECU, I cannot think of anything else that would cause the engine to drop to idle without associated misfire.

I still think there is mileage in investigating the brake light system tho, because it is a no expense thing to be eliminated. I would disconnect the brake light switch and remove the stoplight bulbs and see if this cures the fault. Should only take 10 mins and will eliminate it for sure.

The fact that it happens only on light throttle suggests a possible problem with the EGR valve or MAP sensor, but I would have thought these would make it misfire, not just return to idle.

[Eightpot]

I still think there is mileage in investigating the brake light system tho, because it is a no expense thing to be eliminated. I would disconnect the brake light switch and remove the stoplight bulbs and see if this cures the fault. Should only take 10 mins and will eliminate it for sure.

.

GENIOUS!

problem solved! Removed the brake light connector and problem gone. Put it back on again, problem returned. Reversed up towards a window spo I could see what the brake lights were doing on the reflection and noticed they were permanently on - I'll have a fiddle with the switch as it may just be an adjustment - in fact as I thik about it, the pedal probably sits in a different place since I swapped the servo. SIMPLE!

But WHO THE HELL designed a system that fecks about with the engine if a brake bulb fails

[EggNChips]

GENIOUS!

problem solved! Removed the brake light connector and problem gone. Put it back on again, problem returned. Reversed up towards a window spo I could see what the brake lights were doing on the reflection and noticed they were permanently on - I'll have a fiddle with the switch as it may just be an adjustment - in fact as I thik about it, the pedal probably sits in a different place since I swapped the servo. SIMPLE!

But WHO THE HELL designed a system that fecks about with the engine if a brake bulb fails

It's usually because twin filament bulbs have been fitted where it should only be single. This shorts out and backfeeds to the ecu fooling it into thinking that the brake pedal is pressed. Obviously this is not in your case. A failing bulb won't do this, only an incorrect bulb, e.g. twin filament instead of a single.

Glad you got it sorted tho