Technical Guess the problem...

[DoIDon'tI]

One for you long-distance fault diagnosis people. Here's the story; I went to see Keithglos the other day to pick up some wheels, it's about 175 miles so it was nice to remember how well 2.4 Cromas handle motorways. Well it was, until I realised on the M5 that I seemed to be using a large amount of accelerator pedal travel to keep with the traffic.

My immediate thought was that the DPF was perhaps getting clogged, so as I was leaving the motorway I gave it some hoof and the car suddenly lost power, accompanied by the 'check engine' light and warning. I was near Keith's house so carried on but struggled a bit up the hills as the car had gone into 'limp home' mode. At this point the DPF was also trying to regenerate as I was getting the customary 'rumble' from the rear silencer.

Got the wheels and had a very pleasant cup of coffee and shortbread biccie from Keith, who is a gentleman and perfect host. On the way back I was still toying with the idea of the DPF being clogged so tried using some revs but the car wasn't really very happy. Got back on the motorway but decided it was too dangerous to continue (due to lack of power and throttle response - limp home means just that).

When the recovery van arrived the code given by the car was P0238 - Turbocharger Boost Sensor A Circuit High. When it was reset it would come back on again once the car was revved. Cue a 150-mile journey with some new company to talk to.

I've since fixed the car, but I'd like to hear what everyone thinks it was...

 

[keithglos]

Hi L, Sorry to hear you couldn't make it home, must have made it a long day. I think EGR stuck open, or MAF/MAP sensor, but first check the air filter.
How's that for a permutation?
Call in for coffee any time.
Keith

 

[Doofer]

A carrier bag stuck over the front grille.

 

[s130]

A carrier bag stuck over the front grille.

I was going to suggest a cat stuck up the exhaust pipe or rodent in the intake system. Failing that a

"Driver Error"

Notice how I duck and run fast into the "Not Me Me Lord" defense mode.

Are you sure it was the plastic bag and not that oil rag you left under the bonnet.

 

[keithglos]

Blocked the intercooler? Plus high summer air temperature?

You'll get a DPF regen now.

 

[DoIDon'tI]

Some good efforts there but Keith was closest, no prizes I'm afraid. The boost controller is connected to the (metal) sensing line by a short length of small diameter rubber pipe, this had split at the end and fallen off so the boost controller told the turbo to stop blowing. The car then became a normally aspirated 2.4 diesel with a restriction in the exhaust, hence the struggling on the motorway.

With the turbo inactive, the car was running inefficiently i.e. producing lots of smoke (before the DPF, obviously) hence the DPF regeneration. When I gave it some hoof the large amount of smoke completely clogged the MAP sensor, which then put the light on and sent the car into 'limp home' mode.

After removing the split portion of pipe (there was plenty of spare pipe) and cleaning out the MAP sensor my car now feels amazingly fast - compared to how it did on the motorway, anyway

Nice to know not all Croma problems are expensive or involve electronics!

 

[s130]

When I gave it some hoof the large amount of smoke completely clogged the MAP sensor, which then put the light on and sent the car into 'limp home' mode.

After removing the split portion of pipe (there was plenty of spare pipe) and cleaning out the MAP sensor my car now feels amazingly fast - compared to how it did on the motorway, anyway

MAP = manifold absolute pressure ?

I've never had to remove or replace one of these. When you say "cleaning out" the sensor how did you do this? I would have thought the sensor was a blind chamber and thus with no large net amounts of air flowing into the sensor it would be difficult for it to get clogged.

Waiting to learn more.

 

[DoIDon'tI]

Hello again Nick, correct on the acronym. It's not a blind chamber, the sensor has a small 'cage' around it which was crammed full of soft carbon. Gentle application of an electrician's screwdriver on the gaps in the cage to loosen things up followed by application of compressed air was sufficient. Very easy to remove and refit - just one bolt on the rear of the inlet manifold, and access is easy too.

The next time I change my cambelt I will remove and clean the inlet manifold, having seen the state of the sensor I reckon there must be a good layer of carbon in there. It's not as much of a problem as some folks think, due to the turbo pressurising everything on the way through - if it was a normally aspirated engine I don't think you'd get away with it quite so easily.

Anyway, hope that clarifies things...

 

[s130]

Thanks DoIDon'tI

No doubt I will have to go there at some time in the future.

On a funny take I always read your title DoIDon'tI as Don'tDoIt which always make me smile.