Misfire on all cylinders, plus lean codes on both banks - 2003 325xi

[Specialty]

Hello folks,

I recently fixed a big vacuum leak on my car (bottom ccv dipstick tube) as well as replacing the upper and lower intake boots. The car runs absolutely fabulous (700 rpm idle speed, drive or park, no rough idling or anything like that). I also cleaned the MAF sensor and did some other regular maintenance.

So as of recently, after doing all of this work, lean codes for both banks show up. Then, shortly after, I get misfire codes for every single cylinder, keep in mind the car was running totally fine, no shaking or vibration or big rpm change (rpm was staying in the 694-706 rpm range). I unplugged the MAF to see if that was the issue, and the car died right away. Today, I cleaned the MAF sensor with MAF sensor cleaner, and the car did indeed run better at cold temps, it stayed at higher RPM's for a more amount of time, but the codes would still show up. I haven't done a smoke test, but I have done a carb cleaner test and there are no signs of vacuum leaks. The oil cap doesn't have much if any suction.

Also, the car has 227,800 miles on it. I am mainly concerned about it passing inspection. I know that on a car with lower miles a CEL is an instant fail, but I've had other cars that had a CEL for other reasons (including misfire issues that were not actually noticeable misfires), and they checked the emissions test and they passed... I really need to drive this thing around, I did buy a bottle of fuel system cleaner just to see if that will help. The fuel is about 75% 93 octane and uh... 25% 3 year old gas (lol), I'll run it almost till empty, and see if this fuel system cleaner does anything.

Also, there is no 'mayo' or any sign that the CCV system has failed. Everything else checks up, the exhaust note doesn't sound like there are any misfires.

Any help would really be appreciated. Thanks!

[MarcoZandrini]

The only way to find all of the vacuum leaks is to professionally smoke test the intake manifold. That may be why the engine is misfiring.

[Muzz258]

You most like have introduced a vacuum leak with the recent work that you have done. Check your work. The lower intake boot has a tab that locates between two aluminum webs on the throttle body. You can't see it, only feel that it is located correctly. Check it. Often novice repairers don't locate it right and end up with a vacuum leak right at the throttle body.

Smoke test the engine to find the vacuum leaks. A can of carb cleaner often does not work in locating vacuum leaks.

[harrier]

Read this post. Will help you diagnose and understand
https://www.e46fanatics.com/threads/...agnose.1284608

[Specialty]

Sorry for such a late response, but I may have found the issue.

I checked the Short term fuel trims on both banks, and they are both running 15.6%! I did the ol' vacuum leak STFT test (meaning that at higher rpm/load, the STFT should go back down to normal) and surprise surprise, it didn't go down very much (between the 8% and 14% range). I tested it at multiple RPM ranges, anywhere from 2k to 4.5k, and they all had very similar results.

I'm thinking its the fuel pressure regulator inside of the fuel filter. It would certainly make sense and probably would explain the codes, as well as the incredible loss of power (this thing feels like a prius at WOT). I'm probably going to be ordering a fuel filter anyway, the ol' thing thats on it right now actually looks pretty darn old.

Thanks for the replies, and again, sorry for the late response!

EDIT: The fuel pump sounds fine, too. It makes a fairly decent whirring sound (as it should).

[harrier]

Sorry for such a late response, but I may have found the issue.

I checked the Short term fuel trims on both banks, and they are both running 15.6%! I did the ol' vacuum leak STFT test (meaning that at higher rpm/load, the STFT should go back down to normal) and surprise surprise, it didn't go down very much (between the 8% and 14% range). I tested it at multiple RPM ranges, anywhere from 2k to 4.5k, and they all had very similar results.

I'm thinking its the fuel pressure regulator inside of the fuel filter. It would certainly make sense and probably would explain the codes, as well as the incredible loss of power (this thing feels like a prius at WOT). I'm probably going to be ordering a fuel filter anyway, the ol' thing thats on it right now actually looks pretty darn old.

Thanks for the replies, and again, sorry for the late response!

EDIT: The fuel pump sounds fine, too. It makes a fairly decent whirring sound (as it should).

Did you read the post I shared above?

If you have high trims at idle and cruise, it is your O2 sensors and/or MAF. Fuel delivery is low at idle high at cruise.

Cleaning the MAF on our cars does nothing, as there is no upstream source of contaminants. You need new precat O2 sensors and likely a new MAF. Bosch for sensors, VDO Siemens for MAF.

[Specialty]

Did you read the post I shared above?

If you have high trims at idle and cruise, it is your O2 sensors and/or MAF. Fuel delivery is low at idle high at cruise.

Cleaning the MAF on our cars does nothing, as there is no upstream source of contaminants. You need new precat O2 sensors and likely a new MAF. Bosch for sensors, VDO Siemens for MAF.

I forgot to mention that I did replace the MAF with an OEM specimen. I haven't done the O2 sensors yet, but judging by the looks of things it appears that they already have been replaced (they look shiny). I read the inputs coming from both sensors and they both line up, they both fluctuate fairly quickly (as if they aren't lazy). I'm not doubting that it is the O2 sensors, just seems like that would be an odd culprit. I saw on a video that if you have high trims at idle but low trims at cruising speeds, its a vacuum leak, and that if you have high trims at idle and at cruising speed that it might be either 1: bad O2 sensors or 2: bad fuel pressure regulator. From what my tests have shown, the computer is trying to give the engine more fuel, but since the regulator valve is stuck open, all that excess fuel pressure is just going back to the tank. Like I said, this thing really is sad at WOT, it doesn't really want to move (not hesitation, just super low power). Those trims have been going up for the past couple months I have owned the car, they started at 8% and gradually went up to 15.6% (what its at right now).

[harrier]

I forgot to mention that I did replace the MAF with an OEM specimen. I haven't done the O2 sensors yet, but judging by the looks of things it appears that they already have been replaced (they look shiny). I read the inputs coming from both sensors and they both line up, they both fluctuate fairly quickly (as if they aren't lazy). I'm not doubting that it is the O2 sensors, just seems like that would be an odd culprit. I saw on a video that if you have high trims at idle but low trims at cruising speeds, its a vacuum leak, and that if you have high trims at idle and at cruising speed that it might be either 1: bad O2 sensors or 2: bad fuel pressure regulator. From what my tests have shown, the computer is trying to give the engine more fuel, but since the regulator valve is stuck open, all that excess fuel pressure is just going back to the tank. Like I said, this thing really is sad at WOT, it doesn't really want to move (not hesitation, just super low power). Those trims have been going up for the past couple months I have owned the car, they started at 8% and gradually went up to 15.6% (what its at right now).

Was the replacement MAF new or used?
Have you tested the fuel pressure? How?
How did you determine the o2 sensors are not lazy? Best way is to graph them and compare against known good. When they start acting lazy they look like normal, they are just “late”

I suspect you have multiple issues, and would do the diagnostics in the post.

[Specialty]

The MAF is new, and today or tomorrow I am going to test the fuel pressure.

[Specialty]

Alright, this is a revival of an old thread and I'm at my wits end.

I've replaced basically every single vacuum hose and tube. Through all of that I found 4 broken off hoses that were pretty old and crusty in the back of the intake manifold. Anyway they're all new now and the fuel trims still aren't good. I replaced the fuel filter, fuel pressure is at 50 when running. Everything sounds alright but now the car has even more STFT. What I have noticed recently is that the LTFT are at flat zero on both banks, but the STFT went up from 15.6 and one day suddenly spiked to 27.3 and its staying there. Like I said, the LTFT is still at 0, which is really confusing me. I've replaced the MAF, replaced the entire CCV system, the only thing I can think of now is the O2 sensors.

Something else I have noticed is that when pumping the gas at idle fairly quickly, the fuel trims go all the way down to -27.3. As soon as I let off, the car nearly stalls, then the fuel trims go all the way back up to 27.3 positive. This doesn't make any sense because the LTFT should be doing something.

[Muzz258]

Generally, if the LTFT's are at zero, I don't worry about the STFT's, as they are just reacting to the instantaneous trim conditions in the engine. But in your case, with them pegged positive and major swings to pegged negative, without the LTFT changing, there is something else going on.

Before you go to the expense of buying and installing O2's. Get your DME checked to see if it has the latest updates. I recall one case over the last few years where the LTFT's were not changing and a DME update fixed it. Send a PM to user BaliDawg. He has the capability to update DME's over the internet.

[Specialty]

Generally, if the LTFT's are at zero, I don't worry about the STFT's, as they are just reacting to the instantaneous trim conditions in the engine. But in your case, with them pegged positive and major swings to pegged negative, without the LTFT changing, there is something else going on.

Before you go to the expense of buying and installing O2's. Get your DME checked to see if it has the latest updates. I recall one case over the last few years where the LTFT's were not changing and a DME update fixed it. Send a PM to user BaliDawg. He has the capability to update DME's over the internet.

Whats interesting today is that I was thinking about updating the DME. Also something I did today was as soon as I made the post, I went outside and started the car, and as usual nothing had changed. However, it was until I unplugged the DISA valve that the STFT started moving up and down, and actually went all the way down to 10.3 for a few seconds before going up a little bit. As soon as I plugged it in, the values spiked all the way up to 27.3 again. Really odd, and when I would pump the gas, the values would go back down smoothly, eventually going to the negative zone all the way down to -15.6, then as soon as I'd let off it would jump back up to the 10-19 range. I did buy a non OEM DISA valve... I don't know if that has something to do with it for what. it still behaves great and I put good seals on it. I just don't see how a DISA valve could do that to fuel trims...