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Aygo Engine Problem (Petrol)


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Hi,

We have had a 55 reg petrol engine Aygo for a couple of years, no significant problems until recently. I thought I would post here to see if anyone has had a similar experience or knows what the issue might be ... please :-)

The summary is I think we are looking at petrol contaminating the Oil ... details:

We noticed that the engine / exhaust was getting increasingly noisy but I ignored this as the Aygo doesn’t have much noise insulation for weight and cost reasons. We later found out after a trip to my local trustworthy independent garage that the Cat had been melted, parts of which were getting spat out along the exhaust towards the rear silencer.

After one particular trip the car was just about refusing to run at all – misfiring badly. I took the plugs out, they were black with carbon.

When the garage got hold of the car the first thing that he called me with was his finding that the Oil was overfilled, so either the last people to fill it had done a really poor job or it was getting contaminated some how.

He then spotted the Catalyst problem, checked the oxygen sensors, looked for fault codes in the ECU etc.

The cat needed replacing as there wasn’t much left of it.

One of the oxygen sensors was a but slow to respond, but within limits.

No fault codes in ECU.

Plugs were replaced.

Rear silencer was cleaned as best as they could.

Injector cleaner was added to petrol.

The car was returned to us with the understanding that it was not 100% and we needed to watch the Oil level. Essentially – if the root cause was overfilling the Oil we might be OK now but if it was something else we would probably not be.

We've run it for maybe 60 miles total since, it’s not been running 100% and I checked the Oil level only to find that it appears to have risen again suggesting petrol contamination. It’s done just about 40,000 miles.

Has anybody seen this kind of problem? Know what it can be - piston rings? Fault with injectors?

I have a feeling that we are in for another big invoice to get this sorted.

Any comments or ideas gratefully received.

Chris

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The only way petrol could get in to the Oil is if it was leaking through the cylinders when pumped in to them. I would find this strange as the petrol should really ignite before it could do this so maybe some timing problems. If this is the case then I'm afraid its a massive job. Could try part exchanging it in for a new model.

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The CAT melted because unburnt fuel was getting into the exhaust at a fairly massive rate. The engine must have been running very poorly and eating fuel - did you not notice such changes.

Once this was detected the cause should have been identified before doing any repairs.

A few simple tests such a checking the ignition, injectors and compression would be the ideal way of finding what was wrong.

Obviously the garage have failed to diagnose what is wrong.

Take it to another garage or mechanic who knows what they are doing.

None of these simple test require the use of a computer or specialised test equipment - just a mechanic with the right skills.

In my opinion the diagnostoic skills of many mechanics today is appalling.:)

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Hi Jamesbelfast,

Thanks for taking the time to reply…

It’s my wife’s car so I couldn’t comment on the fuel consumption, but I think she would have noticed if it were only doing 20 mpg for example. Perhaps it was just slight loss to the sump for a longer time initially?

The thing is with this – it looked originally like the Oil had just been overfilled, but now the Oil level seems to have increased again I think we can say that something (petrol to my untrained nose) is getting in there. Don’t think its water / head gasket or anything – I had that in my youth and would recognise it again.

So I guess if the compression was way down there would be something wrong with the piston rings and possibility of petrol getting through. Other folks have mentioned injector problems cause these symptoms – fuel injected when it shouldn’t be and getting sucked to the sump.

Just wondered if it’s a common fault seen before on this forum etc or if we are just really unlucky.

Thanks all …

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It must be that fuel is not burning in the cylinder so its either going out through the exhaust or leaking through the piston. Does the engine run very lumpy or funny at all? Being a 3 cylinder it would be very noticable.

My advice, part exchange it before the problem gets worse......

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Hi MartyB,

Yes the engine seemed to be misfiring / lumpy and I think now we are certain that it is overfuelling and burning in the exhaust manifold (hence melted cat) and also getting into the sump (hence petrol in oil) as people have suggested.

The garage has tested the oxygen sensors (and many other things) which seems to be in spec but after further inspection, it doesn't really seem to be responding / changing its readings as the engine warms up and hence I assume the ECU will be telling the injectors to pump more/max fuel?

If the root cause does turn out to be this sensor, my question to Toyota (if they would listen) is why am I not getting a warning light / fault codes when this happened. It's cost me a £500 cat + investigations + labour etc .... the car is a '55 reg though so i'm sure they will show me the door.

Chris.

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Chris

Before you set fire to the car change the temperature sensor at a cost of less than £10.

It sounds to me as if the automatic enrichment device is staying on all the time (in olden days this was a choke).

This is a very common problem on modern cars of all makes that are driven infrequently and on short local journeys.

I wish you luck as it may well be end of engine already.

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Chris

Before you set fire to the car change the temperature sensor at a cost of less than £10.

It sounds to me as if the automatic enrichment device is staying on all the time (in olden days this was a choke).

This is a very common problem on modern cars of all makes that are driven infrequently and on short local journeys.

I wish you luck as it may well be end of engine already.

I'd second that.

A friend had a similar fault with a VW Polo.

Stalling at lights, lumpy tickover, high fuel consumption

Temperature sensor fixed it.

Ian.

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I don't know about the Aygo's in particular, but sometimes if a car is not getting the right signals back to the ECU from sensors such as the lambar sensor (for example) it will just dump all the fuel in that it could possibly need just in case.

(*edit - Just as the previous posters mention^)

However if this was happened you should notice high fuel usage, but if it's being doing that since you had the car you might think what it is doing as normal.

If water is getting into your Oil you should see signs in either the Oil and/or the water. Take the cap off your expansion tank and look for signs of what looks like cork deposits. Does the Oil filer cap have any milky residue on the inside?

Do you ever have to top up the water system? If it was leaking that badly into the Oil system you'd have to keep topping that up too.

The only place where fuel meets Oil really is as mentioned at the piston. However you would be more likely to experience the Oil level dropping as the pressure of the Oil system would most likely blow it out past the rings (I killed my Smart this way).

Without seeing the car I would guess it's two separate issues. 'Emergency' fuelling could cause the cat problems, but I've no idea why your Oil level keeps rising.

(Although I'm a qualified mechanic I have next to zero experience so I'm prepared to be proved wrong on my theories)

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Actually this is interesting from:

http://www.polarisatvforums.com/forums/atv-repair-maintenance/9116-oil-level-rising.html

There could be a few possabilities.

1) when you run the engine and then add more oil you are actually overfilling it. unless your engine is a dry sump you need to let the oil settle for 15min after the engine runs to check the level

2) your carb float is not set properly or leaking which could cause fuel to run through your intake past the rings and right into the oil. This happens on cars when their fuel injectors leak. The oil level will seem to rise caused by the dilution of gas in the oil. If the oil has a strong gas smell this could be your problem. This will only happen when the engine is not running, like on your trailer. Turning off your petcock while trailering is always a good idea to combat this possible problem.

personally I would go with #1 but it's good to rule out #2, because once oil gets diluted enough it's flash point is greatly lowered and can eventually cause a fire in the engine.

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A simple exhaust emissions test would reveal if the engine was over-fueling and a dry compression test folowed by a wet compression test would be helpful. Any bog standard garage can do these tests without the need of computer equipment.

The lack of diagnostic skills of so-called modern motor techs never cease to amaze me.

:ffs: Let's be honest for the Oil level to rise by itself something serious is amiss and if the garage concerned can't detect what's going wrong it's time to try another garage.:)

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Actually this is interesting from:

http://www.polarisatvforums.com/forums/atv-repair-maintenance/9116-oil-level-rising.html

There could be a few possabilities.

1) when you run the engine and then add more oil you are actually overfilling it. unless your engine is a dry sump you need to let the oil settle for 15min after the engine runs to check the level

2) your carb float is not set properly or leaking which could cause fuel to run through your intake past the rings and right into the oil. This happens on cars when their fuel injectors leak. The oil level will seem to rise caused by the dilution of gas in the oil. If the oil has a strong gas smell this could be your problem. This will only happen when the engine is not running, like on your trailer. Turning off your petcock while trailering is always a good idea to combat this possible problem.

personally I would go with #1 but it's good to rule out #2, because once oil gets diluted enough it's flash point is greatly lowered and can eventually cause a fire in the engine.

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Carb float height??????? no carb on an Aygo or any other modern car. Electronic fuel injection since about 1993.

I realise that, I meant the bit after that where he talks about the injectors leaking. I was ruling out the petrol getting into the Oil when the engine was running. I forgot about when the engine is not running. If you read that post, although it talks of carbs, they do talk about petrol getting past the rings when the engine is not running (I took it for granted that people would realise I wasn't referring to the carb adjustment as a fix).

I had my injectors ultrasonic cleaned, I was very pleased with the results. You should think about getting yours done :) I posted mine out as my car was off the road (my Honda), so wasn't much of an issue waiting, but if you need your car daily you may be able to find somewhere who can do it same day.

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Presuming the car was running way too rich, possibly flooding the engine, definitely one cylinder, so maybe with one cylinder not firing, surely with extra fuel being injected into it, that fuel was being compressed and maybe that could be how it was getting into the Oil and not Oil escaping through the exhaust?

Just a theory

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Presuming the car was running way too rich, possibly flooding the engine, definitely one cylinder, so maybe with one cylinder not firing, surely with extra fuel being injected into it, that fuel was being compressed and maybe that could be how it was getting into the oil and not oil escaping through the exhaust?

Just a theory

petrol is very seaching can get where Oil would not.

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  • 4 weeks later...

I thought I would follow this up with an explanation of what turned out to be the root cause of the problem.

It turned out to be all down to fuel contamination in the end thanks to a Shell garage near St. Albans (my wife filled up 29th Dec just in case someone else has had similar issues) and Shell have just admitted that this ‘may have been the cause’ and are putting us in contact with their insurers.

I guess that whatever contaminated the petrol (diesel dumped into the underground petrol tanks possibly) might have damaged various sensors telling the car to over fuel causing all the other problems.

Now that all the damaged parts have been replaced and it has a new tank of petrol it’s running perfectly again.

I wonder if Shell and their insurance will pay up fully, that’s the next battle!

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  • 8 years later...

I had the similar issue which caused the engine ight came coming up, exhaust noisy ,the garage changed my exhaust first , engine light came up again so then they replaced new oxygen sensor ,cost me another £140, a week later, engine light came up again, they garage said this type cheap car's car's engine swallows Oil, patrol contaminating mixed with Oil , the Oil cannot be overfill or under fill, has to be exact right ,check once a week, I done all that,  light came up again , the garage refused to fix this engine right problem even though I want to pay new engine , they said the car is not worth an engine value,  Toyota Aygo 2008 

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So they just threw random parts at it, charged you nice money, and blamed the car in the end, nice place.

 

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On 8/1/2019 at 6:32 AM, furtula said:

So they just threw random parts at it, charged you nice money, and blamed the car in the end, nice place.

 

I used to have a Renault,  some horror stories on Renaultforum!

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