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Engine surging noise

507 Views 2 Replies 3 Participants Last post by  20swrt
We recently purchased a 2021 Sienna XLE AWD (with VMI wheelchair conversion, so quite a bit heavier than stock). When driving up longer hills (Colorado Springs area) or under steady, moderate acceleration, the engine makes a surging noise. It accelerates loudly (which seems to be normal based on what I’ve read in these forums) but I haven’t found any mention of the surging noise. Every 2-3 seconds, the engine noise seems to change pitch/surge higher for a half second, then go back down. Alternating until I release the acceleration. Is this normal? We’ve had a few issues with the van already, so I think I’m just a little leery of any additional issues.
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I have also heard something similar in mine when I have it loaded going up some steady inclines on the highway. pretty sure its normal, it just means you are at a speed where the computer cannot decided where to keep the engine speed. as long as the van itself isn't surging, i would not worry about it.
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Im no automotive or mechanical engineer but critical thinking seems to indicate that it is very normal. For the hybrid transmission to operate properly - it needs to maintain a minimum voltage to provide enough torque to MG1. Otherwise the ICE will be rendered useless if the MG1 just free wheels due to low voltage. So during low voltage - IcE needs to run faster to charge the HV battery.

To help visualize this - look at my avatar. MG1 is the central (sun gear). ICE is connected to the 3 planetary gears. The outer ring gear is directly connected to the wheels (and MG2).

Next time this happens - see how many bar are left. Let us know how many bars are added.
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