S40 T5 Stuttering, stalling, jerking under load

mdziobas · Jul 19, 2019

Hi,
BTW I've got some leaks that are still not fixed.

Recently I got also a fault code P0193, which is Fuel Pressure Sensor.

I have plugged in OBD and watched on FPS readings. Can you have a look at the readings?

If there are some weird jumps and downs in it's readings is this for sure the problem in FPS? Could the exhaust/vacuum leaks cause those strange readings?

The vehicle:
1) Has leaks hearable under high load/accelerating
2) Got also P1526 code (changing throttle didn't help)
3) Stutters, jerks, stalls under hard accelerating/hard load.

Stuttering is not happening all the time. Since the FPS code became visible it has also stuttered under moderate accelerating.

https://drive.google.com/file/d/1--CNaYmBmQ5tgyyWg2ztXQdZfcfwazQm/view?usp=drivesdk

mdziobas · Jul 30, 2019

Update

Didn't get any reply (sadly

), but for anyone who would have problems similiar to these.

P1526 disapperead after replacing FPS sensor. Also hard stalling when accelerating is not happening anymore. Earlier the car was not accelerating as it should - it was accelerating, then for a split second it stopped, there was something like power cut and then it went further. It was happening at more than 40% throttle position (or more?). Really noticeable, annoying and stopping from doing any sick and fast road challenges/rides.

Today I have tried disconnecting the MAF sensor - wow! - the car was running like new. There is no more any jerking, stalling, stuttering, nothing, just runs and goes fine all the way! So now I have to try cleaning the old one or just buy another, new.

And.. try to find the leak which whistles and is really annoying and embarassing.

tmtalpey · Aug 1, 2019

Disconnecting the MAF does not necessarily point to an issue with that component. When the MAF signal is missing, the ECU goes to a preprogrammed fuel demand curve, so it cuts pretty much all the inputs out.

You should definitely track down this "whistling". One place to look is the pressure line from the manifold down to the CBV. THis is hard to see, it connects to the underside of the intake manifold, and runs under the various engine covers over the top of the head/camshaft area and down behind the engine. The connection to the manifold can split or simply pop off. When this happens, boost air escapes, and the ECU will sometimes work just fine until the split opens up and starts dumping air. This causes all sorts of extreme protection measures like cutting boost, pulling timing, etc. And it will go back to working fine under light load.

The other prime candidate for whistling is the PCV diaphragm. The quick test is to pull the dipstick out while the noise is happening. If it goes quiet, you've found it.

mdziobas · Aug 1, 2019

RE

tmtalpey said:
Disconnecting the MAF does not necessarily point to an issue with that component. When the MAF signal is missing, the ECU goes to a preprogrammed fuel demand curve, so it cuts pretty much all the inputs out.

You should definitely track down this "whistling". One place to look is the pressure line from the manifold down to the CBV. THis is hard to see, it connects to the underside of the intake manifold, and runs under the various engine covers over the top of the head/camshaft area and down behind the engine. The connection to the manifold can split or simply pop off. When this happens, boost air escapes, and the ECU will sometimes work just fine until the split opens up and starts dumping air. This causes all sorts of extreme protection measures like cutting boost, pulling timing, etc. And it will go back to working fine under light load.

The other prime candidate for whistling is the PCV diaphragm. The quick test is to pull the dipstick out while the noise is happening. If it goes quiet, you've found it.

Thanks for answer!
I'll tell you something more about the leak.
Some time ago (before I spent ~350€) there was also a whistling at cold start (as hard as a jet, something really similiar to the alternator's V-belt). There was a leak on the hot side, exactly there was a leak on the head of exhaust manifold. The head was so curved that you could even notice it on it's photo. They told me they've repaired it, they have done head planning, new gasket etc.. There is no more whistling at cold engine, but the "load whistling" is still happening. Since that time I did not visited them again, I had no time, no mood to hear again some more bad news and spending. Load whistling was becoming harder, even before repairing the main exhaust manifold's leak. At beginning it was only happening on cold engine, when engine got hotter, there was totally no whistling even under the load. In time it went further and worse. So I am pretty sure that those things are different, there is also other leak than this one on exhaust manifold. TBH I thought that they've done ****ty work and did not repaired the exhaust manifold.

So.. replying to your suggestions - I also thought that if:
MAF is connected - ECU could react to readings caused by leak -> engine would behave wrong
MAF is disconnected - it does not react to those readings and it goes clean

I see that most of the symptoms with stuttering etc. was caused by FPS.
I've ordered MAF cleaner - to be sure I will also try to clean it in a few days.

1) About the pressure line - is there any way to easily find it? Any gas? Spray with some detergent to look for a bubbles? Or just lay down and track the whistles?
2) PCV - I tried. It's not the PCV - pulling out changed nothing.

BTW The biggest problem is I have no place to lay down or just have a time with my car.. sadly.

tmtalpey · Aug 1, 2019

Ok, well to service the exhaust manifold gasket they'd definitely be moving or possibly disconnecting that CBV line, it goes right past it.

I would not bother with the MAF cleaner. Some will say go for it, but I'll say it risks more harm than good. With the old "hot wire" type MAF it made a difference, but this is a "thin film" one and is relatively trouble free. Mine has never been cleaned, in 15 years now. MHO.

Do you know where the FPS is? If so, the upper end of the CBV pipe is right next to it, just below and behind as you look at the engine from the front. It starts out pointing straight down, then makes a U turn upward and under the top cover. It comes out directly behind the engine and continues downward where it connects to the CBV. If you pop off the hose at the manifold end, it should hold pressure when you blow or pump air into it. Worth a test.

If the hose is the problem, it's relatively easy to replace, it's just a few feet of tubing. The tricky end is the CBV, where it's really hard to reach and you definitely have to do it from below. If it's the upper end, no big deal.

It is certainly possible that the whistling is the exhaust gasket or manifold flange. Many of our cars have this issue. Generally, the gap closes after a few seconds of running, but full-boost turbo pressure can cause the exhaust manifold pressure to rise (pushing against the turbo) and this can induce leaks. But it would be a really bad one, and I can't imagine it would close up fully, so it should be findable even at idle. Maybe!

mdziobas · Aug 2, 2019

tmtalpey said:
Ok, well to service the exhaust manifold gasket they'd definitely be moving or possibly disconnecting that CBV line, it goes right past it.

I would not bother with the MAF cleaner. Some will say go for it, but I'll say it risks more harm than good. With the old "hot wire" type MAF it made a difference, but this is a "thin film" one and is relatively trouble free. Mine has never been cleaned, in 15 years now. MHO.

Do you know where the FPS is? If so, the upper end of the CBV pipe is right next to it, just below and behind as you look at the engine from the front. It starts out pointing straight down, then makes a U turn upward and under the top cover. It comes out directly behind the engine and continues downward where it connects to the CBV. If you pop off the hose at the manifold end, it should hold pressure when you blow or pump air into it. Worth a test.

If the hose is the problem, it's relatively easy to replace, it's just a few feet of tubing. The tricky end is the CBV, where it's really hard to reach and you definitely have to do it from below. If it's the upper end, no big deal.

It is certainly possible that the whistling is the exhaust gasket or manifold flange. Many of our cars have this issue. Generally, the gap closes after a few seconds of running, but full-boost turbo pressure can cause the exhaust manifold pressure to rise (pushing against the turbo) and this can induce leaks. But it would be a really bad one, and I can't imagine it would close up fully, so it should be findable even at idle. Maybe!

I'll try with the mentioned CBV hose first and then my second question is - can I try to find the leaks with smoke? Friend has got vape e-cigarette so I could blow it into any vacuum hose (the one you're talking? brake booster I heard also?) and it would be easier to find it. First to see if without runned engine it leaks somewhere and then run it and see what happens after.
I do really appreciate your help!

tmtalpey · Aug 4, 2019

Some leaks can be detected with a smoke pencil, others not so much. There's no magic in diagnosing these things, just careful hard work.

mdziobas · Aug 14, 2019

tmtalpey said:
Some leaks can be detected with a smoke pencil, others not so much. There's no magic in diagnosing these things, just careful hard work.

Hey,
Coming back with some fresh info.
I left my V in a service. They've double checked their job (new exhaust manifold gasket with planning etc.) and also were looking for another whistle sources.

They've told me there are no places near engine where the whistle comes from. The only side, they could hear something from, was the catalytic converter. They allegedly didn't found any leaks there anyway.

Some time ago one guy told me there was everything flying inside when he knocked the cat. He were searching for leaks just before exhaust manifold repair. There is a chance it could be clogged or just damaged and not working properly inside.

My Q:
a) If car drives well without MAF is there a possibility it has something to do with damaged cat?
b) If it would be necessary - better to cut the cat or get new? It's expensive thing as we all know. Keeping in mind it is 2.5T and what (if any) consequences would be after.

PS Using OBD2 car does not pass emission tests - exactly the Oxygen one and Catalytic.
PS2 They've checked everything we were talking here before (hoses, CBV, exhaust gasket behind the manifold).

avenger09123 · Aug 15, 2019

Damaged Cats seem to be becoming a common thing around here.

So in theory - metered air from the MAF, Pre-CAT O2 sensor and Post CAT o2 sensor are supposed to mathematically align in terms of air intake. While the Pre/Post Cat O2 sensors are specifically there to adjust fuel mixture trims and comply with EPA regs, it would make sense that the computerized table performs better than the actual MAF reading in the case of a bad or damaged cat. Reason for this is the MAF is a hard reading - whereas a table is based on theoretical flow and the O2 sensor calcs - which if bad, can cause high/low trims and run much better since it "thinks" it's doing exactly what it should be.

My .02 - If you have to pull the entire pipe anyways to get it cut out - get a new pipe - or one off a junkyard, otherwise, buy a QUALITY CAT to get welded in it's place.

mdziobas · Aug 16, 2019

Okay.. I see removing cat gives a big difference in car sound. Didn't know that.. anyway I don't want my car sound like a tuned honda.

I'm still searching for an answer to cut or not to cut. First they would have to open it and check if it is really not worth using, then would have to make decision.

Q - If even.. straight pipe through cat or just left an empty box? In our country it is illegal to drive w/o.. but having a view there is a cat box could be enough sometimes. Second problem is a CEL after. O2 should be a bit ousted as far as I read.

Jirv0id · Aug 16, 2019

Yes no cats is illegal everywhere, Second O2 sensor needs to be tuned out by a performance company. Solution is to get a high flow cat, they're legal and don't cause restrictions in the exhaust.

07S40Guy · Oct 30, 2019

Any update if this was fixed? My cars getting same thing but with a p0101 issue MAF related. Got a new MAF still have this issue. My stalling / rough idling happened after a PCV replacement. I have followed ENVYs posts but he has replaced everything there is to replace to no avail at this point I think. I don't want to retrace his steps if it wont fix it. I am going to try to disconnect my batteries tonight and see what is going on.

mdziobas · Nov 1, 2019

07S40Guy said:
Any update if this was fixed? My cars getting same thing but with a p0101 issue MAF related. Got a new MAF still have this issue. My stalling / rough idling happened after a PCV replacement. I have followed ENVYs posts but he has replaced everything there is to replace to no avail at this point I think. I don't want to retrace his steps if it wont fix it. I am going to try to disconnect my batteries tonight and see what is going on.

Hey,
Replacing MAF (and FPS before) resolved stuttering. For some time I also drive with DSTC turned off and I found no more related problems to this, maybe several exceptions happen.

S40 T5 Stuttering, stalling, jerking under load

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