LJ78 1KZ-TE Question (1 Viewer)

[slvrspec]

About 3 weeks ago, I was driving my Prado and when I was parked with the truck running the CEL turned on and the diesel chatter got a bit louder. I was running the AC on full since it was over 100 degrees out. I turned off the truck, and when I turned it on again the light had gone off but after driving a few feet the light came back on.

I drove it back home and noticed significant smoke coming out the exhaust when I would accelerate. Didn’t lose any power and the truck wasn’t behaving differently other than the stated issues. Next morning I checked all fluids and everything was fine but I decided not to drive it. About a week after I decided to turn it on again and see if the light was still on, and to my surprise the light was off. We took a trip to Philly (300 mikes round trip) in the Prado that weekend and everything went perfectly fine, no issues whatsoever. Once I was home, I parked the truck and didn’t drive it again till today (about a week and a half)

Today, I take the truck out again, and the CEL turns on. Today was also over 100 degrees, and I had the AC blasting again. The truck behaved the same exact way as the first time this happened, drove it back home and I don’t plan on driving it again for another week or so.

Could the hot weather be affecting the truck? Or any idea what else it could be? Anyone else experience this before?

Any help is appreciated!

 

[jblueridge]

What color smoke?

 

[slvrspec]

What color smoke?

I’d say grayish, it wasn’t fully black but not clean white either. And it would only happen once I would accelerate, while cruising there was no visible smoke

 

[Rigster]

Since this is a computer controlled engine, I would say that the issue will either be with a sensor that is adversely affected by the heat, or the ECU and it is affecting the fuel mixture. I have never owned one of these, so I have to ask... is there a way to pull electronic diagnostics from the computer? That might help to narrow it down.

Another test to see if it is just heat related... does the CEL come on when it is over 100 degrees and you are NOT running the AC?

Otherwise, it would be a case of researching sensors via the EWD, and testing them. Also, you could pull the ECU and inspect for leaking capacitors.

 

[Paddler Ed]

Have you checked for codes? The diagnostics box will be somewhere, probably in the engine bay, and will require 2 pins jumping and then count the dash flashes with the key in position 2.

 

[Black94Prado]

Have you checked for codes? The diagnostics box will be somewhere, probably in the engine bay, and will require 2 pins jumping and then count the dash flashes with the key in position 2.

Yeah what Ed said. Check the codes jumping pins. To make it easier here's a link.

Link to Guide

Just note Toyota codes are different between diesel and gas trucks.

 

[LutherLM]

I will revive this topic. 1KZ-TE suddenly turned off and does not want to start. 9.6 volts goes into the coil on the pump at start-up, which seems low to me. Does anyone know how many volts should go there? or what could be the problem? thanks

 

[GTSSportCoupe]

I will revive this topic. 1KZ-TE suddenly turned off and does not want to start. 9.6 volts goes into the coil on the pump at start-up, which seems low to me. Does anyone know how many volts should go there? or what could be the problem? thanks

The spill valve gets pulsed, not a constant voltage. Best to check resistance of the coil and compare to spec in manual.

 

[LutherLM]

thanks for the reply. the resistance is 2 Ω, so according to the service manual it is fine. despite this, the pump does not give diesel. I don't know which way to look for the problem.

 

[GTSSportCoupe]

thanks for the reply. the resistance is 2 Ω, so according to the service manual it is fine. despite this, the pump does not give diesel. I don't know which way to look for the problem.

I would carefully inspect grounds from the battery. (My engine doesn't start if the smaller one has a poor connection for example). Also inspect battery terminals and all fuses. Then I'd move to checking the engine error codes by jumping the test connector and reading out the blinking LED. This might give some clues.

When you try to start, does the engine turn over fine? Any smoke out the tail pipe, or nothing?

 

[blinkerfluid]

thanks for the reply. the resistance is 2 Ω, so according to the service manual it is fine. despite this, the pump does not give diesel. I don't know which way to look for the problem.

the spill valve gets +12v from a the spill valve relay and -ve pulse from the ECU

 

[LutherLM]

I would carefully inspect grounds from the battery. (My engine doesn't start if the smaller one has a poor connection for example). Also inspect battery terminals and all fuses. Then I'd move to checking the engine error codes by jumping the test connector and reading out the blinking LED. This might give some clues.

When you try to start, does the engine turn over fine? Any smoke out the tail pipe, or nothing?

No smoke. Diesel does not flow from the injector inlet pipe. can error codes be flashed even when the engine is not running? I did not know that. I still want to check the relay 85915-60030

 

[GTSSportCoupe]

No smoke. Diesel does not flow from the injector inlet pipe. can error codes be flashed even when the engine is not running? I did not know that. I still want to check the relay 85915-60030

Yes, the ecu stores error codes and you can read them out just with the key on.

Have you ever checked your ecu? The ECU's of that vintage can have electronic problems due to capacitors leaking and eroding PCB.

 

[LutherLM]

I found this problem on the ECU. could this be the reason for the failure?

 

[GTSSportCoupe]

I found this problem on the ECU. could this be the reason for the failure?View attachment 3468757

Pretty good chance!! Someone did a write up on repairing these. @Tigris , was it you?

There are a few outfits around that can do the repair if you're not up for it. I fixed one for a fellow; but generally too busy to do that regularly.

 

[Tigris]

I found this problem on the ECU. could this be the reason for the failure?View attachment 3468757

I found this problem on the ECU. could this be the reason for the failure?View attachment 3468757

Sadly, that is almost definitely the culprit.

Judging by the picture, the electrolytic leak may have etched off some traces. I have seen worse (mine was worse for example) so this ECU is likely repairable. There are services that can recap and re-trace the PCB, but I can't speak of the quality of their work as I have not used them.

If you feel ambitious, you can take my route and repair it yourself. I have posted a detailed writeup on that process here

Feel free to reach out with questions. BTW like I have said before, replacing the capacitors while you have no issues is both trivial and highly recommend as it will mean that you can avoid this situation, which is almost inevitable otherwise.

Best of luck.

 

[Tigris]

@GTSSportCoupe you beat me to it. Yes sir that is correct.

I actually thought it was the ECU before I even finished reading the thread, as the symptoms were all too familiar.

@LutherLM

As GTSSportCoupe said, there are services that can fix this, IIRC some folks here had good results with some. My advice to you is even if you won't end up doing the job yourself, talk to the service and plan on ordering and supplying the caps from the list I published and send them with the ECU, as this way you can guarantee that they will use genuine and correct components.

 

[LutherLM]

thanks for the tips. ECU checked, cleaned, capacitors replaced, except for one - bipolar, which could not be obtained. but the vehicle still won't start. I have a new insight: it does not switch on the coil on the pump. volts are fine, but amperes are not. after connecting the coil to a 6V 7.5ah battery, the coil works. could a bipolar capacitor be causing this? or something else in the ECU?

 

[Tigris]

thanks for the tips. ECU checked, cleaned, capacitors replaced, except for one - bipolar, which could not be obtained. but the vehicle still won't start. I have a new insight: it does not switch on the coil on the pump. volts are fine, but amperes are not. after connecting the coil to a 6V 7.5ah battery, the coil works. could a bipolar capacitor be causing this? or something else in the ECU?View attachment 3472779

Man, sucks to still have problems but wow, awesome progress!

I am sure that you would agree that the ECU recap was the right thing to do despite the persistence of the symptoms. Here are my thoughts on this:

. The bipolar capacitor is not an electrolytic capacitor, i.e. it's construction does not involve an electrolytic solution. The bipolar capacitor resemble a typical electrolytic capacitor only superficially and operates using a different design. These bipolar caps are known to be reliable and typically are not required to be replaced in a recap service. That being said, they (like any other electronic component) can still fail or operate outside their design parameters, but that is rather rare.

. I did replace the bipolar capacitor on all the 1KZ-TE ECUs I worked on ( I have repaired a total of 4 units so far) and I do have two new bipolar capacitors in stock as I have ordered six iirc. If you want, I can mail you one in an envelope free of charge. But I really doubt it is the culprit. Which brings us to the next point.

. Sometimes, when capacitors fail catastrophically in-circuit, they damage the surrounding traces causing disconnections or spikes in current at other parts of the circuit, leading to failures in other components. That was the case in two of the ECUs I worked on, where one had a diod that went out, the other (my personal one) had a dead switching transistor. These components are also cheaply available from Digikey.

. Obviously, your troubles could be caused by a non ECU issue of some sort, although my money is on the ECU as being the culprit still. It is possible that some traces were not rerouted correctly, a through-hole (via) not connecting the two faces of the PCB, cold solder joint, or some other faulty component is still in-circuit, clearly this is just a speculation and not based on anything in particular other than the fact that it was something that I'd encountered before.

. I don't know how inclined you are when it comes to diagnosing circuits, but with a multimeter, patience, and basic electronics knowledge you can check the relevant traces on your board, and test many (but not all) of the components in-circuit (without removing them) both upstream and downstream of the damaged portions.

Let us know how this plays out man.

 

[LutherLM]

corrected! a friend checked the ECU again and found a fault. thank you very much for the advice and willingness. I can continue editing