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Yes, there is room for a ZIP if you plug the zip into a standard socket on the board. Otherwise, there is a good chance it will foul against the 74A573 chip. Brutus and I have been making good progress pulling the code apart and understanding the MCU details. We will need to summarize things...

There are check valves in the heater valve and booster. With the engine off step on the brakes and after a few pumps you will run out of vacuum and the pedal will be much harder to press. The cruise control actuator also runs off vacuum, and Toyota added an electric vacuum pump on it to...

Start by going through the tests described here... http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=119

The brown and yellow-red (yellow-black on my 90) is for the EGR temp sensor. If your car is not a California model, it is left disconnected. The other is probably the transmission speed sensor ( its should be red/black, black and yellow as well as a blue/yellow, four wire in total) connecting...

You are running rich in both tests. For the second test you have A/F cruise:13.285:1 idle: 13.373:1 So you are not in closed loop. You need to find out why. Check the TSRM for troubleshooting this condition.

A little tidbit... the D151801-xxxx part number is used for multiple different Toyota ECU families. There is another marking underneath and it must read 7433-XXXX to be a member of the 12kB 8-bit MCUs as used for the Supra. I have been studying the interrupt operation by writing test code...

JJ's black tape trick is well thought out. If you can force the surface to be approximately a black body then you will get better results. The hardest surfaces to measure are highly reflective ones, as they behave like a mirror, and you end up measuring whatever is being reflected, which...

If you want accuracy, nothing beats a thermocouple. IR guns are convenient, but they need to be calibrated to the surface you are measuring, if you want accuracy. If, for example, you mostly use it to measure exhaust systems, then an hour spent calibrating the IR gun to a thermocouple reading...

Unless you know the IR emissivity of the object being measured, its really just a guess. Off angle measurements are even more unpredictable. For a reflective surface, the measurement is of whatever object is imaged by the reflection off the surface, and for an absorptive surface (true...

Gunnnar, that's a different rev from what we have been working with (D151801-3920). It will be interesting to see the differences.

Although not much has been posted lately, there has been good progress. I have been able to write a Denso module for the free version 4.9 of IDA. I was told the free version did not support custom processors, but apparently that was bad advice. This is now definitely the disassembler to use...

You have all you need to figure it out. Post #59 even provided the wiring diagram for your convenience. I paraphrase the situation 1) Its not the 'old' wiring 2) The circuit already has a relay, why would you need to add another one! 3) Trace the circuit and find the source of...

Never mind! I see it is part of the new evap test where they look for fuel leaks. I don't recall the tech looking too hard when he did mine last year, probably just uses his nose.

Interesting JJ. For a moment I thought they were actually going to inject smoke into those systems and check for leaks. The actual test doesn't seem to be too bad. 9. What is the technician supposed to do? The test requires the technician to look for visible smoke coming from the tailpipe...

I don't see CO2 and O2 in post 5.

The Denso A/F sensor is biased at 0.4V and the resulting current is used to compute the air-fuel ratio. The attached chart shows the behavior. This is a very modern sensor, with better performance and durability than the old 5-wire Bosch design used by most aftermarket widebands. Read a...

Post up your CO2 and O2 readings as well.

The loom can rub on the intake pipes if the plastic harness clamps fail (which they tend to do after 20 years of high underhood temps. After a while the rubbing will go wear through the insulation and into the copper. This is not easy to see even if you are looking for it. Follow your engine...

There are 24 engine wiring harness variants for 89+. Many are obsolete, but the point would be that this is not as simple as made out on this thread. 82121-14530 1 08/1988 - 08/1989 MA70..5F..TWC 82121-14531 1 08/1989 - 08/1990 MA70..5F..TWC 82121-14540 1 08/1988 - 08/1989...

I haven't found any checksum routine yet. I thought it should be the first thing executed from a reboot. According to Ross there is a ROM checksum and a double pass RAM test (write all 1's, then write all 0's) in the 3SGTE ECUs of the same vintage.