CIS issue...Final chapter

First my thanks to Steve M and Larry F for their help in clarifying and insight in resolving this CIS related problem. I had a breakthrough this weekend and my 88.5 TR is finally running closer to what it should - minor idle tweaking required!

I am posting a more detailed explanation for the benefit of future searches. The solution might appear obvious to some... always is when you have the answer

Issue: "New to me" 88.5 TR, stumbles under partial throttle as it reaches 3K rpm range - appears to be running lean, pops through intake - Slow down light have come on a couple of times but could be a short (per PO). Car has EXTENSIVE maintenance history, with many parts replaced (injectors, Lambda sensors - by the bucket, catalytic converters - 2 sets, all in the span of 2000 miles) Starts fine, briefly runs well when cold but goes south after warming up, still drivable but not quite right.

Basic Diagnostics:
Checked Lambda and both are sending voltage left bank is varying - right hand bank is pegging around 1.0V suggesting rich situation - appears to conflict with assumption of lean condition
Checked right bank upper and lower chamber CIS pressure (thanks Larry for the fixture). Pressure differential is ok at 0.3 bar BUT does not change when EHA is removed (no wonder it is running lean I think). It should change increase 0.1bar - is EHA dead?
Checked EHA resistance - OK at 20 ohm - bench test works fine
Measure voltage or current to EHA - should be 10 milliamp or 200 millivolt - WITH EHA connected. Result of test "zero" volt. Changed the mixture screw and nothing happens - Does this point to ECU not functioning?

Here is where it gets tricky when you have a preconceived notion - I think that the car is running lean, yet the Lambda is showing rich, voltage is at EHA is zero which means the CIS is lean, changing the mixture doesn't do anything...I am thinking that the ECU is not working correctly.

Verdict:
Well after switching parts around I determined that the ECU is working fine, EHA is working fine, Lambda is fine, wiring is fine, so what is the problem? Simple answer - the mixture screw on the R bank CIS is way rich....5 or 6 turns which is way way off since typically you are adjusting by 1/10 of turns. So when I tweaked the screw in my testing process nothing would happen, pressure wouldn't go up (b/c the Lambda reads rich the voltage to EHA would not change off zero).

Lesson:
Understand how a system works before replacing parts!! The CIS on the TR is quite simple, in fact it is so simple that anyone feels they can fiddle with it... and send it out of whack. Looking at the MANY maintenance bills on my car, I have little doubt this has been an ongoing problems that has been address by replacing parts but never quite understand how the system actually works.

BTW, manual suggests measuring pins 7 and 8 to measure resistance across Lambda sensor with ECU disconnected - this is confusing - ECU is connected but power off - I removed the connector from ECU and could not get the right values for the Lambda resistance. If you don't have a break out box you can remove the back of the connector and probe the pins that way.

 

At first glance CIS looks similar, but the "E" piece meters the differential pressure btw upper and lower chamber - that apparently - is the tricky part as 0.1 bar off can throw the system off. CIS is not as sensitive. Larry F is the expert and go to guy, super helpful.

 

Not sure about the free play, I did test according to the WSM and both "felt" the same, smooth travel and one bounce on release. Also tested the voltage change back to the ECU through the motion and it was correct. I will check once I take the covers off again, while I have solved the warm running condition, the cold start is not great.. looks like I have reversed the problem