1.8t BAM misfire problem

[ExiledWeegie]

I just went through 8 months of misfire problems, changed nearly everything including injectors, turned out it was my half moon and tensioner gaskets causing it, I spent probably more than £500 chasing the misfires in the end for it to come down to a £15 couple of gaskets. mine was random misfires across all cylinders though, but sometimes it would go 10-15 minutes or more without any but then throw up 1 or 2 and then none for a while.

 

[AceD909]

I just went through 8 months of misfire problems, changed nearly everything including injectors, turned out it was my half moon and tensioner gaskets causing it, I spent probably more than £500 chasing the misfires in the end for it to come down to a £15 couple of gaskets. mine was random misfires across all cylinders though, but sometimes it would go 10-15 minutes or more without any but then throw up 1 or 2 and then none for a while.

Yeah i was thinkg the same, leaks or something but i have problem with only 1 injector misfiring.
But also it started to random misfire so it could also be for change.
I will do smoke test to cover that up.

 

[AceD909]

I installed my cleaned injectors, reconnected the MAF, and reset the learned values using VCDS. I also performed a throttle body alignment.

Now, the car idles between 850-1000 RPM, and I’ve noticed that it maintains RPM while driving, even when the throttle pedal is not pressed.

Here are the fuel trims at idle:

 

[nd-photo.nl]

Do the values change at all with bank 032?

 

[AceD909]

Do the values change at all with bank 032?

Not sure at all, when they need to change, i don't really know how this works.
I will check again later or tomorrow.

 

[nd-photo.nl]

It should fluctuate as the car is always trying to correct the mixture for the most efficient combustion

 

[AceD909]

It should fluctuate as the car is always trying to correct the mixture for the most efficient combustion

https://youtube.com/shorts/sb8k5C6DY0Q?si=TTOw3dbfKE0RxeBp -- Fuel Trims at idle.

https://youtube.com/shorts/sJp6e6qS7cw?si=D0BsC9DcJkx9k_1s -- Fuel Trims at idle but i was using engine starter to look for leaks.

And also i got 2 fault codes

16891/P0507/001287 - Idle Control System RPM: Higher than Expected. -- Intermittent

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

Sorry about the youtube shorts, size was to big to post them here.

 

[Alexis27]

I just went through 8 months of misfire problems, changed nearly everything including injectors, turned out it was my half moon and tensioner gaskets causing it, I spent probably more than £500 chasing the misfires in the end for it to come down to a £15 couple of gaskets. mine was random misfires across all cylinders though, but sometimes it would go 10-15 minutes or more without any but then throw up 1 or 2 and then none for a while.

Forgive my ignorance, but how would the half moon gasket cause a misfire? A small seepage of oil shouldn't have any effect on anything?

 

[ExiledWeegie]

the half moon and tensioner gaskets create a seal much like the rocker cover does I'd imagine if they dont seal up it creates a vacuum leak.

A "half-moon" vacuum leak on a 1.8T engine, often found on the valve cover, refers to a leak around the valve cover gasket, specifically the area shaped like a half-moon. This can cause a variety of issues, including misfires, poor acceleration, and even stalling

 

[AceD909]

the half moon and tensioner gaskets create a seal much like the rocker cover does I'd imagine if they dont seal up it creates a vacuum leak.

A "half-moon" vacuum leak on a 1.8T engine, often found on the valve cover, refers to a leak around the valve cover gasket, specifically the area shaped like a half-moon. This can cause a variety of issues, including misfires, poor acceleration, and even stalling

Can i test it somehow, using brake cleaner in the places where vacuum leaks probably happens, would it raise rpm or something?

 

[ExiledWeegie]

I tried that with mine and the idle/rpm didnt change, it was only when I left the smoke tester connected for a good while I noticed smoke coming from that area, thought it was the rocker cover at first but after changing it it was still smoking from there, then I read about the half moon and tensioner gasket and decided to change them and its been fine since, no misfire or hesitation at all.

 

[AceD909]

I tried that with mine and the idle/rpm didnt change, it was only when I left the smoke tester connected for a good while I noticed smoke coming from that area, thought it was the rocker cover at first but after changing it it was still smoking from there, then I read about the half moon and tensioner gasket and decided to change them and its been fine since, no misfire or hesitation at all.

If I leave the smoke tester running for a long time, will it create too much pressure and potentially cause damage?

I always remove the oil filler cap to avoid over-pressurizing the valve cover.

 

[ExiledWeegie]

just turn the pressure down if your worried about it, eventually the smoke will work its way out

 

[AceD909]

just turn the pressure down if your worried about it, eventually the smoke will work its way out

I will give it a go, clean the throttle body, should i get the one-way valves changed in the pcv system?
Visco fan is making noise so it will be changed and i will have plenty of space to work under the intake manifold.

 

[nd-photo.nl]

The PCV system only holds 1 valve, its under the intake manifold (and off course the "hockey puck"). I would advice to get the pcv valve replaced. Double check the hoses there as they are prone for splitting. I was chasing a boost leak and in the end it was one of the hoses under the intake manifold.

 

[AceD909]

The PCV system only holds 1 valve, its under the intake manifold (and off course the "hockey puck"). I would advice to get the pcv valve replaced. Double check the hoses there as they are prone for splitting. I was chasing a boost leak and in the end it was one of the hoses under the intake manifold.

I already changed the PCV and the hoses but never checked the valves.

I have misfires on cylinders 1 and 2, mostly on cylinder 2.

When I clear the fault codes, the Lambda Control Bank 1 Sensor 1 (block 033) shows 25%, while block 032 (Adaptation Idle) is 0%, and (Partial) is also 0%. During this time, the misfire occurs.

After idling for a couple of minutes, the misfire stops, and block 033 fluctuates between -1.6% and 4.7%, while block 032 (Idle) remains constant at 5.3%, and (Partial) stays constant at 10.9%.

Questions:
Can "false air" (unmetered air) after the MAF cause all these issues?

Why do only cylinders 1 and 2 misfire during the first couple of minutes after clearing the codes?

 

[nd-photo.nl]

25% means that it tries to correct in a very big way, thats not good.

Could very well be false air. Too much unexpected air, then tries to adjust fueling. Swap 1 of the injectors (cilinder 1 or 2) to cilinder 3/4 and see what happens

 

[AceD909]

25% means that it tries to correct in a very big way, thats not good.

Could very well be false air. Too much unexpected air, then tries to adjust fueling. Swap 1 of the injectors (cilinder 1 or 2) to cilinder 3/4 and see what happens

Could it be that the system is trying to correct the air-fuel ratio (AFR) because the mass airflow sensor (MAF) is reading about 3 g/s at idle? If the inlet hose has a crack near the turbo or after the MAF, wouldn't the O₂ sensor detect it and signal the ECM to add more fuel?

Could the issue also be that injectors 1 and 2 are clogged, causing less fuel to flow through them?

When they were tested, both provided the same amount of fuel within ±2 g/s—does that mean there's likely nothing wrong with them?

I plan to work on the car this weekend and swap the injectors since I don’t have the free time to do it right now.

 

[AceD909]

So, I was working on my car and found the following issues:

The intake hose has a crack on the connector to the hockey puck, which is after the MAF, so false air is getting in.

The VVT gasket is also leaking.

The PCV hose had a tiny hole. Could this cause low boost?

I will get a new rocker cover gasket (or valve cover gasket) with the VVT gasket included, probably on Tuesday.

I tried to fix the intake hose and will test it again tomorrow for leaks.

I added a little RTV silicone to the PCV hose to cover the crack, tested it, and there are no more leaks.

Other vacuum and pressure hoses are in good condition—I already replaced them with upgraded ones.

 

[nd-photo.nl]

Yes, the 1.8T is susceptible for boost leaks with the elaborate PCV system