Intercooler bypass valve

[Piwoslaw]

I found this on a Citoën C4 forum:



It is called an air doser or officially "Butterfly double air metering device". It measures the temperature and pressure of the air coming from the turbo and decides whether it should go through the intercooler or bypass it. I believe it also has a heating element to preheat the air on a cold start.

Here's a picture I found of what it looks like installed:



EDIT: For comparison, here's a picture of my set-up:



I tried U-ing the rubber plumbing to bypass the IC, but it's too tight for that, so no luck Fooling around with the plastic stuff won't be easy since it's stiff and has sensors in it, and very expensive to replace. So I'll keep an eye open for the whole "butterfly etc." set-up. If I find it cheap in a junk yard, then I'll see if I can do a switch-a-roo.

[Piwoslaw]

It's hard to find any info on exactly when and how this works, but here are a few more scraps.

• Supposedly this valve can partially block the intake to allow more EGR into the engine.
• The valve closes the intercooler when the diesel particulate filter needs to be burned out. Allowing warmer air into the engine helps raise the exhaust gas temperatures.

[Arragonis]

Could you disconnect the two ends of the flexible rubber hoses and substitute a flexible hose from something else, e.g. some hoses used for dynos as per here ?

Exhaust and Emission Other Exhaust and Emission System Parts Compare Auto parts Price Buy Auto Parts 1 on Just Parts

or parts nornally used for those induction kits. Although it would have to stand the pressure from the turbo.

My thought is that even if the radius of the U-bend would be quite long it would probably sit down below that part arrowed. This would be permanent though.

It would be interesting to see the results. My IC is in the front, right wheelarch and fed air from around the foglight in the bumper. I think I may try blocking the intake and see what happens.

A '5 minute speed shop' tuning method on the old XUDT was to turn up the fuel pump to get more power - adjust until you get smoke and then turn it back a little. When people tried it on the early HDis (306s) the engine, or perhaps the turbo and then the engine, would occasionally go bang. However I wonder about turning it down. You get less power obviously but it would use less fuel too.

[ShadeTreeMech]

I would be suprised if his diesel had an injection pump that you could adjust. Looks like it may be a commonrail injection which would be controlled by the computer. Not adjustable without some sort of computer.

I'd block off the intercooler to simply see if it does anything for your economy first before you possibly cock up a good car.

In consideration of the two engines seeming to be identical, woudln't simply getting the right parts be the best route? Might have to just change out the ECU and put in the wiring once you get the valve.

To be quite honest, I would put doubts on this helping economy at all. You would be warming up the air a fair bit, but simply staying away from the go pedal would accomplish the same goal. What's the listed economy figures for the 2 vehicles? I somehow think the newer one may be less efficient.

[Piwoslaw]

Arragonis - I looked around for longer tubes but couldn't find anything locally, and since this is supposed to only be a test I don't want to invest too much unless I know it would help. The best bet is to remove all of that ductwork that goes from the turbine forward to the IC, then back to the manifold, and replace it with a straight tube. But the only tubes the local shops have are paper, which just won't work for warm, pressurized air. The pressure between the turbo and intake manifold goes up to 2-4 atm (30-60psi), if I remember correctly. I read that even the OEM tubes (rubber with metal reinforcing ribs) tend to bulge when revving.

ShadeTree - Yes, it's a commonrail, electronic everything I'm not ready to re-map the ECU yet, though it has crossed my mind.

Originally Posted by ShadeTreeMech

I'd block off the intercooler to simply see if it does anything for your economy first before you possibly cock up a good car.

It's already mostly covered by the grille block, which has an operable opening for the IC. I open it only when the engine gets too hot. The blocking helps keep the air warm, but the bypass would reduce the drop in boost by shortening the distance from turbine to manifold. The idea was to control both the IC valve and the IC grille block with one switch, ie the IC would be blocked whenever it was being bypassed. Later it would get automated to open whenever the engine is under load (an IC supposedly increases low end torque - good for pulsing).
I totally agree about mods being reversible, that's why I'd have to transplant the whole intake plumbing. I found the butterfly device thingy for the equivalent of US$80, but the rest of the plumbing and wiring would cost more than that I doubt this would be worth it, especially if I get a block heater. But I'll snoop around, maybe I'll find the whole shebang at a reasonable price.

Originally Posted by ShadeTreeMech

What's the listed economy figures for the 2 vehicles? I somehow think the newer one may be less efficient.

The new version officially gets about 10% better fe. This may be b/c of better aerodynamics (Cd=0.30 instead of 0.33) and low rr tires. But it also has a FAP particulate filter, which increases fuel consumption since the filter must be occasionally burned out by higher exhast gas temperatures. I'm willing to bet that official fe tests are done with a clean filter. Ollie (vtec-e) test drove a Peugeot 308 with the newer 1.6 HDi engine version. Check out I booked a test drive in something special and his photo album.

[ConnClark]

I saw a link to this thread and decided to check it out and chime in with my two bits.

In some cases an intercooler bypass is helpful such as quicker warm up time or trap ox regen. But other than that the only time its helpful is when the boost drop across the intercooler causes less air to be packed into the cylinder than the charge cooling achieves.

Also I would like to add that an intercooler does play a role in improving efficiency. It reduces peak combustion gas temperatures which reduces heat lost to the cooling system.

I don't know about other peoples diesels but on the highway my car generates about 5 to 7 PSI of boost. That raises the air temp about 40 degrees C. More than enough to benefit from an intercooler.

[EdKiefer]

This looks like a more advanced ,electronically controlled bypass value found on gas turbo cars .

The idea here is at low loads bypass intercooler and/or turbo so turbo response is better at low throttle conditions, it also helps in boost conditions by bypassing the butterfly (reducing pressure build up at throttle are rerouting to intake of turbo .
The difference here with TDI is there no routing the bypass to turbo and able to control more volume than types used in gas .
My guess is at low loads they bypass intercooler trying to keep temps high, then under boost phase in the intercooler to lower temps .
With gas turbos the intakes go to like 250F and then intercoolers bring it down to the 130F range (of course this depends on boost amount and intercooler size (there generally around 70% efficiency ))

[Piwoslaw]

Found more onfo on how the air doser works:

The airflow can be restricted in two places: one ("warm air doser", WAD) is between the 'to' and 'from' intercooler stretches, this is normally closed, forcing air through the IC. Second ("cold air doser", CAD) is on the exit from the IC, this is normally open.

When starting a cold engine, the WAD opens to allow warmer air into the engine. Once the temperature rises, WAD closes, directing air to the intercooler.

During normal operation, when exhaust gasses are recirculated into the engine, the WAD is closed and the CAD is partially closed, restricting the amount of air that goes to the manifold (also, the variable turbine pumps less air, I'm guessing). This reduction of air pressure in the intake allows more EGR to enter the cylinder.

When the diesel particulate filter needs to be burned out, the WAD opens again, helping to raise exhaust temperature.

I read that in early TDI's a similar set-up would close both valves when shutting the engine off. Supposedly, blocking the airflow was safer than having a rush of high pressure air hit the suddenly stopped engine. Maybe this is still the case in newer versions of the TDI, and the HDi.