N55 - Misfire after valve cover replacement

[IrvesBMW]

this issue. I will try to be concise; but, this has been a week-long ordeal, so I apologies if my account is rather disjointed.

The vehicle is a 2011 F11 535i.


I rebuilt the valve cover and now see a pronounced misfire at idle around one minute after startup. Code: 12A902 Lambda sensor - short circuit to ground.


The whole edition:

Last week, I began some tasks that I had been procrastinating on for some time.

The valve cover and gasket need replacement due to significant oil accumulation in typical areas, leading me to anticipate a leak from one or both components.

Oil shift is imminent.

Clean the vanos solenoids and the oil pressure control valve, since I have seen sporadic error codes associated with oil pressure and exhaust vanos.

The works need significant disruption, including disconnection of lines and electrical hookups, so I recognise the multitude of possible complications that may arise.

During my investigations, I found that the cage inside the oil filter was absent, which I assume contributed to the vanos and oil pressure issues. Nevertheless, I proceeded to clean the solenoids, among other components, since I was already engaged in the task.

The OFHG was completed without complications; however, it is noteworthy that the intake manifold required little repositioning, and I did not replace the gaskets, which may have been advisable.

The valve cover was changed with no difficulty; but, when purchasing the replacement cover, the only available option I encountered was a Ridex product, which I acquired with much reluctance. In hindsight, I regret not exercising more patience to get a higher quality alternative.

Upon reassembling the components, the vehicle initially seemed to start properly; but, after about one minute, it had a significant misfire and displayed error code 102002, indicating an air mass plausibility problem. I reviewed all my work and saw no apparent problems; but, considering Ridex's reputation for subpar quality, I opted to reinstall the original valve cover with a new gasket, since there were no misfire issues before.

After repeating all the previous steps, I restarted the vehicle, which initially functioned well; however, it began to misfire again after about one minute. This time, I encountered a different problem. 101F01 - Throttle valve angle - absolute pressure in the intake manifold, comparison: pressure too elevated.

At this juncture, I was persuaded that I had either compromised a vacuum line or was displacing the valve cover gasket due to my fitting approach; hence, I resolved to get a smoke test equipment before proceeding further.

On Saturday, I activated the smoke machine and saw a wisp or two of smoke originating from the back of the valve cover. Ah, I realised. I have damaged the gasket; yet, there is hope on the horizon.

I removed the valve cover for the third time, cleaned and reinstalled the gasket, and ensured it remained properly positioned throughout assembly. On this occasion, I conducted a smoke test prior to reassembling the fuel rail and electrical connections, and I saw no indications of leaking; hence, I proceeded to reassemble all components. This time I started the vehicle, again, starts good, idles smoothly for a minute or two then begins misfiring. Curiously, the only code I received was 12A902, indicating a short circuit to ground in the lambda probe after the catalytic converter. No other faults; nonetheless, the vehicle is idling quite poorly.

I saw a little gurgling sound emanating from the PCV valve. Given that this was the original cover and I had invested some time in its restoration, I began to contemplate if I had inadvertently introduced cleaning solution into the PVC region, perhaps leading to obstruction. I opted to remove the valve cover once again and reattach the Ridex unit.

Consequently, I executed my tasks yesterday with painstaking attention to detail throughout the process. During the smoke test, there were no indications of leakage whatsoever. I started it again; it idled OK for a minute or two before misfiring, with a recurring 12A902 Lambda fault.

That is my current situation. I am quite perplexed, to be honest.

I see that I have three alternatives, but I would really appreciate feedback from others.

1. Substitute the post-cat lambda, since I may have damaged it due to the many initial misfires, perhaps associated with hoover leaks that I have now resolved. I read that the lambda is disregarded at the cold start for a brief duration, which aligns with my observations. I am rather hesitant due to the additional £80 expense, which may out to be a complete misdirection, as I had none of these concerns prior to my modifications to the valve cover and input manifold.

2. Acquire ISTA, since I am uncertain about the necessary components to become operational, given that I presently own just Bimmerlink. Perhaps there is further information to be obtained from ISTA or methods I might explore?

Tow it to a garage, concede defeat, and provide a blank check.

alternative 3 is a last recourse for me, as I am much more inclined towards acquiring knowledge, investing in appropriate equipment for the future, and maintaining cost management; nonetheless, I finally need to rectify the issue, making it a viable alternative.

I apologise for the digression. It has been a challenging task. Any assistance would be highly appreciated.

[drummer]

The post-catalytic lambda sensor just serves to assess catalytic converter efficiency and does not modify fuel delivery, unlike the pre-catalytic sensor. Have you verified that no damage has been inflicted on the wiring during the removal or reinstallation of the rocker cover?
Utilising ISTA would likely be advantageous for addressing such a defect. I examined a N55 last year, and frankly, I would have found it challenging to detect without the ISTA test plans.

[IrvesBMW]

Salutations. Upon examining RealOEM, I saw that the connections for both oxygen sensors are positioned above the valve cover, and I have manipulated both connectors and their cabling many times this week. Additionally, there are the connections for the fuel injectors and coils, the MAF sensor, and the sensor connector located on the intake pipe at the front of the engine.

I also disconnected the vanos solenoids and the oil control valve.


The symptoms of the misfire have almost remained same since the first restart. Everything seems OK, however it begins to malfunction after one or two minutes. However, the codes have inexplicably altered, and coupled with the observation of a hoover leak during the smoke test, it led me to believe that although I may have rectified the first issue, another problem persists.

It is unfortunate that the post-catalytic converter sensor does not affect fuelling, among other parameters. That may have constituted an impressive response! Regardless, it seems crucial that the vehicle idles well at first and thereafter begins to misfire after about one minute. That is likely pertinent to an operational change occurring shortly after the chilly start.


Is there a standard ISTA kit available for purchase that requires little effort to set up and operate?

[drummer]

ISTA is difficult to configure unless one has IT expertise; I lack such knowledge and thus had it completed by someone else.
Considering if it is feasible for the O2 sensors to be incorrectly connected or whether the connectors are dissimilar. I cannot recall at all.
It is an unusual flaw you possess, however.

[IrvesBMW]

Products of this kind claim that they are very simple to configure or provide guidance during the process; nonetheless, it would be beneficial to have feedback from an individual who has used it about its ease of implementation for someone without technical expertise.

We apologise for the disruption...



I believe the sensors may be confused, however I have remained attentive to that issue. They are discreetly colour-coded, with one containing four cables and the other five. I should verify, although it is improbable that I would have committed that error consecutively.

I must admit, it is exasperating at this juncture. Until now, I have contemplated potential solutions, considered various approaches, and examined components in the post, all with the expectation of discovering a remedy. I am now perplexed and making no progress.

[IrvesBMW]

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