Missing knock sensor

I have a 85 Toyota Supra. I purchased a while ago with a bad engine. I replaced the engine from a junk yard. The engine came from a if I recall correct a 83, perhaps a 82. The junk yard told me the engine would work for my 85. They closed down in a short time after I purchased the entire car.

I put that engine in my 85 and I have had problems with the car running like crap. I put in new plugs and wires. I had the timing checked. I was told the timing was originally off by a jumped timing belt and it was then set to specs. They said it had good vacuum and that the check engine light was specifically on for the knock sensor.

Depending on the mood of the car, or perhaps the day of the week, it will sometimes start and idle so so, some days like crap. I have to rev it up to get it started down the road. It has a hard time getting up and moving. Some times when I go down the road, if I do not put the pedal to the floor it will help. The max I can get is perhaps 60mph.

I did try to rig up a spot for it. I took out a motor mount bolt, took a piece of steel, drilled out a hole all the way through and one half ways through. I tapped out the half way hole. Then bolting the piece of metal to the block where the motor mount bolt was. Screwed in the knock sensor and plugged it in. It did not help any. This spot is a bit far from where it is supposed to be.

What are you diagnosis? Do you think it would be the knock sensor giving problems or something else? I have pondered taking off the intake and either drilling and tapping a spot where it is supposed to be, or taking JB weld and sticking a piece of metal to the block and then putting the knock sensor in that. How exact to the factory spot does it need to be? a inch or 2 off factory spot ok?

I tend to think the problem is not related to the knock sensor, or lack of. There’s a lot of unknowns so it’s near impossible for me to make much of a guess.

By good vacuum, did they by chance tell you what that vacuum reading was? An engine in good condition should show about 20" (give or take a bit) of rock steady vacuum at idle.

In most cases an engine that runs like garbage. is sluggish, has limited top speed, etc usually has a problem with:
Clogged converter.
Retarded ignition timing.
Clogged intake.
Fuel pressure issue.
Driveline problem; clutch slippage or transmission slippage.
Worn out engine.

If the ignition timing is set correctly the knock sensor should not have that much of an effect on engine performance. If it detects any pinging it will momentarily send a signal to the ECM which will briefly retard the ignition timing.

A jumped timing belt is highly unusual. The first thing I do with an engine is run a compression test; especially if it’s one from a boneyard.

The clutch is good, and the engine many times runs poorly at a stand still. But if the timing is getting retarded, would that not cause it to run poorly like it is?

I may try changing the fuel filter. I will also rent a compression tester from Autozone. Thank you for your response.

I agree with @ok4450 the lack of a knock sensor is not the root of your problems. Make the CEL happy (or not) by plugging in a knock sensor. Don’t worry about where its mounted, I don’t think these things do a self-check to see if they are mounted to the engine properly so it should take that OBD code away. Now check the codes and see if you what it tells you.

Go “old school” and check all the things on ok’s list. I’d add vacuum leaks as well. Check vacuum, check compression, timing, read the codes… Is it lean? A fuel flow problem would cause a lean condition.

The problem may be a mismatch between the computer and the engine. When you swapped engines, was the ECU swapped also?

b

+1 to BillRussell’s post.

I have already plugged in the knock sensor. I installed in in front of the factory spot, by the motor mount.

Where is the electronic control unit ECU located? Is it with the intake? I do not recall, been a long time since I put that motor in there.

Thanks, I will check for vacuum leaks, compression, timing has already been checked, code comes up as knock sensor for the check engine light.

I concur, the poor engine performance probably not related to the knock sensor. But it could be related to a mis-match between the engine sensors and the engine computer revision. But the place you purchased the engine said the engine was compatible with an 85? Those places usually know this kind of engine/car compatibility info … so … hmmm …

fyi, the knock sensor is used by the computer to know when to retard the ignition timing; i.e. when it senses a knock. With no knock sensor presumably you might hear some knocking (pinging). But since you aren’t complaining about that symptom, I don’t see how installing a knock sensor will do anything to help your engine performance.

If I had this problem , here’s what I’d do

  • Research if there’s a need for a computer software and or hardware update to make the engine and computer match-up.

  • Remove and inspect spark plugs, note if any cylinder’s plug tips look much different than the others

  • Compression test

  • Intake manifold vacuum test

  • New engine air cleaner

  • Temporarily remove/disconnect exhaust system, see if that helps.

Everything, supposedly, was compatible except it does not have the spot for the knock sensor.

I have looked at the plugs and the only difference is some are more blacker than others. Some look more like brand new.

I will be doing a comp test and vacuum test. I took it to a college mechanic shop and they said it had good vacuum. The exhaust is a good idea.

I do have the original intake and all the parts from the original engine. Would that make any sense to put those back on? What parts exactly would I have to transfer over?

Given what you say, might be a good idea to check the valve clearances.

Tested compression. lowest was 105 highest 130.
Tested vacuum. was very steady at about 19 1/2 psi.
Tested fuel pressure. was steady at 26 - 27, which is on the low side from what the book says, but should be ok.
Found 2 wires that were not connected. One was a ground to the side of the intake, just above the block. Believe it to be a ground for the temperature gauge inside car. Gauge did not work before, now it does. Car is not over heating by the way.
Other wire went to the vicinity of the electronic coil.
Since I hooked both of these wires up it has ran worse. Tried adjusting the timing, no timing light, but would not run very decent.
Checked ERG valve by removing and looking over, seemed not to be much vacuum there, but seems to be working fine.

Car idles ok, it will idle perfect for a couple minutes and then back fire for a half minute or so and then idle perfect again. Has little power to move.

I may drop the exhaust before the cat converter to see if that does anything, which I doubt it will.
I may also swop distributors that i have from a parts car of the exact same year. By the way, I did notice tiny metal deposits inside the distributor. Any idea what that is about?

Any other suggestions on what to try?

I think your junkyard engine is junk. The compression readings are way too low and there’s too much of a variation between cylinders.

I would suggest going back and performing a wet compression test. This means a small squirt of oil into each cylinder before it’s tested. If the number jumps up from say 130 to 160 or whatever this means the piston rings are shot.

An engine in at least very good condition should have about 180 PSI per cylinder and at those numbers it’s preferable there be no more than a 10 PSI variation among them.

I hope there’s some kind of a guarantee on that motor.

Looking at the book it says standard is about 160 and minimum around 125 with no more than 15 between cylinders. I do not think there was much more than 15 between cylinders, I do not have the recording with me here. From the first to last there was a diff of 25, it did go up as I went along. I do not know if that means from one cylinder to the next or between all. It would seem to me that even if the compression is low, that would not be the reason why it is running the way it is. It seems to want to fly, but something is restricting it, holding it back.

I will try the oil in the cylinders. No guarantee on motor.

I may drop the exhaust before the cat converter to see if that does anything...

Do this and report back.

Edit: Close this duplicate thread.

I’m fully aware of what is published in a lot of those manuals. Those manuals are dead wrong and published by people with little or no clue.

was told the timing was originally off by a jumped timing belt and it was then set to specs.

How did they reset the timing? The ONLY way to fix this is to change the belt.

A belt or chain that’s off just one tooth can cause the engine to knock very badly. Besides the already good advice…it could also be they put the belt on wrong. Hopefully they used a new belt.

MikeinNH has a good point about the timing belt. If the belt was replaced and is off a tooth or two the compression will be affected and could be lower. If the belt is properly timed you have a worn engine.

Being you have a wife variation in compression pressures I still think the engine is junk because a belt timing variation would affect all cylinders.

I believe George is on the right track with the valves

If this thing has adjustable valves, by all means adjust them

Be warned . . . it may use shims, which means it’s a fair amount of work

After adjusting the valves, do a second dry compression test

if the numbers are still low, do a wet compression test

Have you done an exhaust backpressure test yet?

It’s very simple, and it will tell you if your catalytic converter is plugged

If it is, your car won’t get out of its own way

But that lower compression would not cause it to barely move at times. I am not talking a bit sluggish, it is more than that. This poor running is not totally from a worn engine, it is more that that. At times the engine seems to have super power and then at other times will barely move.