I am in the process of putting a donor '80 5.0l in my '92 f-150. I ran across one sensor in the '92 that i don't have a spot for on the '80 block. It is at the very back top of the block. It seems to poke down close to the flexplate. There is no hole or spot for this sensor on the block of the '80 donor motor that i am using for now. any one know what this sensor is and what it is for. How can i by pass it so my unit will run ok?
thanks guys.
Micheal

 

Moved to proper forum.

 

I belive that is the nock sensor. (someone correct me if i'm wrong) You should be alright without it. Not having it won't affect how it runs but might turn the CEL on. Just remember without it the computer won't back off the timing if there is any detination, so you are gonna have listen out for it.

 

Yes, it's the knock sensor.

Take the sensor out of the 92' block, plug it into the wiring harness and tie it asside. Since you can't screw it into the 80' block, you'll have to just leave it plugged in but not installed in the block. This will probably keep the check engine light from coming on.

 

thanks very much, guys. I appreceiate all the excellant info i get off this forum.
thanks alot. I will do that.
Micheal

 

Rather than hanging the knock sensor in the air it might be better to make a bracket to hold it. Take a piece of steel strap drill two holes in it. Tap one hole to the same size as the knock sensor. Bolt through the other hole to a convenient place on the block. Your knock sensor will now have the mechanical connection it nees to be functional. We were in a pinch a while back, with no drill available. We used an old exhaust flange, it was low tech but worked.

 

I don't think there is really anything to bolt to back there. Just the hole for the knock sensor, which is pretty big. The knock sensor doesn't have to be attached to the block for it to "work" in the computer's eyes. As I understand it, it senses the "large" unequal vibrations created from pinging/detonation...and stays "neutral" when that isn't present.

Most applications don't have a knock sensor, so it's ok to run w/o it, you've just got to know it's not working and pay attention if you hear pinging/detonation. It shouldn't anyway, but if something goes wrong and it pings/detonates you have to be the one to stop vs relying on the computer.

 

Latch it down to one of the bellhousing bolts. Drill the knock sensor hole big enough to either thread it or bolt it in. As long as there is a mechanical connection of the knock sensor to the block (either directly or through an adaptor) it should give a vaild signal. If there isnt a place close to the current connecotr to latch to, extend the harness. I agree you can run without one and rely on your ear, but why would you want to? The computer uses the signal to set timing to an optimal position.

 

Are you sure about that? As I understand it, the knock sensor's only in affect when the engine pings, causing the computer to reduce timing and make it not ping. I don't believe it has any affect if the engine is not pinging, it's rare that these EFI systems even have a knock sensor, very few applications got it. I have my doubts that it does anything with timing unless it pings.

I actually cut my knock sensor out of the wiring harness because I'm using a Mustang computer that doesn't even have an input for a knock sensor. So I just removed it completely.

 

Yes I am sure you are better off using a knock sensor with a computer that originally required one. The computer is way better at detecting spark knock (ping) and has a quicker response time than a human.

If your computer needed one originally, why would you want to disable it? Are there performance issues that would make an engine run better without a knock sensor?

Not every engine computer combination require the same sensors. Just because one combination does not require a certain sensor does not in any way mean another combination shouldnt require it either.

 

The knock sensor isn't very advanced on the trucks. It's more of a safety feature best I understand it (on these trucks). The computer doesn't advance timing to the threshold of pinging all the time, but rather takes out 2-3 degrees when knock is sensed, and gradually feeds it back (over the course of a set number of milleseconds). A lot of the high compression, high horse honda four cylinders use knock sensors as you described, where they advance to the threshold of knock. I just don't believe the trucks are that good, and the range of adjustment isn't very large. I find it quite easy to make my truck ping, even with the knock sensor.

 

I've run into this before when swapping a slightly older engine into a newer vehicle. I note the position on the block and mark the other block. I then drill a hole and tap it. Can't remember the tap size but it was NPT (National Pipe Thread) and commonly available. Doing this is suprisingly quick and easy once you find the correct tap.

 

I am not sure whether or not these newer blocks have a safe location to drill and tap a new hole. I myself, wouldn't be drilling holes in my block.

I don't remember asking whether or not you're better off with a knock sensor, what I asked was, are you sure that "the computer uses the signal to set timing to an optimal position". I do not believe that is true, which is why I was trying to point it out.

Like Eric said, our truck's knock sensors are not very sophisticated. The computer does not adjust timing based on the knock sensor reading. All it does, is give the timing it's programed for and if it pings/detonates than the computer will recongnize that and back the timing off. It'll then start to add timing and only be held back if the knock sensor tells the computer its pinging.

The only difference with or without the knock sensor, is that without the knock sensor, if the engine pings the computer won't recognize it and back off the timing. It makes no difference otherwise. So therefore, the only advantage to having a knock sensor, is that the computer will back off timing if it pings. There is no other reason or purpose of the knock sensor in this particular application. Keep in mind, only a few applications even got a knock sensor, so it's really not a big deal to go without one. If you do go without one, than educate yourself about it so you don't have a problem. You've got the info now so if you run w/o the knock sensor installed, be aware of what that actually means. You should have all you need to know by now...