Builds 1990 LJ78 in Montana

[davidp14]

About a week ago I replaced the coolant temperature sensor in the engine block in the hopes that it would solve my torque converter lockup issue. The problem seemed to get better, but it didn't go away, so I ordered a set of replacement solenoids. After spending several hours searching trying unsuccessfully to find some pictures of the valve body and solenoids on an A343f, I just went for it. The install was easier than I thought it would be.

The hardest part of the whole job was getting the trans pan off. The shop that changed the fluid and "tested" the solenoids didn't use a gasket when they put it all back together, they just used a gasket sealant. As a result, I spent nearly half an hour with a thin putty knife separating the pan from the transmission. It left quite a mess.
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The culprit was the black lockup solenoid, but I went ahead and replaced all three. The two shift solenoids are identical and the lockup is different, so it was pretty self explanatory.
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The new filter screen that came in the kit was totally different from the one that was on the transmission, so I just cleaned and reused the old one. I think that the new screen is for an A340E; the packaging said that the kit could be used in either an A343f or an A340E. If anyone needs an A340E filter, let me know.
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The transmission feels like it shifts better, and I haven't had it jump out of lockup yet, so I am hoping that it is fixed.

Hello! First, I love your Prado and what you've done with it!
Second, I realize it's been a few years, but can you elaborate on your lock-up issues were? My 80 with 343f is having what I believe to be an intermittent lock up cancellation under partial load. Basically, when I apply moderate acceleration up hill and rpms are between 2500 and 2900 the TC will lock and quickly unlock sporadically until I have either accelerated past 3k or coast. I have replaced the brake light switch, ect sensor and a whole bunch of other things related to this issue. I'm starting to look at lock solenoids now and wondering if your issues were similar.

 

[AirheadNut]

Hello! First, I love your Prado and what you've done with it!
Second, I realize it's been a few years, but can you elaborate on your lock-up issues were? My 80 with 343f is having what I believe to be an intermittent lock up cancellation under partial load. Basically, when I apply moderate acceleration up hill and rpms are between 2500 and 2900 the TC will lock and quickly unlock sporadically until I have either accelerated past 3k or coast. I have replaced the brake light switch, ect sensor and a whole bunch of other things related to this issue. I'm starting to look at lock solenoids now and wondering if your issues were similar.

Apologies for the late reply! As I recall the lockup issues presented as follows: once the transmission was up to operating temperature the torque converter would randomly unlock regardless of throttle position. Sometimes it would lock up again, but usually I had to press the PWR button a couple of times to get it to lock again. As time went on that worked less and less, until it simply wouldn't lock up once it had unlocked. Solenoid replacement fixed the issue.

 

[davidp14]

Thank you for reply. I think my issue was related to an improperly installed (by me) fuel pressure regulator. The o ring got smashed and air was leaking in around it. I put the old fpr back in and the problem went away.

It caused the truck to behave like there was a tc issue because it really only happened when it was locked up (or as it turns out, throttle at about 40%.).

 

[pradoblivious]

Hey @AirheadNut, you don't happen to remember what size tap you used to install this pyrometer do you? The sensor is going wacky and I'm trying to source a replacement, but not sure on thead size. I think it might be this 1/8npt one? https://www.amazon.com/AUBER-Probe-Exposed-Cable-Clamp/dp/B0DPNJC33T

 

[AirheadNut]

I don’t recall which probe I used, though it was likely 1/8 NPT. My probe recently bit the dust too, I replaced it with this one: EGT Probe, Exposed Tip [TC-KEGT] - $36.50 : Auber Instruments, Inc., Temperature control solutions for home and industry - https://www.auberins.com/index.php?main_page=product_info&cPath=5_22&products_id=69

They have a variety of different options for mounting.

 

[AirheadNut]

Actually, looking back at the photos that doesn't look like an NPT tap. Your best option might be to pull the sensor out and use a thread checker to identify what thread it is. If you don't have one at home any hardware store will have one in their nuts and bolts aisle.

Not sure if this is the same one I used then (product line may have changed in the last 9 years) but it looks similar. Definitely not the probe I would choose now, it is far too short to give an accurate reading in a regular automotive exhaust. K Type Thermocouple (6 ft. cable) [TC-K6] - $7.55 : Auber Instruments, Inc., Temperature control solutions for home and industry - https://www.auberins.com/index.php?main_page=product_info&cPath=5_22&products_id=87

 

[pradoblivious]

Thanks, it looks like 1/4-20 like the one in the link you sent

 

[AirheadNut]

Thanks, it looks like 1/4-20 like the one in the link you sent View attachment 3874398

I would strongly recommend getting a longer probe, I didn't know better when I installed that one originally but you'll get a much more accurate reading with the tip of the probe roughly centered in the exhaust stream. This would be a good time to install the probe in the exhaust manifold or turbo housing if possible, a pre-turbo measurement will be far more useful than post-turbo.

The gauge itself should accept readings from any of Auber's thermocouples.

 

[pradoblivious]

Well it lasted a decade and helped me avoid blowing up two engines so it was pretty successful haha. I will likely move it to the manifold eventually, but for now just want a working egt reading again. My heart just about stopped when it went wonky.. it was leaping between 1500 and 7000 while we were just parked at home-depot

 

[pradoblivious]

Replaced the pyrometer sensor a few weeks ago now with the Auber TC-KEGTS I went ahead and moved it from post-turbo to the manifold while I was at it. I read through a few different threads to decide were to put it on the 13bt exhaust manifold and settled on a spot between piston 3 and the manifold outlet.. mostly to avoid having to dismantle the turbo as it was a complete pain in the neck when I did it for the turbo rebuild.

I used a pencil magnet to draw up all of the shavings after tapping it, and liberally applied FIPG to the threads when I installed the mount

This put the probe in a place where I can get at it just by removing the hood and climbing up there if I need to. The Probe itself is massive compared to the little TC-K6 I had been using, but it lays back along the manifold fine, and isn't really in the way of anything.

I'm not really sure what to make of the results. With the small probe post-turbo I would have to really work the truck to get it up to 900 egt (which has been my hard-stop-foot-off-the-gas-limit since I've owned the truck), like you'd need to get it out on the highway and heat-saturate it, or get it going up a miles-long hill.

Now with this longer probe in the manifold, I can hit 900 from a cold start before I get out of 2nd gear. Touching the gas at all gets me to 675 from cold, and every green light brings me to 850 into second gear at a minimum (usually 900). I've read the threads that say I'm good to 1200 with a pre-turbo reading, but 1200 egt is now an *extremely* trivial number to reach. I've downloaded the manual for my gauge to see if there is some calibration to be done, but no, the meter is already set-up in TC "K" mode, which is what this sensor is. I note a small discrepency between the manual, which lists "k mode" as ranging between -200~1300°C, when the sensor itself claims a max operating temp of 1100°C..

Is it normal for manifold mounted EGT readings to swing this high so quickly?

 

[AirheadNut]

Those numbers sound pretty normal for a stock tune, older Toyota diesel. What temps do you see cruising at 60/65mph?

My TDI can go from ~350ºF at idle to 1000+ on a moderate throttle pull in 2nd gear.

 

[pradoblivious]

Well that's good to know. I haven't had it out on the highway yet since I moved the sensor... I suppose it'll be a bit of an adjustment for we humans, the machines aren't really doing anything differently... So when we're going over a mountain pass I guess my new cut-off temp is something like 1350?

 

[AirheadNut]

With these older tech diesels 1250ºF is generally considered the safe limit for sustained operation. Brief spikes up over 1300ºF are probably ok, but I would start backing off the throttle on long hills once the gauge reaches 1200-1250ºF. Metallurgy, combustion chamber design and piston cooling have all come a long way since the 1980's. I think Toyota tuned their diesels pretty hot back then, they probably weren't expecting drivers to be pulling mountain passes at North American highway speeds.

 

[pradoblivious]

With these older tech diesels 1250ºF is generally considered the safe limit for sustained operation. Brief spikes up over 1300ºF are probably ok, but I would start backing off the throttle on long hills once the gauge reaches 1200-1250ºF. Metallurgy, combustion chamber design and piston cooling have all come a long way since the 1980's. I think Toyota tuned their diesels pretty hot back then, they probably weren't expecting drivers to be pulling mountain passes at North American highway speeds.

pFFFFT highway speeds haha. If I can sustain 40mph I'm over the moon.

 

[bj70bc]

Yes thats normal
Welcome to the world of scarily accurate egt readings
Equally interesting is engine breaking downhill and how fast it will cool the egt's in this scenario, a little too fast in my opinion for head thermal longevity

 

[AirheadNut]

Yes thats normal
Welcome to the world of scarily accurate egt readings
Equally interesting is engine breaking downhill and how fast it will cool the egt's in this scenario, a little too fast in my opinion for head thermal longevity

I've wondered about that too, a couple of weeks ago I was pulling a pass at around 1200-1250ºF, going down the other side my exhaust cooled to 250ºF. I wonder what effect that has on things like the turbo and manifold, too.

 

[pradoblivious]

I'd venture to guess although the gas temps in the manifold are 1200, the steel itself doesn't approach that? I think steel begins to glow red at around 900 right? Anybody ever seen their manifold glowing?

 

[Rigster]

I'd venture to guess although the gas temps in the manifold are 1200, the steel itself doesn't approach that? I think steel begins to glow red at around 900 right? Anybody ever seen their manifold glowing?

Your coolant would boil over and create quite a mess long before this happened. Still, if you come close to boilover, and back over and over, it would take its toll over time I am sure!!

 

[bj70bc]

I'd venture to guess although the gas temps in the manifold are 1200, the steel itself doesn't approach that? I think steel begins to glow red at around 900 right? Anybody ever seen their manifold glowing?

yes
and you can tell exactly how hot it gets as it is tempered and displays the rainbow of colors depending on the heat reached