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Seat Arosa 1.0 ALD over-fuelling issue


BEP51
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Been a few years since I sold my Lupo Sport and eventually stopped using this forum. but recently I bought a 1.0 ALD engine mk1 Seat Arosa for my girlfriend's sister to learn to drive in and for me to use as a cheap commuter. My Lupo was ridiculously reliable and easy to work on so assumed a £375 Arosa, with a fresh MOT, no advisories and only 81k on the clock was a good buy...

 

To save scrolling - Current issue is that it has started to overfuel - mpg has been awful (usual 250 miles a tank, now only 125) and when accelerating there is a notable amount of unburnt fuel coming out.

Just been out to read its codes again and it had the following:

  1. 17748/P1340/004928 - Camshaft Position Sensor (G40) / Engine Speed Sensor (G28): Incor. Correlation

  2. 16514/P0130/000304 - Oxygen (Lambda) Sensor B1 S1: Malfunction in Circuit

  3. 16725/P0341/000833 - Camshaft Position Sensor (G40): Implausible Signal

  4. 17536/P1128/004392 - Fuel Trim; Bank 1 (Mult): System too Lean

  5. 17544/P1136/004406 - Fuel Trim: Bank 1 (Add): System too Lean

 

I have previously had 17748 and 16725 come up repeatedly since i bought the car, even when I replaced the G40 sensor which made no difference - the wiring all seems good too. Is it worth trying to replace the G28 or the lambda, or both as that is a bit more expense i don't really want to throw at what was bought and intended as a cheap car?

History so far:

Bought the car a few months back. Only known history it came with was the cambelt being done and a fresh 12 month ticket. It ran ok, if a little crude - but when i bought it I gave it a full service with Bosch everything and good oil, fuel filter, temp sensor and changed the rusted out backbox and had it running better.

Checked the codes every so often (as the MIL LED is broken). Changed the camshaft sensor after codes 17748 and 16725 still kept appearing which made no difference - wiring all seems fine - so I questioned if the timing was out...

Sooooo I re-timed it and aligned the biggest and clearest of the 2 white dots made by the previous cambelt change to the marker and got the bottom in line correctly, then went to start it - "ping ping ping" = 4 exhaust valves bent - turned out when scratching off the tipex on the sprocket the little dot was obscuring the correct timing divet in the sprocket and the big clear marker didn't correlate to anything - my fault for not scratching it off first - but a full expensive and time consuming head rebuild later with new head-gasket, valve seals. combined with wrong items sent from eurocarparts eventually sorted it and had it running beautifully again driving lovely.

Decided to put a tank of vpower fuel through it for good measure, use it all the time in my TT and in my old lupo. Then began having starting issues, it was not keen to start easily whether warm or cold - I put this down to the higher required compression ratio, the higher than specified octane level from inside the fuel cap and assumed the new valves hadn't had enough time to bed in fully yet - checked the battery which was fine - burnt that tank off and filled it up with cheap stuff and it ran fine again...

Then the starting issue began to return and worsen, now it only starts as you let go of the key, not if you hold it forward, and only if you get the timing of it just right. I had some injector short to ground codes, checked the wiring, no issues, so replaced the coilpack, which did make a little improvement but hasn't solved the issues.

Despite the issues it ran fine until about a week ago when it started getting lumpy, idling badly and threw the above codes, then started seeing 250 miles a tank drop sharply to 125 and noted whitish unburnt fuel coming out the exhaust under acceleration (smells like fuel and no coolant is disappearing). So decided to run a scan and got the above listed codes.

 

With Christmas coming i don't want to spend the earth so want best advise as to which bit to check/change first.

My initial thoughts are now to look at the G28 camshaft sensor which I can get for about £45 (as I already replaced the G40 to no avail). Or go get the lambda sensor which is about another £45. This is the first time i've had the lambda come up, but have had the 17748 and 16725 codes since i got the car.

Should I just spend the £90 and see if it sorts it? or have people come across this issue before?

 

Hopefully someone can offer some advice.

Thanks in advance.

Ben

 

 

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I would do the free stuff 1st like a compression test just to eliminate that side of it and know if it's worth chucking money at. Also your cat wont be happy with all that overfuelling and may well be blocked or have stopped working and so your ecu will be leaning out the engine to compensate. Whip out the plugs and see if they are all similar too, if you have an odd one or two then diagnose accordingly.

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22 hours ago, Sausage said:

I would do the free stuff 1st like a compression test just to eliminate that side of it and know if it's worth chucking money at. Also your cat wont be happy with all that overfuelling and may well be blocked or have stopped working and so your ecu will be leaning out the engine to compensate. Whip out the plugs and see if they are all similar too, if you have an odd one or two then diagnose accordingly.

Compression was good when I rebuilt the head. No notable oil use, and no blue smoke. As for plugs - all 4 drenched in petrol.

Its only overfuelled for a few days, not so worried about the cat, also MOT is ages away and will do that then if needed.

Currently soaking the precat o2 sensor in penetrating fluids as it is seized as per the norm. will give it a clean up when i get it out.

20 hours ago, mk2 said:

Sounds like it might be the cam belt timing???

Timing is bang on, had to get it right after the full head rebuild, didn't want to cock it up after all that £££.

Not seen the o2 sensor code come up before on it so will likely attribute the overfuelling to that.

The crankshaft sensor is a pig to get to, and have had those codes since i bought the car, so reckon I will do lambda first, then if that cures the overfuel, then will change the G40 in the near future.

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if its overfueling then you need to look at the lambada sensor as it is looking at the exhaust gases to get the optimum excess oxygen, this is really important in any combustion process as too little or too much oxygen in the exhaust gases can have a really nasty effect and poor mileage is one of the signs of fuel not being burnt correctly

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5 hours ago, Mobieus_uk said:

if its overfueling then you need to look at the lambada sensor as it is looking at the exhaust gases to get the optimum excess oxygen, this is really important in any combustion process as too little or too much oxygen in the exhaust gases can have a really nasty effect and poor mileage is one of the signs of fuel not being burnt correctly

This. I'd check lambda sensors first. 

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Part of the mapping tells the ECU to ignore the lambda sensors if they give the wrong reading after a set time, like ten mins of running. The ECU assumes that the engine has warmed up by then (using temp sensors) so ignores the readings. It runs in a mode called open loop, where it bases fuelling and timing purely on the inputs it sees - if they are plausible. Lambda sensors only produce an output when over about 400c (hot) and are self cleaning, even if completely caked up after a fault. There is a built-in heating element to get them to warm up quickly. When you first start a cold engine, it runs open loop till it sees a plausible lambda signal. Only then does it run closed loop. My guess is that it is running in open loop mode. But the question is what inputs are making the ECU do that....?

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14 hours ago, Mobieus_uk said:

if its overfueling then you need to look at the lambada sensor as it is looking at the exhaust gases to get the optimum excess oxygen, this is really important in any combustion process as too little or too much oxygen in the exhaust gases can have a really nasty effect and poor mileage is one of the signs of fuel not being burnt correctly

My thoughts too, got one on order, just need to be able to get the old one out now! It's stubborn, but will get it out eventually.

13 hours ago, mk2 said:

is it breathing ok? air filter and the basic stuff (TPS, MAP, temp sensors etc)

Everything else is clean/new. Will get the MA sensor out for a clean, but the brake reservoir is in the way.

8 hours ago, cj1 said:

This. I'd check lambda sensors first. 

Also ordered the crank sensor, will fit it if the lambda doesn't sort it.

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3 minutes ago, mk2 said:

Part of the mapping tells the ECU to ignore the lambda sensors if they give the wrong reading after a set time, like ten mins of running. The ECU assumes that the engine has warmed up by then (using temp sensors) so ignores the readings. It runs in a mode called open loop, where it bases fuelling and timing purely on the inputs it sees - if they are plausible. Lambda sensors only produce an output when over about 400c (hot) and are self cleaning, even if completely caked up after a fault. There is a built-in heating element to get them to warm up quickly. When you first start a cold engine, it runs open loop till it sees a plausible lambda signal. Only then does it run closed loop. My guess is that it is running in open loop mode. But the question is what inputs are making the ECU do that....?

Other causes could be the crank/camshaft sensor issues with them not correlating? Also, I cheaped out on the coolant temp sensor last time - although it hasn't thrown a code, maybe worth changing this too. What is a MAP sensor doing in a naturally aspirated car? Is it just intake air temperature?

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I don't know this engine exactly, but the MAP (manifold absolute pressure) sensor measures the air pressure downwind of the throttle valve. It may have a hot wire or MAF (mass air flow) sensor which measures the volume of air going into the engine. Either can be used to get an accurate indication of swept volume of air into the engine.

Not 100% sure with this engine, but usually if the crank sensor is defective, the engine will not run at all. It is used as the primary timing source.

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