Gerry, you should be correct, yes. On my car I believe the #3 O2 sensor has three or four wires on the connector if I recall from the last time I replaced it but the front two O2 sensors are just two-wire and non-heated.

For 1995+, all three O2 sensors should be heated, yes.

What you say above is leading even more credence to the possibility that the O2 sensors I replaced not that long ago might be not be in the best shape right now after using the 1995 ECU. It would also suggest that the 1995 ECU may have caused the car to run rich with more fuel regardless of (at the time) the new injectors, new plugs and other changes.

I replaced my distributor assembly *after* I installed the correct Reman ECU so I can't imagine it having affected that.

To note, I have not used the 1995 ECU since about January 7th of this year and my CEL issue showed up well after installing the Reman ECU.

I'm very curious to see what my O2 sensors look like. Still waiting on the Denso replacements to come in.

My hope is that nothing was permanently affected as a result of using the 1995 ECU. Parts being worn on incorrectly (O2 sensors, plugs, etc) I now expect and am correcting those possibilities.

Do you see any evidence that the EGR temp sensor circuit is wired differently in that diagram of yours, Gerry? I am guessing that is the same but it makes me wonder.

...

The new Y-Manifold and #1 and #2 catalytic convertor exhaust gaskets come in tomorrow and Tanin received my 1992 ECU today. Fingers crossed.

 

[QUOTE=KahnBB6;9461389]
Do you see any evidence that the EGR temp sensor circuit is wired differently in that diagram of yours, Gerry? I am guessing that is the same but it makes me wonder.
[QUOTE]

EGR VSV is wired on the same pin 75
EVAP VSV is wired on the same pin 74
Intake Control Valve VSV is wired on same pin 39
FPU VSV is wired on pin 36 of 95 ECU but nothing on 93 ECU

 

the fuel changes didn't start till later years in cali.. maybe '94. earlier cali years has the brown federal injector and no fuel pressure vsv. I find most of the differences on cali is on the o2 sensors especially the third one cause its not on most federal cars, but its always good to check the schematics to be sure. one could repin but if you are going back to the other ecu in a few days.. then just let it ride, its not worth it.

running the ecu with only the third o2 code will not result in harming anything, I wouldn't try and pass an emissions test with it but if you needed to drive it then why not as long as the main o2,s are connected. usually its the presence or absence of heaters that are the differences found on the main o2s the signal pins are usually the same on all the variations but again worth a double check I am going off remembering comparing all the pinouts for the tt ecu mod, which was several years ago. max even if the main o2's aren't working you could still drive it without hurting anything, with the stock injectors it doesn't run that rich once the coolant temp is up to full operating temp. you can run a little rich and only hurt the wallet, to run the motor you would be smelling it out the exhaust and the wideband if you had one would have to be in the 11-12's majority of the time to start fouling plugs. I understand there is a difference in the injector shape and whatnot, but they are the same size and all those small variations are handled by closed loop in the ecu, not any major remapping cause those emissions components aren't always on. without the o2 maybe it will be off to notice on the butt dyno, but you wont be washing down cylinder walls or anything.

the one that affects the AFR the most though is the charcoal canister purge,. it can be purged via the ecu and vsv, but what people forget is it also has a ported line from the throttle body, meaning every time you tap the throttle for an instant it relieves the canister which richens up the mixture. toyota purposely does this on initial acceleration and part throttle cruise cause the richer mixture is tolerated under those loads and is generally not noticed much by the ecu, as the o2 waits a certain number os milliseconds to start correction.
In summary, the fuel map is not tuned to compensate for these things... they actually time it to not affect the fuel map.

oh and I don't know why your rotor failed, but it doesn't have to do with the tune unless you are firing timing wise outside the window where the contacts are in touch with the rotor, which would probably cause the motor to knock apart. maybe it was a bad batch or something?? they are a little picky sometimes.

 

Thank you Gerry!! Above and beyond!

That probably means I am fine, other than it being a good idea to replace my first two O2 sensors and my plugs.

From what I understand after calling Lexus a few weeks ago, for 1992-1994 Cali-Spec SC300's there are only three VSV's: EGR VSV, EVAP VSV and a VSV for the ACIS intake butterfly system.

No FPU VSV to my knowledge so that would be consistent with what you've found in your schematics... until we get to 1995 model year chassis.

 

Thanks, Ali!

You are right. From what I have learned the major changes do not occur before 1995 Cali-Spec models.

When I had my injectors redone late last year I found that 1992-1994 SC300's used the same injector part numbers for Federal and Cali-Spec.

My 1993 does have the #3 O2 sensor which is located on my 2nd catalytic convertor.

No fuel pressure VSV on this 1993 model year as you and Gerry have noted.

Currently I have three GE ECU's:

1992 SC300 M/T Cali-Spec
1992-94 SC300 M/T Cali-Spec Factory Reman (compatible for all 1992-1994 SC M/T Cali models)
1995 SC300 M/T Cali-Spec

I haven't used or needed to use the '95 ECU since very early January. I don't plan to use it again and I will put it up for sale in the classifieds soon since it was working fine other than being slightly incompatible with my model year.

No, I never intended to try passing smog with it. I bought it out of desperation last year because it was the only Cali M/T ECU I could find at the time and I needed a spare computer to operate my car while Tanin did capacitor work on my original ECU. It did seem to run the engine just fine other than the permanent CEL and not being sure if it was also running a little rich as well.

And now I know there is a strong possibility that because it (1995 ECU) was looking for heated O2 sensors and an FPU VSV among other things it might have been the ECU's own programming forcing a rich fuel compensation to counteract sensor information it was not getting. Without knowing those things at the time it added to confusion in my attempt to try the "known good ECU" comparison method of determining the health of my original 1993 ECU.

I have had the correct type 92-94 Reman ECU in the car since early January. No CEL incompatibilities other than the Code 71 I've been diagnosing.

Tanin Auto has my '92 ECU for capacitor work as of today and I will try that when they sign off on it as OK and I get it back.

After that, once I know the '92 ECU works I will send the 92-94 Factory Reman ECU in to Tanin to have the same once-over done to it... and they can also confirm whether there are any abnormalities that I've been experiencing with it.

.....


I want to say... Gerry and Ali, you're both amazing to help out as much as you have with this, down to researching and recalling ECU schematic information. The level of time you have both put in to understanding the ECU wiring of multiple years of these cars is tremendous to me. Thank you both for this!

 

sounds like a good plan, I know you want to solve the issue but likely the o2 sensors are fine if they have been recently changed. plugs will foul out before those do, and it takes quite a bit of extra fuel or even oil to do that.

 

Thanks Ali. I am confident that these last few steps will solve whatever the final culprits are. There isn't much else to try. I am also still skeptical about installing a brand new Y-Plenum to solve the Code 71 since Gerry's Plenum seems to be doing its job just fine but we will see. Since I was still able to obtain a new one for a reasonable price I have to try at this point.

I am still going to inspect the EGR tubes of both Y-Plenums later and compare their condition just to understand what was going on there.

The O2 sensors were replaced sometime last year before all the trouble started so I don't mind doing another baseline. The plugs I am replacing just because I've seen two distributor rotors wear very quickly during this whole saga. A new baseline for all of those cannot hurt now that all the other trouble areas have been sorted out.

On the whole, however, the car is running beautifully now despite the last lingering issues.

 

Tanin's staff just let me know they won't be able to get to my ECU repair until May 2nd. Here's hoping they are able to get it back to me soon after. Since I have wanted to cover all bases and send them my Reman ECU once I have the 1992 ECU back and have verified it works I am concerned if I can have both ECU's serviced and returned with a couple of days to spare before the 18th of next month (my deadline for smog and renewal).

This is just how it goes.

One ECU will be newly serviced and available to test with at least. I just hope that the 1992 SC300 Cali-Spec M/T ECU really is exactly the same as 1993-1994 variants in the same specs. Toyota's Reman ECU covering the 1992 and 1993-94 part number ECU's seems to suggest this but here is hoping.

I just went through Toyota's EPC with the P/N 89465-29525 (Denso 234-4214) for the #3 O2 sensor on my car and it does seem to correspond to 1992 SC300 Cali-Spec cars also, so ECU's 89661-24320 and 89661-24321 (and 92-94 Reman 89661-24322) should be the same programming.

 

question, have you ever done a compression test?

was the metal egr pipe clogged also at some point, the one from the head to the Y pipe, or just the y pipe itself.
reason I ask is that if that metal pipe was all clogged up, there is a chance the passages in the head itself are partially blocked. I am not sure how open they need to be to be "in range" but really just grasping at straws here and throwing out all possibilities. I feel like you could have built a spare 2jzge by now and it would be nice to solve this issue and put this problem to rest, I can only imagine how much of your time this issue is taking.

 

I have not. You've mentioned this before and I agree it's a very good idea (especially if I plan to use my original block for the GTE conversion.

The engine does pull just fine as it is and I haven't had any reason to believe there are any internal issues with the piston rings.

Unfortunately a compression test is not something I can do myself where I am living at currently due to the landlord restrictions. I can get away with minor engine top-end repairs and electrical work at night but the noise a compression test would make, especially in the evenings, isn't going to be liked very much. I'd have to take it to my shop to have this done.

I checked into this a couple of weeks ago and it had some carbon buildup but not nearly enough to constitute clogging. I did thoroughly clean out the EGR pipe before putting it back in. I also cleaned my original EGR valve on that same evening (it works fine but the new EGR valve was installed later).

It's a very good thought, Ali. But I did check the open EGR port on the head and it wasn't clogged. There was just a little carbon buildup on the surface edges that I carefully cleaned out before re-assembly but it didn't seem to be an issue. Theoretically you could be right about the passage itself far back into the cylinder head. I couldn't see any of that. I don't think my issue relates to that, however.

Anyway, even if it did the only way to tackle that section would be to remove the cylinder head for cleaning and take out the EGR cooler plate on the rear for cleaning as well, correct?

You're right, and don't stop there. I could have built up part of my GTE by now with all I've spent on this tuneup in the last few months :/

Nail on the head. It's certainly taken up a lot of my spare time off and on to find the next diagnosis, locate the next part and very often plan ahead to not drive the car for at least 24 hours to cool off and depressurize so I can remove that blasted coolant hose on the throttle body over and over every time I have to get to the plugs or plenum.

I'm very ready for this to be over and the 18th of next month is looming with still no way to even get an emission pre-test done to check the *entire* emission system. I am not looking forward to the remote possibility of registering Non-Operational if none of this kills the CEL light by then.

I really had thought I'd have a good chance at swapping the engine by now or at least I couldn't have predicted an emissions issue this insane with how much I stick to my car's maintenance.

Once this is over I am not going to be able to just jump right in and continue with my GTE swap. It's absolutely had a huge hand in delaying progress on that both financially and with my own personal time. Once this car passes smog I have to shift into completely unrelated projects for a while.

Although I will still have to pick up the rarest of the remaining TT parts on my list as I am able to.

...

The new plenum is on its way but it's been delayed until Thursday before I can drive out to get it.

I received the new Denso O2 sensors today but realized I'd made a mistake and ordered the "front" and "rear" sensors thinking they were front #1 and #2 O2 sensors. Instead I had ordered one of the front two O2 sensors and one expensive #3 O2 sensors that goes on the second cat. I ordered another of the front two sensors and will have to return the other one.

...

What's killing me right now is waiting for every part I need to try to fix the remaining problems. There has been no way to actively test or try anything else for over a week now.

Although I can at least try testing the harness connector for the EGR temp sensor to make absolutely sure there is no issue there. I have to look up what electrical readings I should even be looking for for that. The sensor itself is brand new so that's not in question. But the harness connector it plugs into to verify it's getting proper connection to the ECU... I don't know how to do that yet.

 

Progress, today:




And the amazing Luis @ Carson Toyota came up with some very good notes to better approach cleaning that pesky tube on an original Y-manifold. I will be putting all of that in a separate DIY thread later so that people will have a reliable way to clean these things in the future should they need to.

 

Brand new Y-Manifold is in. It was too late to do the new O2 sensors and plugs. That will be today.

(Gerrb's confirmed EGR flowing manifold on the left. New manifold from Toyota on the right with most hardware already transferred. Those are scarce now brand new).






However, I did notice something that completely pissed me off while installing the manifold last night:














I noticed a new mechanic was at my usual shop. The owner, whom I trust, put him onto changing the EGR valve in my car a couple of weeks ago.


Instead of using a long extension to get the pipe off first the correct way like this, which requires you brace the angle bend with one hand to keep the socket centered on each 12mm bolt as you remove and re-torque to 15 ft-lbs...








... he took out the removable studs, put the lower one back in and DRILLED the top stud location so that he could squeeze in a huge bolt and nut in their place. He's ruined the stud location and actually warped the EGR valve mating surface.

I am sorry to say that this was the perfectly good flowing manifold you sent me, Gerry

That's now scrap metal, thanks to this idiot. I am sorry, Gerry. I was planning to clean up your manifold and my original later with my replacement freeze plug project. So angry to see such negligence. I'd have waited or come back the next day if more time were needed. Knowing the shop owner for years now I do not think he was aware of his new hire's shoddy work and nor will he tolerate it when he hears about it.

Still. Totally unnecessary carnage.

I do have it solved for myself now but this upset me to no end. Never have I had an experience like this in years at this shop. I will bring this up to the owner shortly and show him.

Also, the EGR temp sensor was barely tightened in place and the huge 32mm nut was barely tightened to the required 47 ft-lbs as well.

Anyway, onward. All corrected now with the new manifold and the all bolt/nut torque double-checked. The last two items left for today are O2 sensors and plugs. After that hopefully the CEL will stay off. Then I am
just waiting for Tanin to work on the '92 ECU.

 

Well... I've said it before but this time I think it's actually true.

I think I've finally solved the EGR Code 71.

Last night and this evening I installed the following:

--Brand new Y-Manifold (ie: any fully clean Y-manifold)
--new EGR valve (but original was not proven to have gone bad)
--re-torqued all EGR valve bolt and nut connections to correct shoddy work done by negligent rookie shop mechanic
--replaced a couple more suspect vacuum hoses underneath the EGR valve with new hose
--replaced one more vac hose on the EGR modulator (had been replaced recently already but this is better hose)

And also:

--New Denso Platinum - PK16R11 spark plugs gapped to 1.1mm (plugs in car were Denso K16R-U11)
--2x New Denso 234-1055 Oxygen Sensors (#1 and #2).

The battery was reconnected and I took the car for a 100 mile drive. I got home with 101 miles and NO CEL!!!

I'm very happy! And the car is running fine now. No slight rich fuel smell on cold startup.

I am going to have the new factory exhaust system seals (x2 of 90080-43028 for SC300's) installed just to be safe but I think it's finally time to give the car its emission pre-test and get the show on the road

...


There is a last issue (because of course there would be) in the form of what I think is my alternator's voltage regulator starting to go bad. I'm looking up common symptoms for that. The car runs fine but my accessory DC port gets power intermittently as does my hardwired radar detector as it goes on and off at consistent revs below 3000 or when shifting from 5th gear to 4th gear at speed. This has been going on but I've been too busy to bother with it.

The auxiliary DC port I installed into the console (and wired to the same main DC port circuit) isn't suffering from these issues, nor does my cellphone USB cord get intermittent power there.

I will be checking the wiring under the console first before jumping to any conclusions. The car itself is firing just fine. Very smooth.

I have an inexpensive DC port voltmeter that displays my volts to a tenth. I have heard these are not 100% accurate but I get readings anywhere from 12.8V to a more common 13.0V-13.2V driving around town to 13.4V-13.5V on the highway. I never see higher numbers than that.

I know these 90's alternators aren't putting out constant amperage (not confusing that with volts, just noting) like new ones do but this is still abnormal.

Anyway, that's not going to stop me from smogging the car but I want to figure it out since it's a recent issue. I am going to guess that it's probably unrelated to any of the previous issues I've had in this thread so I may take it to a new one.

...

Still... tonight is a victory!

 

good for you Craig ... hopefully all is well with the car .

So what do you think was the real culprit with that CEL 71? Or is it hard to determine now having replaced a lot of stuff ?

 

Gerry, thank you! And thank you so much for all of your help in diagnosing and solving this issue. Yes, as of now everything is fine. No CEL light, smooth idle, good power, clean smelling exhaust and a lot of peace of mind.

I still have the intermittent odd startup issue from before but it only occurs when the vehicle is cold now and never reoccurs when it is warm. I will continue to solve that (will see what the '92 ECU does and will plan to replace the original 239k mile FPR) but it will not affect getting the car smogged and the registration renewed. BIG relief.

As for what actually caused the EGR code 71... it is hard to say. I have a couple of ideas:

Original cause:

I strongly suspect that my original Y-Manifold was gradually becoming clogged up tight and that I was also getting clogging of the original EGR valve's little stem to the EGR Vacuum modulator and the vacuum modulator itself. The EGR vacuum modulator diaphragm failed/clogged and the original EGR VSV failed or intermittently failed until it stopped working altogether somewhere down the line (which could have accelerated these issues).

Also, I cannot be sure when two certain vacuum lines became loose near the EGR valve because I had checked them multiple times during this process and they seemed fine but the last time I went in to replace the manifold and re-seat the EGR valve and pipe... those vacuum lines needed replacing. Plus one other on the EGR Vacuum modulator that I also replaced with a new one weeks ago during diagnosis... but which was curiously not tight upon last service.

Causes upon last time my shop serviced the EGR system:

Besides the horrible ruining of the Y-Manifold EGR valve mating surface area I know that the lack of proper torque to the big EGR pipe nut (should be 47 ft-lbs) had to have been a contributor as well as the lack of proper torque on the EGR temp sensor nut. Also, I have no idea if vacuum lines were fiddled with or not. All of those looked the same yet only after I had the new EGR valve installed did I notice the loose/stretched vac lines in two hard to reach areas.

Unknowns:

("Y" Manifold)
I will never know for certain if the Y-Manifold you sent me was flowing enough, Gerry. My thought is that despite it allowing good EGR valve operation (ie: the pressure test to cause stumbling and stalling out) it may have still been slightly too clogged in the center pipe for the temp sensor's liking. But it is a head scratcher since yours actually worked and passed the test whereas my original was completely clogged.

When I attempt to clean my original "Y" to demonstrate how it can be done I will also open up the one you sent me and inspect that passage so that we can have a definitive answer.

What I do know is that the brand new manifold worked in strong part to eliminate the CEL.

(EGR Valve)

This is also a question mark. I cleaned my original valve up as much as possible, removed and completely unblocked the 90-degree metal stem of carbon buildup and cleared as much of the valve as I could of carbon. It held various Hg pressures with my hand vacuum pump and the valve had full range of motion and seal. The diaphragm did not seem to be compromised.

Still, the aftermarket identical brand new Intermotor/SMP EGR valve was installed and it also works perfectly.

...

Personal conclusions (as close as I can get anyway):

A lot of the failures had to do with carbon buildup over a period of years. This is what caused at least a couple of component failures (the EGR Vacuum Modulator being one) while the EGR VSV could have failed due to age and operation time alone.

Cleaning the Y-Manifold and verifying enough cleaning had been done was the hardest part and I am disappointed that as of this post we still have no conclusive evidence of how clean a "flowing" manifold needs to be for correct EGR operation. Since new Y-Manifolds are in very short supply now from Lexus/Toyota this is why I feel it's important to at least do a small writeup here to show SC300 owners how to completely clean theirs of carbon if they have to pass smog.

The vacuum lines are a mystery to me. I checked them more than once throughout this process but only at the end did I notice two or three of them being suspect. The one I mentioned on top of the EGR vacuum modulator was a NEW length of hose I'd installed weeks prior that only made me curious when it was easy to pop off while changing spark plug #5 or plug #6. I just replaced it with another length of new hose to be absolutely safe.


Perhaps the biggest takeaway I can give from this EGR Code 71 saga is to test, replace and reset one thing at a time (slow and time consuming process) but to not rule anything out no matter how remote. The age of these cars might be the strongest reason not to write off anything when fixing an EGR code :/

What do you think, Gerry? Ali? I'm very happy to have that solved now and be able to take the car in for pre-testing on Monday but I also wish the root causes and culprits were a bit clearer in the case of my car's recent CEL.