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Old 08-13-2015, 05:08 AM   #1
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Hesitation to rev and humming sound

Hi All,

I am wondering if any one can help to troubleshoot my problem, it doesn't seem to be a major problem, but I could be wrong. After I did a oil change I am experiencing a humming noise directly related to engine rpm when driving, not sure if it is related to me doing an oil change or just coincidence.

The other problem I am experiencing is when I rev the engine up in neutral to say 6000rpm, let it drop to 2000 rpm and then rev again, the engine hesitates to get up to the 6000 range, I hope my explanation it clear enough, if feel it is because of fuel starvation.

These are two completely different issues, can any one point me in the right direct of if this has been covered any where?

Note:
-clean oil, new oil filter, accusump fitted
-air filter is clean
-maf is clean
-throttle body is clean

I need to fit new spark plugs. Besides spark plug and fuel pump pressure, what else should I be looking at?

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Old 08-13-2015, 08:41 AM   #2
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What does the engine do when you drive to 6000 rpm, let it drop to 2000rpm, and then get back on the throttle?

If the engine is starved of fuel under no load, then it will be very clear when under load. Do you have any codes?

For the humming, I think a good start (and the only real easy and cheap test you can do) is to remove the drive belt and listen for the same humming sound. If the sound is gone, then it is one of your engine accessories making the noise. If the sound is still there, well...then, its going to get interesting.
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Old 08-13-2015, 07:44 PM   #3
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Good answer, thanks, I will drive the car in the same scenario, and give some feedback. Spark plugs are a given for me to change, I would however like to test my fuel pump, will search to see how I can do this.

I'm going to see if my Durametric throws any codes, I'm not an expert on using the Durametric, not even sure when last I used it. Do I need to get the car acting bad before it will throw a code or not. ie. Rev it so that it hesitates. Hope that makes sense.
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Old 08-14-2015, 10:11 AM   #4
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I don't know about hesitation to rev but I found this blog of a lady in Australia that put an accusump in her 996 and after she installed it she started getting a buzzing sound that turned out to be the stainless lines vibrating:

http://www.oz951.com/public/emmy.htm#Accusump

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