307 SW 2.0 Hdi RHR turbo not blowing - FIXED !

[tmead]

For those of short attention span - turbo actuation fault diagnosis on the Hdi is loads easier with a vacuum gauge. 30 quid well spent!

The turbo stopped blowing, which dropped the engine to what felt like 60 Hp! I only had one error message over the course of a week of driving, something about low turbo pressure on Pug Planet. no lights or bings apart from that, just very low power. Dire thoughts about dead turbos and the shivers down my spine of trying to access the turbo at the back of the engine.....

I've previously had an issue with vacuum pipes coming loose, so ran through checking those thoroughly, making sure they were all plugged in firmly and no obvious leaks.

The mildly ridiculous siting of valves, with two down by the AC compressor on the front of the engine and one on the back of the cam cover makes any checking interesting - and the lack of visibility of the turbo means its difficult to see if the actuator is asking for the turbo to blow or not!

Before I bit the bullet and invested in a recon turbo, I thought I needed to be sure. I swapped a couple of vacuum valves over (turbo valve on rear for one of the valves down front) and there was no change. Not a particularly rigorous check I know, but desperation was setting in.

Last try before condemning the turbo was to spend 30 quid on a vac tool from Sealey. Delivered very promptly from Demon tweaks - nice service there! Shame it doesn't come with a particularly helpful set of adapters, and the four sections of pipe are all the same diameter,
which is too big for the vac connections. The simple check of sucking on each of the two vac pipes from the vac pump in turn showed one that held vacuum and one that didn't. Tracing though the pipes led to the uppermost valve by the AC compressor. Popping the pipes and sticking my finger over the ends held vacuum - getting closer ! Putting the pipe to the pump back on and putting my finger over the other valve connection didn't hold vacuum. Within 10 minutes the leaking valve was identified. Turns out that the vacuum pipe from the pump supplies a valve that actuates a flap in the doser to close the intercooler bypass or open the intercooler flow, and also the turbo actuator. The valve down the front by the AC pump controls the doser flap, and was leaking, meaning no vacuum for the turbo.
Simply pushing a clean bolt into the end of the pipe to the pump gave me the turbo back ! Yeah - we're in business again. Its now been treated to a replacement from ebay, and is running better than it has for months - not sure if that valve hadn't been opening/closing the doser flap properly before it failed and leaked, but its all good now!

I've now ripped the valve open and cant find any particular reason why it was letting air into the vacuum line. Nothing obvious at all jammed or damaged/worn. Time to thrown that one a long way away.
There is a message for anyone that reads a post somewhere on the web about the holes from the vac pump manifold that feed the pipes being too small, and opening them up with a drill. If I'd done that it is likely that the leak would have dropped vacuum from all circuits, and potentially even the brake servo too - the holes are small to restrict the amount of air that can bleed in even from a catastrophic leak and make sure the brakes always work !

The moral yet again is to diagnose properly. Pug Planet may not be able to give the answers, and its not always the most expensive thing you can think of ! I now have a vacuum gauge in the Cambridge area, and would be happy to loan it or help out with diagnosis locally.

[EDC5]

That's really interesting, I am curious about the really odd looking 'double doser' that some RHR engines have like yours:



My C5 also has the RHR engine but a single doser without the inter cooler bypass for some reason.

So was it the case that both of your doser valves were stuck shut with the loss of vacuum and by default the dosers spring shut?

[tmead]

Don't think so EDC5. I'd need to take a look, but its a couple of years since i changed the doser assembly, and I believe one is sprung open and one sprung closed from memory. Makes sense really as a default behaviour, and I suspect the sprung open one is the bypass ? Back then I changed the doser unit as the actuator on the flap had died, and the flap was 'flapping' free, causing pretty crap mpg. IIRC the vac actuator pulls on a rack which turns a pinion on the flap shaft.

This time, the failed valve obviously was not driving the doser flap to where it needed to go, but the mpg was fine and the car drove normally at low revs. From that, I guess that the failed valve would have been used to pull the bypass flap shut against the spring, and without the valve doing that, some air whistled up the bypass uncooled. I'll try to find time at the w/e to double check which valve is connected to which flap.

The only reason I can think of for having the bypass is to get the engine up to temperature more quickly, or maybe for operation in regions where it is seriously cold outside. As part of my investigation I looked up pretty much all of the secondhand rhr kit on ebay, and some ford tdci stuff. I was surprised to see some vac pipes that only had one vac connection up the the doser, and servicebox seemed to indicate a single flap version for some models. Interestingly the single flap version seemed to have the same number of valves on servicebox ?

[EDC5]

That's very interesting, I bought a spare Doser (single port) for my C5 and cleaned it up checking that everything was working, I then swapped it with the one that was on my car... Good job I did too as it was filthy, lots of tar like crud around the manifold air temp sensor, but especially opposite the EGR inlet pipe . I haven't noticed any improvement in performance by changing it with a clean one however.

Just a note, the butterfly valve is actuated by a vacuum diaphragm, but is this a 'All or nothing' type setup? or can the vacuum be varied to partially open the throttle? Same question for the variable geometry turbo that is vacuum controlled... can it be varied or is it just on or off?

From what I gather, the secondary bypass doser was used on some RHR engines (but not all) to bypass the intercooler for DPF regen.



This video explains the dual doser thing.

[tmead]

Just checked the unit I took off a while ago. The intercooler flap is sprung open and could be closed by an actuator. The bypass route flap is sprung closed and weighted at the bottom too.

Neither offers any feedback, so these are either open or closed devices, no partial settings.

Many parts look common between the two actuators, but the rack that turns the pinion on the damaged bypass flap shaft is missing some teeth, so not driving properly, allowing the bypass flap to float free and jam the rack.

Tim

[EDC5]

okay I see. Can you suggest a reason why the RHR engine without the intercooler bypass would need a completely closing throttle if it could be only fully open or closed? what circumstances would the ECU decide to fully close the throttle?

If the flap could be half closed then perhaps it could be used to force more EGR gas into the engine? but that's just speculation.

[tmead]

There was a suggestion a while back that it would close to shut off a runaway ?