(Engine experts needed) Chirp Vibe Pop - What is wrong?

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toximus
Posts: 4
Joined: October 15th, 2019, 9:55 am
Vehicle Year: 2004
Vehicle Make: Jeep
Vehicle Model: Wrangler

(Engine experts needed) Chirp Vibe Pop - What is wrong?

Post by toximus »

I've got a weird one for you guys.

A rattling chirping squealing noise (sounds like saying "chi-chi-chi" using the short "i" sound, but also kind of like a belt squeal except not continuous. The timing seems to be every revolution of something something touches.) has been occurring somewhere in or around my engine bay when the M90 supercharger goes into boost on the 4.0L while the 42RLE transmission is in overdrive -- this primarily happens between 45mph and 55mph. It also seems to be happening over 60mph when running the engine foot to the floor. For either of these conditions if it happens while accelerating the noise eventually goes away once the RPM, speed, or engine load changes. My theory has been that under these conditions a bad idler pulley has been receiving extra load and making the noise, I have a replacement idler on the way, but I think I might be wrong after yesterday.

I found a few big long hills that I could keep the noise happening the entire way up and figured I'd take a video to see if I could make more sense of it. Instead I seemed to have angered the beast and made things even more confusing.

MP4 Video - 53MB.

I put the engine in this boost condition (boost, overdrive, 50mph) to induce the chirping noise and held the throttle to keep it chirping all the way up (chirping starts in the video at 1:08). As I climbed the hill, the frequency of the chirp changed as well as the tone. You can hear the progression of this change in the video at 1:17 until about 1:39 when the chirping changed more suddenly missing a few of the chirps and changed more into a higher pitched "tee-tee-tee" sound. Then the Jeep started violently vibing like driving over continuous rumble strips (difficult to see but starts around 1:45 in the video and continues until the end) the vibe stays consistent and does not change intensity. The first 2 hills I lifted off the accelerator when the vibes started and the vibe stopped. The 3rd hill I angered the beast and kept my foot where it was to see if the vibes would change and I kept my food there until a single pop/thud occurred. It sounded and felt like something thumped against the tub. I immediately lifted my foot and the vibes stopped and I pulled over. My first thought was either the transfer case cracked in half or a ujoint cracked, my second thought was wondering why there was no followup sounds if it was driveshaft related. The engine stayed running the engine time, no CELs.

I looked over the drivetrain and checked fluids etc and I couldn't find any leaks, cracks, or issues.

I drove a little to see what would happen and it felt completely normal. I put a jack under the rear axle and everything spun by hand like normal. Because I couldn't find any issues after 45 minutes of looking I went back out on the trail for 4 more hours and then drove home another 2 hours 55-65mph being careful to let off the accelerator whenever the chirping sound started. Aside from the chirp under those specific conditions, if I were buying this Jeep I'd have no concerns with the engine -- it drives great -- but clearly something is wrong with the drivetrain?

The maximum boost this pulley provides is 8lbs. I've checked the peak gauge and it has never gone over. If I'm hard accelerating I can go up to 8lbs of boost without the chirping noise but the boost quickly drops off again after reaching my desired speed. Is it possible that under the chirping conditions that sustaining the boost for that long is lifting the head allowing for a misfire (causing the vibes) until the boost "burps" (causing the pop) out of the head? Wouldn't that cause lasting damage that would be seen under all driving conditions?
skyway
Posts: 3
Joined: January 30th, 2021, 9:50 am

Re: (Engine experts needed) Chirp Vibe Pop - What is wrong?

Post by skyway »

I might not be of much help but I have a stock 4.0 with almost the exact same sound only happens when I’m climbing a hill .
I’ve checked / replaced the belt drive ,motor mounts , both drive shafts rebuilt the clutch has been serviced twice not all due to this noise . Mine sounds like a belt auto tensioner going but xj don’t have an auto tensioner.
I do have either a blown head gasket or cracked head I’ve stopped trying to find the source of the noise as the motor will be replaced soon .
KarmaKannon1
Making Progress
Making Progress
Posts: 63
Joined: May 21st, 2020, 10:13 am
Stroker Displacement: 4.7
Vehicle Year: 2000
Vehicle Make: Jeep
Vehicle Model: Cherokee
Location: Utah

Re: (Engine experts needed) Chirp Vibe Pop - What is wrong?

Post by KarmaKannon1 »

toximus wrote: May 9th, 2020, 9:29 am I've got a weird one for you guys.

A rattling chirping squealing noise (sounds like saying "chi-chi-chi" using the short "i" sound, but also kind of like a belt squeal except not continuous. The timing seems to be every revolution of something something touches.) has been occurring somewhere in or around my engine bay when the M90 supercharger goes into boost on the 4.0L while the 42RLE transmission is in overdrive -- this primarily happens between 45mph and 55mph. It also seems to be happening over 60mph when running the engine foot to the floor. For either of these conditions if it happens while accelerating the noise eventually goes away once the RPM, speed, or engine load changes. My theory has been that under these conditions a bad idler pulley has been receiving extra load and making the noise, I have a replacement idler on the way, but I think I might be wrong after yesterday.

I found a few big long hills that I could keep the noise happening the entire way up and figured I'd take a video to see if I could make more sense of it. Instead I seemed to have angered the beast and made things even more confusing.

MP4 Video - 53MB.

I put the engine in this boost condition (boost, overdrive, 50mph) to induce the chirping noise and held the throttle to keep it chirping all the way up (chirping starts in the video at 1:08). As I climbed the hill, the frequency of the chirp changed as well as the tone. You can hear the progression of this change in the video at 1:17 until about 1:39 when the chirping changed more suddenly missing a few of the chirps and changed more into a higher pitched "tee-tee-tee" sound. Then the Jeep started violently vibing like driving over continuous rumble strips (difficult to see but starts around 1:45 in the video and continues until the end) the vibe stays consistent and does not change intensity. The first 2 hills I lifted off the accelerator when the vibes started and the vibe stopped. The 3rd hill I angered the beast and kept my foot where it was to see if the vibes would change and I kept my food there until a single pop/thud occurred. It sounded and felt like something thumped against the tub. I immediately lifted my foot and the vibes stopped and I pulled over. My first thought was either the transfer case cracked in half or a ujoint cracked, my second thought was wondering why there was no followup sounds if it was driveshaft related. The engine stayed running the engine time, no CELs.

I looked over the drivetrain and checked fluids etc and I couldn't find any leaks, cracks, or issues.

I drove a little to see what would happen and it felt completely normal. I put a jack under the rear axle and everything spun by hand like normal. Because I couldn't find any issues after 45 minutes of looking I went back out on the trail for 4 more hours and then drove home another 2 hours 55-65mph being careful to let off the accelerator whenever the chirping sound started. Aside from the chirp under those specific conditions, if I were buying this Jeep I'd have no concerns with the engine -- it drives great -- but clearly something is wrong with the drivetrain?

The maximum boost this pulley provides is 8lbs. I've checked the peak gauge and it has never gone over. If I'm hard accelerating I can go up to 8lbs of boost without the chirping noise but the boost quickly drops off again after reaching my desired speed. Is it possible that under the chirping conditions that sustaining the boost for that long is lifting the head allowing for a misfire (causing the vibes) until the boost "burps" (causing the pop) out of the head? Wouldn't that cause lasting damage that would be seen under all driving conditions?
Pictures of your m90 setup on the engine?
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