Engine knocks under load

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Topic author
jakerc02
Posts: 46
Joined: Tue Dec 10, 2019 9:58 am

Engine knocks under load

Post by jakerc02 » Tue Jan 14, 2020 7:01 pm

Hey I'm a noob to the site and the 1979 J10 we got about a month ago, but I was hoping someone could help diagnose a knock in the engine. At first I figured it was spark knock, but after some research I'm starting to think that isn't the problem. Instead of the lighting knock or pinging as described online, it's loud and deep and increases with rpm when it happens. It only happens under acceleration like getting on the highway or just giving her a lot of throttle in general. As soon as I let off the gas it goes away. It also seems to be somewhat related to temperature because the problem isn't as bad when warm. In the morning when it's colder out (Texas cold not actual cold haha) and with the engine not very warmed up yet I'll be gently accelerating to get on the highway and the knock starts happening at about 45mph. If I let off and slowly increase throttle it goes away until I'm able to go about 60 knock free. When it happens in the morning like this, if I'm just gentle as I accelerate, then the rpm at which it happens goes farther and farther up until I'm able to cruise completely fine. Later in the day when it's warmer out it takes much more throttle and rpm for the engine to knock. I can cruise at nearly 70mph just fine. It still happens if I mash the throttle fast or just give it too much at all from any speed. It runs fine when in neutral and can be revved high without problem, but it just doesn't like hard acceleration, especially when cold. I've searched around for possible causes but it's hard to find something for this specific case. If anyone with more knowledge could throw out some ideas as to what it could be then that would be great.


will e
Posts: 4317
Joined: Sat Aug 18, 2012 8:21 am

Re: Engine knocks under load

Post by will e » Tue Jan 14, 2020 7:12 pm

Howdy from Phoenix and welcome to the forum.

This is a weird problem. How is your oil pressure? Can you video the knock? Normally if it is a main bearing or something it tends to get worse when it gets warm. It's possible your knock is a loose motor mount or transmission mount.

What oil are you using?
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge


Topic author
jakerc02
Posts: 46
Joined: Tue Dec 10, 2019 9:58 am

Re: Engine knocks under load

Post by jakerc02 » Tue Jan 14, 2020 7:29 pm

Thanks for the welcome! Oil pressure is almost always between 40-70psi when driving. We did an oil change about 150 miles ago with 10w40 and it was happening before this also. Ill try and get a video then post it as a link to an unlisted video on youtube.


Topic author
jakerc02
Posts: 46
Joined: Tue Dec 10, 2019 9:58 am

Re: Engine knocks under load

Post by jakerc02 » Tue Jan 14, 2020 7:56 pm

Got a video of it. This is just a little first gear pull and with it being warm outside plus engine still warm from earlier it wasn't nearly as bad, but hopefully you can get an idea of it. Its worse in the mornings and at a less rpm.
https://youtu.be/CmZ8y7wEzzM


KJ Ryu
Posts: 990
Joined: Sun Jun 10, 2012 8:03 am
Location: Casper

Re: Engine knocks under load

Post by KJ Ryu » Wed Jan 15, 2020 3:03 am

Sounds like the exhaust is hitting frame, to me. Time for new motor/trans mounts.
Ron

2005 KJ, Hit-n-Run, 2am 6-17-2012, Totaled. :mad:
1977 SJ J10, 4v360, T18, D20, 37x14s, SOA & SF on tons, still ugly.
1978 SJ Wagoneer, 4v360, QT, 33x12.5s, lift by Sawzall :-bd NOT Running :(
1977 SJ J10, SniperEFI 401, QT, D44s, 31X10.5s :fsj:
2006 KJ
Mars wrote:One man's trans leak is another's penetrating oil :D


will e
Posts: 4317
Joined: Sat Aug 18, 2012 8:21 am

Re: Engine knocks under load

Post by will e » Wed Jan 15, 2020 9:36 am

I would tend to agree. That doesn't sound like a classic engine knock.

Often times when you have a knock caused by sloppy or worn bearings it tends to be noticeable at idle and 'quiets' down a bit as the RPM's and oil pressure increases. The fact you have decent oil pressure is also an indicator that it is not bad bearings. (Of course nothing is certain).
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge


Topic author
jakerc02
Posts: 46
Joined: Tue Dec 10, 2019 9:58 am

Engine knocks under load

Post by jakerc02 » Wed Jan 15, 2020 10:19 am

Thanks y’all, I’ll take a look at the mounts later today. If that is the problem then do you have to pull the whole motor on these trucks? Or can you just do the method of gently jacking up the engine from below to change them out?


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will e
Posts: 4317
Joined: Sat Aug 18, 2012 8:21 am

Re: Engine knocks under load

Post by will e » Wed Jan 15, 2020 6:09 pm

jack the engine up to change them out. It might be obvious with an visual inspection. You can also have someone push the gas while the truck is in drive and foot firmly on the brake and see if the motor shifts a bit. Also, check all of the exhaust mounts to make sure none are broken or loose.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge


78 WIDETRAC
Posts: 156
Joined: Mon Mar 25, 2013 9:53 am
Location: Portland, Ore

Re: Engine knocks under load

Post by 78 WIDETRAC » Wed Jan 15, 2020 8:36 pm

After listening to the video, I'd say fan connecting with the shroud, same fix required. New motor mounts and possible trans mount.
91 Grand Wagoneer
89 Grand Wagoneer


Topic author
jakerc02
Posts: 46
Joined: Tue Dec 10, 2019 9:58 am

Re: Engine knocks under load

Post by jakerc02 » Wed Jan 15, 2020 8:46 pm

They look pretty shot so we’re ordering the poly-something ones from bjsoffroad tomorrow. Thanks again for the help!


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KJ Ryu
Posts: 990
Joined: Sun Jun 10, 2012 8:03 am
Location: Casper

Re: Engine knocks under load

Post by KJ Ryu » Thu Jan 16, 2020 1:10 am

78 WIDETRAC wrote:
Wed Jan 15, 2020 8:36 pm
After listening to the video, I'd say fan connecting with the shroud, same fix required. New motor mounts and possible trans mount.
I tried just changing motor mounts, once. The old trans mount gave and tore a new motor mount about a week after changing them. Always done all of them at the same time, since.
Ron

2005 KJ, Hit-n-Run, 2am 6-17-2012, Totaled. :mad:
1977 SJ J10, 4v360, T18, D20, 37x14s, SOA & SF on tons, still ugly.
1978 SJ Wagoneer, 4v360, QT, 33x12.5s, lift by Sawzall :-bd NOT Running :(
1977 SJ J10, SniperEFI 401, QT, D44s, 31X10.5s :fsj:
2006 KJ
Mars wrote:One man's trans leak is another's penetrating oil :D


candymancan
Posts: 2455
Joined: Tue Mar 22, 2016 11:32 pm

Re: Engine knocks under load

Post by candymancan » Thu Jan 16, 2020 3:24 pm

jakerc02 wrote:
Wed Jan 15, 2020 10:19 am
Thanks y’all, I’ll take a look at the mounts later today. If that is the problem then do you have to pull the whole motor on these trucks? Or can you just do the method of gently jacking up the engine from below to change them out?


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Get a wooden block like a 2x10 pressure treated board so it doesnt crack and place it under the oil pan, you can jack the engine up from there to do the motor mounts. Just make sure you use a peice of wood thats about the same width as the oil panel bottom so you dont bend the pan. I use a pressure treated 2x10 board i cut to length as i mentioned. Ive done this on dozens of engines from small 4 cylinders to v8s alluminu. Pans and steel pans. . Luckily the mounts on these jeeps are in easy spots to get too.

I also use the 2x10s i cut in little squares to jack the Jeep up on the frame. This way i dont bend the c channle or scuff the paint
1998 Jeep Grand Cherokee 5.9L Limited 197k
1998 Jeep Grand Cherokee 4.0 I6 laredo 299k
1990 Jeep Grand Wagoneer 138k


jpcoutts
Posts: 29
Joined: Sat Sep 03, 2011 7:30 pm
Location: Hot Springs, AR

Re: Engine knocks under load

Post by jpcoutts » Thu Jan 16, 2020 8:45 pm

I would do further work to eliminate spark knock/pinging as your issue. I'd hate to go through all that to realize it wasn't the problem. AMC engines I've had were prone to pinging even when timing is set to spec.


will e
Posts: 4317
Joined: Sat Aug 18, 2012 8:21 am

Re: Engine knocks under load

Post by will e » Thu Jan 16, 2020 9:12 pm

jpcoutts wrote:
Thu Jan 16, 2020 8:45 pm
I would do further work to eliminate spark knock/pinging as your issue. I'd hate to go through all that to realize it wasn't the problem. AMC engines I've had were prone to pinging even when timing is set to spec.
You might have missed the 'video' he posted of the noise. It's not a pinging sound, it's a knocking or banging sound.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge


candymancan
Posts: 2455
Joined: Tue Mar 22, 2016 11:32 pm

Re: Engine knocks under load

Post by candymancan » Sat Jan 18, 2020 2:49 pm

jpcoutts wrote:
Thu Jan 16, 2020 8:45 pm
I would do further work to eliminate spark knock/pinging as your issue. I'd hate to go through all that to realize it wasn't the problem. AMC engines I've had were prone to pinging even when timing is set to spec.
My 360 in my 90 pings. I have to use 93 octane. Which isnt a big deal as i am a BJs member and their 93 octane is 55-60 cents cheaper then everywhere else.. in fact the 93 there is the same price as everyones 87 lol. Since my 98 5.9 zj has to use 91 or higher im used to pushing the 93 button now.

But it would be nice to get the waggy to use 87 in case im not near a bjs. I tried 89 and same thing.. predetonation crackling sounds at half throttle or more.

No idea why its doing that. Maybe carbon build up i dunno. I dont know how to check or adjust timing on old engines like this. Not yet anyway.. since it starts when warm with no gas pedal and takes only 3 pumps to start when cold i just decided to leave good enough alone for now
1998 Jeep Grand Cherokee 5.9L Limited 197k
1998 Jeep Grand Cherokee 4.0 I6 laredo 299k
1990 Jeep Grand Wagoneer 138k


Topic author
jakerc02
Posts: 46
Joined: Tue Dec 10, 2019 9:58 am

Re: Engine knocks under load

Post by jakerc02 » Mon Jan 20, 2020 10:57 pm

candymancan wrote:
jpcoutts wrote:
Thu Jan 16, 2020 8:45 pm
I would do further work to eliminate spark knock/pinging as your issue. I'd hate to go through all that to realize it wasn't the problem. AMC engines I've had were prone to pinging even when timing is set to spec.
My 360 in my 90 pings. I have to use 93 octane. Which isnt a big deal as i am a BJs member and their 93 octane is 55-60 cents cheaper then everywhere else.. in fact the 93 there is the same price as everyones 87 lol. Since my 98 5.9 zj has to use 91 or higher im used to pushing the 93 button now.

But it would be nice to get the waggy to use 87 in case im not near a bjs. I tried 89 and same thing.. predetonation crackling sounds at half throttle or more.

No idea why its doing that. Maybe carbon build up i dunno. I dont know how to check or adjust timing on old engines like this. Not yet anyway.. since it starts when warm with no gas pedal and takes only 3 pumps to start when cold i just decided to leave good enough alone for now
That’s what we thought for awhile so we tried a higher octane like you did, but it didn’t make a difference it seemed like. Adjusting your advance/timing may help your pinging issue though. I researched this a bunch when we thought it was the issue and it doesn’t seem too hard. Or it could be the carbon build up like you said.


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Topic author
jakerc02
Posts: 46
Joined: Tue Dec 10, 2019 9:58 am

Re: Engine knocks under load

Post by jakerc02 » Mon Jan 20, 2020 10:59 pm

KJ Ryu wrote:
78 WIDETRAC wrote:
Wed Jan 15, 2020 8:36 pm
After listening to the video, I'd say fan connecting with the shroud, same fix required. New motor mounts and possible trans mount.
I tried just changing motor mounts, once. The old trans mount gave and tore a new motor mount about a week after changing them. Always done all of them at the same time, since.
Is the trans mount a similar process to replace?


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KJ Ryu
Posts: 990
Joined: Sun Jun 10, 2012 8:03 am
Location: Casper

Re: Engine knocks under load

Post by KJ Ryu » Tue Jan 21, 2020 3:03 pm

I've always had to lower the transmission crossmember. The trans won't move up enough to get the mount in/out, and you don't want to be moving the linkages around too much. So, basically, support the trans on a jack and board, disconnect trans mount bolts/nuts, then remove the bolts from the crossmember ends and pull it down to swap out the rubber mount.
Ron

2005 KJ, Hit-n-Run, 2am 6-17-2012, Totaled. :mad:
1977 SJ J10, 4v360, T18, D20, 37x14s, SOA & SF on tons, still ugly.
1978 SJ Wagoneer, 4v360, QT, 33x12.5s, lift by Sawzall :-bd NOT Running :(
1977 SJ J10, SniperEFI 401, QT, D44s, 31X10.5s :fsj:
2006 KJ
Mars wrote:One man's trans leak is another's penetrating oil :D


candymancan
Posts: 2455
Joined: Tue Mar 22, 2016 11:32 pm

Re: Engine knocks under load

Post by candymancan » Sat Jan 25, 2020 1:34 pm

jakerc02 wrote:
Mon Jan 20, 2020 10:57 pm
candymancan wrote:
jpcoutts wrote:
Thu Jan 16, 2020 8:45 pm
I would do further work to eliminate spark knock/pinging as your issue. I'd hate to go through all that to realize it wasn't the problem. AMC engines I've had were prone to pinging even when timing is set to spec.
My 360 in my 90 pings. I have to use 93 octane. Which isnt a big deal as i am a BJs member and their 93 octane is 55-60 cents cheaper then everywhere else.. in fact the 93 there is the same price as everyones 87 lol. Since my 98 5.9 zj has to use 91 or higher im used to pushing the 93 button now.

But it would be nice to get the waggy to use 87 in case im not near a bjs. I tried 89 and same thing.. predetonation crackling sounds at half throttle or more.

No idea why its doing that. Maybe carbon build up i dunno. I dont know how to check or adjust timing on old engines like this. Not yet anyway.. since it starts when warm with no gas pedal and takes only 3 pumps to start when cold i just decided to leave good enough alone for now
That’s what we thought for awhile so we tried a higher octane like you did, but it didn’t make a difference it seemed like. Adjusting your advance/timing may help your pinging issue though. I researched this a bunch when we thought it was the issue and it doesn’t seem too hard. Or it could be the carbon build up like you said.


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Unlucky thrn i know for a fact 93 works for me. If i cheat and go to 89 pinging 360 comes back can hear it on the interstate. I also wonder if its because i took all the emission stuff off. The egr is also busted so i blocked it off. Engine has 0 emission stuff besides a new cat.

My engine is probly dirty though the oil pan and valve covers had major sludge when i bought it..like thick wheel bearing grease sludge so i flushed it twice with motor medic. I did seafoam thrpugh thr carb once.. but im thinking of doing seafoam in the gas tank.. carb. And oil to try ti clean it more.. but ive daily druven it for 20k miles now so it deff doesnt sit like it did before
1998 Jeep Grand Cherokee 5.9L Limited 197k
1998 Jeep Grand Cherokee 4.0 I6 laredo 299k
1990 Jeep Grand Wagoneer 138k


KJ Ryu
Posts: 990
Joined: Sun Jun 10, 2012 8:03 am
Location: Casper

Re: Engine knocks under load

Post by KJ Ryu » Tue Jan 28, 2020 3:01 am

candymancan wrote:
Sat Jan 25, 2020 1:34 pm
jakerc02 wrote:
Mon Jan 20, 2020 10:57 pm
candymancan wrote:
My 360 in my 90 pings. I have to use 93 octane. Which isnt a big deal as i am a BJs member and their 93 octane is 55-60 cents cheaper then everywhere else.. in fact the 93 there is the same price as everyones 87 lol. Since my 98 5.9 zj has to use 91 or higher im used to pushing the 93 button now.

But it would be nice to get the waggy to use 87 in case im not near a bjs. I tried 89 and same thing.. predetonation crackling sounds at half throttle or more.

No idea why its doing that. Maybe carbon build up i dunno. I dont know how to check or adjust timing on old engines like this. Not yet anyway.. since it starts when warm with no gas pedal and takes only 3 pumps to start when cold i just decided to leave good enough alone for now
That’s what we thought for awhile so we tried a higher octane like you did, but it didn’t make a difference it seemed like. Adjusting your advance/timing may help your pinging issue though. I researched this a bunch when we thought it was the issue and it doesn’t seem too hard. Or it could be the carbon build up like you said.


Sent from my iPhone using Tapatalk
Unlucky thrn i know for a fact 93 works for me. If i cheat and go to 89 pinging 360 comes back can hear it on the interstate. I also wonder if its because i took all the emission stuff off. The egr is also busted so i blocked it off. Engine has 0 emission stuff besides a new cat.

My engine is probly dirty though the oil pan and valve covers had major sludge when i bought it..like thick wheel bearing grease sludge so i flushed it twice with motor medic. I did seafoam thrpugh thr carb once.. but im thinking of doing seafoam in the gas tank.. carb. And oil to try ti clean it more.. but ive daily druven it for 20k miles now so it deff doesnt sit like it did before
Sounds like a PO used a paraffin-based oil, to me. Probably Pennzoil. Saw that a few times at the engine machine shop I worked at, 30 years ago.

I can't get 93 octane at the pump, here. But, I do run 91 in my high compression 401, and 89 in the "stockish" 360; both ethanol-free.
Ron

2005 KJ, Hit-n-Run, 2am 6-17-2012, Totaled. :mad:
1977 SJ J10, 4v360, T18, D20, 37x14s, SOA & SF on tons, still ugly.
1978 SJ Wagoneer, 4v360, QT, 33x12.5s, lift by Sawzall :-bd NOT Running :(
1977 SJ J10, SniperEFI 401, QT, D44s, 31X10.5s :fsj:
2006 KJ
Mars wrote:One man's trans leak is another's penetrating oil :D

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