Technical Weird misfire intermittent

[NDT]

Hi. Relatively new here, driving a 63 plate Panda Twin air 4x4.
Currently in the middle of France, which is possibly beside the point, but, I am having some issues with an intermittent problem with the car “misfiring”. It starts to happen on long journeys. Fine when I am in 6th pootling along, then, get to a jonction/Roundabout and when I start to pull away the car runs really rough. Like it’s misfiring. If I drop down a gear and get off the accelerator or just back off the accelerator so the engine braking effect kicks in, it sorts it and it is fine. Until the next junction obvs. Any bright ideas. Took it to a dealer in Le Mans and they changed the plugs and brake switch but still not any better. Help.

 

[Goudrons]

What's the oil level like?
Low oil and the Twinair's valve actuation system won't work properly, it uses the engine oil as a fluid link between the cam and the inlet valves.
It also won't work properly when it's broken, which isn't unheard of. Quite a few fail

Something else to look at would perhaps be the wastegate on the turbo sticking.
The shaft into the turbo is known to wear and flap about, if the wastegate if sticking open it might feel like there's a misfire when acclerating as it's not boosting properly.

 

[NDT]

Thanks, I will check the oil, but dont really have the tools here to check the Turbo. Is it easy to do?

 

[NDT]

Oil appears to be fine. I Did top it up before we came away and it still seems pretty much where it was.

 

[Goudrons]

It's not easy getting at the wastegate without taking the engine cover/airbox and heat shield off, but you can just get at the actuator arm.

Just at the front of the engine cover, next to the big fat black pipe on the left (left as you stand in front looking in) is the round actuator vacuum mechanism.
Coming out of that is a rod running under the heat sheild, that operates the wastegate.

It's a bit difficult to test fully by the side of the road with no tools, but without vacuum (no engine running) it should be relaxed and fully extended.

First off, grab the rod and see if there is any loose play at the hidden end.
There will be some play in it but it shouldn't flop about by centimetres, sound too scratchy or rough (though it might click a little)

Get someone to start the engine and apply some steady revs while you watch the rod.
The engine will start to create a vaccuum which should start pull the rod in towards the round vacuum mechanism.
You should see it move as the revs rise, shut the throttle off and it should move the other way.

Get someone to turn off engine and it should return to it's extended state again once the vacuum goes.

It shouldn't move far, there's only a quarter turn needed on the wastegate spindle to full open/close the gate.

You probably won't see the full range of the actuation with the car not under load with the handbrake on as the ECU will limit boost control until you're driving under load, but you should get some idea the rod is operating the gate smoothly with the above tests.

 

[NDT]

Hi. Thanks for that detailed description. Found the rod, it rattles a little, then it, as you say, moves in as the engine starts. However, it comes out again as it revs. Once the engine is off, out it comes. There is a smell of petrol as well I have noticed. By the way, you are being incredibly helpful, so thank you.

 

[Goudrons]

From here, that sounds like it's working ok.

The wastegate is open with no vacuum (engine off) on the mech.
Start the car and vacuum in one side of the mech pulls the rod/arm and closes the gate.

The wastegate then starts to reopen as the pressure on the other side of the diaphragm in the mech starts to even out or drop.
So as the revs rise higher, the more the gate then starts to open to control boost.

The petrol smell is a worry though.
See anything wet down the engine, anything dripping underneath?

 

[NDT]

The wastegate seems to be working as you describe. The car is parked on dry concrete and there is nothing dripping. It’s doing my head in. I

 

[Goudrons]

You might have a leak in the evap system.
It is designed to stop petrol vapours escaping into the atmosphere.
A leak in that can cause surging, misfire and a strong smell of petrol.

You are going to have to do a bit of searching on the forum and internet as I ain't too familiar with the system.

 

[NDT]

Hmmm. Sounds interesting. Thanks again, i will have a search.

 

[Herts Hillhopper]

You might have a leak in the evap system.
It is designed to stop petrol vapours escaping into the atmosphere.
A leak in that can cause surging, misfire and a strong smell of petrol.

You are going to have to do a bit of searching on the forum and internet as I ain't too familiar with the system.

ON cars with a normal filler cap, this effect can happen on a long drive (esp in hot weather) as a vacuum forms in the fuel tank when not enough air gets in to replace the fuel taken out. You can cure that by unscrewing the fuel cap and hearing the air rush in. On the Panda, the same may be happening? No cap to unscrew, but off you have the little 'emergency funnel' supplied with the spare wheel or pump-and-goo kit, pushing that into the filler will open it and let air in. (This is a temp fix and shows that the breather system - which is in the rear wheel arch behind the plastic liner - needs looking at.)

 

[NDT]

Okay, I will try that, thanks. It has been really hot down here and it only really happens on a long drive. I will dig out the funnel and see if that helps. It is frustrating!

 

[Goudrons]

I wonder if it's possible to "lock" the evap system with fuel?

As HH writes, the fuel tank needs to vent. It does this via the evap system as you can't vent to atmosphere.

The vent pipe must come off a high point in the tank/filler system and though a separator
The liquid goes back to the tank, the vapours to a purge valve under the bonnet, then into the manifold to get burnt.

What if the tank has been brimmed right up the filler neck. Normally the fuel is cold out of the underground tank but in hot weather it expands the tank and over comes the separator?
There must be a high point and low point on the separator for the vapours to come off and the liquid to return. What if there's so much in there it's overcome this and there's no room for the liquid to return to the over filled tank and it geting into the pipe to the purge valve?

The pipe between the separator and the purge valve would lock with fuel and everything would stink of fuel, though probably outside the car.

There must be something stopping the liquid getting in the vapour pipe to the purge valve, just it's been over come by brimming and expansion.
It's just a wild guess!


Then again that might be over complicating things. It might be just the pipe from the purge valve to manifold has popped off, not be put back properly or cracked and it venting petrol vapour.
If it was the engine would suck in air from here, run lean and misfire.
If would probably stink of fuel in the engine bay as well.

I would expect a DTC if the purge valve itself had failed.

 

[NDT]

I think the issue with fuel, would be more consistent though. It runs well for a while, then starts to run rough when I have stopped at a junction or changed down and am accelerating out of a corner. If i then take my foot off the accelerator and let the engine brake the car (or change down a gear and do the same thing, it seems to be fine until the next time i get to lights, junctions etc. That is what is confusing me.

 

[jrkitching]

What if the tank has been brimmed right up the filler neck

Then there's a chance the EVAP system has been compromised and is no longer working correctly. I hope this hasn't happened, because it's an expensive repair.

The fuel system is designed to work with an airspace of around 5-7 litres when filled to the normal limit.

There's a clear and specific warning in the handbook about not trying to dribble fuel in once the automatic dispensing pump has shut off.

 

[NDT]

The tank has not been brimmed.

 

[Goudrons]

It's difficult to tell sat here, I can only point out what problems it might be suffering from.

My guess about the evap system was due to the strong smell of fuel and as you're away long tripping, I made an assumption you might have been squeezing in as much fuel as you could.
I done it myself a few times in my Abarth, same size tank though 4 times as thirsty!

Still on the same sort of guess, I thought the problem was showing up when the purge valve was opening (and guessing the purge valve opens under high load, as that's when it's sucking more fuel from the tank)

Again, a split or break in the pipe from the purge valve to the manifold would probably have the same effect.
A fuel/air inbalance which would cause a misfire and stink of fuel under the bonnet.


The engine will natually run lean on the over run when you take your foot off the gas. You usually won't notice an inbalance then, it's effectively pumping air.

The engine will try to balance the fuel/air ratio it's self when it's at idle and driven.
The ECU will add or take away fuel from the ratio depending on the temp of the exhaust gas read by the pre cat O2 senser.
Hot gas = lean so it adds fuel.
Cooler gas = rich so it takes fuel away.

There is a limit to this though, it can only add so much fuel based on the fueling table in the ECU.

You might not notice the issue on lighter loads as the ECU is trying to trim this out, but as the load gets higher, one it will draw more air in but will also run out of fueling adjustments to match what it thinks it needs.

It's adding all the fuel it can but the gases are still lean due to the air leak so it stutters and misfires and you notice it.

A leak in the exhaust system has the same effect.
Unaccounted air enters the exhaust and effects the gases which effect the O2 sensor reading, so the ECU adjusts the fuel trim and you end up with a fuel/air inbalance.
It's not unknown that the flexi pipe, just to the rear of the cat can split and leak and cause this very issue.

As these fueling trims alter from one end of the spectrum to the other so you don't normal get a DTC straightaway if there is a problem.
The ECU usually needs to see the same problem a few times in the same drive cycle before it thinks, hold on I have a problem here and lights up the EML on the dash.

Again, if it's over fueling it might smell a bit fuelly at the exhaust.

Other tell tales of fuel/air inbalances are your mpg's drop and engine temps rise (though modern cooling systems tend to cope better than older systems)

 

[forestgreen]

There is a lot of technical input there - a little bit over my head- but just another, maybe simpler thought.
I have recently bought a 2013 Panda TA which was also running a bit rough. Mainly on start up but also a couple of specific running issues. Firstly, when I didn't let it run for a few minutes on tickover and drove it straight off the engine was getting bogged down under acceleration. Secondly, the other day when passing a slower vehicle I was accelerating in 3rd gear when again it suddenly got bogged down. When I changed into 4th it recovered and carried on. It had also done this under harder acceleration (just seeing if it just needed a blast) when in 2nd gear it just gave up so had to change up early. Ran ok again afterwards. After a plug in at a local garage they suggested changing the coil packs.
This I did this morning ( Bosch
0 221 504 035 ) and although it's not fully proven yet, the car ran better on tickover and when I drove it away ( without waiting for it to settle down too much) it seemed far more responsive with no hesitation under acceleration.It generally felt much smoother.
This may not help but from the original description I think there may be some similarities.

 

[Graham GB]

I know this is an August thread, but our Twinair had an intermittent misfire & would hesitate occasionally, which got slowly worse(this was at around 50K) it was the spark plugs, new ones fitted & still runs perfect at nearly 100K may be time for another set.

 

[varesecrazy]

There wasa recall for Coilpacks for early twinairs

Our 63 plate

'Goes flat'..and throws on the Yellow Triangle... then the engine light.

Codes are for misfire too.. plugs made no difference