Partially block Catalyst specifically a 90 but also interested in 75 experience????

T

TAABVW

A2OC Donor
Does anyone have experience of a partially blocked oxidation cat on a tdi.

I have several TDI90's.

One of them just makes more noise over 3000rpm and the economy is 45 - 50mpg. The other identical cars all produce a bit more power over 3000rpm (but not a lot) and their economy for similar driving is around 60 - 65mpg.

All cars are serviced well. No sticking handbrakes.

In an effort to improve the economy I have refurbed turbo, new air filter, swapped air mass meters (from other cars), swapped EGR valves and cleaned out intake.

She runs sweetly but just feels a bit strangled.

I was wondering if it could be the oxidation catalyst being partially blocked. Any Idea's how this could be checked or diagnosed? I could swap the cat with another car but that would involve cutting the back box off both cars and I'd rather get some wisdom here first.

I've read on here people getting highly variable economies from their TDI and wonder whether this could be the answer.

Any thoughts / Ideas?

Trevor
 
What are the injectors like?

On my project car getting those refurbished and rebalanced when they were fitted according to the manual made a huge difference to smoothness, absence of random revving on startups and overall fuel economy increased around 10mpg.


Secondly though, what about sticky vanes in the 90 turbo? That could impinge both on economy and rev-dependent power output / delivery.

Finally, what condition is the fuel filter in on that particular car?
 
Thanks for response and thoughts. Confident it's not the vanes on the turbo as it's recently been refurbished and performs as it should. I've checked boost levels etc.

Injectors is a fair shout. If the spray pattern was bad due to wear (160k miles), would I not expect other symptoms like poor emission/smokey exhaust.

The emission on the last mot were very good and other than initial start I never see any smoke even at higher revs.
 
When was fuel filter last changed? Maybe injector wiring or coolant temp sensor but I am not really convinced
 
My suggestion would be to find someone with a rolling road who knows diesels - they’d be able to measure what it’s putting out and advise further.
 
Howey said:
When was fuel filter last changed? Maybe injector wiring or coolant temp sensor but I am not really convinced
Click to expand...
Thanks for suggestions as it's ideas from a different brain that I need. However: Fuel filter new. I would expect dodgy injector wiring to cause misfires and fault codes, neither of which it has. Coolant gets up to temp and all reads correct.
 
The injector idea is one I hadn't really considered and I think I have to test that before cutting exhausts up and swapping around. I can rule out / confirm by swapping injectors from a good economy car. I guess I'd need to get new seals or can I get away with reuse if I'm careful? I'm a bit worried about new cheap seals from china no being the correct rubber.

Interestingly (as I suspected) nobody seems to have ever discovered a partially blocked cat as a reason for poor TDI economy. I'm not surprised as changing the cat is expensive or impossible as it seems they are not available. Also you would have to cut off the back box (and fashion a new connector) it seems to get the exhaust over the rear torsion bar.

My brother in law once broke down on the motorway and had to get recovered (A4 AFN TDI). It turned out his cat was so badly blocked it stopped the car....so it can happen. It would be fair to say there is something wrong with the engine if the cat is blocking up since most diesels do very high mileages without cat issues. However it could be a small oil leak from a turbo (which has since been refurbed) that went unnoticed for a while.
 
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