How do I gain access to the CTS on 87 V6 2.8L engine (Page 1/2)
Romsk AUG 19, 01:39 PM
My diagnostic tool shows the CTS reading about -3F and wavering on a 72 degree day. The CTS TEMP_LO bit in the Malfunction Word 1 is set. I can't get error codes (Short DIAG_MODE to GND) because that is not working for some reason - the bulb is good.

Before I order a new CTS, I want to remove it and test the tip in cold to boiling water.

It looks to be buried under the Coolant Cap/Thermostat and I know where it is, but it seems difficult to see. Does any have any tips on how to gain easy access to it? There is a lot of plumbing and wires in that area.

Also, my diag tool was showing the MAT reading 255 and bouncing some - but no bits in the Malfunction Words were set for it - that seems odd. But the MAT was easy to get at. A mouse made a nest near it and decided to chew through its wires. I will fix it and put steel braiding over the wire sheath to keep them from doing that again.

I have a feeling mice have eaten the SES and CTS wires somewhere. But right now... what is a good way to get access to the CTS? Is there anything I should know or pay special attention to before I start removing things to get at the CTS?
Thanks.

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Paul Romsky

fierofool AUG 19, 03:52 PM
Remove the EGR solenoid and its mounting bracket. If you're replacing it, get your replacement first and acquire the proper deepwell socket to fit it and maybe a short extension. Do not remove the thermostat cap or open the cooling system in any way.

By having everything you need at your fingertips, you can remove the old one and insert the new one and lose very little coolant. Sometimes the reducer will want to come out of the lower intake with the sensor. In that event, you're going to lose some coolant while separating the sensor and reducer. It's advisable to add some Teflon tape or plumber's putty to the reducer threads that go into the lower manifold. Nothin is really needed on the sensor, but there's no problem if you put a wrap or two of Teflon tape.

If your scanner is telling you it's -3 F, the sensor is probably defective. Every CTS I've had that failed has gone to the cold side. My first one on my 87 failed suddenly while sitting at a stop light. A scan when I got home showed -28 F. Looked like a diesel truck.

[This message has been edited by fierofool (edited 08-19-2022).]

Rickady88GT AUG 19, 03:59 PM
LOL, sorry but at first I thought you were asking about a CTS (Cadillac) engine swap.
cvxjet AUG 19, 04:39 PM

quote
Originally posted by Rickady88GT:

LOL, sorry but at first I thought you were asking about a CTS (Cadillac) engine swap.



Same with me!
theogre AUG 19, 06:20 PM
CTS = ECT and chart is in the cave, Sensors Quick Ref.

Sensor often is good but have issues w/ the plug and GM et al stopped making the "old style" sensor.
New Sensor Will require a new Metripack plug and many sensors don't come with them. Look on Dorman for it then order from whatever.

⚠️ New plug pigtails should be Soldered and "water proof" or will quickly have problems.

⚠️ Flaky reading from ECM scanners on park car engine on but not running is often a "dying" ECM. Read other sensors, battery volts, and more in Monitor Mode in the scanner.
Why?
Example: Just 1 iffy solder joint can kill the whole ECM or just 1 part in it and cause a lot of problems and never set "codes."
ECT and others go into driver circuits & 1 iffy part can screw up data from 1 or more inputs.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Romsk AUG 19, 09:07 PM
Fierofool,
Thanks for the advice. Ok, mainly remove the EGR solenoid to get at the CTS. My scanner is my home brew ALDL Monitor. The raw data values were converted to degrees C or F based on sketchy info from the web. Before I swap the sensor, I am going to test it at 32F, 77F, 212F and get a resistance curve, then plug it in and see what 0 to 255 values I get from the ECM for the same 3 temperatures. Then I can do polynomial curve fit to make my tool right on the money to display Coolant Temp in C or F. I have to do this for the MAT sensor as well. The only other ALDL word I don't know how to decode is the Unlimited Spark Advance. The other 22 words I have decoded and display those values correctly.

But even though my display of the CTS of -3 is most likely wrong (and soon will be fixed in my code), the COOL_LO bit is set in MALFLAG1 and the raw value is indeed wrong.
I will let you know how it turns out. I did fix the mouse damage on the MAT sensor wires today, but the steel braidng is on order. I will test MAT tomorrow before I replace it.
Romsk

[This message has been edited by Romsk (edited 08-19-2022).]

Romsk AUG 19, 09:19 PM
For those of you that thought I was talking about a Caddy, this is a Fiero site... do you get many posts about non Fiero issues? [smile]
Thanks anyway.
Romsk AUG 19, 09:42 PM
Theogre,
Thanks, fierofool gave me good pointers on the CTS. Thanks for the info on bad solder joints and pigtailed new connectors for reliability.
I fixed the mouse damage on the MAT wires today.

My US Air Force training instills reliability and quality in making repairs:

I cut back the wires an inch from the bite through. Fluxed and tinned the wire ends, adding new 2 inch jumpers between the cut backs and got a nice overlap on the solder joints. I covered all solder joints with a good length of heat shrink tubing, I didn't have the kind that has self sealing glue inside the tubing, so I coated everything with liquid electrical tape. Then I replaced the flexible/split plastic wire cover where I cut away the chewed one. I am going to put stainless steel braid over the entire length - I don't think mice will gnaw through that without cutting their mouths - and thus give up. The braid is on order.

Since the SES lamp is not working, I assume mice got to that wire too. I will pull off the arm rest to get access to the ECM and trace the circuit.

I want to get one of those old 40 foot shipping containers to store my Fiero in - I am told those things close up tight and are very mouse proof...but my wife said Nooooo!
Romsk AUG 19, 10:17 PM
Theogre,

My ALDL data is stable when stopped, ignition on, engine not running. When I start the engine, I get intermittent bad words - for example about every 50 frames or so the PROM ID will change - and I am sure that should be rock steady 100% of the time (right?). My ALDL Monitor is a tool I made about 10 years ago. The adapter I made for it used a Serial to USB converter (my PCs don't have Serial ports) with a Transistor inverter to read the ALDL bit pulses as RS-232 bytes and send that to my PC over USB. It worked well but I was getting bad data a lot with it.

Now, I am pulling my Fiero and ALDL Monitor Tool out of mothballs for 7 years. I made a new adapter that actually measures the ALDL bit pulses and a lot of the intermittent bad words are gone - its a lot better but I still get a bad word now and then. I am going to break out my storage scope and see if I can trigger it when I get a bad word to see if it is the ECM, the adapter, or my GUI. Not only do I get a (wild bad word), but sometimes the Sync Bit in a data word is sometimes set as well (My GUI shows the Sync bit and the 8 data bits for every word). Now, I know the Sync bit should never be a '1' in a data word, but it still may be my adapter.

I did simulate the ALDL using an Adafruit Trinket M0 to put out perfect incrementing ALDL data into my new Adapter, I ran it overnight and my adapter and GUI never missed a bit!
So the problem does point to the ECM, but I need to see a bad word is actually being spit out before I replace it.

I added a feature in my GUI to mask out the Sync in the data words, it helps, but every now and then I still get a wild bad data value.

I suspected it may be the ECM - since the SES lamp SUDDENLY stopped working (bulb is good) when I moth balled it. But your advice will make sure I rule things out and prove it is the ECM dying on me.

By the way... it sat in my garage for 7 years, as I pulled it out of mothballs a few weeks ago, I put in a few gallons of fresh gas, a fresh battery charge, a shot of Fogging Oil into each cylinder, and it started right up!' Not even... ruh, ruh, ruh, varoom.... it was vroom just like it was new! It still runs poorly just as it did 7 years ago, but I have never seen an engine sitting that long start up so quickly. Have you?

Thanks.
Romsk
fierofool AUG 20, 08:52 AM
MAT sensor on a stock 2.8? They don't have one. MAP but no MAT. Are you perhaps referring to the IAT (Intake Air Temperature) sensor in the air filter canister?