I love my 94 but can't stand the computer relearn process (1 Viewer)

[Malleus]

I appreciate your help. Thank you.

I wish I had provided some help for your to be thankful for. Here is why I don't believe your problem is is related to any process (regardless of what it could be called) of storing values in the ECU:

These are pages 54-55 from the 1994 Toyota Land Cruiser service manual. You can see on page 55, specifically the SFI and ESA systems read stored values, obtained from various sensors, and use those values, together with the program that is stored in the ECU, to operate the various engine control systems.

There is nothing in this explanation that describes any process of reprogramming any part of the preprogrammed operating instructions in the ECU.

Additionally on pages 60-61, Toyota lists the various values and ranges of values expected for the various circuits:

These values have to be verified during the operating conditions listed, to ensure that the respective engine control circuits are functioning properly. If the engine doesn't run properly, it's because one or more of these control circuits is not functioning properly.

Unfortunately, there is no simple answer to the question "What's wrong?" that can be had until every item on this list is verified, or found to be at fault. The specific procedures for doing this are found in the engine control and troubleshooting section of the service manual.

Sometimes, conditions exist that aren't covered in the manual, which cause faults that are covered and which have written troubleshooting procedures, which won't resolve the problem. Two examples are the IAC fault, which I described earlier, and one I just corrected on my 1995 DD today. I've been getting a persistent P401 error code for months now. I've ignored it, because I was pretty sure I knew what the problem was. The result of me ignoring the problem was that my gas mileage was 60% of what it should have been.

Bear with me, this won't take long, but it is pertinent to the problem at hand.

 

[Malleus]

There is a 10 page troubleshooting procedure in the service manual (Pages EG-290 to EGE-299) for solving this problem. I didn't use them. The reason I didn't use them was because I knew they weren't written to cover a condition which develops over a period of years of operation: namely, without an oil bypass catch can, the PCV valve will flood the intake with oil laden air and the heat from the normal engine operation will bake the oil onto the inside of the intake and the throttle body. One result of this is that the passage in the upper intake between the EGR sensor (a thermocouple) and the EGR valve becomes blocked and carbon builds up on the sensor. Carbon is an excellent heat insulator, so when the ECU "sees" engine temperature increase above a given threshold, based on coolant temperature, it also expects to "see" a comparable intake temperature. When these two conditions aren't simultaneously met, the ECU stores the P401 error code.

If you follow the service manual, you'd spend literally hours verifying that every component works, and yet you wouldn't have solved the problem. I removed the sensor, cleaned the carbon off and reinstalled it, after I also cleaned to passage between the sensor and the valve. Took me 5 minutes. No more P401.

For the few known faults like this and the IAC failure which the 1994 is prone to have, but not the 1993 (for some reason), you can skip the long troubleshooting procedure and just fix the problem, provided you at least verify that the part you think is good, is actually good (I checked, and verified, the internal resistance of the EGR sensor and the harness voltage, before I removed it).

If you a) don't have a known problem that has a known solution, or b) have a problem with multiple possible root causes, you have two choices. You can start replacing all the parts you can find and hope that one of them is a part which caused the problem, or you can slog through the troubleshooting procedure, making careful observations as you go, so that if a condition which obviously wasn't planned for when the tech writers wrote the manual (such as the sticking IAC or dirty EGR sensor) you'll know it and hopefully understand what to do about it.

I shared all that to illustrate that even if I had replaced every component, including the EGR sensor I cleaned, the problem would recur within a short period of time, because of the blockage in the air intake, which wasn't planned for in the procedure. This makes solving these kinds of problems very frustrating, if swapping parts is the preferred solution method.

 

[Malleus]

I routinely disconnect the battery negative terminal when I service any of my trucks, and I have never experienced any delay in normal engine operation, after reconnecting the battery. I am confident the root cause of your problem isn't the ECU, because under at least one condition, you have a properly running engine.

The troubleshooting procedure on pages Eg-8 and EG-9 list several points to consider (last line of both images). The numbers in the matrix are the order you should check the individual items in. The closest interpretation I read from the list is "Incorect first idle" (remember, these were translated form Japanese, so you have to make some allowance for interpretation and expression):

 

[Malleus]

Let's not skip the Accelerator pedal link, because it's easy to check and who knows, it may be the problem. Probably not, but it's not much work. If that checks out, go to the ECT cut switch and ECU terminals (page EG-243 in the list, item 6 below):

THW is the water temperature sensor in the head and E2 is the ECU common ground:

Note the conditions for the test:
Ignition switch = "ON"
Engine coolant temperature = 176°F (engine fully warmed at normal operating temperature)
Voltage between THW and E2 = between 0.2VDC and 1.0VDC

 

[Malleus]

Next the ECT switch itself:

I've said switch, because that's what the manuals call it, but it's a thermocouple, like the EGR sensor.

Be careful removing the harness connector housing (it's the green one) because although the sensors are readily available, the harness connector is the only one in the entire engine harness that isn't available new. Fortunately, it's on every Toyota made in the 90's and some early 00's, so it can be found, but it's a PITA to do, so be careful with it.

 

[Malleus]

If that checks out, you can skip the IAC, because you did that already. Last on the list is the ECU; pages EG-317 to EG-319:

 

[Malleus]

 

[Malleus]

Unless you really know the board layout well, it's best to check all the terminals listed, to rule out interference between unrelated circuits. You could have a bad trace on the board. Ask @cryorunner

Pages EG-322 to EG-324 list all the relevant electrical service data in one place.

If you believe that a poor cold operation can be described as "Incorrect first idle", this should find the problem.

 

[Malleus]

Or, you could throw parts at it:

 

[Mark W]

I routinely disconnect the battery negative terminal when I service any of my trucks, and I have never experienced any delay in normal engine operation, after reconnecting the battery. I am confident the root cause of your problem isn't the ECU, because under at least one condition, you have a properly running engine.

Just to toss my 2 cents in to agree with the above... I could not even begin to keep track of how many times I have de-powered various '80s here at the shop. Obviously my own (I have three currently as I sold three over the last couple of years) and more customer rigs that I can keep track of. In any event, we are talking hundreds of de-powers over the years. I have never experienced any type of "re-learning" symptoms or indicators whatsoever. And I have never had a customer indicate that they had any unusual behavior from their rig after picking it up from me. I have also never come across any mention of such in the FSM. (I will not claim to have memorized every page of the FSMs... But I AM in them routinely.)

Yeah, I have seen talk of this "re-learning" in the forums too. But you see all sorts of stuff in the forums.

Maybe my experience is some sort of outlier. I do not think so.


Mark...

 

[Kkxrw]

Can you please post who rebuilds 93-94 VAFs on Mud? I remember someone mentioned there’s an eBay seller that does it a while back.

I checked and I can't find his info. He is out of south Carolina and advertises on ebay. He will rebuild your vaf. He has been mentioned in several posts on here. If I find I will post

 

[jonheld]

Coffee is still brewing, so I may not be thinking clearly yet on Sunday morning.

First of all, the ECUs in these trucks are mid to late 1980s technology. There is very little voodoo here and it is a stretch to call it a "computer". It is basically a comparison device.

ECU relearning: From 1991-1997 when the ECUs power is removed, either from disconnecting the battery or pulling the 15 amp EFI fuse, all stored error codes in memory are cleared out, all current running parameters in memory are cleared out, and the ECU has to "relearn" all of the sensors and make comparisons to its internal base mapping.
Perhaps the term "relearn" is a misnomer, but it works in my geriatric brain. You can substitute "reboot" as it works as well.

Typically, after a "reboot" of the ECU, the idle speed will be slightly higher, but that's it. After a few drive cycles it always comes back to 650 rpm. This has always been the case on my 91 and on my 97 along with my neighbor's 89 and 96, and my club member's 93 and 94. There has NEVER been any rough running/poor idle or any of that nonsense in the 30 or so years I have been involved with these things after an ECU reboot of any kind on any 62/80 Series I've worked on. The truck in question has an issue.

1. The OP mentioned that after reaching normal operating temperature the engine runs well, so this is a cold startup problem. Top end vacuum leaks would be first on my list. All rubber parts are now brittle and cracking if they have not been replaced in the last 20 years. When they heat up, they start to seal again.
Any unmetered air entering the system is going to play havoc with the A/F ratio. Remember 1980s tech. The ECUs have very limited memory and very limited operational "windows" with which to push/pull parameters back to base. All mechanicals have to be correct first.

2. Cold start fuel pressure issue. Has the fuel pressure been checked according to the FSM? Has the fuel filter under the intake been changed? Has the fuel pump pre-filter (sometimes called a "fuel sock" for some reason) been changed?

I'm sure I'll think of more as the caffeine does its job.

 

[Kkxrw]

Just to toss my 2 cents in to agree with the above... I could not even begin to keep track of how many times I have de-powered various '80s here at the shop. Obviously my own (I have three currently as I sold three over the last couple of years) and more customer rigs that I can keep track of. In any event, we are talking hundreds of de-powers over the years. I have never experienced any type of "re-learning" symptoms or indicators whatsoever. And I have never had a customer indicate that they had any unusual behavior from their rig after picking it up from me. I have also never come across any mention of such in the FSM. (I will not claim to have memorized every page of the FSMs... But I AM in them routinely.)

Yeah, I have seen talk of this "re-learning" in the forums too. But you see all sorts of stuff in the forums.

Maybe my experience is some sort of outlier. I do not think so.


Mark...

I can not thank you enough for your help and guidance. Even without the information above I was very thankful. I am going to go through this today and will keep everyone posted on my findings.

 

[Kabanstva]

Coffee is still brewing, so I may not be thinking clearly yet on Sunday morning.

First of all, the ECUs in these trucks are mid to late 1980s technology. There is very little voodoo here and it is a stretch to call it a "computer". It is basically a comparison device.

ECU relearning: From 1991-1997 when the ECUs power is removed, either from disconnecting the battery or pulling the 15 amp EFI fuse, all stored error codes in memory are cleared out, all current running parameters in memory are cleared out, and the ECU has to "relearn" all of the sensors and make comparisons to its internal base mapping.
Perhaps the term "relearn" is a misnomer, but it works in my geriatric brain. You can substitute "reboot" as it works as well.

Typically, after a "reboot" of the ECU, the idle speed will be slightly higher, but that's it. After a few drive cycles it always comes back to 650 rpm. This has always been the case on my 91 and on my 97 along with my neighbor's 89 and 96, and my club member's 93 and 94. There has NEVER been any rough running/poor idle or any of that nonsense in the 30 or so years I have been involved with these things after an ECU reboot of any kind on any 62/80 Series I've worked on. The truck in question has an issue.

1. The OP mentioned that after reaching normal operating temperature the engine runs well, so this is a cold startup problem. Top end vacuum leaks would be first on my list. All rubber parts are now brittle and cracking if they have not been replaced in the last 20 years. When they heat up, they start to seal again.
Any unmetered air entering the system is going to play havoc with the A/F ratio. Remember 1980s tech. The ECUs have very limited memory and very limited operational "windows" with which to push/pull parameters back to base. All mechanicals have to be correct first.

2. Cold start fuel pressure issue. Has the fuel pressure been checked according to the FSM? Has the fuel filter under the intake been changed? Has the fuel pump pre-filter (sometimes called a "fuel sock" for some reason) been changed?

I'm sure I'll think of more as the caffeine does its job.

What's the easiest way to check if you have a vaccuum leak?

 

[jonheld]

What's the easiest way to check if you have a vaccuum leak?

There's no shortcuts.
I would inspect every rubber part. If you can use a piece of tubing for a hammer, then it should be replaced. More than likely it will display cracking where it mates to hard lines.
If your PCV valve grommet is like concrete, it no longer seals properly.
If your oil fill cap is 30 years old, the gasket is past its service life.
And on and on.

 

[mudgudgeon]

What's the easiest way to check if you have a vaccuum leak?

If you don't know the history of rubber vacuum hoses on your vehicle and you're chasing a stumble, assume all hoses are leaking, and same for any other seal, grommet, bush etc that seals in the engine vacuum.

 

[Malleus]

I checked and I can't find his info. He is out of south Carolina and advertises on ebay. He will rebuild your vaf. He has been mentioned in several posts on here. If I find I will post

Try @Engineer8000 I don't know if he's ever rebuilt a VAF before, but I'm pretty sure he could.

 

[Malleus]

What's the easiest way to check if you have a vaccuum leak?

Spray carb cleaner on the hoses. If there is a leak, the volatile spray will correct the air/fuel mixture and the idle will increase, as long as the spray continues. This is less pronounced on fuel injected engines, because they are sealed better than carbs.

Not he correct way, but certainly the fastest. Of course, this only affects the vacuum lines going into the intake, and not all of them do.

 

[Kabanstva]

Spray carb cleaner on the hoses. If there is a leak, the volatile spray will correct the air/fuel mixture and the idle will increase, as long as the spray continues. This is less pronounced on fuel injected engines, because they are sealed better than carbs.

Not he correct way, but certainly the fastest. Of course, this only affects the vacuum lines going into the intake, and not all of them do.

great advice, thanks!

 

[Kkxrw]

Coffee is still brewing, so I may not be thinking clearly yet on Sunday morning.

First of all, the ECUs in these trucks are mid to late 1980s technology. There is very little voodoo here and it is a stretch to call it a "computer". It is basically a comparison device.

ECU relearning: From 1991-1997 when the ECUs power is removed, either from disconnecting the battery or pulling the 15 amp EFI fuse, all stored error codes in memory are cleared out, all current running parameters in memory are cleared out, and the ECU has to "relearn" all of the sensors and make comparisons to its internal base mapping.
Perhaps the term "relearn" is a misnomer, but it works in my geriatric brain. You can substitute "reboot" as it works as well.

Typically, after a "reboot" of the ECU, the idle speed will be slightly higher, but that's it. After a few drive cycles it always comes back to 650 rpm. This has always been the case on my 91 and on my 97 along with my neighbor's 89 and 96, and my club member's 93 and 94. There has NEVER been any rough running/poor idle or any of that nonsense in the 30 or so years I have been involved with these things after an ECU reboot of any kind on any 62/80 Series I've worked on. The truck in question has an issue.

1. The OP mentioned that after reaching normal operating temperature the engine runs well, so this is a cold startup problem. Top end vacuum leaks would be first on my list. All rubber parts are now brittle and cracking if they have not been replaced in the last 20 years. When they heat up, they start to seal again.
Any unmetered air entering the system is going to play havoc with the A/F ratio. Remember 1980s tech. The ECUs have very limited memory and very limited operational "windows" with which to push/pull parameters back to base. All mechanicals have to be correct first.

2. Cold start fuel pressure issue. Has the fuel pressure been checked according to the FSM? Has the fuel filter under the intake been changed? Has the fuel pump pre-filter (sometimes called a "fuel sock" for some reason) been changed?

I'm sure I'll think of more as the caffeine does its job.

Hi thank you for your assistance. Yes. The fuel filter under the intake, fuel pressure Regulator, fuel pump, resistor and relay have been changed with no luck. I also changed the coil and Most if not all vacuum lines have been replaced. I need to double check the ones under the intake. All parts are Toyota eom. I do have an AC Delco throttle position sensor that I am double checking. I have been going through all the information that is posted above.