Noise Diagnosis

[chazsandiego]

Hello, hope all of you are well.

Been having an intermittent noise coming from passenger side engine bay. It sounds like the clicking noise a bad CV axle would make or the clicking a baseball card would make in the spoke of a bicycle wheel.

The noise only occurs when the vehicle is moving but load does not seem to be a factor as the noise is not present when power braking. It does occur (lightly) when coasting in D or N.

I also feel that the noise will only occur after the vehicle has been warmed up, but not every drive cycle.

I suspect that it could be misfiring but only because I noticed a crack in my distributor cap while replacing my spark plugs, but again I'm not completely sure.

Any advice or input is always greatly appreciated!

[shogun]

Does the noise change in frequency depending on the RPM of the engine? If so, it could be sparking. In any case first change the distributor and see if the noise is gone.
Is it more on the lower side of the engine? brackets for power steering. LAD lines? Had that once on my 750, typical problem here, my wrenching buddy has a long list, see in index noise and scroll down to see the pics http://e32b12.blogspot.com/

[chazsandiego]

Installed the new rotor today and I'm glad I did. The old one had a trench worn into the contact points.

Unfortunately my issue still persists.

The noise seems to increase in frequency with vehicle speed and it will only occur with the vehicle moving, even if it's just inching. The noise is coming from the passenger side of the engine bay, but its difficult to pinpoint exactly where.

It may just be coincidence but I feel like the noise will generally occur after using the full pedal distance to brake. It even seemed like the nosie was especially noticable while power brake, coasting and coming to a stop with the noise stopping when the vehicle came to a halt. But again it could just be coincidence.

I had ordered new pads and rotors when this issue was more intermittent but I'm still not sure this is whats causing the noise.

Any input is always appreciated!



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[Cactuar]

Can you lift the front of the car and try rotating the front right wheel?

[chazsandiego]

Can you lift the front of the car and try rotating the front right wheel?

Not a bad idea. I'll give it a shot while I'm at work today. Gives me something to do to keep from obsessing on it.

Thanks as always!

[chazsandiego]

Hello all!

Just an update. After spending a couple nights with Bentley I'm confident that I've been hearing two different noises. My front right caliper is dragging and the rotor is warped (already have those covered).

The original noise has been either a lean misfire or detonation from excessive carbon build up. I'm leaning towards lean misfire mainly because the issue seems more likely to occur when I get low on fuel.

I know this vehicle uses a vane sensor to meter incoming air, but does it also use a hot wire to measure the incoming air temp as well?

Always appreciate the assistance

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[shogun]

IAT on the M30 is inside the airflow meter https://www.bimmerforums.com/forum/s...M30-IAT-sensor
https://www.bimmerforums.com/forum/s...ensor-location
example repair M20 AFM https://www.r3vlimited.com/board/for...afm-s-for-sale
Testing IAT on M30 engines is described in detail in the Bentley page 130-16 fuel injection.
Using a digital voltmeter test for voltage across terminals 1 and 4 in volume air flow sensor connector. in total there are 5 terminals.
at 14 + - 2 degree F resistance 7 - 11.6 kohm
at 60 + - 2 degree F 2.1 - 2.9 kohm
at 187 + - 2 degree F 0.27 - 0.40 kohm

if any fault, replace air flow sensor, Bentley says

[chazsandiego]

Another update

Spent some time testing the IAT and Vane, injectors, IACV and Throttle position sensor and all were in good shape.

Finally broke down and had my buddies at the auto shop take a look. It only took them five minutes on the lift to discover that my transmission mounts are shot.

They are so bad that while they were wiggling the transmission a huge chuck of rubber fell out.

After having my mindset focused on an engine issue I'm a bit hesitant to believe that this is the cause of the issue. I hoping that someone can help shift my focus.

My main concern is that the noise only appears when the vehicle has been warmed up. From there it will only occur at lower speeds. For instance, it takes me about 15 minutes of highway driving to get to and from work. The noise will start after getting off the freeway, usually at the second or third stop light. A longer idle time after freeway tends to increase the probability of the offending noise.

Regardless I'm going to do the mounts but I'd like to know if the symptoms I described are consistent with bad transmission mounts.

TL;DR
My suspected misfire is actually bad transmission mounts.

As always any assistance is greatly appreciated!

[shogun]

if the trans mounts are shot, then probably the engine mounts and the driveshaft center bearing are also not the best or also damaged now. If you want to make it perfect and long lasting, change engine mounts, trans mounts, center bearing, (and maybe even the differential ones)then you have the complete driveline straight again.
Old engine mounts get shorter over the years, here an example of a new and old one from an M30 engine, all this can cause noise

[chazsandiego]

Thanks Shogun,

Luckily I'd replaced the engine mounts a couple months back. Transmission mount is on the way as well as that center bearing mount.

Rear diff support I will replace when I do my trailing arm bushings which are also shot. I had a suspicion before that all the rubber on this vehicle was I need of replacement and this just confirms that.

Until i get these new mounts installed I'm not gonna stress it too much.

Thanks again!

[chazsandiego]

I just wanted to put this one to bed. The auto shop guys, with their fancy lift, flashlights and working eyeballs were right.

It was the transmission mounts and not a misfire like a thought (so happy to be wrong).

Now to get started on that 5hp18 with the trans program error.....

Thanks again for all the assistance!

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