[Mohawk]

A quick explanation is in order. Diesel’s Don’t use a throttle butterfly to control the engine, it’s all done via the fuel injection. So why does the SDV6/TDV6 have a butterfly in the throttle body(TB) ? It’s there to allow for the use of an EGR system, when you lift off the throttle the butterfly closes causing a vacuum in the TB which draws in exhaust into the engine intakes from the EGR valve. This works via an electronic actuator motor connected to the butterfly. In normal use the butterfly is open, but snaps shut when commanded when the throttle is released.

Here is a picture of the butterfly actuator & butterfly in the TB, but separated from each other. You can see the connector arm attached to the actuator spindle arm top right.

On the bottom right at about 4 o'clock you can see the the little button this arm connects to. At 3 o’clock you can see a flat part on the butterfly spindle/lever. This is the important bit.

So on a traditional petrol TB, the butterfly has an adjustable idle screw, to set idle rpm, by controlling where the butterfly rests. The engineers designed an adjustable stop into this TB design & the housing is there, but not drilled & NOT fitted with any parts. The picture below shows the TB butterfly in its closed position, NOTE the plastic housing on the left side under the flat area of the spindle actuator @9 o’clock above the bottom left screw hole. This was for an adjustment screw that was never implemented.

This looks exactly like a traditional TB butterfly idle stop screw setup. I measured the gap between the blanked off idle housing & the flat stop on the spindle, @2.5mm the butterfly sticks, @3mm it is free to return correctly.

Your options are to glue a spacer of the correct thickness on the flat part of the butterfly spindle, or to build it up with some Liquid Metal etc the file to the correct thickness to adjust the stop point of the butterfly, or drill & tap the idle fitting to take an M6 screw as per below, to allow you an adjustable stop. Either way, once you stop the butterfly from galling on the TB & sticking, it will work as intended. This could possibly be done on the car if you can get the 4 screws that hold the actuator in place off without removing the TB. The butterfly spindle can be levered out a little then removed by hand, keep hold of the butterfly, as you don’t want it falling deeper into the TB.

Temporary adjustable stop for testing my theory, I’ll clean the TB & set this up correctly, then refit it to the car to confirm it all works as intended.

Just blame the bean counters!

 

[Mohawk]

So after a little work & some clean up. I drilled & tapped the adjuster position with an M6 thread. Here it is with a temporary M6 threaded rod to show the relative position & the actuator arm. When you rotate the butterfly to the closed position the button on the butterfly arm lines up with the cutout to the left of the threaded rod & it has to be vertical to remove it as the actuator arm is keyed for this.

Another pic showing the adjuster position on the butterfly rod stop section.

I cut 8mm off the length of the adjuster plastic protrusion, to allow me to use an M6 allen head bolt I had to hand & to make the finished length the same. The removed piece is free bored, not threaded, probably to accept a spring for the adjuster that was never fitted by the factory. I then filed the bolt threaded end flat so as not to damage the butterfly stop & give it the largest surface area to rest on. I used Blue Hymolar & a small rubber washer (cut from a spare piece of hose) to stop the bolt from backing out.

To adjust press the butterfly closed with your fingers then screw the adjuster bolt in until it touches the stop. Now press the butterfly closed & listen / feel for it sticking, adjust bolt in until it stops sticking & add 1/16-1/8th of a turn in. Now reconnect the actuator arm & screw the actuator back in place. Test the butterfly again, it should spring back to the fully open position, use a little force when testing to make sure it does not stick & releases as expected.

The butterfly spindle is located in a needle roller bearing, so you should not have trouble with this sticking in the future. If you do just turn the adjuster bolt in 1/16-1/8th of a turn😁

I hope this helps many people in future keep their TDV6 + SDV6 diesels working as intended & saves them a load of money. This TB in theory has 56k miles on it, but the butterfly plate has a 2021 manufacture date on it which was before I acquired the car.

I assume this is valid for all TDV & SDV6 engines, so Ford, Citroen, LR, Range Rover & Jaguar, plus some others.

 

[Mohawk]

The off centre butterfly is a false positive.

The actuator only closes the butterfly, it returns under spring within the actuator.
When you lift off the "fly-by-wire" throttle under your foot the ECU sends a close message to the TB butterfly actuator to close the butterfly, its pretty instant, whilst also sending an open command to the EGR valve.

So throttle is off/reduced sufficiently to trip EGR activation, but it needs a vacuum to make EGR work, but the Turbo is still spooling down keeping pressure in the inlet, hence the butterfly valve, its there to isolate the intake from turbo feed & allow enough vacuum to develop to suck exhaust gases in from the EGR valve.

A brand new throttle body does NOT seal, as the parts are not made to that tolerance. If you shine a torch in the intake manifold ends, you can see light around most of the butterfly. It binds due to heat & the fact that two plastic parts are hitting each other forcibly many thousands of times at the top & bottom of the butterfly, which wears into the TB body. This positive stop is only stopping the butterfly wearing into the TB, it closes just as much as before, without over rotating once worn.

I'll get the refurbed one back on the car this week for testing.

 

[Mohawk]

Small update. I just refitted the old TB this evening with my throttle stop modification & refitted the TDI Tuning box set to Mode7, which is the max setting. Previously I couldn't even get this TB to work with Mode4 for more than a handful of miles before it would go into limp mode & DTC's would show P0234-77 Turbo Over Boost.

So 16 miles driven with a 30mph 5 minute warm up before testing the throttle, it's definitely a Beast now.
I tried all double digit speeds with multiple hard accelerations & quick lift offs which activates the flapper for EGR vacuum. Tried high speed dual carriageways & some steep hills at lower speeds, both hard acceleration & steady climb & low gear downhill rolls. No issues seen or detected. I checked DTC's & nothing is showing, so all looks good. I'll run it for a week & if nothing untoward appears, I'll call that a fix, leave it on & modify the new one the same, so it should be good for life & I'll always have a spare. 😁👍

 

[Mohawk]

Latest update. Took the car for a few trips up heart break hill, which in the past with the TDI Tuning Box & car on cruise @ my normal speed it would go into limp mode approx 3/4 of the way up. And leave Turbo Over Boost error code. The good news is that code did not appear, but the car did go into limp mode, so stopped off the motorway & checked codes which showed only a P2279-64 Intake Air System Leak.
I left OBD attached & monitored the boost pressure & this was occurring around 30psi manifold pressure, so approx 1bar boost.

This code usually points to a vacuum leak on normally aspirated cars & a boost leak on Super/Turbo charged cars. As the car is under high load on steep hill at speed, this makes sense.

So thinking about the old TB that is now on the car, I noticed that the elbow from the intercooler was much harder to fit over the new TB O-ring, than the old one & the old one had been leaking oil here. I'll switch the O-rings over & try again, plus check the EGR pipe connection is good. I found a thread where a Disco owner had similar issue & it was the big O-ring.

Watch this space, will be a couple of days before I get a chance to test on heartbreak hill again.

 

[Mohawk]

So as I had to travel up heartbreak hill again today & having thought about the last code, which I now suspect was caused by swapping the TB back to the old one & fitting TDI Tuning Box set on mode 7. So I fitted the tuning box Bypass puck, which leaves the harness in place & loops all connections back like stock. Did a 70 mile round trip & no errors codes or issues, including cruise control up heartbreak hill. So the TB butterfly fix works.

A forum member has asked me to do a video, but I'm hopeless at such things, but I will do a detailed step by step for everyone on the new TB.

 

[Mohawk]

Sorry not seen the IL6 engine. I would assume it has a similar setup for EGR if it's turbo/super charged. This TB is used on all versions of the V6D.

 

[Mohawk]

So this is not holding the butterfly open, it’s just providing a positive stop at the fully closed position, like every petrol engined butterfly, rather than letting the butterfly stop by fully contacting the TB body shell & wear into it. So give or take a smidge it stops in the same place & allows Exhaust Gas Recirculation to occur. I’ll keep running mine as is for a few weeks & see if any codes pop up, before I retry the tuning box.

Unfortunately the amount of crap that builds up in the TB is a consequence of the state of the rest of the engine. Worn rings provide blow by during combustion, which increases crankcase oil mist which gets sucked in via the turbo & blown through the intake path & if enough oil mist makes it to the TB & intake manifolds, then it will wet the surfaces such that EGR ingested soot will mix with it to make the sludge that I see in many TB swap videos or LR manifold clean ups. The fuelling is tuned to work on this exhaust gas induction cycle & the MAP confirms EGR is working by the reduced pressure in the intake. If someone had the means to data log the intake & fuelling as stock, it would potentially be possible to block the EGR inlet to the TB & adjust the butterfly stop position such that vacuum remains within permitted parameters & just enough air gets injected rather than exhaust gas, such that the NOx sensor does not detect anything untoward, this may require fuelling tweaks to keep the NOx sensor happy.

This is one reason I’m looking at water/methanol (or ethanol) injection (WME). From what I see from my research WME, has basically no down sides, other than having to refill another tank. If used in a stock engine, then running out just returns it to standard & no worries. Just using distilled water acts a charge cooler & steam cleans the combustion chamber. WM or WE act as charge coolers, knock resistance increasers & the M or E adds a degree of energy to boot, plus it would reduce the EGR mess build up. Methanol is hard to come by in the UK/EU, but Ethanol is easily available &/or you can make your own from E10 petrol, just add 10% water to E10 & the ethanol combines with the water & separates out in the bottom. You just need a bottom drain tap container with a clear wall so you can see the separation level to drain it off. Return the rest of the petrol to your petrol vehicles as pure go go juice.
It also improves mpg by a smidge, reduces soot emissions in diesels, increasing the miles between DPF regenerations & there is anecdotal evidence that it keeps the EGR setup cleaner. I’d probably would just run water injection, it’s not really required in our cold winter periods so no worries about the water freezing so just disable the system in the winter.

 

[Mohawk]

I'm pretty certain the EGR & TB butterfly are on off only. The thing that needs monitoring is how much O2 is available during EG ingestion to match the limited fuel flow & associated burn, which directly leads to the NOx level in the exhaust. To keep the NOx sensor happy, the exhaust content has to be within parameters.

I agree with Cutlea01 that the Ad-Blue/DPF nonsense is just that. But until our society crashes a bit more & MoT emissions testing goes the way of the dodo we are stuck with it ☹ So will do our best to keep them running sweet.

 

[Mohawk]

Please explain why "not possible" ?

 

[Mohawk]

So you are saying your car has passed multiple MoT's complete with emissions tests ? With the EGR disabled ?
I know my previous 4x4 precluded brake tests & driving emissions tests, due to MoT station only having a 2 wheel drive rolling road. So they can't do rolling road brake & emissions testing. Just idle & rpm hold tests in neutral & a test drive for the brakes.

 

[Mohawk]

How did you ascertain this information ?
AFAIK EGR can only work on a closed throttle & as Diesel does not have a throttle they added the butterfly into the intake to create the necessary vacuum.

As to whether the EGR valve in the exhaust takeoff is variable or open/closed I have no knowledge.

 

[Mohawk]

Any more long term updates on this? Going to give this a go at some point.

Well both TB's still work. No issues stock, but have had a few temporary DTC's, still looking into those. But with the tuning box still get the dreaded Turbo over boost condition.

I refitted the new TB modified with the adjustable stop & did 250 miles combined driving then took it up the hill that always causes it & bam restricted performance ☹

Done some more research & the issue may be related to a sticky actuator which I intend to look at this weekend

I have modified the new TB to have the stop & took a load of pics, so will do a write up on that soon. Sorry silly busy ☹

 

[Mohawk]

No confusion re the butterfly's purpose. Any old school diesels I have worked on never had one, as to kill a diesel you just shut off the fuel & the engine winds downs nicely. No chains to worry about on most modern engines.

I assumed the actuator was on/off like a solenoid due to the spring return. Why you would use a PWM strain motor instead of a stepper motor is beyond me, possibly for its instant open capability as stepper motor would be slower. Again the whole Euro6 Diesel config is just a fudge & achieves nothing in real terms.

I thought the new SDV6 only uses a low pressure EGR & the takeoff is after the DPF, supposedly to reduce soot ingestion, but does not appear to work well, so I'm working on an EGR gas flow filter idea to capture most of the soot. Apparently the manufacturers know that the soot ingestion kills the engine, why both filtering intake air then allowing hard carbon particles straight in from the exhaust ? Research shows that 5-20um are the worst & that is a lot of the soot that gets ingested!🤷‍♀️ They knew it would be a problem, but decided NOT to add a fine particle filter to the EGR gas circuit, because it would require regular maintenance, by that they mean owner accessible so it can be emptied & reverse flushed. So I'm working an idea for one of these.