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1uz running better with AFM unplugged

Jay351

Member
Thread bump!

Been a few years since I’ve really gotten back into this issue with the truck. I ended up restoring the rest of the truck and am now just sorting out engine details.

I recently purchased a used Snap on mt2500 scanner. After wiring up the semi circle diagnostic plug, I’m finally able to see What’s going on.

I noticed that after the engine started to warm up, the ecu would go into closed loop and would begin detecting knock at idle. At 10 degrees, 900rpm, idle switch closed it was detecting knock. Up to around 2500 it would see knock off and on but after then it would be fine. Timing would pull down to 40-50 degrees at that point.

Engine sounds fine, no questionable rattles. Great oil pressure 90psi cold, around 20psi hot at idle. Engine has all new oem ignition components including coils. Replaced capacitors in the ecu (also tried a spare ecu) New denso primary o2 sensors. New injector seals. New 3vze replacement denso fuel pump, new oem fuel filter (new lines as well due to rust).

I recently had an issue with a bad starter trigger wire under the manifold. So I ended up sourcing new connectors for the engine, bought some shielded wire and made my own harness. I left the original knock sensors in place. Wondering if these sensors can become more sensitive as they break down?


I’m going to get the truck licensed so I can run it down the road with the scanner to see what it does under load. Just been playing with the “new” scanner in the shop.
 

cribbj

"Supra" Moderator
Staff member
Thanks for the update Jay! Good to hear you're still fooling with it and hope you get the knock sorted out! Changing the knock sensors would definitely be high on my To Do List.

They can't be that expensive - or shoot, just try picking up some used ones from a junkyard pull and see what happens?
 

361UZ

Member
Hi all.
Excuse my ignorance, but can you remove the kmock sensors, but still leave them connected? So they dont see any vibration?
 

Jay351

Member
Thanks for the update Jay! Good to hear you're still fooling with it and hope you get the knock sorted out! Changing the knock sensors would definitely be high on my To Do List.

They can't be that expensive - or shoot, just try picking up some used ones from a junkyard pull and see what happens?
New oem sensors are pretty pricey. I really didn’t think these sensors would slowly fail or anything. I figured they would either work or not work then throwing a cel.

Im hoping to get some licence plates on the truck so I can take it down the road and see what’s going on under a sustained load.

I have another ls400 that I’m parting out right now. I’ll have the engine pulled in a week or so. I may just grab the sensors off that one to see if anything changes. I’m getting very good at removing the intake manifolds thanks to the vacuum and coolant lines I’ve deleted (thanks to Kelvin at the cartune company and his YouTube videos ).





Hi all.
Excuse my ignorance, but can you remove the kmock sensors, but still leave them connected? So they dont see any vibration?

It’s my understanding if the ecu detects no knock at all it will register a cel for a faulty knock sensor.
 

gloverman

Well-Known Member
Ive just done a video on knock sensors. They shouldn't detect any knock at idle. If they are then there is an issue.
 

Jay351

Member
Ive just done a video on knock sensors. They shouldn't detect any knock at idle. If they are then there is an issue.
I’m not very knowledgeable about the knock sensors themselves. It’s my understanding that they either work or they don’t, not something that would tend to slowly fail and provide false information. Would you agree with that? If the sensors were cheaper I would’ve just replaced them when I assembled the replacement harness.

If that’s the case I suppose I possibly have something else at play. I’m going to flush out the fuel and try some fresh fuel to eliminate that possibility. Then I’m going to make sure the flywheel and clutch are still solid. After that point I suppose I would have to start taking things apart.
 

Jay351

Member
So I managed to take the truck for a quick drive the other day. The ecu is still seeing knock with the timing pulled back to 10 degrees at mild acceleration. Once it kicks over to open loop under heavy acceleration it pulls good.

I noticed the old clutch fan bracket was starting to make some noise so I took the belt off to eliminate that source of noise. Still have the presence of knock at idle.

I’m in the process of removing the intake so I can do some testing on the knock sensors themselves.
 

Jay351

Member
Thanks Kelvin, You can bet your ass I watched that video. Your other video in regards to the wiring of the neutral switch also had my attention (the part of timing being frozen at 10 degrees ). I wish these things would be easy and throw a code.

After removing the intake I’ve verified the wiring is good. I checked the knock sensors with the help of my FSM. They did pass the ohm check test. I took the plunge and ordered two knock sensors from MR Toyota. Damn expensive but I’d rather be able to rule these things completely out in this process.

I’m told I should have the sensors in a week to two weeks. I will post up an update when I get my new sensors and go from there.
 

Jay351

Member
Okay update time. First of all I have been laid off because of the covid-19 pandemic so funds will be low, I’m unsure if I’ll be able to afford to install insurance on this pig so I can get it on the open road... we’ll see.

I received my new knock sensors from Toyota on Monday. I threw them in, fired it up and went for a quick boot down the road.

At cold idle there is no knock detected. Once she is warmed up it appears that it detects some knock off and on at idle.
At a standstill, holding the throttle at around 3000rpm timing advances to around 50 degrees so I know the ecu is not frozen and is able to pull/add timing as needed so I’m doubtful I messed up the wiring when I initially installed this setup.

Once you drive it seems to detect knock when on the throttle, still has a dead spot until it goes into open loop once the throttle is wide open. It is moving timing around but I can see it only ranges from about 5-20 degrees or so while driving. Timing will advance then the knock sensors pull it back pretty quickly.

I wish I had a second person to film my scanner as I drive, very difficult to watch the reading while driving and keeping an eye out for people out and about.

At this point I’m going to try draining the last of the fuel from the tank (older 94 octane from around October 2019) and will try a half tank of fresh fuel to eliminate this as a source of knock.
 

361UZ

Member
Hi Jay. Sorry to hear about your being laid off. I (like everyone) hope this virus thing will be over soon. Hopefully your emplyer will be ready to rehire very soon!
Regarding the scan tool you are using, what model is it?
Thanks.
 

Jay351

Member
Hi Jay. Sorry to hear about your being laid off. I (like everyone) hope this virus thing will be over soon. Hopefully your emplyer will be ready to rehire very soon!
Regarding the scan tool you are using, what model is it?
Thanks.
Thanks for the kind words my friend!

I picked up an old snap on mt2500 scanner. Got it off eBay with a bunch of extra bits and pieces for $250. I really wish it would tell me which bank(s) are actually detecting knock. It just tells me knock is detected in a yes/no fashion.

I did a little more work on it yesterday. I removed my headers and tried a new set of flange gaskets to try to help the substantial exhaust leak I was experiencing. Got most of it sealed up now.

I also got the engine nice and warm and then tried some combustion chamber cleaning. I found some cans of seafoam on my shelf so I gave them a go. Tossed a little into the oil to help remove any deposits. Then ran about a half a can through the intake. I used a few different spots on the upper intake to allow a more even distribution into all the cylinders.

The engine had about 380k when I pulled it out of the parts car and I had no info on its history, other than it was owned by an older Asian gentleman. From what I can see through the spark plug holes it looks like there is a decent amount of carbon inside the engine. I’m wondering if this could be adding to the problem. If there really is spark knock happening...

After I finished the cleaning process and all the smoke cleared up, it appeared that it wasn’t detecting knock quite as often as it was before. Now I want to add, for the life of me I cannot hear any pre ignition whatsoever. This thing is trying my patience!
 
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