Good crap please help.... knock sensor?

[skipnrocks]

Ok heres the run down I have a 86 k5 with sbc350 700r4 241doubler to dana 300.. I dont know if there is any other info needed to help with this. Anyways I have out of ideas, i have a knock sensor that goes off after the engine has been running for a while, I have replaced the sensor its a newer crate motor sounds great, I dont hear anything out of the norm.


Please help this is real frustrating...

 

[dhcomp]

What? Good Crap?

What crate motor? What exactly is your problem?

 

[NorCal_Chris]

timing off?

crappy gas?

bad knock sensor?

running lean?

all causes that need to be checked

 

[skipnrocks]

The motor is a chevy crate motor, with 87 burban fuel injection, the crate motor is gm certified for a 79 350 block.

Timing is double checked fuel is new been through 3 tanks no changes,
i put a crane cam in there they said it wouldnt mess with the computer.
I dont know how to check if its running lean. knock sensor is new.

I adjusted the valves when I put it in to make sure they were spec do I need to go back in now that its been driven a 1000 miles on it? could valve noise even trigger a knock sensor . do valves need to be set with the motor hot?

It just seems crazy that it wont register till 30-40 minutes of run time

if the knock sensor is too close to the exhaust can it cause it to trigger a code? I think its by the exhast on the drivers side in the middle of the block...

Sorry if this seems a bit un focused I have been messin with it for a year or better and its driving me nuts and sends the computer into limp mode...

 

[NorCal_Chris]

The motor is a chevy crate motor, with 87 burban fuel injection, the crate motor is gm certified for a 79 350 block.

Timing is double checked fuel is new been through 3 tanks no changes,
i put a crane cam in there they said it wouldnt mess with the computer.
I dont know how to check if its running lean. knock sensor is new.

I adjusted the valves when I put it in to make sure they were spec do I need to go back in now that its been driven a 1000 miles on it? could valve noise even trigger a knock sensor . do valves need to be set with the motor hot?

It just seems crazy that it wont register till 30-40 minutes of run time

if the knock sensor is too close to the exhaust can it cause it to trigger a code? I think its by the exhast on the drivers side in the middle of the block...

Sorry if this seems a bit un focused I have been messin with it for a year or better and its driving me nuts and sends the computer into limp mode...

hrmm well to check if it is running lean you need a wideband o2 sensor/gauge.


Has it ever ran right? or always been this way? Try retarding the timing a few degrees and see if it still happens.

I would think loud valvetrain noise could trigger the knock sensor, not sure on that one but that would make sense. Ive only adjusted valves while the motor was warm... dont know if that could make too much more of a difference, but may be a cause.

On the side of the block is the stock location for almost all knock sensors, so i dont think the exhaust would interfere... maybe an exhaust leak could produce the right tone to set it off... maybe it takes 30 or so mins for the manifold to get hot enough to warp to that certain point who knows?

Try to retard the timing and see if that changes anything

 

[skipnrocks]

Well busy evening, its running good as far as o2 goes, not lean not rich, went in and respect the valves and drove it for a bit without issue, but usually we run it for much longer before it hits. The battery was toast so I got a new battery and will be driving it alot over the next few days to see if it will trip again..

 

[Fordum]

A knock sensor will usually hear a knock before you can. And normally the computer just retards the timing a little until the knock goes away. I was not even aware that it could put the computer into limp-home mode.
It can make the engine run really bad, if it keeps retarding the timing more and more. I suspect that that is what is happening.
I really do not think this is your problem, but I have heard of it happening, so I will throw it in.
I once knew of a fellow whose car only ran really bad when he was towing his small utility trailer.
Normally the car ran great, but let him hook the little single axle trailer up, and in just a few miles it was running terrible.
I heard about this from the mechanic who finally found the problem. He took it out for a run, and found no problems. Finally, after doing this several times, the guy finally mentioned that it only happened with the trailer hooked up.
He brought the trailer around, and as soon as it was hooked up and going down the road, the knock sensor started triggering, and the computer retarded the timing more and more.
Turned out he had a really loose and crappy bumper hitch. As soon as they started down a dirt road, the banging and slamming of the hitch and trailer triggered the knock sensor.
Fixed the hitch and it all went away.

J.

 

[skipnrocks]

LOL thats funny! I dont know of anything that would make enough noise but if the valve thing didnt work I will start looking for other noises...