[Yourrid]

Hey guys, I'd like to get your opinion on a problem that seems to be getting worse on my E46.

*UPDATE* I just ran my codes again and am getting a P0171 - Powertrain Systme too lean (Bank 1). It's a pending fault, and no CEL.

Car:
2004 325CI Coupe
M54 Engine
5-speed manual
203,000 miles

Problem:
No CEL, but at low RPMs in 3,4,5th gear, and about 50-75% throttle, I get a surging/bucking in the 2,000-3,500 rpm range. It feels almost like a misfire. If I drive normally, it is almost unnoticeable. Idles good, but I've noticed the A/C causes the RPMs to drop a noticeable amount. The surging/bucking has been going on for a while now (usually only when I floor it and am at very low RPMs in 4-5th gear). Now it seems like it is getting worse.

High RPMs have no issue even with full throttle in any gear.

Very cold starts are accompanied by low (400-500 rpm) for a few seconds, then go away.

Randomly, when I start off in 1st from a stop, it will bog down when I try to give it gas and release the clutch. Yesterday it bogged down so bad, I tried to give it throttle and it stalled the engine before I could even begin rolling.

Replaced:
Fuel pump - 3 years ago - bought from Pelican Parts
Fuel filter - same time as pump, with new fuel lines
DISA valve - 3 years ago
New intake - 3 years ago (had a suspected vacuum leak)
1 new coil pack - 1 year ago - had a misfire cylinder 1
Spark Plugs - 1 year ago - NGK laser iridium, I think

Possible issues?
I keep reverting back to VANOS thinking this fits the description pretty well. But with no CEL, it's difficult to narrow it down.
I'm also considering the fuel pump, idle air control valve, A/C compressor, A/C pressure sensor, coil packs, vacuum leak... the list only goes on. :tsk:

I'd appreciate any insight you guys might have. I'm planning on taking my car to my buddies shop to have him do a fuel pressure test and check the A/C system pressure just out of curiosity.

 

[TobyB]

Eliminate all your air leaks first.

But at 200k, the vanos is likely leaking, too.
Do you get the rattle at idle?

t

 

[Mango]

Have you considered the dual mass flywheel has lost its step.

In addition, VANOS seals kit should be done regardless. Did mine on my 02 back around at 130k miles even though no symptoms from it. And no the ICV only matters at idle so I would rule that out. If you have no codes (Check LTFT anyway) then I doubt vacuum leak. doubt your entire list.

you should clean your throttle body if you haven't yet. you need to ensure anything that fuel, air, or spark runs through is in factory operating condition. as i said too consider the mechanicals. You have a car that's served two lifetimes so don't be surprised (or upset) if part of the ownership cost is renewing the car again.

 

[Mr Podman]

Could be something as simple as an intake or exhaust camshaft position sensor.
They're known to fail.


podman

 

[DBecker]

I agree with the advice to check for intake air leaks first. That generally means taking off the intake boots and inspecting them closely, replacing the Secondary Air vacuum hoses, and replacing the two or three intake manifold vacuum caps. The hose and caps are inexpensive and annoying to get to, so it's best to just buy replacements before starting.

If that fixes your problem, great. Otherwise you should plan on the VANOS seal refresh.

If you haven't replaced the spark plug connector boots in the past 100K miles, inspect them. Or, at about the price of spark plugs, buy a set of new ones. A cracked connector boot can cause mid-RPM stumble.

 

[TerraPhantm]

Flash your dme to the latest software: https://forum.e46fanatics.com/showthread.php?t=966614

 

[Nick DeZan]

I did my vanos seals at 230K miles, noticed no difference in engine performance or mpg.
Had a bucking issue like yours when the weather turned warm every year in the spring.
I have a manual trans, and quick accel in 3rd thru 5th gear would lead to bucking, like the fuel pump shut off for a second.
After clearing the adaptations using the DIS the problem went away only to reappear the next year when it got warm out.
After reading posts here by one of the BMW experts regarding O2 sensors, i looked at the sensor outputs in INPA and it looked like they were responding slowly and the trims were a bit off.
I replaced the O2 sensors and the problem never came back and provided about one mpg increase.
The original sensors had 270 k miles on them

 

[RayPooley]

Hey guys, I'd like to get your opinion on a problem that seems to be getting worse on my E46.

Car:
2004 325CI Coupe
M54 Engine
5-speed manual
203,000 miles

Problem:
No CEL, but at low RPMs in 3,4,5th gear, and about 50-75% throttle, I get a surging/bucking in the 2,000-3,500 rpm range. It feels almost like a misfire. If I drive normally, it is almost unnoticeable. Idles good, but I've noticed the A/C causes the RPMs to drop a noticeable amount. The surging/bucking has been going on for a while now (usually only when I floor it and am at very low RPMs in 4-5th gear). Now it seems like it is getting worse.

High RPMs have no issue even with full throttle in any gear.

Very cold starts are accompanied by low (400-500 rpm) for a few seconds, then go away.

Randomly, when I start off in 1st from a stop, it will bog down when I try to give it gas and release the clutch. Yesterday it bogged down so bad, I tried to give it throttle and it stalled the engine before I could even begin rolling.

Replaced:
Fuel pump - 3 years ago - bought from Pelican Parts
Fuel filter - same time as pump, with new fuel lines
DISA valve - 3 years ago
New intake - 3 years ago (had a suspected vacuum leak)
1 new coil pack - 1 year ago - had a misfire cylinder 1
Spark Plugs - 1 year ago - NGK laser iridium, I think

Possible issues?
I keep reverting back to VANOS thinking this fits the description pretty well. But with no CEL, it's difficult to narrow it down.
I'm also considering the fuel pump, idle air control valve, A/C compressor, A/C pressure sensor, coil packs, vacuum leak... the list only goes on. :tsk:

I'd appreciate any insight you guys might have. I'm planning on taking my car to my buddies shop to have him do a fuel pressure test and check the A/C system pressure just out of curiosity.

I see no mention of fuel trims. Why is that? They are the first step in diagnosing perforance issues. Check them out.

 

[Sapote]

A leaky VANOS seal cannot cause engine bucking.

 

[Yourrid]

Let me see if I can answer everyone in turn here... *UPDATE* I just ran my codes again and am getting a P0171 - Powertrain Systme too lean (Bank 1). It's a pending fault, and no CEL

TobyB: I'm going to do a smoke test in the intake and see what I get. I don't get much rattle noise. Maybe a little lifter noise, but it doesn't seem to be coming from the VANOS as far as I can tell.

Mango: Yea my car is old, and looking at prices of A/C compressors, flywheels, and VANOS, I'm anticipating some $$$ will be spent... I hadn't given the flywheel a thought. I think I'm coming up due for a clutch replacement, might be time to look into that as well.

Mr Podman: Do these camshaft position sensors go out without throwing any codes? Might be worth looking into as well.

DBecker: I changed out spark plugs last year and looked at the boots; they all looked pretty good. I'm going to pull them again and take a look. I think the VANOS is going to get resealed regardless.

TerraPhantm: I remember reading about the DME flash a while back. Seemed to stumble at 2900rpm if I recall correctly. I'm going to call my local BMW dealership tomorrow and see how much it would cost to get it done.

Nick DeZan: Those symptoms sound exactly like mine. I just scanned my car again and got P0171 - Powertrain Systme too lean (Bank 1). I wonder if this is 2 red flags for replacing my O2 sensors??

RayPooley: I've read a few threads talking about fuel trims. I've got an older ELM327 v1.4 clone and the Torque app on my android. I'm going to find a DIY on recording fuel trims and post it here once I do.

Sapote: I might do the VANOS just to be sure, but I'm beginning to wonder if it is an O2 sensor issue.

 

[Mango]

Yeah put some money into her. I assume you have no payments so you're already in the lead. Tuning up your car as needed will give you peace of mind and a better running more reliable car.

at 200k your car owes you exactly what you are willing to put in it.

 

[Yourrid]

Yeah put some money into her. I assume you have no payments so you're already in the lead. Tuning up your car as needed will give you peace of mind and a better running more reliable car.

at 200k your car owes you exactly what you are willing to put in it.

I agree. I really enjoy this car so I'd like to keep her running for years to come.

Hopefully having this P0171 code will give us a better idea of the way to proceed.

 

[TerraPhantm]

TerraPhantm: I remember reading about the DME flash a while back. Seemed to stumble at 2900rpm if I recall correctly. I'm going to call my local BMW dealership tomorrow and see how much it would cost to get it done.

I would diy it. Cheaper and less of a hassle

 

[Yourrid]

Alright so I'm still looking for exactly how I need to set up my fuel trims... but this is what I have for now.

Idle and warmed up:
Bank 1: 9.3%
Bank 2: 9.4%

2,000 RPM:
Bank 1: 7.2%
Bank 2: 7.0%

4,000 RPM:
Bank 1: 7.2%
Bank 2: 7.0%

I attached screen shots. I've got the OBD Fusion and Torque apps, I'm still trying to figure out what data is needed. I remember seeing a DIY on how to set it all up, but I can't find it on this site anymore.

 

[Archbid]

Some of this advice is good and some is really not.

Don***8217;t do the VANOS first. Deal with the lean code. It causes your symptoms.

You are facing set of maintenance issues that are very common for an e46 at this age. Get OBDFusion and take a look at your long term fuel trims.

LTFTs are long term adaptations to the fuel/air mixture. The computer reads air inflow via the MAF then the oxygen levels via the precat sensor and determines whether to add (if lean) or remove (if rich) fuel to achieve the right mix. STFT are basically real time trim to adapt to immediate conditions and LTFT evolve over time from the short term adaptations.

You get 0171/4 when your fuel trims are over 10%, but understand that spec is +/- 2%. What this means is that most folks at this point have out of spec fuel/air even if they don't have a check engine light or code.

If you have these codes, the greatest likelihood is that more than one of these issues is present (all of this is covered in Jfoj's Post on e46fanatics - Read it). Here are the most common causes:

1. Computer is asking for fuel but not getting it - old fuel filter (60k maintenance interval), failing fuel pump (120k is when some pumps go, some seem to last much longer). Computer sees "lean" mix at precat o2 sensors and demands more fuel. You replaced both

2. Unmetered air is changing the mix due to vacuum leaks - the MAF measures the air, then the computer adds fuel to get the mix right. If air is entering after the MAF it is unmeasured, and the system gets confused because the o2 sensors are saying there is too much oxygen relative to fuel. Smoke test then replace all rubber bits including vacuum lines and caps behind manifold, boots, and all CCV parts if original. Remove and inspect DISA (if it is not hard to remove either replace the unit or dig out and replace the seal). Consider replacing brake booster (won't show on smoke test). Leaks will tend to have a more pronounced effect at low rpm when the air introduced through the leak is a higher percentage of overall air flow.

3. Sensors are getting old and sleepy and under-reporting. Precat O2 sensors have 100k maintenance interval per Bosch. As they wear they will under-report. This will not necessarily trigger an o2 sensor code, but the lack of a code doesn't mean your o2 sensors are healthy. The MAF can also get tired and misread air flow. If the fuel trim issue still occurs at high rpm it is more likely a sensor issue. Frankly, it is almost always part of the problem, so I would replace with an OE unit only (not eBay, not used) after 120k when you get actual lean codes. Cleaning the MAF doesn***8217;t do anything on these cars.

Lots of folks say these sensors don't have to be replaced ever or at least until they go kaput, but folks also say that if there are no codes there is no problem - high LTFTs are suboptimal even if they don't reach the 10% or more required to trigger the code.

There are more obscure causes, for example it is not rare that someone replaces the precat sensors and swaps the wires for the two banks by accident. Easy to happen, simple to diagnose and will definitely trigger codes.