Block flex!!!

[JJacobs]

I doubt it. Under load, loose converter bolts would have a pretty strong side loading and would be quiet. At idle the small fluctuations in engine rpm versus the inertia of the torque converter could cause some noise if the bolts were loose- but not under load.

All you really have to do is put a socket on the crank damper's center bolt and move it back and forth with a breaker bar- not a ratchet- and see if the noise is evident.

Sounds more like detonation (pinging) to me though.

 

[arsxj1]

Yea detonation is what ive been told but I dont understand why! The timing isnt adjustable, new plugs, cap, rotor, wires and even tried 93 octane fuel and no change...

 

[Talyn]

could be a vacuum leak, or excessive carbon build up. Try a sea foam treatment for the carbon.

 

[FlexdXJ]

Tighten the crap out of the bolts.

By that you do mean torque them Properly right? :dunno:

 

[arsxj1]

could be a vacuum leak, or excessive carbon build up. Try a sea foam treatment for the carbon.

Ive checked all the vacuum connections and seafoam thru brake booster line and in tank.

 

[Talyn]

Did you check your fuel pressure?

 

[cruiser54]

You can't get a torque wrench in there, so tighten the crap out of them with as long a wrench as you can fit in there.

 

[Talyn]

If you know what you are doing you can get a torque wrench on the bolts. Position the bolt just below the block on the driver's side and you will have plenty of room for a torque wrench. That is with the oil pan still on and exhaust still connected.

And doing as you said is a good way to snap a bolt. They only require 28 ft lbs.

 

[cruiser54]

The reason I suggested the method I did was I assumed the OP had no torque wrench. And besides, I've done a few of them with just the wrench and since you're trying to keep the flexplate from turning with a screwdriver in one hand, and the 15mm wrench in the other hand, I doubt you get any more than 28 ft/lbs of torque on the bolts in that confined space..Most importantly at tis point is that they need to be checke dand Loctited to eliminate them as a possible source of the knocking noise.

 

[JNickel101]

Are there two sets of bolts for the flexplate? One set halfway to the outer edge and one in towards the center?

 

[88 Wagonman]

Are there two sets of bolts for the flexplate? One set halfway to the outer edge and one in towards the center?

yes, there are the ones that hold the flexplate to the crank, and the ones that hold the flexplate to the torque converter. You need to concern yourself with the ones attached to the torque converter, unless you feel like separating the trans and engine.

My vote is for excess carbon. Even sea foam doesn't get all of it if there is a major buildup. Do you idle a lot?

 

[ceb0217]

how about a worn out timing chain

 

[FlexdXJ]

If you know what you are doing you can get a torque wrench on the bolts. Position the bolt just below the block on the driver's side and you will have plenty of room for a torque wrench. That is with the oil pan still on and exhaust still connected.

And doing as you said is a good way to snap a bolt. They only require 28 ft lbs.

Yeah I have never had to do that but I kinda figured it didn't take a lot of torque on the flexplate bolts. Thats why I suggested a torque wrench.:wave:

 

[arsxj1]

Did you check your fuel pressure?

I do need to check the fuel pressure. I want to put a guage on the fuel rail but all the ones I have seen here only go to 15psi and XJ's run at 49psi correct?

 

[arsxj1]

yes, there are the ones that hold the flexplate to the crank, and the ones that hold the flexplate to the torque converter. You need to concern yourself with the ones attached to the torque converter, unless you feel like separating the trans and engine.

My vote is for excess carbon. Even sea foam doesn't get all of it if there is a major buildup. Do you idle a lot?

Yea i do idle alot but the problem of rough idle comes and goes. Its really got me pulling my hair out.

 

[88 Wagonman]

Yea i do idle alot but the problem of rough idle comes and goes. Its really got me pulling my hair out.

My point is that excessive idling causes heavy carbon buildup, which could raise the compression ratio enough to cause it to knock under a load.

 

[Mutant_Xj]

How would you go about cleaning out excessive carbon?

 

[Talyn]

Use seafoam

 

[arsxj1]

**UPDATE** I paid attention to the sound today and if I hold the rpm's up so it makes the noise the noise cuts in and out... It will make it then instantly dissapear then instantly come back and so on. It doesny slowly come and go its bamm and its there bamm and its gone. Could it be a knock sensor or something?

 

[Talyn]

91+ 4.0L never had a knock sensor.