Audi A5 2.0tdi 2010 B8 poor fuel consumption, misfire and knocking when cold start

4661 Views 3 Replies 4 Participants Last post by madonnajess, Oct 10, 2021

Rocheyno1

Discussion Starter · Dec 18, 2020

Hi. Im brand new to this. I try and use previous posts to find out my problems so thought id give it a try and see if anybody can help 🙏

So, issues i have is the car sometimes has a slight misfire on tick over. Its not major and doesnt seem to be present when driving and only at tickover. Also since the winter has come my fuel consumption has dropped massively. Im only doing short journeys at the moment due to working from home but its down to around 30mpg and only getting around 90 miles to £20. I know diesels do drop a bit when its cold but i was getting more like 160 miles to £20 before so massive drop. Ive also noticed a knocking noise when starting on a cold morning. It only seems to be when its under 4 degrees and it goes away after a few seconds.

if anybody has suggestion where i should start that would be great.

Its just had full service with new oil, air and fuel filter just to rule any of them out.

Thanks

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moonmileage

· #2 · Dec 29, 2020

Hey, have you taken a look at your timing belt (visually check tension) and with a mirror can you get eyes on the tensior? (Should have a indicator point which will tell you if it’s hard/soft)

The reason I suggestion is, I recently experienced a rough idle, reduced power, poor start then crank with no start

Checking my book about Diesel engines, I realised the early warning signs I missed pointed to timing belt which right enough, on checking has lost tension.

Poor fuel consumption, misfire and knocking could be early warning of timing belt losing tension. A visual inspection (depending on the engine) should be fairly straight forward and free.

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Schod

· #3 · Jan 20, 2021

Rocheyno1 said:
Hi. Im brand new to this. I try and use previous posts to find out my problems so thought id give it a try and see if anybody can help 🙏

So, issues i have is the car sometimes has a slight misfire on tick over. Its not major and doesnt seem to be present when driving and only at tickover. Also since the winter has come my fuel consumption has dropped massively. Im only doing short journeys at the moment due to working from home but its down to around 30mpg and only getting around 90 miles to £20. I know diesels do drop a bit when its cold but i was getting more like 160 miles to £20 before so massive drop. Ive also noticed a knocking noise when starting on a cold morning. It only seems to be when its under 4 degrees and it goes away after a few seconds.

if anybody has suggestion where i should start that would be great.

Its just had full service with new oil, air and fuel filter just to rule any of them out.

Thanks

Better if you show which engine you have.
Missfire - disconnect /reconnect the injector connectors apply WD 40 to the contacts.
Check all earth points are good.
Fuel consumption - injection is controlled by an ECU check the sensors for the engine management.
Timing belt tensioner pulleys seize and the belts wear - a bit out of time or the belts jump - big damage..
Most diesels now have glow plugs which are activated when the ambient temp is below 5C.
The knocking or is it tapping could be a bit of pre ignition / excessive fuel or and the hydraulic tappets not getting any oil?
Some diesels are very nutty - knocky until they warm up. Some diesels are nutty when warmed up.
Knocking is usually associated with mains and small ends.

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madonnajess

· #4 · Oct 10, 2021

moonmileage said:
Hey, have you taken a look at your timing belt (visually check tension) and with a mirror can you get eyes on the tensior? (Should have a indicator point which will tell you if it’s hard/soft)

The reason I suggestion is, I recently experienced a rough idle, reduced power, poor start then crank with no start

Checking my book about Diesel engines, I realised the early warning signs I missed pointed to timing belt which right enough, on checking has lost tension.

Poor fuel consumption, misfire and knocking could be early warning of timing belt losing tension. A visual inspection (depending on the engine) should be fairly straight forward and free.

I really liked these suggestions

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