Header / exhaust related?
Engine vibration/resonance
- Thread starter OregonLC
- Start date
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Header / exhaust related?
I've noticed this recently too. The only varible I can detect is ambient temperature and my tires. In the mornings, when the temperature is below 95 degrees; no resonance. When the ambient temperature reaches 100 (and the pavement temperature is much higher) the resonance is horrible.
- Thread starter
- #23
It's possible, but I don't think so. It feels like a first-order vibration from the engine resonating in the chassis. I can feel it in my feet and if I'm touching the shifter I can feel it there. It's not something you can hear - not like the sound a pipe makes when it's touching the frame or a heat shield makes when it's loose and vibrating. Imagine holding the t-case lever - it's that type of vibration but it's subtle and felt by my feet/seat. Really don't think it's downstream of the engine because it's not speed/gear dependent. In fact it happens with the TC locked in 4th just as much as 1st at 10 mph. So if it's TC related it has to do with the shell and not the coupling. Although I can't reproduce it in N and that would be spinning the TC as well. The only common denominator is a) 1600 rpm +/- 25 and b) under load.
The more I think about it it's gotta be an engine mount or body mount. Funny story but I had a friend with a 3000GT VR4 Turbo (back in the day) and it had a similar problem. The solution was to 'dimple' the footpan with a jack to stop the resonance.
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I agree with you there.
I have a similar resonance at similar rpm. In fact sometimes it even makes a slight hum in the headliner right behind my head. Mounts look good so I've just learned to live with it.
- Thread starter
- #26
Just for fun, I tried reinstalling the hangdown weight thingy thinking that after a couple of weeks of it gone that maybe I'd notice a change with it back on. It did make a change - the resonance point shifted from 1600 to about 1450. It's maybe 20% less with the balancer installed.
Makes sense. It's disrupts, thusly alters, the natural resonance frequency of the frame.
- Thread starter
- #28
So long about the same time this started, I pulled the OEM hitch and swapped the spare to a full size. I read somewhere that the LX had a TSB for an NVH issue which was remedied by repositioning the spare. Wondering if this has anything to do with it. I guess I could always pull the spare for a few days and see what it does... or get a bumper ordered with a carrier.
- Thread starter
- #29
So - knock on wood - I think I've solved the riddle.
After a particularly dusty trip into the Wallowas I ordered some replacement air filters. When I replaced the element I noticed that some dust had made it past the filter and was lightly coloring the intake. I pulled the MAF and it was no longer shiny even though it had been cleaned withing the previous 5k miles. My mileage had also eroded from 16+ on the highway down to 13 and in town I was down around 10. Post-cleaning I am at 200 miles (224 tire adjusted) with just over 1/2 down.
Honestly, I don't remember if the vibration went away on the same day I cleaned the MAF or not. Yesterday I was driving and admiring the new-found economy when it occurred to me that the vibration had also subsided. I wouldn't say that it's completely gone, but it's gone to the point that it doesn't bother me any more. There's probably just a natural harmonic in the chassis at that rpm. I'm not 100% sure that the problem is cured for good, but it seems to have mitigated itself over the last several ignition cycles at least.
As for what was happening? Not completely sure. My understanding is that the LC uses a heated element MAF. As air blows across it lowers the temp of the heated wires which changes its resistivity and therefore the signal back to the ECU. If this is correct, then I would thing the crud would act as an insulating layer and would result in the ECU 'seeing' less airflow than actual and thereby leaning the mixture. The lean burn could account for the additional roughness. And I'm guessing that the fuel economy hit was either due to fuel trim cycling by the O2 not liking what the MAF was doing or inefficient power development
Lastly the source of the particles: my air filter box is missing a clip in the front. Never thought that much about it and the top comes down in contact with the base so I assumed it was good enough. Further, I had assumed that the vacuum of the intake would seal the filter against the intake side of the housing. I was wrong. It's now sealed with gorilla tape although I'd like to come up with a more elegant solution. I'll probably need to either fab something or maybe even strap the entire assembly with a clamp. At some point I do need to remove the entire intake and wipe it out. The TB and MAF are super clean but I'd like to kill the residual klingon particles.
After a particularly dusty trip into the Wallowas I ordered some replacement air filters. When I replaced the element I noticed that some dust had made it past the filter and was lightly coloring the intake. I pulled the MAF and it was no longer shiny even though it had been cleaned withing the previous 5k miles. My mileage had also eroded from 16+ on the highway down to 13 and in town I was down around 10. Post-cleaning I am at 200 miles (224 tire adjusted) with just over 1/2 down.
Honestly, I don't remember if the vibration went away on the same day I cleaned the MAF or not. Yesterday I was driving and admiring the new-found economy when it occurred to me that the vibration had also subsided. I wouldn't say that it's completely gone, but it's gone to the point that it doesn't bother me any more. There's probably just a natural harmonic in the chassis at that rpm. I'm not 100% sure that the problem is cured for good, but it seems to have mitigated itself over the last several ignition cycles at least.
As for what was happening? Not completely sure. My understanding is that the LC uses a heated element MAF. As air blows across it lowers the temp of the heated wires which changes its resistivity and therefore the signal back to the ECU. If this is correct, then I would thing the crud would act as an insulating layer and would result in the ECU 'seeing' less airflow than actual and thereby leaning the mixture. The lean burn could account for the additional roughness. And I'm guessing that the fuel economy hit was either due to fuel trim cycling by the O2 not liking what the MAF was doing or inefficient power development
Lastly the source of the particles: my air filter box is missing a clip in the front. Never thought that much about it and the top comes down in contact with the base so I assumed it was good enough. Further, I had assumed that the vacuum of the intake would seal the filter against the intake side of the housing. I was wrong. It's now sealed with gorilla tape although I'd like to come up with a more elegant solution. I'll probably need to either fab something or maybe even strap the entire assembly with a clamp. At some point I do need to remove the entire intake and wipe it out. The TB and MAF are super clean but I'd like to kill the residual klingon particles.
I test drove my LC for 40 minutes at 3am this morning trying to replicate this problem as it was driving me nuts. Happened last night on the way home. I couldn't replicate it even once this morning so the ambient air temps and pavement temps clearly contribute.
I'll try cleaning my MAF.
I just replicated the vibration or resonance : 1,600 RPM w/AC on. Shutting the AC off seemed to reduce it.
Strange though as this morning I cycled the AC on/off on the exact same road at the exact same speed/RPMs/etc. and couldn't replicate it even after six or more attempts. Combo of cold start and fully warmed up runs after 40+ mins.
Strange though as this morning I cycled the AC on/off on the exact same road at the exact same speed/RPMs/etc. and couldn't replicate it even after six or more attempts. Combo of cold start and fully warmed up runs after 40+ mins.
