(Engine experts needed) Chirp, Vibe, Pop (What is Wrong?)

[toximus]

I did cancel the order of octane booster and the knock sensor. Costs about $250. If we're still thinking detonation is on the table of primary causes of what's going on I'll place the order again. If we're thinking that it's a secondary issue I'd rather wait until after we figure out the primary issue.

 

[toximus]

I can zip tie the bypass valve open and there's no chirp. Essentially the same as running the engine stock. Of course that also means the engine is driving the same speeds at different RPMs with different torque than if it's able to go into boost.

 

[Apparition]

It could be. Is there a way to figure out if it is?

If it doesn't go into boost there's no problems.

Maybe the 7th injector is causing it. Too much fuel? Timing issue?

If I understand it correctly it only comes into play under boost.

 

[Rick Flair]

I can zip tie the bypass valve open and there's no chirp. Essentially the same as running the engine stock. Of course that also means the engine is driving the same speeds at different RPMs with different torque than if it's able to go into boost.

And that is the part that has going hmm. It could be the SC/tune is all funky, and OR too much power to a hurting transmission. It’s a damn devil in the details.

 

[toximus]

We seem to be going full circle.

 

[Rick Flair]

I can zip tie the bypass valve open and there's no chirp. Essentially the same as running the engine stock. Of course that also means the engine is driving the same speeds at different RPMs with different torque than if it's able to go into boost.

I’d honestly get a clean bill of health on the transmission. Once that is good, then you KNOW for sure it’s in the tune and/or SC.

 

[toximus]

If I understand it correctly it only comes into play under boost.

That's how it's supposed to be but idk how to validate that.

Maybe the 7th injector is causing it. Too much fuel? Timing issue?

It could be the SC/tune is all funky

I know my AFRs probably aren't great and are dumping too much fuel to run conservatively. Is anyone familiar with tuning the 4.0L? Are the AFR ratios in the first video enough to cause chirping sounds or the issues that are happening in the second video?

@Alex0413 ?

 

[toximus]

I’d honestly get a clean bill of health on the transmission. Once that is good, then you KNOW for sure it’s in the tune and/or SC.

At that point couldn't it even be an oiling issue in the engine unable to keep up due to the SC?

 

[Daryl]

Is there a page 2? What's good pressure? Is it supposed to be tested while on the hoist or when the issue is presenting itself?

Pressure testing is done at operating temperature on a hoist. You should download the 42RLE pdf. Personally I would check the torque converter on/off pressures while the issue is presenting itself (driving).

Edit: Here’s the link. Also edited for correct information.
https://wranglertjforum.com/attachments/42rle-automatic-transmission-pdf.14078/

 

[Rick Flair]

At that point couldn't it even be an oiling issue in the engine unable to keep up due to the SC?

if oil starvation is a concern, you might just be at the point of a return to stock on the engine. I don’t know enough about the 4.0, SC’ing it and known issues that could happen. I’ve only known of guys who stroked them and swapped. Never boosted.

With the amount of guys on here that have or owned boosted 4.0’s I’m shocked more haven’t chimed in. Then again, maybe they haven’t had this issue OR you are in tune so much you noticed something others have not!?

 

[toximus]

@ObiWanWebWheelr Are you still around? What does your AFR go down to when in accelerating in OD under boost? Which pulley and tune are you running on the SC?

 

[toximus]

I checked the OBD and there are no codes.

 

[toximus]

I thought again about the pop noise. There's no way that was the sound of the belt snapping back or whipping. The belt doesn't appear to have hit anything that could have caused the metallic sound.

 

[Juggernaut]

I know my AFRs probably aren't great and are dumping too much fuel to run conservatively. Is anyone familiar with tuning the 4.0L? Are the AFR ratios in the first video enough to cause chirping sounds or the issues that are happening in the second video?

@Alex0413 ?

While I have experience with tuning the 4.0, I don't have any with the FTC system and software Boostedtech uses. I believe I saw AFRs in the low 10 range (maybe a 10.1) in the video and the AFR didn't seem very stable. I'm not familiar with a S/C 4.0L but typically you're targeting 10.5 on the very conservative rich side to about 11-11.5 under boost in typical applications. So it looks like your running rich and they probably also pulled timing to be on the safe side and avoid detonation. Is it enough to cause a backfire from the unburnt fuel - maybe? Hopefully someone with a boosted 4.0 will chime in with more application specific info.

 

[AndrewLJR]

That's how it's supposed to be but idk how to validate that.





I know my AFRs probably aren't great and are dumping too much fuel to run conservatively. Is anyone familiar with tuning the 4.0L? Are the AFR ratios in the first video enough to cause chirping sounds or the issues that are happening in the second video?

@Alex0413 ?

I forget the name of the guy, but @Chris made a post about tuning. May be worth getting a tune done once you get the belt figured out. To be honest, I wouldn't do anything else until you address the simplest of the "issues" and work your way down the list

 

[Juggernaut]

I forget the name of the guy, but @Chris made a post about tuning. May be worth getting a tune done once you get the belt figured out. To be honest, I wouldn't do anything else until you address the simplest of the "issues" and work your way down the list

I agree 100%. I feel bad offering observations as I don't want you chasing multiple issues at once. Regarding tuning - I do know Flyin Ryan FRP Tuning has very good experience with the Dodge Chrysler Jeep products. Its a shame Boostedtech hasn't been more helpful with support as they do advertise remote tuning.

 

[Apparition]

While I have experience with tuning the 4.0, I don't have any with the FTC system and software Boostedtech uses. I believe I saw AFRs in the low 10 range (maybe a 10.1) in the video and the AFR didn't seem very stable. I'm not familiar with a S/C 4.0L but typically you're targeting 10.5 on the very conservative rich side to about 11-11.5 under boost in typical applications. So it looks like your running rich and they probably also pulled timing to be on the safe side and avoid detonation. Is it enough to cause a backfire from the unburnt fuel - maybe? Hopefully someone with a boosted 4.0 will chime in with more application specific info.

I’m wondering if unburnt fuel is causing a backfire at the cat. It could very well sound like a tinny pop and would explain the smell.

 

[Juggernaut]

I’m wondering if unburnt fuel is causing a backfire at the cat. It could very well sound like a tinny pop and would explain the smell.

That was my train of thought as well

 

[toximus]

I’m wondering if unburnt fuel is causing a backfire at the cat. It could very well sound like a tinny pop and would explain the smell.

Does it explain the progression of the chirp, the belt oscillation, and the vibration?

 

[mrblaine]

Still seems like throwing darts and hoping for a bullseye.

I’m curious to see @mrblaine ’s thoughts on the video

Without other inputs to see any correlations between events, what it looks like is as the load on the charger increases as it builds boost, is that becomes uneven as in the charger has something inside that is causing a variable load on the tensioner. If you watch the tension, it starts bouncing and that increases in frequency until it pops and then it settles back down. I can't tell if the settling is due to throttle reduction, release of load at the charger pulley or what.

It just seems that the load at the charger pulley is variable like it isn't building boost smoothly. I'm fairly aware of how they work internally, but not aware enough to fully understand how it could do that.