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· Your ignorance...
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985 Posts
Discussion Starter · #1 ·
What difference to the ECU is there when you are idling, or when you are off-idle?

What I mean is, aside from a 300 rpm difference in engine speed, what happens when you go from 600 rpm and throttle fully closed to the throttle slightly open and running at 900 rpm? What things change? What inputs and outputs to/from the ECU change? What operates differently? How is timing affected? I know the TPS's IDL line opens, but thats about it. I need to know what else is happening that could make such a drastic change.



If you haven't seen my "mystery overheating" thread, that is the reason I am asking. When I am off-idle (anything 800rpm or higher), the water temp will steadily climb until it boils over. When I am AT idle (throttle closed, 600rpm), it will not only NOT heat up, but will in fact COOL DOWN from overheating condition. I can idle the car for almost two hours and it will NEVER rise above 160 degrees, if I run at 800 rpm for even THIRTY SECONDS, the temperature will start climbing. It will do this with the TPS plugged in or unplugged, btw.
 

· Your ignorance...
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985 Posts
Discussion Starter · #5 ·
Lol I so wish it was that easy/any of those things. I have been busting my ass on this for weeks.

TPS is good and is set right and I verified with a spare.
Test of injector resistance all passes. Injectors were sent in for cleaning.
Temp sensor is okay, resistance is consistent with temps.
And I have verified engine temp with an aftermarket gauge and a multimeter with temp probe.
Thermostat was originally the stock 195*, I went to a 180*, then a 160*
Heater core flows like mad from both sides, and blows plenty of heat. Also the car behaves the same with the heater core valve closed (vac line off&capped)

I have literally done everything I can think of, and I have tracked it down to this idle vs off-idle condition. When at actual closed throttle idle, it is great and runs perfectly cool at 160 for over an hour and a half, but the minute I go off of idle and raise the rpm's AT ALL, it will begin to heat up and if I let it go, will boil over at 235*, however if I release the throttle and let it return to idle it will not only NOT continue heating up, but within a few mintues it will cool it back down to 160*. That's the reason I am trying to figure out whatall happens going off of idle, or what happens ONLY at idle and never off-idle, and why I made a seperate thread from the overheating thread for this.


As far as I have determined thus far, the following happens:

IDL-E2 signal from the TPS goes from closed to open
More air enters engine due to throttle plate opening further
AFM consequently measures this air and reports to ECU via KS-E2
ECU sets new injector pulse & timing advance based on all sensor inputs, which are:
* Air temp (THA-E2) -- varying resistance of 5v (VC)
* Water temp (THW-E2) -- varying resistance of 5v (THW)
* RPM (Ne-G-) -- generates its own signal from magnetic pickup
* CPS crank angle (G1-G-) -- same as above
* TPS (IDL-E2 & VS-E2) -- VS-E2 = varying resistance, IDL-E2 = 5v on/off switch
* Air volume (KS-E2) -- 5vdc square-wave generated from reference 5v (VC)
* O2 content (Ox) -- Only in closed loop to fine-tune to 14.7-1 for emissions


Basically the ECU ignores the O2 sensor any time except warm idle and warm cruise. If accelerating, decelerating, cold, or under load the ECU totally ignores Ox. If any of the other sensors are off/missing they will trip a code. I have checked resistance/continuity of all of these wires to the ECU and all are under 3 ohms, and do not falter if I hit, shake, bend, twist, or pull anywhere on the harness.

What I need to know is what ELSE happens and EVERYTHING that is going on, because all of this stuff is working like it should, yet the engine still runs too hot OFF OF IDLE only.
 

· Overlooked
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4,693 Posts
Well. IIRC you stated in the other thread that you didn't change the O2 since it's 150 dollars. Sounds like this is allowing a lean condition. Try swapping with a new or known good one and see how that works. The only thing changing when off-idle is the amount of air in which raises fuel demand. Obvious. That's why I mentioned the two relays in the other thread but you said they are good. Maybe the O2 is tripped by the removal of the EGR system and is trying to lower emissions by leaning out. Did you swap for a JDM ECU when you removed the EGR system?
 

· Your ignorance...
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985 Posts
Discussion Starter · #7 ·
Nope I left the american ECU in, and used the american sensors with it. At this point anything is possible, but I don't think the EGR really has much to do since it's been off for 4 years and I never had a problem.

As far as the O2 sensor, I unplugged it and it runs identically, so some bad input from it would never reach the ECU which is why I never justified the $150 cost. If it made some difference I would have.

I've been working on getting ahold of my friend who lives near here to see what he's got in the way of known-good parts to test, so we'll see how it goes.
 

· Overlooked
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4,693 Posts
The metal lines running under the exhaust manifold, could the upper pipe have a clog in it or was this in your check? Looking at the diagram it could heat up the water inside this line which runs straight to the sensor but would also allow flow through the heater core when heat is on.
 

· 7M POWAH! baby ;)
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2,360 Posts
Stop looking electrically at your mechanical problem. The electrics in no way control the heat of the engine.

Components for water control:
Thermostat
Radiator cap
Water pump
Radiator
And the thing that stops exhaust gasses pissing around with water
 
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