Random misfire / P0401 EGR Insufficient Flow

[jaxabin]

Hi

I've had this issue for about 6 months or more, all 8 spark plugs were replaced in May last year.

I've taken out the EGR valve and cleaned it with carb cleaner, twice, and it makes the car run a lot better but still MIL light keeps coming back, after like 10 miles each time

Whenever I clear the code, the car idles perfectly and runs perfectly, but then the P0401 code comes back and then its back to rough idle again. I usually clear with ODB2 device, but I also tried by removing the 15A engine fuses and waiting. The misfire is very rare, it was the only error last year and the replacement 8 spark plugs did seem to fix that but the engine light has been on since then, it fixed it for a bit but came back

I've ordered a new EGR valve and gasket coming. I dont think it had a gasket when I cleaned it? Also put contact cleaner on the contacts of both the valve and the wire

Also may be slightly unrelated but I had the exhaust replaced about 2 years ago because the backbox fell off (sounded like a boy racer), I heard that the code could be because of a leak in the exhaust pipe? I don't know how to investigate because I can't lift the car

Any recommendations on what to do? I cleared the code and it passed its MOT easily so maybe I'll jsut keep doing that and just keep the light on and ignore it

[CRC]

My understanding of the egr valve is that it's an analogue valve (the valve can modulate and is not just a straight "on / off" valve) with an analogue position sensor to tell the ECU that the valve has actually moved to the requested position.

The purpose of the egr valve is to allow exhaust gas to mix with intake air under certain load and speed conditions as determined by the ECU.

By doing this, it effectively reduces the oxygen content of the air and reduces the temperature of combustion which then apparently reduces the formation of NOx gases in the exhaust.

The valve should be fully closed at tickover and only open at much higher rpm and load conditions.

If the valve is sticking open at tickover, this would give a lumpy tickover as the engine is now breathing it's own exhaust.

I can't really see why clearing the code would improve the tickover, unless the ECU controls the egr valve  differently when it has logged a fault?

Not sure about the effect of the back box, though the engine never seems as powerful when the exhaust has a gaping hole downstream of the cat, perhaps because of back pressure effects or perhaps because you are consciously restricting it because of the noise ?

[jaxabin]

I think I’m going to try taking out the intake manifold this weekend if the weather is good and cleaning that. I saw another post where someone took it off and it fixed it so let’s see, fingers crossed

Yeah it’s really strange how whenever I clear the code the engine seems fine for a while but it doesn’t last long. It’s always a P0401 code so will try taking off the intake manifold first before trying anything else

[CRC]

I think I'd hold fire on the inlet manifold and see if your new egr valve and gasket makes a difference?

The Haynes manual shows an egr plate within the intake manifold, but it also mutters about replacing the various gaskets in there. If it ain't broke ...... don't fix it is a very wise old engineering saying.

It's a puzzle why the fault mentions insufficient flow as I can't see how the ECU can measure flow of the exhaust gas recirculation? As far as I know, the engine doesn't have a mass flow sensor to measure air intake, but instead relies on a manifold pressure sensor..... similar, but different.

I'm wondering if the insufficient flow message relates to the fact the the ECU is not seeing the valve position feedback sensor showing that the valve is correctly opened enough, so it then assumes that the flow rate is insufficient?

[jaxabin]

I think I'd hold fire on the inlet manifold and see if your new egr valve and gasket makes a difference?

The Haynes manual shows an egr plate within the intake manifold, but it also mutters about replacing the various gaskets in there. If it ain't broke ...... don't fix it is a very wise old engineering saying.

It's a puzzle why the fault mentions insufficient flow as I can't see how the ECU can measure flow of the exhaust gas recirculation? As far as I know, the engine doesn't have a mass flow sensor to measure air intake, but instead relies on a manifold pressure sensor..... similar, but different.

I'm wondering if the insufficient flow message relates to the fact the the ECU is not seeing the valve position feedback sensor showing that the valve is correctly opened enough, so it then assumes that the flow rate is insufficient?

I’ve sprayed some contact cleaner on the sensor (MAP?) but haven’t turned the engine on or used the car yet so far, so will see if that makes a difference.

Yeah I guess i’ll wait for that first, should arrive tomorrow