Notorious P0171 / P0174 - lean condition

[vilkas88]

Hello, I have been working to resolve rough idle and "check engine"/SES light with codes P0171 / P0174 (system too lean). Here's my data:

2002 BMW 325xi about 140,000 miles.
Changed parts:
Valve cover gasket
DISA valve gasket and new flapper with metal pin
CCV valve and hoses
Throtle gasket
Purge valve
Break booster check valve and hose with F connector
Top and bottom air intake boots
MAF sensor
Front O2 sensors
Sparks plugs

I purchased a smoke tester and eliminated all smoke leaks by tightening all rings/connectors. Vacuum seems to hold when I drive, acceleration is good, engine sound is also good. But I only drove 2 miles.

My complaint - rough idle at stop light. So I also, cleaned ICV valve and injectors - but rough idle did not subside much - I have CDs in side pockets of the doors and they rattle!

at Idle a

Short-term (STFT)
Long-term (LTFT

[justinca540i]

How old is your fuel pump

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[vilkas88]

at Idle driving flat driving uphill
Short-term (STFT) +20-27 0...+3 +3...+8
Long-term (LTFT) +4 0...+4 0...+5
Load 8-10 20-30 40-52
RPM ~650-750 ~1200-1500 ~2800-3200

After driving 11 miles, SES light comes back, with codes P0171 / P0174, during the stop light i.e. at idle. So my question: could it be brake booster? The brake pedal is not stiff... the only symptom that maybe breaking distance is long... not sure where else a vacuum leak could be happening.... and where is my vacuum pump - is it by VANOS? Thanks for your help!!!

[vilkas88]

My fuel pump is original. I did replace the 12 yr-old fuel filter and installed the secondary fuel line check valve 7 months ago. At the time, I thought that fuel pressure might be weak - but it isn't the case anymore. Crank and start were never a problem. And it seems that I took care of most vacuum leaks. Smoke isn't escaping from manifold or under during smoke test - which is why I am thinking about either ICV valve, or brake booster. However - I don't think that smoke can travel up past the break booster check valve -to the booster's vacuum chamber. How could I diagnose for sure that break booster is falty?

[vilkas88]

I continued to examine the brake booster on a cold car. With engine off, I pumped the brake pedal 6-7 times. It stiffened up, I tapped the pedal gently and held foot on it. Then, I started the car - and indeed, the pedal went down a bit. So, perhaps, the booster chamber has built and held a vacuum - on a cold start. Should I conclude that the booster should NOT be replaced? However, the lean condition has been returning in a hot engine and at idle. I will go back to do a smoke test. I very much would like to avoid dismantling the manifold, but the orange manifold gaskets to engine, might be the last area to check. Let me know if you suggest other ideas about idle elimination.

[harrier]

Attach a scan tool like OBD fusion.
Start car.
Detach the brake booster line from the booster.
Watch stft as you plug the hose with your thumb

Then:
Do a fuel pressure test at the rail. Needs to be 50psi
Inspect caps at manifold and replace vacuum lines to sap and solenoid
Replace o-rings on dipstick



What brand MAF?
O2 sensors?

[vilkas88]

Thank you for your feedback, harrier! I hooked up OBD scantool, and cleared the memory of old fault codes.
Then I started the engine and pulled out the brake booster hose. The suction in vacuum hose was strong and here's my fuel trim observations:


before pulling out the hose
STFT bank 1: 0
STFT bank 2: 0




after pulling out the hose
STFT bank 1: -8 ... -14
STFT bank 2: -20 ... -28


I put the hose back and drove around the neighbourhood (about 5 min):
STFT bank 1: +4 ... --8
STFT bank 2: -4 ... -18


upon return to parking at idle:
STFT bank 1: +20 ... +2
STFT bank 2: +2 ... -4


The strong vibration at idle is still there. The car isn't "coughing" but at stop light when I have a foot on a brake pedal, I see my STFT rise from +4 to about +20. SO now, your tip to check the fuel pressure - I will go to a mechanic to do it tomorrow, since I don't have my own gauge. It might actually have smth to do with this odd idle - since I noticed awhile ago - there are two annoyances with the fuel system.
1) when I fill gas tank at FULL - and re-start the car, I get a misfire and the car dies temporarily. I wait 1 min and then it starts normally (as if, delayed priming).
2) sometimes when I drive - I do notice in half-second lag between my pressing the foot on gas pedal and the actual acceleration of the car (i.e. delay in acceleration).
Thanks again for the help, I will report fuel pressure readings next time.

[harrier]

Thank you for your feedback, harrier! I hooked up OBD scantool, and cleared the memory of old fault codes.
Then I started the engine and pulled out the brake booster hose. The suction in vacuum hose was strong and here's my fuel trim observations:


before pulling out the hose
STFT bank 1: 0
STFT bank 2: 0




after pulling out the hose
STFT bank 1: -8 ... -14
STFT bank 2: -20 ... -28


I put the hose back and drove around the neighbourhood (about 5 min):
STFT bank 1: +4 ... --8
STFT bank 2: -4 ... -18


upon return to parking at idle:
STFT bank 1: +20 ... +2
STFT bank 2: +2 ... -4


The strong vibration at idle is still there. The car isn't "coughing" but at stop light when I have a foot on a brake pedal, I see my STFT rise from +4 to about +20. SO now, your tip to check the fuel pressure - I will go to a mechanic to do it tomorrow, since I don't have my own gauge. It might actually have smth to do with this odd idle - since I noticed awhile ago - there are two annoyances with the fuel system.
1) when I fill gas tank at FULL - and re-start the car, I get a misfire and the car dies temporarily. I wait 1 min and then it starts normally (as if, delayed priming).
2) sometimes when I drive - I do notice in half-second lag between my pressing the foot on gas pedal and the actual acceleration of the car (i.e. delay in acceleration).
Thanks again for the help, I will report fuel pressure readings next time.

My instructions weren’t great. When you have the hose out, plug and hole the end with your finger to create a seal. If the stft stays low when the hose is blocked, it means that when that hose is in the booster it is leaking. Make sense?

[jclausen]

Though your smoke test should have found them if they were leaking but you have those vacuum hoses and caps under the rear part of the intake manifold, the secondary air valve and hose live there also. We did have an e46 once that the brake booster did cause a vacuum leak smoke came out onder neath the dash

[vilkas88]

Thanks for great tips!

harrier>> so, yes, - that makes sense, and that's what I observed. Kept the thumb on the tip of booster hose - and STFT were hugely negative and did not change much, thus it must be the leaky booster.

jclausen>> perhaps, when I did the smoke test - the smoke did travel into the cabin under the wheel. However, I had my flashlight in the engine bay and did not even consider that the smoke could leak past the booster. However, I did smell the smoke scent the next day. The secondary line, sec. air check valve have been changed too - I did not see any smoke whiffing there. And I didn't see any leak via the caps on manifold. Thus I focused on the booster recently - so will do one more smoke test and will report back and I expect smoke via rubber pear end in the cabin. Btw, when I drove and pressed really hard on the pedal to the bottom - the rough idle sound worsened. It is looking like the booster replacement job.

[harrier]

Thanks for great tips!

harrier>> so, yes, - that makes sense, and that's what I observed. Kept the thumb on the tip of booster hose - and STFT were hugely negative and did not change much, thus it must be the leaky booster.

jclausen>> perhaps, when I did the smoke test - the smoke did travel into the cabin under the wheel. However, I had my flashlight in the engine bay and did not even consider that the smoke could leak past the booster. However, I did smell the smoke scent the next day. The secondary line, sec. air check valve have been changed too - I did not see any smoke whiffing there. And I didn't see any leak via the caps on manifold. Thus I focused on the booster recently - so will do one more smoke test and will report back and I expect smoke via rubber pear end in the cabin. Btw, when I drove and pressed really hard on the pedal to the bottom - the rough idle sound worsened. It is looking like the booster replacement job.

There is a one-way valve, so smoke shouldn't go through. That is why you need the thumb test.

[vilkas88]

harrier>> Understood about the brake booster hose check valve. this morning, I did a different smoke test -- on a cold car outside -- and the result is still inconclusive, in my opinion. This is what I did. I started a cold car, hooked up OBD, and drove around the neighborhood about 1 mile with many stops - specifically targeting low RPMs at idle state. After secondary air pump stopped (1-2 min) - my ST fuel trims were negative (-8 and -14) for banks 1 and 2. I have recently cleaned the 6 fuel injectors (ultrasonic bath), so I thought that with secondary pump off - my negative trims made sense, more gas than air was injected, when cold.

When car warms up – observed STFT are about +20-28 the other day – I suspect a vacuum leak somewhere.

So today, with warmish car running, I unplugged the brake booster hose – AND – watched vacuum line suck the air – increasing my STFT from -8 to +14. When, it stabilized at +14 - I then closed my brake booster hose. The car is running, the STFT are now falling to about 0 … +6. I stuck the booster hose back in to the booster… STFT up to about +10-14, I figured that it is sucking a bit of air out of booster chamber (probably a small leak).

Next, I shut the engine and prepared smoke machine. Stuck smoke hose tip into grommet/hose of brake booster itself. Got the flashlight – under the dashboard in the cabin. And – nothing! No smoke was observed, in the brake pedal area. That is what I find odd. If the brake booster vacuum is compromised – I should be able to see some smoke leakage. The smoke build enough pressure in the booster– and then pushed out the smoke hose tip out.

That is what I find inconclusive – no smoke was leakage was observed with STFT +10-14. Conclusion – perhaps the vacuum leak happens on a hot car – when driven 10 miles or more, when I see STFT +20-28, that what causes rough idling at stop light – coincidentally – the foot is also on the brake pedal – so maybe that too bends the rubber in the brake booster, thus increasing vacuum leak.

[vilkas88]

Today I did fuel pressure tests, and need your help interpreting [2002 BMW 325xi] with these readings:

Test 1: Key on - Engine off: pressure jumps to 44 psi --> wait 5 min --> pressure declined to 35 psi.
Test 2: Key on - Engine on: pressure at 50 psi - very stable - not jumping up or down as engine is running.

So, do I need to change the fuel pump? Seemed like test 1 and 2 contradict each other...

[jclausen]

It seems good, what about a bad purge valve?

[vilkas88]

Thanks! Purge valve is fairly new (Aug 2019) - no codes with that. I suspect that I need to change brake booster - since the idle is bad when car is cold and when I have foot on brake pedal at stop light. If I switch to Neutral gear - and release the brake pedal - the rough idle subsides - and when I watch the STFT - in real time - I see values drop a bit as well. Thus probably there's a vacuum leak in the booster - although I could not physically catch it with smoke machine.

[tice23]

With how old your fuel pump is you should probably change it anyway as preventative maintenance. might fix it, might just cross off another item on the list. I had to go over every vacuum system in mine and it didn't go away until I replaced both fuel pump and filter with new rubber on the vacuum line too. Here is a pretty comprehensive thread on it.

https://forum.e46fanatics.com/showthread.php?t=929501

also to add to it there's another thread going over some trouble shooting stuff as well for vacuum leaks

https://forum.e46fanatics.com/showthread.php?t=897616

[vilkas88]

Wow! Very valuable info, and I appreciate the links. I will now consider replacing both the brake booster and the pump. I never thought that eliminating P0171/P0174 codes would require nearly $2000 cost, which is unfortunate. Prior to this, my annual maintenance cost was about $800 (tires, oil and fluids, electric, minor parts).

[justinca540i]

Sounds kinda dumb but is your rear main seal leaking oil?

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[jclausen]

Interesting thought, I wonder if the oil cap is hard to remove when the engine is running, meaning excessive crankcase pressure, ccv problems?

[vilkas88]

Quick update about newest developments! I installed a new power brake booster and a new fuel pump. I also took a 60-mile road trip to test things out.


The car sounds better at idle, responds to acceleration beautifully.
During heavy load 1000-3000 RPMs the LTFT are about +2...+4, STFT are in range -8...+8 (for both banks).
However, during low load of 650-750 RPM (at idle) here's what I noticed before and after brake booster replacement:


AT IDLE (~650 RPM)
STFT before +20-27 (bank 1) +20-27 (bank 2)
STFT after +20-27 (bank 1) +0-7 (bank 2)


after:
O2 Bk 1 Snsr 1 0.045
O2 Bk 1 Snsr 2 0.065
O2 Bk 2 Snsr 1 0.430
O2 Bk 2 Snsr 2 0.715


MAF was replaced about 7 month ago - Siemens brand.
At mile 55 - I stopped at the intersection and SES light comes on - codes P0171 and P1083. Freeze frame confirmed: load 14, rpm 694, stft +24 (bank 1), speed at 0.


Could the cause be some internal vacuum leak? It's not V-engine, but does have CCV. The only modification that I did earlier was installing a small check valve in the middle of breather line that connects bottom of CCV with the oil pan. 50sKid on youTube video said it would help to increase vacuum/prevent oil sucking up from the pan. I also wonder about possible O2 sensor malfunction - but don't have experience to interpret O2 readings, and I am surprised that OBD shows vacuum leak in bank 1 but not in bank 2.
And it seems to confirm that O2 is showing lean condition on bank 1 -but why is it not in bank 2?
Like before - smoke machine does not show any leaks externally.

[vilkas88]

Tonight I worked on the back of manifold - and I discovered another tube/nipple, which I capped with 7 mm rubber vacuum cap. This particular tube has a flat plastic edge along the round surface (shown on photo in red rectangle). So I made a slit in vacuum cap and made it fit. It wasn't a snug fit - so added extra tape later (not shown). When I drove later - the idle improved my STFT is now about normal +10 at idle, 650 rpm. Does anyone know the part - or how to properly seal that tube/nipple?

20200426_194127.jpg

[vilkas88]

Here's another example how someone from e46fanatics capped theirs tube (see below).
ByBimmerApp1322193803.740228.jpg

[harrier]

Yes, you need a new fuel pump and filter. Engine off, key on should be 50psi and should hold that for 20-30 minutes. VDO Siemens only for the pump.

Which brand of O2 sensor did you install?

It cost around $2000 to do a reasonable 150-175k maintenance, including:
CCV
MAF
O2 Sensors (precat only)
Intake manifold gasket
Heater hoses
Various o-rings (dipstick tube, air temp sensor, etc)
Cooling parts

These cars really take about $1,500 per year for maintenance. Gets expensive when you don't spend much and defer what should be done over time. It is also very likely you need a complete suspension refresh by now - shocks, struts, RTAB, FCAB, and likely control arms. Also the two flex discs (giubos) and the CSB.

Here is a schedule I put together:
https://forum.e46fanatics.com/showthread.php?t=1268849

[harrier]

11611727176

Tonight I worked on the back of manifold - and I discovered another tube/nipple, which I capped with 7 mm rubber vacuum cap. This particular tube has a flat plastic edge along the round surface (shown on photo in red rectangle). So I made a slit in vacuum cap and made it fit. It wasn't a snug fit - so added extra tape later (not shown). When I drove later - the idle improved my STFT is now about normal +10 at idle, 650 rpm. Does anyone know the part - or how to properly seal that tube/nipple?

20200426_194127.jpg

Looks like the cap you have is too small. Get part number 11611727176

[vilkas88]

I moving on with replacing 15 rubber grommets on the valve cover. (Valve cover and cylinder gaskets were replaced 7 months ago). When I took one of the grommets - it was stiff and fully baked. The prior mechanic cheapened out on me... Maybe that is the cause of vacuum leak. After watching several videos - I am told that the torque on those screws should be either 6 Nm or 10 Nm. I will go with 10 Nm on these grommets.

I also purchased an intake manifold gasket - which will be my next project if the vacuum leak continues. There are 9 screws that hold the manifold attached to the engine block. Could you tell me - what torque in Nm, I should tighten it back?