Power loss at 60/70 AFTER VCU/Drive shaft installed

Hi All,
2005 TD4 Sport - 110 000 miles.
I posted about the VCU/drive shaft removal last year. Turned out it was actually a rear diff brush issue. As a consequence I had the VCU/drive shaft put back on the car last week and all seemed fine. However I took the car on a 60 mile motorway journey on Saturday and had a power loss issue at around 60 or 70 mph. As the car was approaching a hill (not to steep) the power loss resulted in the car dropping down to 50 mph before recovering to around 70mph. It really struggled to get above 70. The car ran perfectly well for 18 months or so without the VCU/drive shaft and had NO power loss issues. So my question really is why would the car now suffer power loss following the re-installation of the VCU/drive shaft when it had been fine without it? The car pulls well at lower speeds and there is no other problem (ie all the hoses are good, engine well maintained, no smoke from the exhaust etc). Thanks in advance for any assistance. Cheers, Rikky

I think you need to check out your vcu as soon as possible, start with one wheel up test !

This is a known issue that is not related to the VCU. There is a sticky thread about it....

https://www.landyzone.co.uk/land-rover/td4-lack-of-power-at-70mph-fixed.77147/

Probably coincidence but as already said, check your VCU immediately. If it is stiff enough to cause the car to slow down then you have a major transmission failure coming in the next few miles.

Thanks for the replies. Is the power loss/VCU connected because of the temperature of the VCU at higher speeds? And is that why there is no power problem at lower speeds below 50mph? Thanks.

GrumpyGel said:

This is a known issue that is not related to the VCU. There is a sticky thread about it....

https://www.landyzone.co.uk/land-rover/td4-lack-of-power-at-70mph-fixed.77147/

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Thanks, I have looked at this. If the solenoid was the problem wouldn't the power loss have been evident when the VCU/drive shaft weren't on the car? Or would putting that back on have shown up the solenoid issue? Thanks

Just a brief update. I've just taken the car along the local dual carriageway which isn't inclined much. The car got up to a good speed c 70 without any loss of power. So was it the hill that the car found an issue when it lost power last week, or to put it another way did the VCU do something differently for the hill that it wouldn't do on a flat road? If the VCU wasn't working surely I wouldn't have been able to do a good speed without power loss? Sorry for the ramble but just want to make sure all the info is here and also want to avoid breaking the car further if there is an issue............cheers

or to put it another way did the VCU do something differently for the hill that it wouldn't do on a flat road?

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if the vcu is in good condition .. then ..
no .. not unless the front wheels lost traction and were spinning
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The VCU can only have any affect if the front and rear props want to turn at different speeds - eg turning corners or mismatched tyres.

It has been seen by a member who put rev counters on the front and rear props, that with a good tyre setup, they will turn at exactly the same rate at a steady speed going straight on a level road. Going up a hill though, the props did turn at different speeds. However, the difference in prop speeds was very minimal - I think even with a completely siezed VCU the tyres would give enough for the differences found not to slow the car down that much. If the VCU were that bad, I'm sure you would notice it 'binding' more at slow speeds trying to turn corners.

I'm pretty sure your power loss is not related to the VCU.

You should do the one wheel up test regardless of whether another issue is found to cause this - just to make sure everything is OK and healthy.

I suggest you check for mismatched tyres and do the one wheel up test asap. If the tyres are odd and the VCU is past its best, then you can get mild power loss at speed. This overloads the IRD and diff giving serious and expensive problems very quickly.

Just a quick one on the one wheel up test...........should the car be in 1st gear or neutral? Thanks

https://www.landyzone.co.uk/land-rover/vcu-torque-test-results.109486/page-13#post-2141449

" .. Q. How do you do the test?
A. Chock front wheels. Release handbrake. Doesn’t matter if it’s a manual or automatic gearbox, or what position the gearbox is in. Jack up one rear wheel. Remove plastic centre wheel cap. Fit a 1.2m bar (made up of ratchet and wood) with a 32mm socket on the drive shaft nut. Raise bar and add a known weight (8kg is preferred). Allow the bar to start turning before the 45 degrees start point, in order to take out the slack in the transmission. Time the bar while it turns 45 degrees to the horizontal. Use masking tape markers to help you with the 45 degrees and horizontal stop/start positions. "

more info in that link

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Thanks. The test indicates that the VCU is fine. Also no issues when turning on full lock either forward or reverse and tyres on front and back same make and size/wear. So I don't think the loss of power was a VCU issue..........don't know if relevant but the loss of power occured driving up an inclined dual carriageway when the temp was around zero and snowing, although the car had been driven about 30 miles by then so up to operating temp............thanks to all for your input. Cheers

starting to sound like a fuel issue
or turbo vane actuation issue

when was the fuel filter last changed
and the low pressure fuel pump
and the turbo solenoid filter

if the fuel pressure is too low for go-pedal demand
the ecu will limit power / rpm to prevent damage to the high pressure pump
common symptom being the engine rpm will hit a brick wall ..
happened to me .. 3000rpm ..
changed lp pump and filter .. issue solved

if the turbo vanes get stuck and cause an overboost
the ecu will again limit power to prevent damage

when was the fuel sedimenter last drained ..
if water is present .. in very low temps it could ice up in the filter
( rare in the uk i imagine )

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What time did you record for the OWUT?
How come the front and rear tyres have the same wear? The front wear faster than the rear.

The next culprit for power loss on hills is low lift pump pressure. So really you need to take a look at the live data while climbing a hill. It should hold above 350Kpa at full power.

To briefly answer the above - when was the fuel filter last changed and the low pressure fuel pump - about 15 000 miles ago. Old pump failed so did both at same time.
Time for the OWUT was around 35 seconds. Tyre wear - had new tyres put on front 12 000 miles ago (which as the VCU/drive shaft not on was ok) - they have now worn to exactly same as rear tyres.......have just measured them and they are identical.
I have just spoken to the mechanic who re-fitted the VCU last week (he's got 50 odd years experience and has worked on alot of Landys) - he said there may've been some water in the fuel..........now that might be right as 20 mins before the power loss I did re-fuel and it was snowing heavily so possible some water did get in..........and as I've not had the issue since then perhaps that could be the culprit..............I'm off to have a drive on the dual carriage way to see if any issue..........also there have been NO other issues such as odd noises, all the hoses are good, no smoke etc..............thanks again

he said there may've been some water in the fuel

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drain the sedimenter ..
get a glass or clear plastic container .. undo the sedimenter plug
and let fuel drain out until the fuel runs clear ..
do that once a year .. or twice ..
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suggestion .. buy some 'diesel rhino' and use it in the fuel
be the only additive that i know of that will combat water-in-fuel
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The day before my transmission went bang I drove up to Arthurs Pass which is a drive into the Southern Alps up to 740m - a mixture of flat, slight inclines and steep inclines - I didn't notice any slowing/binding on the inclines (above what's normal). When the transmission went bang, I was a couple of hundred yards from returning home after a day out to Akaroa. This is a drive which has twice left my old D1 V8 expired at the summit spewing its coolant. That involves a fairly steep and twisty 500m ascent to the crater rim followed by a similar decent down into the bowl of the old volcano, obviously going out and returning. Once again, no noticeable slowing/binding on the inclines or twisty bits. Obviously something was up cos the IRD turned to mush but no noticable problems - definitely nothing so obvious as drastic loss of power (although I would not have reached 70mph as the speed limit it 60mph).

Hi All, just a brief update on this. Have just driven the car 500 miles over two days without any issues at all so I suspect the lack of power was due to water in the fuel (heavy snow that day and just a coincidence that the VCU/drive shaft had been re-fitted a few days before. Over the 500 miles no power loss, even on steeply inclined motorways and the car drove as well as ever (even though it's now done 115000 miles. Hope that helps and thanks for everyones help..........cheers

GrumpyGel said:

The day before my transmission went bang I drove up to Arthurs Pass which is a drive into the Southern Alps up to 740m - a mixture of flat, slight inclines and steep inclines - I didn't notice any slowing/binding on the inclines (above what's normal). When the transmission went bang, I was a couple of hundred yards from returning home after a day out to Akaroa. This is a drive which has twice left my old D1 V8 expired at the summit spewing its coolant. That involves a fairly steep and twisty 500m ascent to the crater rim followed by a similar decent down into the bowl of the old volcano, obviously going out and returning. Once again, no noticeable slowing/binding on the inclines or twisty bits. Obviously something was up cos the IRD turned to mush but no noticable problems - definitely nothing so obvious as drastic loss of power (although I would not have reached 70mph as the speed limit it 60mph).

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Is that a picture of your lie detector test Grumpy ?
60 mph ? Did the car in front forget to untie the towrope lol