1998 LS400

CIR open relay won't open due to ECU failing to ground it.

Capacitors in ECU all replaced (with the exception of the unavailable BP 47uF). All of the removed caps in spec for capacitance but not tested for leakage etc.

OBD port is giving "bad connection or power" and won't communicate at all

If you hotwire the CIR relay the car will run but misfires on at least one cylinder.

Seriously losing patience with the thing now.

Any helpful suggestions greatly appreciated.

 

Did you check the ground points? Saw a video recently of electronic gremlins. Turned out to be a loose ground connection to the body.

 

Did you use a correct scanner specially designed for Toyota cars such as a S2000?
A 98 LS400 for non North American market is not OBD-II compatible although it has a same connector for it. The communication protocol is different from the OBD-II.

 

Regarding the circuit opening relay inhibiting to supply the +12V, you must know that the ECU works so to avoid the serious engine damage when one of following conditions is detected.

1, No signal from the MAF for more than 3 seconds.
2, No signal from the crank position sensor for more than 5 seconds.
3, No signal from the cam position sensor for more than 5 seconds.
4, No IGF signal from the igniter for more than 3 seconds although the IGT signal is sent.

 

Thanks Yamae, I'll check those sensors next. Much appreciated.

Ground points are good btw.

 

Since you already have found misfires, the car might have some ignition problem.
The term "IGT" stands for "IGnition Trigger" and "IGF" "IGnition Feedback". The ECU is checking all 8 igniters sensing the IGF is properly coming back when the IGT is sent to the igniter. "Properly" here means that the phase and the voltage are within the range.

Check those first. An oscilloscope is the best tool to check those but you can somehow check the "IGF" signal level by a voltage meter comparing with others.

 

These are the resistance values for each of the 8 coils :

# pin 1-4, pin 1-2 (kOhm)

no1 74.8, 75.1
no2 72.0, 72.4
no3 68.4, 68.8
no4 75.1, 75.5
no5 72.3, 72.7
no6 73.4, 73.7
no7 69.7, 70.0
no8 73.6, 74.0

What are the min/max resistance values for these pencil coils please?

When number 3 is lifted from the spark plug it makes no difference to engine running so I'm suspecting that one is likely to be toast given its low resistance also.

 

And unplugging a coil pack from the spark plug could ruin it if the engine is running as that high voltage has to go somewhere. And he said to check the IGF signal not the resistance values. And if it wasn't toast it maybe now.

 

There's not only a coil but also transistors and resistors are there in the ignition module and the resistance check can check only a part of it and is mostly difficult to find out a failed one. The best way is to find out is to observe the IGF signal and IGT signal. But since you already tried to lift up the module and No.3 is the suspect. Swap it with some others and see any difference.

 

I'm sure it is, however,

1. I don't have an oscilloscope or a high freq multimeter.
2. If the car won't run (which it won't other than sporadically) I can't check for an IGF or IGT signal.

I have tried swapping it with another to see if the fault moves however it won't then start with it on the other bank. (Possibly because more than one is knackered)

 

I meant the multiplug from the coil, not the coil from the plug. So no harm done.

 

Couldn't a person use a logic probe to check for the signal?
https://www.amazon.com/s?ie=UTF8&pag...Alogic%20probe

 

Given that 4 IGF returns are wired together how are you going to know which of the four is returning the wrong signal without an oscilloscope and concurrently monitoring the IGT signal?

 

Simply separate No.3, if that is the suspect and confirm.

 

Simply separate it where? Whilst still keeping it plugged in cos it won't run for more than 3 seconds without signal??