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alexp999

Car Bit Weird After Long Trip, Just Dpf Regen?

5 posts in this topic

Just got back from a 3.5 hr journey from Cornwall to Dorset, about 170 miles and as I was going round the roads leading up to my house it sounded like the fan was on.

I pulled up to our gate and as I got out, the fan must have been on full blast, I could literally feel a strong draught sucking through to the radiator. The temperature reading on the dash was normal, the needle right in the middle.

The fan on its own wouldn't have particularly bothered me as I had been driving pretty hard on the way back, but then I noticed the exhaust sounded odd, I put my hand behind the exhaust and it felt like the engine was misfiring, with big pops of air, almost spluttering.

After about 10-20s of idle it stopped. Exhaust pressure was perfectly smooth and fan turned off completely.

I have heard of the fan running during a regen, although the car seemed to wait a long while into the journey to do it, but not the spluttering exhaust. I guess if it is that, the car must be somehow creating extra pops of pressure to try and clear the dpf, but I don't want to just assume that is the case.

Any thoughts?

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Sounds quite likely that you had a DPF regen in my opinion. I cant think of anything else it would be!

Leaving it till the end of the journey, I have a feeling that the car was doing the regen for a while, it does actively regen as long as the conditions are right (temperature etc) and also the breathing ability of the exhaust is not at the level it should be.

The popping I believe is as you say is using pressure to fluctuate the conditions in the exhaust and to help push the cack out.

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Sounds quite likely that you had a DPF regen in my opinion. I cant think of anything else it would be!

That's what I thought too, but never heard of the exhaust "popping" before, even though it seems quite clever.

Was amazed at just how much air the fan can shift too :o

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Indeed, the fan shift is a large part of it, it runs at full whack during a regen as the temperatures in the exhaust get so high, it needs to keep the engine cool enough though to prevent it overheating.

The popping is a reaction based on slightly more fuel in the combustion and a fluctuation in it to increase and decrease the amount of air in the combustion cycle as far as I know. so one minute it kind of starves the cycle of air (this can put a bit more diesel in the exhaust just to encourage the clean burning of the DPF contents) and then the next will have more air in it, so that a clear burn can be done. During this cycle it can also increase the amount of fuel pushed in, along with the EGR valve to increase the exhaust gas temperature. this as the pressure increases in the exhaust pipe, can cause a little pop as the diesel in the exhaust is put under pressure between the incoming exhaust gas and the DPF filter itself. I believe that much to the similarity of the combustion cycle, the pressure is used along with the fuel in order to create the explosion which pops in the DPF and helps to shake its cack loose.

I am no expert in these things, but that is how I understand the general premise to work.

alexp999 likes this

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If it happens again, especialy on a short jouney, start keeping an eye on your MPG. If that starts reducing it could a sign your dpf is not clearing all the soot away properly. Random cutting out of the engine is also a sign of trouble ahead?

Check your oil level regularly too. If over maximum on the dipstick get it changed.

What year and engine size have you got?

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