Turbo Wastegate Percentage %

ES4 · Jul 16, 2023

Hi, I have a problem on the Discovery 2 TD5 that it surges when towing a horse trailer up a hill,
The wastegate is free easy to move, I checked the actuator using air pressure and it cracks off at 15psi
and fully open at 24 psi, The manifold pressure on the hill builds up to 175kPa and the the wastegate shows 7%,
at 209 kPa the wastegate still shows 7%. the boost never go's over 215 kPa. However when the pressure drops to
156kPa the wastegate is still showing 7%. When the boost is increasing and passes through 156kPa the wastegate
is 0%. should it not drop back to 0% on the way back down. it eventually drops to 0% at 130 kPa.
Any idea what's going on ?

johnlad · Jul 16, 2023

Probably needs a new boost modulator

ES4 · Jul 16, 2023

One on order should get it this week, I'll let you know the outcome

Stanleysteamer · Jul 16, 2023

Could this be useful?

TD5 D2 engine - Wastegate Modulator (1)

Td5 Discoverys are fitted with a Turbocharger Wastegate Modulator controlled by the engine ECU. It allows greater control (modulation) ...

hx52.blogspot.com

ES4 · Jul 16, 2023

Thanks That's an excellent in depth write up, there's always more you don't know

if it is sticking, changing it will obviously help which is my first port of call and then move on to the next suspect.

ES4 · Jul 16, 2023

Some read outs

sierrafery · Jul 16, 2023

Hi, i doubt that your problem is with the wastegate modulator, that would lead to overboost not low boost... your problem might be fuelling or turbocharger related as that boost is too low for towing, MAP should be around 230(up to 240) uphill under load with MAF at least 500(up to 600)... the wastegate duty ratio reading has nothing to do with that, the ECU keeps it low cos the boost is not increasing enough to be "wasted"... seems simply low on power...is it manual or auto and which engine(Eu2 or 3)?

ES4 · Jul 17, 2023

Hi, Its a 2004 Auto, I think its EU3 as it has a 4 wire air pressure sensor in the air filter box.
best readings obtained
Max Boost 208 and 213 kPa
Air Flow 385 and 302 kg / hr
Wastegate 6.97 and 6.8 %
RPM 3037 and 2150
Thankyou

sierrafery · Jul 17, 2023

That's weak, run a stall test on it first then based on the result we'll speak again

ES4 · Jul 17, 2023

Hi, Did Stall test as suggested and it is 2800 rpm

Stanleysteamer · Jul 17, 2023

ES4 said:
Hi, Did Stall test as suggested and it is 2800 rpm

So a bit on the high side.
Tell us, when doing this uphill towing do you not pop it into third?
If you have a handbook it talks about towing with an auto.
I do a lot of heavy towing and find it is better to do this.

Stanleysteamer · Jul 17, 2023

ES4 said:
Hi, Did Stall test as suggested and it is 2800 rpm

I'd also change the ATF and the filter, then drive it around a bit and change the ATF again, as per the manual.

sierrafery · Jul 17, 2023

Seems that it's an autobox problem

ES4 said:
it surges when towing a horse trailer up a hill,

describe exactly how this happens... are the revs increasing while it doesnt pull well?...cos if it's so it's a clutch slip as the stall test suggests cos i think there was more than 20*C outside when you did it so that 2800rpm would be higher in normal conditions(as shown in the green note) and if there is a clutch slip te boost would not increase to max as the load on the engine is lower due to the slip

ES4 · Jul 17, 2023

Hi, We do always lock it down into third to avoid the box changing we also try to keep the revs a 3000 when climbing, there is definitely no rev increase. its the surging is the only reason why we noticed there was a problem. I'll try climbing in second at a lower rpm and see if it still surges. The oil has been changed in the past so its not like it has never been changed.

Stanleysteamer · Jul 18, 2023

If it is slipping, changing down you'll notice it even more. I take it the all up towing weight isn't over 3.5 tonnes?

Stanleysteamer · Jul 18, 2023

ES4 said:
I'll try climbing in second at a lower rpm

Always a good idea, just going more slowly uphill is what needs to be done when the vehicle is what you have plus a big tow behind. We have to join the slow lane on Autoroutes going up steep hills. When all's said and done it is just a 2000s 2.5 litre motor! You can't expect it to fly up hills like a newer model or a V8, when towing.

sierrafery · Jul 18, 2023

I'll say again cos it seems that i was ignored even though i'm trying to help...you can't expect anything good while towing uphill with around 210 KPa MAP and below 400 MAF reading... that's simply not enough power and has nothing to do with the "wastegate percentage" as this thread has begun, the duty ratio increases up to 40% when there is extra boost to be wasted in order to not overboost while the ECU is fuelling the sh*t out of the engine to cope with the load and then the MAP and MAF readings are going up fast, provided everything is working as it should which is not the case here... the wastegate ratio is low here cos there is not enough boost to "be wasted", this can be due to a clutch slip as the stall test revealed, a fuelling issue or air flow/exhaust restriction... the catalyst used to be clogged on Eu3s which can have such effect... believe me or not

ES4 · Jul 18, 2023

Hi, Good advice but we do climb at a steady pace, and avoid gear changes trying to keep the revs at max torque, 3000 ??
I'll try and describe this a bit better so you will understand what's happening. When we hit the bottom of the hill we'll be locked into third gear and remain in that gear all the way up, the gradient is such that normally we would go all the way to the top at a steady 3000 rpm approx. But what's happening now is at the bottom were doing about 2000 approx. accelerating up (plenty of power) when we reach 3000 + approx, the rev counter drops back to approx. 2000 this happens in about 1 to 1.5 secs. it then goes back up to 3000 in the same time period. this swinging between 2000 / 3000 continues till we get to the top. this results in the surging ( slowing and picking up again). This is not a auto gear change between 2nd and 3rd because it happens to fast. It does this if locked into 2nd. as well. Its a smooth power on power off. PS Towing weight is about 1500Kg box empty.

ES4 · Jul 18, 2023

Hi, I was also thinking cat blockage at the higher revs, would that explain the low MAF readings, how do you know if the cat is blocked? would this not show up when not towing?

sierrafery · Jul 18, 2023

OK, i understand but the issue remains... IMO the problem is that there is not enough power for some reason whicn i can't guess right now... untill you dont get at least 235 MAP and above 500 MAF readings while you struggle uphill the whole thing is mixed up...if you still have the catalyst fitted undo the downpipe to improve flow and try that way, with MAF unplugged as well, i hope the air and fuel filters are OK also the DCV is good to be renewed if it's old

EDIT: i wrote while you replied

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