Just replaced my Engine Coolant Temperature Sensor (long overdue) with after market from IPD and also put on new connector and spliced into wires, removing old suspected bad splice. I immediately had cold start problems and codes 123 and 224 and the check engine light coming on.

Will now order OEM ECT as saw other threads which may be the reason. Too bad you can't order these with a new connector and some lead wires from IPD for the 240.

Question - good or bad to use teflon tape on the ECT threads, which I did on the OEM threads? Same question for teflon tape on the Coolant Temperature Guage sensor?

Any other suggestions or thoughts are always welcome.

thx. Mark

Hi,

The other poster "aleekat" is correct that you cannot use any kind of sealant film that is not conductive. As far as I know there isn't any to be had but I haven't contacted the minds of NASA. (:)

The ECU's on all cars use ground circuits to accomplish their tasks. Even though the electronic books I read say, "the electrons flow the other way - to +." I think they say this just to keep several things confusing from real life.
When my bank account does "work" for me, most of the time it goes positive to the negative.

On the 1989 on or the LH 2.4 systems onward are especially critical in this area as they incorporate a check engine light.
On these ECT's the thermistor comes with a pair of them inside. One wired to the ICU and one to the ECU. Either the ICU or the ECU or both can trip the check engine light if it does not see the proper resistance it's to ground or its corresponding voltage & current draw. Totally myself is the one guessing here!

I recently tried to exchange a blue colored ECT from an earlier LH and immediately got a CEL.
This was with those threads bare going into the engine block.
The 2.4 system recognized the difference so fast that the dash CEL did not even go out after letting go of the crank position

The 2.4's ECT has a black housing and I ohmmetered the two and got different resistance paths and amounts.
I then squinted very carefully to spot lines crossing at the base of the ECT on the diagrams.
GROUNDS of regular or computerized cars cannot be ignored for quickly be half of a circuit, to many circuits, at the same time. Fuses work the same way but are labeled for a "positive" reference.
I said what? {#}? about electrons? Yikes, there is diode device symbol that means forward bias current flows against the arrow direction. Sick huh! Electronics is my last frontier!

I think I may have been doing the same thing you were doing, looking for irregular mixture issue.
I too thought a possible bad wire or high resistance connection!

My car would only run rougher, from a rich or lean mixture, first thing in the morning. Crank and hit on the first roll over idle fine then run lumpy rough for about ten seconds and smooth out. Run the rest the day like it never has a problem.
I have concluded that the FPR was aged in such a slight way it was only gradually getting worse.
Changing or chasing the problem and messing with the ECT was a price I had to pay for not doing one thing at a time or thinking it though more.

I'm Not convinced the mixture during early warmup is dialed in.
I'm still waiting for it to come back after the innards of the car settle back into their normal positions.

Phil

Phil - a follow up. Thx much for all past help. Replacing the ECT with Bosch did work but as said I smelled a richer fuel mixture. While car seemed to run fine I quickly fell back into the old ongoing problem of the car running and then just dying. I had thought this might be related to the ECT so I replaced it. Now upon dying I got again codes 113 and 232 (injectors or ?) on pin 2 and 224 (ECT code) on pin 6. I am not sure why this car dies and have done lots of things to try to fix to no effect. I have not changed out amm or ecu/icu. I have not changed out fuel pressure regulator. I have replaced crank sensor, fuel pump and relay, fuse under hood at firewall and connections, tried an older other amm, tried an other ecu from my other 1990 (now gone). I never could figure out what causes the dying.

I first noticed it acting up again after replacing ECT and temp sensor when car seemed to bog out at 60mph driving on freeway. After that it would just die after running for a couple minutes idling in the driveway and that's when it threw the codes. I have never actually checked the voltage at the ECU or ICU as not sure how. Not sure if ECT could actually cause engine to die but as said ECT is bosch and new and no sealant or great or tape used on it so ground should be good.

I am taking the car in to the salvage yard repairman in two days as one final attempt to figure out why this thing dies. After that sadly I will donate car or sell very cheap with full disclosure if it can't be decisively determined why it dies and that will end my volvo saga. I've owned 5 of these and this one I could never figure out. thx again. Mark

Hi Mark,

I remember working with you on a 1990 before and I thought you found out it to be a basic spark issue. Is this the same car? You said here that you let the other 1990 car go.

The last time you were dealing with the ECT and whether Teflon tape would fool with its operation.
We concluded that it would affect the resistance signal. You said you got it in there so that good.

I too believe that the ECT will not kill the engine randomly at idle either.
The ECT is only an input perimeter factor of the ECT and ICU programs that would adjust mixture and spark timing. In extreme cases of an overheating, that signal from the ECU would enrichen the mixture to cool the combustion flame and the timing would shift to retard to reduce detonations.
For safety reasons there should not be away to shut off the engine without lots of warning lights or actual falling into a limp mode.

From this stand point of the codes given they are saying its a mixture problem mostly caused by a bad reading from the O2 sensor input. Of course this cannot shut the engine down.
You can have the engine running and have verified voltage reading to know if it's is working.

A voltmeter set on the lowest range for sensitivity to read a range of less than one volt is the ticket. You clip one lead of the meter onto the exposed and connected part of the wiring spade, out there by the firewall.
Clip the other lead of the meter to a ground point on the engine, body of the car or even the negative post of the battery. The voltage will constantly vary in the middle of the one-volt range.
I have a meter made with 10 led lights that run up and down like race track Christmas tree. It's very visual to show up if the sensor is lazy or hanging at one end of the scale.

This also tells me that the cars electronics are shifting the mixtures from that output. I can rev the engine and the O2 sensor will respond quickily to rich and lean but once the rpm stabilizes the O2 rolls more back to bouncing in the middle. This is a normal temperature running engine.
If there is a misfire the sensor will show it went rich and then dive lean when the engines electronics try to correct it.
The AMM just keeps putting out a steady signal as this does not effect incoming air metering as that cylinder just keeps sucking even with a burnt intake valve. The AMM affects overall performance and starting. Just shutting off to kill the engine is a stretch for me to believe at this point.

So going to basics that like a hundred years old I'm talking ignition. It use to be points, then hall sensors and now proximity sensors.
We are at the other end of a century but we cannot get away from the plagues of creating sparks.

Here is where we got a doubling down going on with a trigger mechanism not just doing a spark but telling the other electronics to get their act together!
We know the CPS can go bananas in many strange ways that it can throw erroneous types of signal waves!
Of what I know how computers, they can be absolutely finicky on what you tell it and how it reacts.
I want to say start there and know it's a good one if you haven already.
Especially, if you said it bogged down at high speed and now just turns off.

The next thing would be the electronic relay out behind the battery. Service its conductor paste and mostly it's connector.

If you have to go farther the ICU's becomes suspect. I have read that in areas like Maylasia they get overheated. This was found out by mounting a computer fan to blow on it and the problem of shutting down went away.

So if you are going to junkyard mechanics try these ideas.

Ok good luck, keep us posted.
Phil

Thank you Phil. I have chased most of those issues other than the icu. I've replaced cps etc. I had at one point thought it to be fuel pump connections. Currently it will idle in driveway and just die after a couple minutes. I will give these guys a shot and post back. Thanks for your kindness.

Hi Mark,

The next time it’s starts that turning off in a couple minutes try having a timing light on the spark wires.
You want to see if the plugs wires are still getting spark the “whole time” the engine is coasting down to a stop.
This would mean the ICU is still responding to trigger pluses for ignition from the CPS. This should be keeping the ECU on and holding the system relay on.

If it is it’s more likely that the injectors might not be firing on their on, if it thinks it lost spark.
Knowing spark is a key to the ECU to do both, fire the injectors through that closed system relay ground circuit. Dropping injectors is a fault function in safety. The computer just resets each time, not know it did so through normal channels to trip a known fault code.

I have a story about this on a Aprilia motor scooter. TWO bad ECU’s.

If you have spark and a closed relay, know by observing 12v power on the orange wire of the AMM, then the ECU body could not be grounded properly at the chassis or body point, Or bad ECU?

Just a thought to see if this method my catch something?

Phil

Enjoyed your post much! BOsch ect worked great. Did seem to smell a rich fuel mixture at first. It Seems it is settling down.I am now chasing why my headlamps seem to periodically not work. Not sure if intweaked should something. Thx!

Not recommended per FAQs:
Installing the Sensors. [Editor] Do NOT use Teflon tape or Teflon pipe sealer on the threads when reinstalling since they may interfere with temperature readings and with grounding against the block. Better to use thin coat of a conductive grease such as OxGard or apply pipe joint compound above the threaded area.


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Post Back. That's whats makes this forum work.

Thanks so much.