TD5 losing power at full throttle at 70MPH

Hi - I've got what looks like the classic overboost issue with my TD5 - at 70-75MPH after a few mins it loses power and drops to ~55MPH. If I back the acclerator off a bit power returns. On the flat it can maintain ~70 constantly but as soon as a bit more power is needed for a hill the issue nearly always happens.

Nanocom shows negative boost when this happens, but nothing else obvious at the time (i.e no change in the voltage readings from the accellerator), and the wastgate feels nice and loose.

Ive now fitted a turbo boost gauge and a fuel pressure gauge (on the input to the regulator). The boost gauge never hits 1 Bar, and Nanocom never shows more than ~180, so agrees with the boost gauge. I replaced the MAF (which was faulty), and this now reads correctly according to Nanocom, and Nancom logs no errors when the power loss happens.

I also just did the injector seals, but there was no obvious blowpast on the copper washers, and no raise in oil level

I just took it for a bast with the Fuel pressure gauge (gaffer taped to the windscreen as I don't really want 4 bar of fuel in the cab !!). The pump does wine and gurgle a bit on start up, but maintains ~3.9Bar all the time (I am not sure how accurate the gauge is) - it does not budge from this when the issue happens so the pump (and by extension the fuel filters) seem to be OK.

I've got newish silicone hoses from the turbo up to the inlet manifold, and a newish alisport intercooler - ive not yet taken them off to check they are not collapsing, but that seems to be the only "classic" issue I've not check for this fault.

Does anyone have any other suggestions as to what I can check!

thanks

Robin

Warped exhaust manifold?

It is, but Ive cut the webbing out and emery clothed 4 of them level (front 4 cylinders), and packed out the 5th one (nearest the bulkhead) with some extra bits of gasket (the proper metal one) so it all seems to be nice and well seated with no leaks. I only did this this weekend, as it did have a stainless tubular one on it, but that kept cracking so I gave up welding it and put the original one back on with some extra packing to account for the warping. THe same issue was happening with the tubluar manifold, and they are not massive cracks - its not noticeably quieter with the original cast one back on.

Are you thinking its warping enough to cut boost? Would that not make lots of noise? Its the negative boost (~50Kpa) that is confusing me - Thats got to either be the ECU cutting fuel or the hoses collapsing (not checked that yet, but they are silicone ones). Its rock solid at 65MPH as well.... If only it was just the fuel pump!

thanks

There's also a possibility that the crank position sensor is on the way out. I had a few episodes of this, accompanied by a 'high speed crank error' fault and some very large cylinder balance values. A new one was much better and it was more reliable at motorway speeds.

TD5 ECUs are getting very elderly now and do fail. Sometimes along the way, they can give some odd running symptoms such as misfires and power loss. I've had this once or twice myself.

Brown said:

There's also a possibility that the crank position sensor is on the way out. I had a few episodes of this, accompanied by a 'high speed crank error' fault and some very large cylinder balance values. A new one was much better and it was more reliable at motorway speeds.

TD5 ECUs are getting very elderly now and do fail. Sometimes along the way, they can give some odd running symptoms such as misfires and power loss. I've had this once or twice myself.

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Bloody hell, oil in red plug hasn't been mentioned

robink99 said:

It is, but Ive cut the webbing out and emery clothed 4 of them level (front 4 cylinders), and packed out the 5th one (nearest the bulkhead) with some extra bits of gasket (the proper metal one) so it all seems to be nice and well seated with no leaks. I only did this this weekend, as it did have a stainless tubular one on it, but that kept cracking so I gave up welding it and put the original one back on with some extra packing to account for the warping. THe same issue was happening with the tubluar manifold, and they are not massive cracks - its not noticeably quieter with the original cast one back on.

Are you thinking its warping enough to cut boost? Would that not make lots of noise? Its the negative boost (~50Kpa) that is confusing me - Thats got to either be the ECU cutting fuel or the hoses collapsing (not checked that yet, but they are silicone ones). Its rock solid at 65MPH as well.... If only it was just the fuel pump!

thanks

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You'd think it'd be screaming but I had one warping on my 110 and it gave loss of boost at motorway speeds when hot, very faint whine almost like turbo but was from exhaust, so thought I'd have a stab. Brown's post just reminded me, oil in red plug but you've just done injector seals so would've had harness out..?

There is a bit of oil in the red plug. Not much, but I also replaced the injector loom when I did the seals. I just dunked the plug in some brake cleaner - I'm going to try and find one of those secure star drives and take the top of the ECU to see if there is any inside...

I think I am going to have to bite the bullet and get new sensors. I'll start with the crank one seeing as nanocom seems to show the MAP/MAF/AAF are reading sensible values...

RE the manifold, I can drive it 5 mins down the road to the A3 and get it to lose power within 5 mins of leaving home so its not running hot at that point..


Thanks for all the suggestions! I've spend the last month or so checking various forums and tried most things :-( I'm going to take a closer look at the Nanocom data, but its not logging any errors at all (other than the one about Aircon, which I don't have...)

I have discovered that a TD5 ECU can check out fine on the Nanocom yet be useless for starting the car. So they don't necessarily tell you what's wrong with them when they fail. In the Defender the red plug is quite a long way from the engine, under the seat, so it would take a long time for the oil to get all the way along there. I think it's more of an issue on the Discovery, where it has less far to go. I check by looking at the multiplug where the wires go into the cylinder head as that gives you an earlier warning.

Quick Update. I replace:

Crank sensor - No change
MAP - no change
disconencted the AAP (cos a new one is EXPENSIVE!!) - no change....

I have noted that nanocom only seems to have a resolution of about 1 second, so it is going to miss short term peak values, but the engine still never goes over 200KPA boost, and I've now mounter the fuel pressure gague inside the cab - it never moves from 4 bar.

Note - it does have the issue where it won't start for ages if its under about 1/8th tank of fuel, but other than that it has always started instantaly with no isssues. I was wondering if there was air getting in, but the fuel pressure gague (other than on inital start when the tank is low) never wavers from 4 Bar

Did you check the throttle pot readings? I can’t remember off my head but the tracks should add up to ten or something @sierrafery will know!
I also had an awful throttle problem on mine where there was a short in the wiring on my accelerator. I re-wired it. Problem solved. @KISSMYAURA had to do the same.
Either way, sierra is clued up on such mysteries.
God I’m glad I didn’t buy another TD5!! Amazing when working but owning one drove me nuts

Oh and my pump gurgled and whined for a couple of weeks before it shat itself too. I’d change for a new Siemens one anyway as it will go at some point so might as well put in a fresh one and know it’s age.
Once the stupid fuelling and any sensor issues are sorted you’ll be chuffed with it

Tracks 1 & 2 are supposed to add up to the supply voltage (5v), which according to nancom they do. I'm not sure what track 3 is supposed to do but its some form of error correction for the other 2.

I'm beginning to wonder if Nanocom is just not fine grained enough to see any short transient erros though. Ite behaving exactly like an overboos cutout, but the analoge gague does not blip up when it happens and both say it never reaches 200KPA (I backed it off a while back just in case)... If it stops raining I am going to take the ECU apart and check for oil intetnally. Other than that I think I will need to find a local garage that undersandts td5's with a better diag tool..

Ive had the thing for 15+ years and done about 90K in it and its never missed a beat untill this started happening in the last year or so - its just relaibly happing now within 2-3 mins of hitting 70+ MPH... It used to cruse at 85 (with the fuel gague moving noticeabley!)

Sounds like turbo waste gate, two bolts and a little c clip, then when it’s off spray a decent release spray where the arm goes into the turbo and keep working it

the saga continues. I noted the turbo had alot of play so had it rebuilt at a local specialist. I also took the intercooler and hose off and checked them all (and cleaned as there was alot of oil due to the turbo leaking a fair bit). The hoses are all silicon and seem fine, and the air input one is solid other than the bend where the engine vent connects. (i also replaced the vent valve as well as that was not closing when i sucked on it..)

I re setup the waste gate so that nanocom peaked at about 205-210 and have driven it 7 hours to the lake district. +first 6 hours no issues at 70 (lots of rain/spray if that makes any difference) but it cut out again with same symptoms both on the motorway, and on a hill in the lakes in 4th gear. Coincidentally once id got north of all the bad weather???

Same synptons. Boost goes negative. And i dont mean it just drops off. It goes to about 50kpa in nanocom, and the boost gauge, connected at the inlet manifold, agrees. And i never see it go over 1 bar on the gauge, or about 205 on nanocom, with no error light or issues logged. Back off the accelerator and boost comes back up to zero on the boost gauge and i can generally be careful on the throttle to get it mostly back to full power for a while.

It cant be the waste gate sticking as there is full boost at high revs when it happens so the gate is already mainly open and i dont see the boost spike id expect if it was a bit stuck. The fuel pressure sits solidly at 4 bar the whole time (measured with an inline tap and analogue gague on ingress to the regulator)

Its like i am getting hose collapse even though i checked them all. What else can cause real negative boost? (as shown on an analogue gauge, not just nanocom). I think overboost protection goes to a cut down fuel map?, but would that cause negative boost as opposed to just a low level of boost?

Ive not got the nanocom readings at the moment but the accelerator pedal track 1 and 2 values on the ones i check the other week always seem to match the supply voltage so it doesnt look like the accelerator pedal.

Thanks!

I'm not an expert so I'll state the obvious.. faulty boost pressure sensor?

Interesting, I have similar symptoms but only on really hard acceleration (usually half way through an overtake) which can be unsettling. I turn the ignition off and let it jump start in 5th and I'm back off limp mode and able to accelerate as usual, until I thrash it again...Browns suggestion of crank sensor is interesting, I presumed it was slightly sticky actuator as I haven't had mine off for a while, it usually registers as overboost when I plug the lynx in...I'll keep watching this thread!

With mine i dont have to turn it off. Boost comes back within a few seconds of lifting the clutch pedal. I think my next move is to replace the wiring from the crank sensor to the ECU. (i already changes the sensor - no change) I get no issues starting it or running it, or even max load for minutes at a time.

Another test i did yesterday was engine braking down a 25% hill in the lakes in 1st gear. Even that did not produce negative boost values and it was revving its nuts off so would have been sucking air as opposed to being boosted...

I meant lifteing the accelerator pedal!

I got my self convinced that something was occasionally blocking the intake, so took it all apart when I got home as had the same symptoms - it worked fine whist it was peeing down on the motorway, but once the rain stopped it started cutting power again.

I had checked the airbox with a mirror as had heard storys of rags getting sucked in and causing issues, and had been running without the link pipe to the snorkel for a few months this spring as it had perished.

It turns out a dead bird is fine when its wet, but when the outside air is dry and it drys out it must fluff its wings/feathers across the rest of the air spinner causing a blockage and negative boost!!!. It could not be seen with a mirror and torch - it was not till I took the box out and the inlet pipe off the box off that I saw it. I've now got the turbo back up to ~230KPA and have just done about 20 miles at "a bit more" than 70 Its working fine now!!!!

At least I did actually need to get the turbo re-conditioned as the seals were totally shot on it... You live and lean! Thanks for all the suggestions!

Robin