I have struggling for the past 18 months with this problem and I’m ****ed off totally because of it because and have no ideas what to do further on.

 

Since I’ve bought this car (2.0i-85 KW-AQY-y2000) I have only one major issue with it and that is a partial fuel combustion (afterfire) in exhaust and respectively a rich fuel trim in general because of it (I guess) and the car have a rough idle (760-800 rpm drift 90% of the time, not always).

 

For the past 18 months I have:

-changed new OEM front O2 sensor

-changed new catalyst (universal)

-changed 2 times OEM set of NGK sparkplugs

-changed spark plugs cables (BERU)

-changed new OEM ignition coil pack and cleaned all ground contact point on engine

-changed new BOSCH MAF sensor and air filter

-changed new battery

-cleaned all 4 injectors

-measured a cylinder compression (14 bar on each)

-checked fuel pressure (ok) and fuel pump

-cleaned EVAP canister (ok)

-cleaned throttle body and calibrate the TB and cleaned all secondary air injection hoses

-change all vacuum hoses (0.6 bar vacuum on idle and 0.8 bar at higher revolutions)

-change thermostat and checked CTS (ok)

 

After everything I did, and a few more maintenance jobs also, there is an afterfire present in the exhaust (90% of the time). Sometimes everything is ok and there is no afterfire, but most of the time it’s present (no new tank refills).

 

Before this huge “swap” there was a P0172 System too Rich (Fuel Trim) with over -17% LTFT on measuring block 32.

Now, there is a -10.9% LTFT on measuring block 32 in VCDS.

 

So, my first problem is fault:

P0172 System too Rich (Fuel Trim), and second is:

P0422 - 35-00 - Efficiency Below Threshold

 

These two faults are swapping from time to time. Sometimes it’s a rich fuel trim, sometime it’s an insufficient CAT temperature and sometimes is CAT low efficiency, but all the time there is a negative and over 10% LTFT readings on VCDS measuring block.

 

I’m guessing that the CAT problem is because of the poor/insufficient mixture/combustion so the CAT can’t operate properly (engine is spitting fuel on it) and it’s not up to the CAT at all (my guess).

 

Can anyone PLEASE help me solve this problem?!

LOG-01-032-033-xxx.pdf

Edited 15 November, 201411 yr by mister8ight

Has the air filter been replaced? Poor air flow can increase richness of mixture

Yep already written in my first post..

Edited 16 November, 201411 yr by mister8ight

Have you checked cam timing?

Don't know what to look for in cam timings...so no I did not.

Please advise...

Edited 26 November, 201411 yr by mister8ight

There is nothing in groups 091, 092 and 093 on VCDS for this car..(blank fields).

Is this ok?

Edited 26 November, 201411 yr by mister8ight

For what they cost I would replace the Coolant Temperature Sensor as if faulty this could cause over fuelling.

CTS is ok 100%.

Update:

There is no more after fire in the exhaust, but there is still problem with rich fuel trim, which has killed two CATs so far.

LTFT Idle is -10.9 %

LTFT Partial is 0.8 %

There is no MIL, but this trim is killing universal CATs for short period of time (4-5 months).

Is there anyone experience enough who can help me diagnose what could be a problem based on the attached diagram please?

Vacuum leak is still most likely...check the hose into the brake booster

But...that level of rich mixture still doesn;t explain the afterfire,I think rich mixture + another problem cause that.And I woult check the timing belt ,alignament next.1 tooth too advanced timing and rich mixture is the perfect combo for afterfire,because that mixture is not burned by the engine ,apart is released on the very hot exhaust and fires there.Very hot exhaust because the engine allready runns too rich.

Thx..

Vacuum on idle is lover (0.6 bar) than on revolutions (0.8 bar) and I find this not ok, but I just can't find a vacuum leak. 

I have checked timing belt alignment before and it was ok based on eye examination. Are you suggesting me to move timing belt one tooth backward do decrease possible advanced timing, or to advanced it even more from current position?  

Edited 28 March, 201511 yr by mister8ight

Check the timing to be set on marks on the camshaft and crankshaft.

As for the vaccum leak I still bet on that....I strongly advise you to warm up the engine take a spray bottle fill up with water and then spray over the hoses while engine runns,if you hear a change in idling a change in rpm even the slightliest you have just spotted a vacuum leak.

 

Measuring negativve pressure is not relevant at all

Thx mate.

I have already done that with carburetor cleaner (dangerous job), but I will do it again with water.

You don't think that this condition (rough idle especially) is not caused by EGR valve not being closed all the way down to the end?

yes it might be....but even the richest mixture on theese car won;t detonate on the exhaust

There is no more exhaust fuel burning after releasing the gas pedal like in the past. This after fire could also be due to the insufficient gasoline octane number (bad fuel).

It was when LTFT Idle was above -17% and more, and now is around -11%. Now it's just a CAT killer

New Update:

According to the voltage of O₂ sensors (upstream and downstream) in picture, in first period of time downstream O2 is mirroring upstream O2 sensor, which indicates a bad CAT, but in second time period, downstream O2 sensor is 0.15V which indicate a lean FT. It should be indicating 0.45V or slightly more and not oscillate???

Could this Rich FT be "a false rich trim" due to a bad upstream O2 sensor...or it's just a bad downstream O2 sensor (it's old in general, and the upstream is new and OEM)???

Edited 28 March, 201511 yr by mister8ight

Done water test for vacuum leaks and still no luck.

After fire is present, but only after I harshly step on a gas to highest rpm and instantly let it go (there is "blump-blump" sound in the exhaust). Not sure is this normal for highes rpm in still position..

When I apply suction on EGR valve (on idle) engine doesn't die. There is only strange hissing noise during suction. Not sure is this suppose to happen..I was in believe that engine will shutoff instantly.

Edited 28 March, 201511 yr by mister8ight