Hi everyone,

I drive a 1.2 Polo (my first car) that's recently been suffering from a loss in power and a intermittent misfire.

The car drove fine when I bought it however it had an engine management light on.

When I bought the car it was really low on oil, less than a liter including the oil flush came out of the engine, so that was changed quickly with some recommended 5w30 Castrol Magnatec and a new Bosch oil filter.

After reading up online I decided to buy a Fault Code reader to diagnose the faults myself.

The faults came back as;

16687 - Cylinder 3 Misfire

16556 - Fuel Trim System Rich Bank 1

16804 - Catalyst System Bank 1 Efficiency Below Threshold

later on that week a new fault came up;

16490 - Manifold / Barometric Pressure Sensor (G71) / (F96) : Implausible Signal

I then found out that a misfire on cylinder 3 was very common and usually due to burnt exhaust valves or bad guides. When misfiring this caused me to only reach 20mph and on some occasions only reach 2000rpm.

I had changed the small things first before spending a lot of money on new valves, guides, seats and the tools to do the job or on a new cylinder head and gasket set.

Changing the spark plugs caused the misfire to disappear for about 2 weeks and then it came back.

Swapping the ignition coils and injectors didn't move the problem to another cylinder.

So to ensure this was the problem I then bought a compression tester and then found out that the compression across all three cylinders was absolutely fine, reading 160 psi on all three.

At the moment I'm at a loss. I've cleared all the codes and only Cylinder 3 Misfire and the Fuel trim running rich are the only faults to reappear.

The misfire only seems to occur when the engine reaches its operating temperature. Starting the engine on some occasions causes a low idle.

So further research has brought me to buy a new coolant temperature sensor and MAF sensor, which I haven't yet to install.

I was hoping if anyone would be able to lend a hand in helping me diagnose the problem?

Any help is very much appreciated!

Sorry to have dragged on in this explanation but I think its the best way for me to have a hope in getting the problem fixed.

Thanks,

Eoin

Welcome to the Forum.

When you removed the old spark plugs, did you notice any difference at the 'business end' of the plug that came out of cylinder number three?

You can gain a lot of information from the state of the plug, from oil contamination (ignore any oil that may run down from the outside as you remove the plugs) to plugs running too hot (due to the wrong type being fitted maybe) and the state of the mixture (black and sooty = too rich; white = too weak).

When buying new sensors ( like your MAF and temperature sensors) - avoid the cheap aftermarket ones - I have been led astray before now by people saying, "I've just fitted a new (whatever) sensor, and the fault has come back". I tend to use genuine VW ones, or ones made by Bosch.

Regards

Thanks for the reply,

Yes, the spark plug on cylinder 3 had what looked to be a build up of carbon on it which defiantly didn't look good. They were NGK plugs, and I had swapped them out for some new Bosch plugs that I picked up from Euro Car Parts.

I've installed the new coolant temperature sensor, cleared the fault codes again and took it for a 10 mile drive about 10 minutes ago. There was no misfire, however I don't believe that's entirely fixed my problem at all, the misfire is intermittent and kind of pops up when it likes. The car was still struggling for power and really didn't want to reach the 40mph mark at all. It really struggled to accelerate.

When I got back I scanned again for faults even though the engine management light had not come back and I got a 16556 - Fuel trim system rich in bank 1. I'm starting to think i may need new lambda sensors? You can defiantly smell it's running rich.

Thanks again,

Eoin

I haven't worked out how to attach images so I've screen shotted a picture of the spark plug from cylinder 2 (left) next to the spark plug from cylinder 3 (right)

https://gyazo.com/2a64d5c595ac7fe0a54da3d238c8a62e

Hi again everyone,

Today I tried to drive the car and couldn't get any more than a mile before the whole car died on me.

I managed to pull into a lay-by and scan through the fault codes with my scanner.

The scanner had brought up 4 codes, the permanent 16556 as well as again a random misfire code and a misfire on cylinder 3 and now this time on cylinder 2! Two cylinders were misfiring! I was amazed I made it home to be honest.

I had swapped round ignition coils 2 and 3 about 3-4 weeks ago. Could bad ignition coils be my problem? The engine sounded like it was smothering itself and when revved it really hesitated, rose to about 1500rpm maximum and then dropped drastically to about 500rpm before either rising slightly or cutting out completely. The engine shook badly and was very hot too reaching operating temperature in less than a mile.

Another question is could bad ignition coils cause a car to run rich? This doesn't sound likely to me but I'm no expert or could this again be a lambda problem?

Any help is much appreciated, I'm starting to lose faith in this car.

Thanks,

Eoin

It is certainly possible that if there is a misfire, fuel will pass through the engine in an unburned state - You would probably smell this at the exhaust tail pipe.

Another possibility is that, should you have a faulty coil pack, the pugs are wet with petrol, leading to the 'additional' misfire on number two.

Both of those plugs look to be carboned up - the sort of thing that I would expect if the engine had not reached normal operating temperature (around 90°c) maybe being used on lots of short journeys.

Regards

Thanks again for replying,

The car is unusable at the moment. I've been spending countless hours seeing if I can visually see any loose connections anywhere in terms of the ignition wiring and everything seems fine.

I can definitely smell un burnt fuel, the fault code reads that its running rich but I've used redex to clean out my fuel system and have also swapped injectors 3 and 1 and the problem doesn't follow around. I'm starting to think it could be the lambda sensors causing it to use so much fuel, but again I don't entirely know and I don't have the guessing money to find out as I am a student.

I've again cleared the fault codes and started the engine back up on the driveway. I am now only getting one fault code, a cylinder 3 misfire. As I can't drive the car at the moment I still don't know whether there are any more problems.

Since my breakdown yesterday the car is struggling to rev. When warmed up to 90 degrees I can't rev any further than 3000rpm even at that rpm it almost instantly drops to 2000rpm where it begins to struggle and the misfire seems to kick in. From there it will begin to slowly decrease in rpm and struggle to stay alive and then die from low rpm's. Strangely the cabin light even dims when the car begins to die.

Has anyone had any similar problems and found a solution?

Does anyone have any suggestions as to where I should go from here?

The problems are getting bigger by the day and so any help is appreciated greatly.

Thanks again,

Eoin

Hi Eoin,

As a second car I have a 1.2 6v AWY and had similar problems to you but nowhere near as severe!! I firstly found that the vacuum hose at the back of the engine from the throttle body to I forget where had perrished. Replacing that with some suitable pipe helped. Then I replaced all three plugs and coil packs, cleared the similar codes to yourself and have never seen them since :-)

I wonder if it's possible that your timing chain has jumped as that will cause starting issues and inability to high rev. When was it last changed?

Thanks,

Ian

How did you get on with your MAF sensor?

You said you bought one in the OP but I couldn't find anything about fitting it.

Was it a cheap aftermarket one or Bosch/VW?

Thanks everyone for the replies,

I had previously removed and cleaned the trottle body which looked in pretty good shape. And I reckon my igntion coils are bad but I'm not 100% sure.

More research has brought me to believe a jumped timing chain could be a solution.

I changed my MAF sensor a couple of days ago and unfortunately had made no difference at all. I bought a Bosch one online and right away had to swap the o-ring with a slightly smaller one.

I'm having my dad's friend, a mechanic to have a look over the car more comprehensively, I'd do it myself but don't have the specific tools!

I should get a definitive cause by the end of the week.

I'll keep you all posted.

Thanks,

Eoin

I had a cylinder 3 misfire changed the usual items and compression test was fine.  Was told timing chains can slip but took the chance and had exhaust valves done and no surprises cylinder 3 gone and 2 was on the way so had those done and new timing chain and problemail solved

Edited 17 February, 20179 yr by David Pearson
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