wierd engine behaviour

asilvah

I have an Astra MK4 (G) with 120,000 km. Engine was overhauled around 90,000 km because of a faulty synch chain. I have had this car for 7 years, brand new assambled in germany.

The engine is not performing good. Mileage is contrasting, in sppedways, I can get 12Km/ltr, but in the city I can get 5-6Km/Ltr. Engine performance in general is not what it was in the past, is right now like 90-100hp in my perception.

Anyway, if I accelerate slowly, I can reach aroud 130Km/hr with 3,000 rpm. However, if I accelerate quickly, as the engine overpasses 3,500-4,500 rpm the engine looses power as if I wouldn't have enough fuel pressure. Regardless of the acceleration, If I press the accelerator all the way down, I get engine response so I can keep accelerating, but when I release the accelerator, the engine looses power and stumbles. During full power acceleration, gas consumption is bad like 4km/ltr.

Also I noticed that exaust tail gets full of coal, which suggest a too rich fuel/air mixture.

What I have done...

I changed the ECU because it had some pins damaged, also changed plugs, air and fuel filters as well. I changed CAT like 8 months ago.

I have a friend with another astra, same engine which runs great, so I had the chance to try different parts.

I exchanged, coil pack, acceleration body and MAP sensor with no change at all, same problem.

I have a tech2 scanner which is not registreing any DTC, also got an ELM scanner so I can register sensor data, but I have no way to compare or derive a problem from the data seen.

What else can I check or try?

Alfonso

edbutler

Sounds like it could be a blocked Catalytic Converter stangling the engine - there have been a few people suffer from this on here. An exhaust leak and/or a bad mixture lambda sensor can also cause rich running.

Also you could take out your sparkplugs to see if they are all Blackened like your exhaust. It could be a cylinder specific problem like a stuck injector. Be VERY gentle re-inserting the plugs though as the pre-2007 heads are fragile at plug #4.

vocky

some very good advice above, the lambda can cause over fuelling but it does sound like the cat is duff

MikeS

talking about plugs -the vxhall dealer was the last people to change my plgus and boy they were like welded in

i snapped the spark plug removal tool trying to get em off and in the end i had to buy a heavy duty one

i always grease the threads of the plugs before i put em back and always do em to a bit over hand tight

it took me 30 mins to get the plugs out - as if the garage used a fricking air gun on em

asilvah

Forgot to tell that O2 sensor was replaced like 4 months ago. Is it the same as lambda sensor?

Can a CAT be duff with only 10 months of usage?

alfonso

edbutler

O2 = lambda yes 🙂

Its very doubtful that these can fail in such a short time, but anything is possible! Have you cheacked for your exhaust manfiold and downpipe for cracks/leaks - they are quite common in Vauxhalls.

Your fuel economy is not too bad to be honest - 34.5 and 17mph respectively. Ignore the reading on the Car's computer though, especially on hard accelleration, take the readings with a pinch of salt (dont trust them completely)

Good luck in tracking it down!

asilvah

Latest news. I replaced the O2 sensor with the previous one and the problem was solved. Something I noticed is that faulty sensor and wire is couple inches shorter than the original one, so I think I got an incorrect one.

Now, not everithing is ok. Engine performance is worst than it was, I have power all the way up in RPMs without any hesitation. Also mileage is worst too.

I think I will replace the O2 sensor for the right one expecting this to solve the problem.

Keep you posted.

alfonso