Peugeot 308 CC - Falling apart now?

Unread post by **xantia_v6** » 17 Mar 2017, 01:00

I replaced the boost control valve today. It is not nearly as difficult as I had feared.

The exhaust pipe under the engine needs to be removed for access, but I didn't need to remove anything else.

I am not sure that it has fixed all the problems, I took the car for a test drive, and it still seems to surge a bit on acceleration, and it threw a P1385 super knock error code. Other than that it is driving really nicely.

I will attempt to watch the live data as someone else drives the car uphill, as we should be able to keep the throttle stead long enough to geet some readings while the surging is happening.

Unread post by **RichardW** » 17 Mar 2017, 08:50

You can get Diagbox to graph the live data....

Unread post by **xantia_v6** » 25 Mar 2017, 03:50

As an intermission from the engine faults, we are on a weekend break in Queenstown, about 500 km south of home.

: Crown Range Road, Lake Wakitipu in background

We are lucky that a relative has lent us their house for the weekend.

: Lake Wakitpu from our lounge

I wish i had a dashcam for the Crown Range Road, it is the sort of alpine road that you see on car shows with lots of helicopter shots.

Unread post by **CitroJim** » 25 Mar 2017, 07:11

Gosh, that's a gorgeous place to be Mike... Just lovely

Do enjoy!

demag · Unread post by **demag** » 25 Mar 2017, 09:30

My aunty and uncle lived that way from the 50's to the 90's.

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Unread post by **xantia_v6** » 27 Mar 2017, 08:26

Back home now, for those who are interested, we covered 1400 km, at an average speed of 73 km/h (the speed limit out of town is 100 km/h). The average consumption was 7.2 l/100km, which is about 39 MPG.

I am still not 100% happy with the way that it is running when on-boost, but have a few more ideas to try.

Unread post by **CitroJim** » 27 Mar 2017, 10:01

Great economy Mike!

Unread post by **elma** » 27 Mar 2017, 10:15

Yes, I'm surprised you are doing that well with a turbo.

Unread post by **xantia_v6** » 19 Apr 2017, 08:16

Now where were we?

xantia_v6 wrote:I replaced the boost control valve today. It is not nearly as difficult as I had feared.

The exhaust pipe under the engine needs to be removed for access, but I didn't need to remove anything else.

I am not sure that it has fixed all the problems, I took the car for a test drive, and it still seems to surge a bit on acceleration, and it threw a P1385 super knock error code. Other than that it is driving really nicely.

I will attempt to watch the live data as someone else drives the car uphill, as we should be able to keep the throttle stead long enough to geet some readings while the surging is happening.

RichardW wrote:You can get Diagbox to graph the live data....

The live data recording takes a snapshot every 7 seconds, which is not much help when the issue only exists for about a second at a time.

The car usually drives fine, but sometimes when accelerating you get much more or much less acceleration than expected from the right foot pressure applied. About once a fortnight, while accelerating hard it throws an over-boost error code. I assume that this is not a common problem with these engines, so is likely to be a sensor or actuator issue.

Looking at the live data, particularly when flooring the accelerator with the transmission in D, stationary, with the brakes on, I note that the indicated boost pressure lags the other live readings by about a second and does take fairly wild excursions. Having no other car to compare, I don't know if this is normal.

Assuming that the lag in boost pressure (both going up and coming down) is not normal, then I can only think of it being a faulty (slow) boost pressure sensor, or a sticky waste-gate valve.

Unread post by **xantia_v6** » 19 Apr 2017, 09:53

I have just read on a French forum that the fault code I am seeing can be caused by a pinched vacuum hose between the boost control solenoid and the waste-gate actuator. This makes sense, and would explain the delayed boost that I am seeing. Unfortunately it is not easy to see most of the length of the hose, nor to get at the end where it goes onto the solenoid... but worth further investigation.

Unread post by **xantia_v6** » 20 Apr 2017, 04:51

I removed all the stuff that is in the way of inspecting the hose from the boost control valve to the actuator (and there is quite a lot to remove), but inspection showed that the hose was not kinked, and sucking on it indicated that there is no restriction (although with the valve on the other end it is not a conclusive test.

I then need to find an alternate theory, and I think that I have nailed it (although it seems to be an unbelievably stupid design error).

The boost control valve has 3 ports, one to the (brake) vacuum pump, one to the waste-gate actuator and one that vents to atmosphere. On BMW cars with this engine, the atmospheric port has a clip-on filter to stop dust being sucked into the valve. PSA decided that improvement was needed, and run a hose up the back of the engine with a (different design of) filter situated just behind the cam cover.

The problem is the design of the filter. it is a rubber tube with a small cylinder of foam inside. Over the opne end is a rubber cap that is (apparently) a loose fit so that air enters some small cutouts at he end of the cap, then finds its way between the 2 rubber parts and then through the foam element.

On mine, the cap is a snug fit, and makes the whole assembly quite restrictive of the flow of air (the element itself has much less restriction). I refitted the filter without the rubber cap, and took the car for a test drive, and I am fairly confident that the problem has been solved. Acceleration is now gernerally much smoother and more closely coupled to accelerator movement, and I was unable to provoke and over-boost fault (previously it was not very hard to provoke). All in all, the car has never been nicer to drive.

Filter unit assembled, note the 4 tiny air gaps between the body and the cap.

Cap removed

Unread post by **CitroJim** » 20 Apr 2017, 09:45

Good result Mike

Let's hope it really is nailed now...

Unread post by **xantia_v6** » 20 Apr 2017, 21:03

Having driven the car (with spirit) a couple more times, it is still behaving itself.

Now for the simple explanation of the fault...

When the car is in first gear and accelerating from rest at full throttle, initially the ECU holds the waste-gate closed to spool up the turbo and build some boots pressure, but in first gear, the engine RPM, the turbine RPM and boost pressure all rise rapidly, and by about 3000 RPM, the boost pressure has reached the target value, and ECU instructs the boost controller to start opening the waste-gate to prevent over-boost. In this design, the waste-gate is opened by reducing the the vacuum at the waste-gate actuator, which means sucking some air in through the little vent filter. Because the filter (with cap fitted) is too restrictive, the vacuum can't drop immediately, the wastegate remains closed for half a second more than intended, the boots pressure has continued to climb, and the over-boost fault is triggered.

Now for the more complicated explanation...

Although the above is a reasonable explanation of the fault codes, it does not really address the drive-ability issues, particularly why sometimes, the engine would feel quite sluggish with noticeable turbo-lag.
I think that the answer lies in the cleverness of the ECU. In this design, it appears that to get good drive-ability and fuel economy, the ECU controls the boost pressure quite tightly, so that there is only just enough boost generated for the current driving conditions. The control path from the ECU to boost pressure is however highly non-linear, and must vary quite a bit from car to car, involving the boost control valve, the waste-gate actuator, the actuator spring and the characteristics of the waste-gate valve itself.
So it is fairly obvious that the ECU must have a learning algorithm to calibrate the waste-gate valve, so that it knows how to get a required amount of opening.
With the restriction on the vacuum dump path, the delay in opening the waste-gate will be misinterpreted by the learning algorithm as being a static calibration error, so the ECU will learn to leave the waste-gate more open than it should, resulting in under-boost, and the poor performance at mid throttle. The delayed response and mis-calibration would also cause the boost control loop to become marginally unstable, resulting in the occasional, rather uneven, almost jerky acceleration at mid-throttle.

There is the little blighter in position. The photo is rotated, up is on the right hand side. The photo was taken with the camera up against the side or the brake fluid reservoir

demag · Unread post by **demag** » 22 Apr 2017, 00:29

Would it not be possible to relocate it?

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Unread post by **xantia_v6** » 22 Apr 2017, 01:53

The location isn't the problem. You can actually get to it with your fingertips without removing anything else once you know where it is.

The problem is the filter itself. Maybe the rubber cap shrinks with age, but it is not a good design

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