Engine Acceleration reduces with a mild hissing sound from engine bay
 

Hi all! This is my first post, probably on any blog ever.

Anyway I have a 2003 E53 BMW X5 4.6is. It has about 85,000 km on the odometer bt has had a brand new engine and a brand new gearbox installed only about 15,000 km ago (although about 10 years ago).

Since about 9,000 km ago, I have been noticing a phenomenon wherein the (usually great) acceleration of the engine abnormally experiences hesitation when the engine is within the RPM band of 3000 to 4000 RPM. After 4000 RPM the acceleration kind of restores itself to the usual level; however when the acceleration restores, it does so with the vehicle experiencing an abnormal sudden push (or a forward leap or a sudden step-up in acceleration). This sudden push forward feels as if the vehicle suddenly got released from something which was holding it back.

Also, about the time when the acceleration is lessened within the usual RPM band of 3000 to 4000 RPM, I can hear a 'hissss' coming from the engine bay. The sound is almost like that of an air leak.

This phenomenon initially took place in about every two or less out of 4 acceleration attempts. Now this phenomenon takes place in every 3 or more out of 4 acceleration attempts. Also, nowadays it seems to me that the overall acceleration , even in the other RPM band outside of the range of 3000 to 4000 RPM, is getting hindered. However it is to be noted that the acceleration deterioration in the other RPM band (outside of the range of 3000 to 4000 RPM) is more subtle than that within the range of the 3000 to 4000 RPM.

I will really appreciate some opinions on the matter.

Parts of that sound like a plugged exhuast and parts sounds like a fuel issue and it could even be a timing issue. You need to pull codes and do some checking and testing to find the problem.

Agreed on the checking codes. Doesn't sound like a plugged cat to me though, because that normally wouldn't present itself intermittently.

Definitely need to check the codes and live data looking for anomalies. The sound you are hearing (hisssing) doesn’t match anything similar from my 4.6 motor, but I will say the power from my engine comes on with a very noticeable “bang” around 3500 rpm. It pulls strongly before that, but really rips at and above that approximate rpm. So the hissss and power surge may be somewhat unrelated. I do have a mild tune running on my car, but other 4.6 owners tell me theirs is biased to higher rpm.p too.

Have you done a detailed visual check of the vacuum and intake plumbing? I was having odd issues with my e53 early in its new life (2002) which turned out to be the intake boot which had (very) partially slipped off the throttle. The cars are also very particular about the vacuum plumbing integrity it seems.

Dear Henn28, thank you very much for the response.

I am fully aware of the fact that the vehicle is designed as such that it rips at and above 3500 RPM and I used to love it! I am fully aware of this vehicle’s natural instincts as my family has owned this vehicle since brand new.

But, wherein at about 3500 RPM the vehicle used to level up its acceleration in a steady, confident, smooth fashion, these days it actually hesitates between 3000 and 4000 RPM and then after 4000 RPM it opens up abruptly as if it was let go of its leash.

I actually have not checked the intake boot and nor have i checked the vacuum system. Any further specific guidelines on both of these aspects will be greatly appreciated.

In the meantime, the updated fault codes are as follows:

000001
000002
00000A
000014
00001D
00003C
000062
00008C
00008D - DME: Activation, electric fan
00008D - IKE: EGS signal line disturbed
000090

Dear 80stech, thank you very much for the response.

The fault codes are as follows:

000001
000002
00000A
000014
00001D
00003C
000062
00008C
00008D - DME: Activation, electric fan
00008D - IKE: EGS signal line disturbed
000090

Hello guys, will appreciate if someone can shed some light onto my issue, especially in view of the fault codes as below:

000001
000002
00000A
000014
00001D
00003C
000062
00008C
00008D - DME: Activation, electric fan
00008D - IKE: EGS signal line disturbed
000090

Erase the codes and recheck listing what your scan tool says they are and tell us what scan tool you are using. Check all the basics (fuel,air,exhaust) first. You might even have a transmission issue the way you are describing it.

Thanks a lot for the response. I will relay your msg to my service team.

Dear BMW Patrons,

Actually since my last post, I decided to engage the dealership’s service centre to diagnose my acceleration hesitation issue.

In December 2023, I obliged the service centre to inspect the air intake system. Initially the service centre was hesitant to do so as apparently there were no related fault codes. However upon my insistence, they performed a smoke test nonetheless and indeed detected a leak in the intake manifold gaskets. [Link of video: <https://www.dropbox.com/scl/fi/y7hfd76cq1y8zzdlqeq18/Intake-Manifold-Gasket-Leak-2023-12-14.mp4?rlkey=fmvio2f8et0zll36f8ds2z9ar&dl=0>]

The gasket set replacement work was conducted in June 2024. After the repair-work there are some apparent improvements in the overall response. However my chief complain of the (intermittently occurring) acceleration hesitation between the 3000 to 4000 RPM band still persisted. It is noteworthy though that the frequency of the occurrence has somewhat reduced.

I took it back to the service centre and requested them to inspect the vacuum system, the crankcase ventilation (ccv) system, the exhaust system, and check again the air intake system.

According to the service centre:

i) there is no issue with the vacuum system

ii) they inspected the ccv system including the pcv valve and found no issue

iii) they additionally inspected the fuel pressure and found it in order [Link of picture: <https://www.dropbox.com/scl/fi/kik9memfhm96z5xn5lepw/Fuel-Pressure-2024-06-07.jpeg?rlkey=fqsmvisr2amonok50htg3whon&dl=0>]

iv) they visually inspected the exhaust system and found no issue

iv) they did another smoke test inspection of the intake system and yet again found another leak, this time on the intake manifold itself [Link of video: <https://www.dropbox.com/scl/fi/9827rjsodbdiqy4uc0jr0/Intake-Manifold-Leak-2024-06-07.mp4?rlkey=merv9ovcr3glfh6x8u592ka8p&dl=0>]

According to the service centre the leak is not major enough to result in the significant acceleration hesitation that I am intermittently experiencing. However to get closer to the ultimate solution we have decided to proceed with the repair (through replacement of the manifold). Now waiting for the part to arrive from Germany.

My one question at this point is why the fault codes do not appear even though there are evident air leaks (which I believe are altering the fuel/air mixture inside the engine)?!

I really hope the intake manifold replacement contributes to a solution of my issue. I guess I will further update this thread after the next phase. However if anyone has any opinion in the meantime, your participation will be much appreciated.