Engine Noise Diagnosis Questions

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Engine Noise Diagnosis Questions

Post by rpdalton » Wed Oct 09, 2019 8:18 pm

I am attempting to troubleshoot an engine knocking noise at the top of the front bank on a 2001 Mazda Tribute V6. I am brand new to NVH. See the attached docuement


1) Why is there a order 1.5 and 3 spike? Does that mean the issue is at 1.5 times the crankshaft speed?
2) Why are there negative G values at the same time as the positive G values?
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Steve Smith
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Re: Engine Noise Diagnosis Questions

Post by Steve Smith » Thu Oct 10, 2019 1:18 pm

Hello and thank you for the post.
The vibration orders you have indicated in the .pdf file are E1.5 and E3
You are correct that these indicate 1.5 & 3 disturbances per engine revolution.
Typically, E3 is quite normal on 6-cylinder engines because we have 3 combustion events felt by the crankshaft per engine revelation, this is also felt in the chassis (Even with sufficient engine mounts)
There is a forum post here that will help

Looking now at E1.5, this is typical of 3-cylinder engines where we have 1.5 combustion events per engine revelation (which I find hard to interpret, “half a combustion”)
E1.5 is also typical of Bank to Bank combustion anomalies.
Could you take a look at Help>Show Vibrate Help>Engine Speed related vibrations (Within the NVH software)
Engine orders
Looking at the spikes/knocks you have indicated in the .pdf file these may be better viewed in the Time Domain view as these are instantaneous events containing a lot of energy but occurring for a very short time period.

The time between knocks/spikes or frequency of these events will present a clue as to the offending component (engine area)

It is difficult to determine from the .pdf but we have 2 spikes every 2.5 seconds approx. which is low speed (0.8 Hz) with some spikes sporadic in nature

The spikes do indicate positive and negative “g” as we have an acceleration in one direction and deceleration in another.
Accel Decel

Think of this as bound and rebound of the accelerometer in response to a single knock (like driving over a pot hole). As it moves from rest, we have an acceleration (bound) followed by deceleration (rebound)

I hope this helps, take care…….Steve

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