Those pesky 171 and 174 codes

[geeveejay]

I have read so much on these codes my head is spinning. Have the 171 174 codes appearing on a regular basis and cant find the problem. Car is a 2002 2.2 with M54


So far I have replaced the lower boot ( that was split) gave a 303 code first, but thats never come back
Checked the manifold blanks at rear
Replaced Rocker cover gasket ( slight leak )
Replaced whole CCV system
Replaced DISA seal and upgraded to alloy flap
Small hose from F connector
Cleaned MAF with proper cleaner
o rings dipstick tube and dipstick

Can anyone see something obvious I am missing. Attached is a record of faults ( couldn't attach spreadsheet so its over 2 pages in PDF sorry )

Dont like to be beaten but dont want to keep throwing money at it randomly, car drives fine with no issues otherwise

Garage suggests it might be O2 sensors but they show Ok on my cheap scanner and surely 171 and 174 suggests both banks have an issue at the same time which is why I have been chasing vacuum leaks.

One thing I have noticed is a hiss of air a couple of seconds after shut down, cant figure what would make that noise, Next step is to take for smoke test but I am missing something obvious first

 

[Mario]

I would do two things - check for leaks with a smoke test, that's the sure fire way. if no leaks are present I would check the fuel filter and the fuel pump that's the only thing that would make the car run lean if you have a problem with fuel delivery

 

[colb]

Looks like your fuel trims are high which would be consistant with the car thinking its running lean and its trying to compensate by adding fuel. This is usually down to air leak(s) in the vacuum system, if you cant find them visually then smoke testing is the way to go. Had a mates 2.2 last year that had high fuel trims, smoked it and found leaks on the intake hoses and sucking jet pump just below the throttle body, this was replaced and improved it a little but were still presented with leaks which the smoke then picked once we sorted the inlet side. It looked like it was leaking from one of the plug wells around No 4 plug, no oil down there so just suspected the centre plug well gasket was at fault. Stripped the cam cover off and replaced the main and centre gaskets, buttoned up and retested, still had smoke around No 4 plug well, pulled the cover again and on close exam found it had cracks around No 4 plug well, having a poke around revealed the plastic had gone hard and brittle and started crumbling away. Heating and cooling of this material over time degrades it, hence the cracks and air leaks. Used part obtained and fitted solved the problem. As soon as we had a sealed vacuum across the engine fuel trims returned to normal and car was transformed with regard to performance. Smoke is your best bet to ensure you don't have leaks.

 

[NZ00Z3]

Vacuum leaks are most easily seen at idle as the ratio of leaked air to throttle air is higher. Try the below test.

With a hot engine at idle, check you fuel trims. If any are >8% then you have a vacuum leak. Confirm it by reving the engine to 3,00 rpm for 30 seconds while watching the fuel trims. If the short term trims reduce, its confirmed.

 

[t-tony]

Have a look at this, it may help.

View: https://www.youtube.com/watch?v=3eMJ9bBlaE8


Tony.

 

[geeveejay]

Looks like your fuel trims are high which would be consistant with the car thinking its running lean and its trying to compensate by adding fuel. This is usually down to air leak(s) in the vacuum system, if you cant find them visually then smoke testing is the way to go. Had a mates 2.2 last year that had high fuel trims, smoked it and found leaks on the intake hoses and sucking jet pump just below the throttle body, this was replaced and improved it a little but were still presented with leaks which the smoke then picked once we sorted the inlet side. It looked like it was leaking from one of the plug wells around No 4 plug, no oil down there so just suspected the centre plug well gasket was at fault. Stripped the cam cover off and replaced the main and centre gaskets, buttoned up and retested, still had smoke around No 4 plug well, pulled the cover again and on close exam found it had cracks around No 4 plug well, having a poke around revealed the plastic had gone hard and brittle and started crumbling away. Heating and cooling of this material over time degrades it, hence the cracks and air leaks. Used part obtained and fitted solved the problem. As soon as we had a sealed vacuum across the engine fuel trims returned to normal and car was transformed with regard to performance. Smoke is your best bet to ensure you don't have leaks.

Looks like your fuel trims are high which would be consistant with the car thinking its running lean and its trying to compensate by adding fuel. This is usually down to air leak(s) in the vacuum system, if you cant find them visually then smoke testing is the way to go. Had a mates 2.2 last year that had high fuel trims, smoked it and found leaks on the intake hoses and sucking jet pump just below the throttle body, this was replaced and improved it a little but were still presented with leaks which the smoke then picked once we sorted the inlet side. It looked like it was leaking from one of the plug wells around No 4 plug, no oil down there so just suspected the centre plug well gasket was at fault. Stripped the cam cover off and replaced the main and centre gaskets, buttoned up and retested, still had smoke around No 4 plug well, pulled the cover again and on close exam found it had cracks around No 4 plug well, having a poke around revealed the plastic had gone hard and brittle and started crumbling away. Heating and cooling of this material over time degrades it, hence the cracks and air leaks. Used part obtained and fitted solved the problem. As soon as we had a sealed vacuum across the engine fuel trims returned to normal and car was transformed with regard to performance. Smoke is your best bet to ensure you don't have leaks.

Thanks I am not sure how to interpret those fuel trims so appreciate the incite

Diolch yn fawr iawn

 

[geeveejay]

Vacuum leaks are most easily seen at idle as the ratio of leaked air to throttle air is higher. Try the below test.

With a hot engine at idle, check you fuel trims. If any are >8% then you have a vacuum leak. Confirm it by reving the engine to 3,00 rpm for 30 seconds while watching the fuel trims. If the short term trims reduce, its confirmed.

Thank Murray, ill try that now

 

[geeveejay]

Vacuum leaks are most easily seen at idle as the ratio of leaked air to throttle air is higher. Try the below test.

With a hot engine at idle, check you fuel trims. If any are >8% then you have a vacuum leak. Confirm it by reving the engine to 3,00 rpm for 30 seconds while watching the fuel trims. If the short term trims reduce, its confirmed.

Hi Murray

I let the car get hot, it entered CL

At idle FT1 is sitting between -1.6 and +1.6 fluctuating, that same goes for FT2 , although both occasionally hit -2.3

At approx 3000 the STFT 1 varies between + 2 and roughly -2
STFT is at -7 and is pretty constant

 

[gookah]

when my missus comes in the garage nattering, I find the STFU works well.

 

[NZ00Z3]

You should have 4 fuel trims to look at.

Short term fuel trim bank 1 (STFT 1)
Short term fuel trim bank 2 (STFT 2)
Long term fuel trim bank 1 (LTFT 1)
Long term fuel trim bank 2 (LTFT 2)

Your idle information is only showing the short term fuel trims. What are the long term fuel trims at hot idle?

Guessing here, but as STFT 2 is dropping to -7%, I am picking the LTFT2 at idle is around 8% showing a vacuum leak on bank 2 = cylinders 4, 5, and 6.

Reading your first post, shows that you have replaced all of the basic causes of vacuum leaks. Well done. A smoke test is the next thing to do, which I see on your Bimmersports post, you are organising now.

 

[Mario]

Be aware that the fact that you get positive fuel trims most likely cause is a vacuum leak but also it could be bad maf, soft failing fuel pump etc

 

[colb]

Mario makes a good observation regarding the Maf, I noted that you spray cleaned the Maf, can you see it in live data with your diagnostics just to see how its performing. After all fueling is governed by how much air the Maf is reporting to the engine management, if its mis reporting then you would get fueling problems. Smoke test the car just to confirm you have no leaks, if it passes that test have a look at the Maf, I had a duff Maf, cleaning it with Maf spray killed it. As soon as I replaced it with an oem unit, car was cured. Maf's dont always set codes when they go wrong. Its very easy to throw parts at a car but gets expensive. Reckon yours is either an air leak or duff Maf.

 

[Mario]

Which maf did you put on? Vdo?

 

[colb]

Pretty sure it was a Bosch unit from BMW which was expensive but cured the problem I had.

 

[geeveejay]

You should have 4 fuel trims to look at.

Short term fuel trim bank 1 (STFT 1)
Short term fuel trim bank 2 (STFT 2)
Long term fuel trim bank 1 (LTFT 1)
Long term fuel trim bank 2 (LTFT 2)

Your idle information is only showing the short term fuel trims. What are the long term fuel trims at hot idle?

Guessing here, but as STFT 2 is dropping to -7%, I am picking the LTFT2 at idle is around 8% showing a vacuum leak on bank 2 = cylinders 4, 5, and 6.

Reading your first post, shows that you have replaced all of the basic causes of vacuum leaks. Well done. A smoke test is the next thing to do, which I see on your Bimmersports post, you are organising now.

Thanks Murray both the long terms sat at about 14.8 % and dont vary, sorry should have quoted those'. That seems to be the same in the freeze frame data

 

[geeveejay]

Mario makes a good observation regarding the Maf, I noted that you spray cleaned the Maf, can you see it in live data with your diagnostics just to see how its performing. After all fueling is governed by how much air the Maf is reporting to the engine management, if its mis reporting then you would get fueling problems. Smoke test the car just to confirm you have no leaks, if it passes that test have a look at the Maf, I had a duff Maf, cleaning it with Maf spray killed it. As soon as I replaced it with an oem unit, car was cured. Maf's dont always set codes when they go wrong. Its very easy to throw parts at a car but gets expensive. Reckon yours is either an air leak or duff Maf.

Just curious what you would expect to see in the live data at the MAF. I understand that the lean code would be caused either too much air or not enough fuel, so if air is fine finger points to fuel or at least what the MAF is telling the ECU I understand the basics but cant tell what is normal when it comes to Fuel trims, Maf output etc

I am more of a DCOE carb person so all this is quite new to me, but I am enjoying the learning !