Pulsating acceleration between 50%-70% throttle engagement 1KZ-Te

[jimmymango]

Hoping for some advice. I have a 93 KZJ78 that was just brought into the US 2 months ago from Japan. All the major fluids/filters have been changed, truck runs fantastic, with one exception. When accelerating with the throttle between 50%-70% , there is a pulsating or oscillating feeling where it rhythmically fluctuates power. If I’m just below that point or maintaining speeds, it doesn’t skip a beat. If I depress the accelerator past 70, it will drop down a gear and do run as it should. I’ve already put close to 1,500 miles on it and been through at least 4 tanks of diesel, always allowing the tank to run almost to E to make sure its not just a bad tank of fuel. fuel filter was also changed once the truck got here. Has anyone else dealt with something similar, and have any advice of what else I should be chasing down To solve this issue?

 

[GTSSportCoupe]

Hoping for some advice. I have a 93 KZJ78 that was just brought into the US 2 months ago from Japan. All the major fluids/filters have been changed, truck runs fantastic, with one exception. When accelerating with the throttle between 50%-70% , there is a pulsating or oscillating feeling where it rhythmically fluctuates power. If I’m just below that point or maintaining speeds, it doesn’t skip a beat. If I depress the accelerator past 70, it will drop down a gear and do run as it should. I’ve already put close to 1,500 miles on it and been through at least 4 tanks of diesel, always allowing the tank to run almost to E to make sure its not just a bad tank of fuel. fuel filter was also changed once the truck got here. Has anyone else dealt with something similar, and have any advice of what else I should be chasing down To solve this issue?

The ECU's in these can fail from capacitors leaking dielectric out. The dielectric eats circuit board traces and things start getting strange. Often it shows up as weird transmission issues. It could be what is causing the strange behaviour on your truck. Pull your ECU out (its behind the glove compartment), and open it up to inspect.

If you see this, then it's probably your problem (black stuff around the caps):

 

[jimmymango]

The ECU's in these can fail from capacitors leaking dielectric out. The dielectric eats circuit board traces and things start getting strange. Often it shows up as weird transmission issues. It could be what is causing the strange behaviour on your truck. Pull your ECU out (its behind the glove compartment), and open it up to inspect.

If you see this, then it's probably your problem (black stuff around the caps):

Thanks, will give this a look just in case. But from a transmission standpoint, everything there seems just fine, it feels more like a fuel issue.

 

[GTSSportCoupe]

Thanks, will give this a look just in case. But from a transmission standpoint, everything there seems just fine, it feels more like a fuel issue.

On a simpler note, check your vacuum hoses around the motor; especially the ones that run to the boost sensor. Make sure the connections are good and there are no holes etc. I have had weird resonance issues with my boost sensor before that caused something similar to what you're talking about. Or the sensor itself may be bad.

 

[jimmymango]

On a simpler note, check your vacuum hoses around the motor; especially the ones that run to the boost sensor. Make sure the connections are good and there are no holes etc. I have had weird resonance issues with my boost sensor before that caused something similar to what you're talking about. Or the sensor itself may be bad.

GTS, when you dealt with that, did it end up being the boost sensor itself, or simply one of the hoses?

 

[GTSSportCoupe]

GTS, when you dealt with that, did it end up being the boost sensor itself, or simply one of the hoses?

That particular problem was with the hoses. But my setup is a different motor and far from stock; so unlikely it will be an identical problem to yours.

 

[baashie]

how many miles do u have on your fuel filter?

 

[jimmymango]

Was replaced within the last 6 weeks

 

[mudgudgeon]

Also look for split fuel lines, or loose fuel hose clamps, or loose fuel filter.
If it's only showing up under heavy throttle when fuel demand is high, it could be indicating a small leak in the fuel system pre injection pump that is drawing in air

 

[mudgudgeon]

This ^^^ is a simple low cost thing to diagnose and fix, and often overlooked

 

[jimmymango]

Also look for split fuel lines, or loose fuel hose clamps, or loose fuel filter.
If it's only showing up under heavy throttle when fuel demand is high, it could be indicating a small leak in the fuel system pre injection pump that is drawing in air

Ok, will check that too. Bit of new info, this vehicle was recently (2months) imported and was most likely sitting for at least 2-3 months prior to getting here. We ran a diesel fuel additive (BG) and it has minimized the oscillating by about 75%. Is it possible this is just a result of the diesel sitting too long without running, and fouling up the injectors?

 

[GTSSportCoupe]

Did you ever check the ECU?

 

[djsolution]

Proud new owner of this Prado here! I wanted to follow up with more info on this issue. I’ve put about 600 miles on it over the past few weeks and have noticed a few more transmission gremlins.

First, the power oscillation is still there. I’m running another fuel additive in the current tank (amsoil) but haven’t noticed an improvement. I think I’ve nailed the timing of the issue down to when the tranny tries to engage overdrive while climbing up an incline (which seems like a bad time for the ECU to make that decision). If feels like it could be the fuel delivery or maybe the transmission slipping, hard to tell.

Second issue, at the start of a 250mi round trip down to NC, I noticed the engine was running a high RPM on the highway. It was about 3400 RPM at 80km/hr when it normally runs around 2000/2200 RPM at them at speed. I tried clicking O/D off and back on a few times, no change. Seemed like it couldn’t kick into high gear. Cycled ECT Power on and off, no change. Pulled over and stopped, cycled through the gears and took off again and it was fine, didn’t act up the rest of the trip. Then last weekend did another long drive on country roads and it started doing it again. This time though it was hunting all over for gears, downshifting randomly during a downhill coast, not upshifting to O/D. This time when I clicked ECT Power, it seemed to fix the issue. Immediately shifted to high gear and maintained appropriate gear per engine speed.

I did an ATF drain and refill today, didn’t fix the problem. It’s still oscillating and shifting sporadically at higher speeds.

Last issue, I noticed right after startup the AT Oil Temp light comes on. Doesn’t make sense on a cold transmission. Light will turn off when I let my foot off the brake, turn back on when I depress the brake. Happens sometimes while driving too. I pulled up the center console to look for frayed wiring or a bad ground, didn’t find much. The wires leading up to the ECT Power switch look a little pinched but the casing isn’t split.

I have to admit I don’t know much about auto transmissions. Do these issues seem to be related? ECU issue maybe? Solenoids? I still need to pull the ECU to look for melted caps.

 

[djsolution]

Did you ever check the ECU?

I pulled the ECU this morning. I’m seeing what looks like failed capacitors. What do you think? I’ve

never opened an ECU before.

 

[GTSSportCoupe]

I pulled the ECU this morning. I’m seeing what looks like failed capacitors. What do you think? I’ve never opened an ECU before.

So those capacitors definitely did fail at one point, but it almost looks to me like someone repaired it already. It's hard for me to tell from this end of the internet. I can say that I have repaired one of these before, and it was pretty tricky. It's possible that whomever repaired it did not do the job 100%. I'm going to say there is a pretty good chance this is causing a lot of your problems. And if it wasn't repaired at all; again, there is a good chance it's causing your problems.

Did you ever pull the ECU codes? The 1KZTE manual describes how to do this. Basically it's a jumper and you read out the flashing CEL codes. This might give you ideas for what else to check. 1KZTE manual is out there for download.

 

[djsolution]

So those capacitors definitely did fail at one point, but it almost looks to me like someone repaired it already. It's hard for me to tell from this end of the internet. I can say that I have repaired one of these before, and it was pretty tricky. It's possible that whomever repaired it did not do the job 100%. I'm going to say there is a pretty good chance this is causing a lot of your problems. And if it wasn't repaired at all; again, there is a good chance it's causing your problems.

Did you ever pull the ECU codes? The 1KZTE manual describes how to do this. Basically it's a jumper and you read out the flashing CEL codes. This might give you ideas for what else to check. 1KZTE manual is out there for download.

GTS thanks for the insight. I’m going to start looking for a place that can do this kind of a repair. Not sure where to start with that.

I haven’t pulled the ECU codes yet but I definitely will. I’m assuming it’s the same process I used for my FJ62, using a paper clip to bridge the ECU port in the engine bay. Thanks for the advice on this!

 

[GTSSportCoupe]

GTS thanks for the insight. I’m going to start looking for a place that can do this kind of a repair. Not sure where to start with that.

I haven’t pulled the ECU codes yet but I definitely will. I’m assuming it’s the same process I used for my FJ62, using a paper clip to bridge the ECU port in the engine bay. Thanks for the advice on this!

I'm not sure who in the US officially does these repairs. I design and build electronics for a living, so was able to repair the ECU for a guy in Canada. I have all the tools in the lab I work in. I don't have the time to get into doing these though. I think there are a few companies in New Zealand who do these repairs though?

I do have a parts list of all the capacitors I ordered if you want. I could dig that up and post it here.

One of the biggest challenges with repairing the ECUs, is the black dielectric is corrosive. So it eats away at the copper traces underneath it. Replacing the capacitors is not that hard, but replacing all the perforated (or completely disappeared traces) is more difficult, and takes specific experience. After the repair I carefully cleaned the board and re-applied a conformal coating also - to help seal it up against moisture etc (they have this from the factory).

 

[djsolution]

This is great info. I found an automotive electronics specialty shop locally that say they specialize in ECU and transmission repair. At very least I can ask them somewhat informed questions. We’ll see what they say, I may or may not need that parts list. Thanks again man, big help.

 

[djsolution]

So I sent the ECU off for repair. Should get it back in about a week. I’ll report back with results! Huge thanks to Brian @jimmymango for hooking this up!

 

[epaul]

Did this ever get sorted? I’ve Been having a similar issue.