Question about knock after letting of the throttle

[obrut]

I have a 87 t that has a scanmaster and a casper knock gauge. Today when I was driving I noticed something that has never happened before. I would roll on the throttle a little to speed up from 45 to 60 mph hitting about 5 pounds of boost. When I would let off the gas and start to cruise at 60 I saw the LEDs on the knock gauge slowing increase then go back to just the single green. I drove some more and it happened again and I looked at the scanmaster and it showed 7.8 knock.

WOT shows no knock and O2s in the 790-800 range.

Any ideas?

 

[we4Mateo]

Something metal is hitting something else metal.

 

[MaxVO2]

I had a similar problem years ago that ended up being my downpipe being a bit too close to the control arm. Everything was ok driving slowly but on the highway doing what you described would cause my knock gauge to light up when I let off the gas. The downpipe looked like it had enough space but I guess with suspension movement plus letting off the gas just caused it to hit enough to give me problems.

Also, my drivers side motor mount was not 100% and seemed to allow the motor to not have a problem going up and down (I had a tie down..) but a bit side to side which cause the downpipe and perhaps other stuff to clank a bit. Ironically, I couldn't hear a darn thing - I just got lucky one day changing my oil after jacking the car up a bit when I noticed the motor mount thing and saw my downpipe touching the control arm, but only when the control arm on the pass side was a bit compressed after jacking up the car a bit. Although mine was ok, you may also want to check the control arm bushing on the pass side by the downpipe - mine was ok but had been replaced by the previous owner as it was a totally different color, etc..

Hope this helps

Billy

 

[obrut]

I took it for another ride about 15 minutes ago. I'm getting knock and a rattle at around 2000-2200 RPMs. If I rev the engine in park there is a rattle from the engine. This engine only has about 800 miles on it, oil looks clean, no noise at idle

 

[forcefed3.8's]

Loose torque converter bolts?

 

[wantattype2]

I took it for another ride about 15 minutes ago. I'm getting knock and a rattle at around 2000-2200 RPMs. If I rev the engine in park there is a rattle from the engine. This engine only has about 800 miles on it, oil looks clean, no noise at idle

Pull the plug wire off one cyl at a time and rev the engine to that RPM if the knock goes away the problem is on that cyl.

 

[obrut]

Thanks for the help everyone

I dropped the accessory belt - no change
I pulled the fuel injector wires one at a time - no change (I couldn't pull the plug wire without them arcing all over the place)
I pulled the cam sensor cap and it looks nice inside.
I pulled the cam sensor out and there seems to be some wear on the teeth (see pics), the car has 94000 on the original sensor. There also seems to be a little back and forth play in the cam sensor shaft,whats acceptable and whats not?
I will check the converter bolts later tonight or tomorrow after work.

Also, it doesn't do this when the engines cold, its only after it starts to warm up.

I have a 210/210 roller cam, the cam gear looks great.

 

[SS502]

Something metal is hitting something else metal.

Did you check the heat shields on the headers?

 

[obrut]

How much back and forth play is acceptable for the cam sensor?

I'm going to try and check the converter and flywheel tonight.

I will also check my heat shields on the manifolds.

 

[DaRonne Edwards]

Make sure intercooler is not hitting anything also.

 

[Amelio]

with that cam you are also running the heavier behive springs correct? check your rocker shafts for tiny cracks as the car heats up the metal is going to expand making the crack worse.....ask me how I know

 

[bison]

If there is no knock under load what is the concern? You could have piston slap that will be audible at low rpm and more pronounced when cold. You will go crazy trying to diagnose. Make sure the engine isn't moving around.

 

[obrut]

Loose torque converter bolts?

Checked converter and flywheel, everything is tight and no cracks in the flywheel.

Did you check the heat shields on the headers?

All the heat shields are tight

Make sure intercooler is not hitting anything also.

Intercooler and all brackets are tight

with that cam you are also running the heavier behive springs correct? check your rocker shafts for tiny cracks as the car heats up the metal is going to expand making the crack worse.....ask me how I know

These are new but I pulled the valve cover anyway, rocker arms are in place, shafts are not cracked. I rotated the engine by hand and watch all of the lifters move - everything looks good.

If there is no knock under load what is the concern? You could have piston slap that will be audible at low rpm and more pronounced when cold. You will go crazy trying to diagnose. Make sure the engine isn't moving around.

Never made noise before, something came loose or something in the engine is wrong.

 

[highboostgn]

put it in second and slowly bring it up to around 5,000 rpm...if you dont have any knock then your good.

 

[V6sleeper]

i had the same problem,turned out to be needing body bushings...