Re: What are dumb reasons for knock?
So, seeing the thread below about knock, made me wonder why I get knock occasionally as well. So, I've heard of trans lines, brake lines, heat shields... etc. But what about things that are far out in left field? Like things that are a million to one?
On that same though... what are the most common contributors (mechanically)? Loose motor mounts? Bad sensor?
-P
I'll add some to the list....
-Too much fuel pressure. (Detonation is more likely to occur in a lean condition. It also occurs in too rich conditions).
- Loose or Missing brackets. I will explain...many times I have seen trucks with missing or loose brackets for example: the brackets that hold the Upper IC above the valve covers if missing. The IC can bang on the throttle body if pushed into the hose is too tight between the IC and TB and the brackets don't hold it in the correct place, Also it can bang on a valve cover, and the AC accumulator and make false knock (detonation). / The brackets (two "L" shaped) behind the AC braket if loose they can rattle and be picked up as false knock. / Many trucks are missing the "U" shaped 3 hole bracket on the downpipe that attaches to two transmission bolts and the downpipe -this also causes the exhaust manifold to crack between #2+#4 Cyl. because of the weight of the turbo. Two problems from one missing bracket. This is very common because if an engine is removed this braket is removed commonly and also for transmission removals.
-Misc. Items. This one needs explination also... Ever drop a socket or tool? Where did it go? Probably on top of the transmission case -Right next to the knock sensor and it bounces and rattles around and makes false knock.
-Knock Sensor Torqued incorrectly. Not only should the knock sensor be torqued correctly to read accurately but they should be installed only once according to GM. Install it to the correct torque and if you remove it replace it. If it gets dented during an engine removal replace it any distortion in the metal can make it read inacurately. -Knock sensor is a sensitive little microphone that listens for knock if damaged it will give you problems.
-Wrong Part # Knock Sensor. Very important to get the corrrect sensor. There are ones that look just like ours but are not the same.
-Bad Ignition Wires / Wires not secured. If an ignition wire has a nick in it or a rub thru on the insulation the electrons flowing thru the wire can arc to any grounded metal. -Also if it arcs to the exhaust the arc can ignite unburned gases in the exhaust and cause a lean pop in the exhaust which is not knock but can be picked up as false knock.
-Missing chip. Yep, I have seen this too...Some one I know (name is not listed here to prevent embarrasment) installed a chip which used a carrier. The stock chip was to be piggy backed on the pins of the carrier for the ESC portion of the chip. He installed the carrier which contained a modified .bin chip but did not install the stock chip onto the carrier and the knock was just counting up and retarding the timing to the max. -believe it or not the truck still ran.
...these aren't ones you would probably think of first but I have seen all these conditions.
