Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

Volvo v40 2.0t my 2001 P0171

More
2 years 2 months ago #53852 by bobe84
Hi there Forum, I have been having this issue with my Volvo for some couple of days.
Currently it is -5C in Serbia and it did turn on CEL. P0171 is the error.
LTFT +4 STFT +50% at idle on fully warmed engine.
When i raise the RPM to 2k situation is improved, total trim goes to 10-20% aproximately.

I did clean the MAF since my MAF was reporting aproximately 1.67g/s when fully warmed up.
6-7 years ago, my MAF was showing aproximately 2.78g/s when fully warmed up.

Driving wise, no problems at all. At WOT engine pulls up to 135g/s second and third gear and O2 sensor does report rich.
Only problem i have is when engine is fully warmed up and idling.
It tends to have sort of random "fish bite" misfire, which is very hard to even detect.
If I push the gas pedal, engine responds well and does not hesitate... but once it returns to idle it starts misfiring some more until it sorts it out.
Only at idle fuel trims start to climb.

I did have in past (6-7 years ago) have exhaust leak on one side of the header, which i fixed by tightening the bolt.
I did take the picture of the bolt on the exhaust manifold, looks like it is all out.
Please take a look at the attachment, you can also see a sooth build up...

Now, I do plan to tighten the bolt.

Now my Q is really, can this exhaust leak manifest like this?
Facts:
-When driving upstream O2 sensor responds nicely and acceleration is good, no problems with lack of power and no misfires at all( which eliminates FP problems i guess?)
-Only slight misfire at idle when fully warmed up. And yes P0171 only appears when fully warmed up.
-MAF now under-reports at idle when fully warmed up. Goes as low as 1.67g/s which is low for this kind of engine. It should be 2.5g/s
-MAF also reports correctly at WOT (~135 - 140 g/s ). Engine does boost nicely and creates the power it is supposed to.
-Quite high fuel trims at idle and relatively normal fueltrims at load/driving.
-If i raise RPM on standstill the fuel trims improve.
- I am not sure about fuel pressure because i do not have FP gauge.

Q - Can this exhaust leak manifest like this? I mean, adding fuel at IDLE and normal fuel trims on load.
I pretty much discarded MAF as being faulty with seeing values at WOT. Engine is 165HP so it should read about 135g/s at WOT at 5200RPM where the peak power is.
Q - Can somehow going rich lower MAF value to 1.65g/s at idle?

Shall i go ahead and clean the throttle body? I have never done this and i own the car since 2010.

What if tightening the bolt does not fix idle fuel trims? What else to chase ( i know vacuum leaks are top on the list )

I do plan to tighten this bolt somehow or go to a mechanic shop and ask for exhaust gasket replacement.

I know i just piled up a lot of info here and i would appreciate some guidelines here. In Serbia, majority of mechanics are classic part changers and i asked if they have smoke machine to test for vacuum leaks.... they were literally laughing.

This car is 21 year old and i am afraid if i choose to replace the exhaust gasket, our mechanics here can snap some of the bolts (they are parts changers and they do not care)


Engine is b4204T3, classic volvo style with MAF and 2 MAP sensors. Has 2 O2 sensors and 1 bank. 2.0L capacity 4 cylinders DOHC.

Also, religiously following SD channel on YT. Great fan of those kind of channels, along with Eric O, Ivan and ETCG. :D

Please Log in or Create an account to join the conversation.

More
2 years 2 months ago #53853 by bobe84
Replied by bobe84 on topic Volvo v40 2.0t my 2001 P0171
Have no idea why image does not want to be uploaded. But here is the link of the image on my google drive... drive.google.com/file/d/1_GGJ5oMVeSMb22e...4Dx/view?usp=sharing

Please Log in or Create an account to join the conversation.

More
2 years 2 months ago #53883 by bobe84
Replied by bobe84 on topic Volvo v40 2.0t my 2001 P0171
Hi there, problem with exhaust leak was fixed, but fuel trims remained very high (no change at all)

So, i managed to pinch EVAP line to the intake manifold and what do you know, it resumed normal operation right away.
MAF is reading 2.5 to 2.7g/s which is normal for fully warmed up engine.
No more surges after snapping throttle.
LTFT is still some high at 5.5% (i think this will correct itself)
STFT is 0 +-5%

Since what i did is essentially block entire EVAP system, i am wondering, does this pose a fire hazard or no?

Please Log in or Create an account to join the conversation.

More
2 years 2 months ago #53895 by Andy.MacFadyen
MAF ---- I think already suspect you need a MAF. I take its a Bosch Hot Film MAF they usually don't respond well to cleaning

Buy the correct factory MAF from Volvo or Bosch

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Please Log in or Create an account to join the conversation.

More
2 years 2 months ago #53907 by bobe84
Replied by bobe84 on topic Volvo v40 2.0t my 2001 P0171
Hi there Andy. It is OEM MAF sensor in it and to be honest i did closely inspect it and it was quite clean.

I consider this fix since STFT and LTFT returned to normal range.

What i will search now is this valve for the EVAP line and replace it.

Please Log in or Create an account to join the conversation.

More
2 years 2 months ago #53921 by ksat22
Replied by ksat22 on topic Volvo v40 2.0t my 2001 P0171
Sounds like your purge valve is stuck open causing vacuum leak thusly affecting fuel trims. Pinching the line doesn't present a fire hazard. The EVAP system is simply for emissions.

Please Log in or Create an account to join the conversation.

More
2 years 2 months ago #53924 by bobe84
Replied by bobe84 on topic Volvo v40 2.0t my 2001 P0171
ksat22, yes, i've got the same thinking here.
Also it gets to -10C here at night, so my theory is that this purge valve is stuck open.

What threw me off in my thinking in the begining was:
1-Fuel trims did improve on partial load but they did not go to 0
2-I discovered that i had one bolt on exhaust manifold almost fully unscrewed
So my diagnosis went initially towards fixing the bolt.

Nevertheless, thanks for the feedback, i appreciate it very much! :)

Please Log in or Create an account to join the conversation.

More
2 years 1 month ago #53969 by oneel998
best thing ive found to upload imagines is to take a screen shot with your pc and paste to paint, then upload as a png. good luck

Please Log in or Create an account to join the conversation.

Time to create page: 0.208 seconds