Injuneer

The CLT sensor circuit problem is causing the PCM to set a very high target idle RPM (1,200 RPM) and set the A/F ratio very rich. It normally does both those things when the engine is cold. Idle speed will come down as the coolant warms up, and the A/F ratio will lean out to the normal 14.7:1 target. The CLT sensor is also keeping the PCM from going into closed loop, where it can control the actual A/F ratio.

Formula Steve

Ok, thanks guys! I will try to test the wiring to the clt later today, and see what I find. If so, I will grab a new sensor and do another scan and give an update.


I didn't really realize (or know what to look for) that the IAC was 'sticking'. I may have touched the pedal on 1 of the scans to try to keep it running but other than that, I think sometimes it will idle up then shut down. Thanks again for the help. Will report soon.

Injuneer

Test the CLT sensor wiring, AND the sensor itself, using Shoebox's guide:

4th Gen LT1 F-body Tech Articles

Formula Steve

Thanks again guys. I shamefully admit that the shbox guide seems a bit vague to me. Unfortunately, I've only used my multi-meter a handful of times...and a 'for dummies' guide would have been more help to me. Basically, when I touch a lead to 1 of the 2 terminals, I'm not sure what I'm looking for...so I didn't attempt anything.


I bugged a friend to come over, so hopefully he will be over in a day or 2.


In the meantime, the thing that I would like to understand is this:


I unplugged the CLT harness, and started the car. She started right up (usually takes a few) and seemed to run like a champ. I decided to let it run for a while just out of curiosity...it idled great! I shifted gears, and all was good.


I ran it for about 7 minutes. There were slight stumbles here and there but it always picked right back up. I played with the pedal, and would rev it to 4000 rpm, and she'd come right back to a go idle (best performance yet). I figured I would perform the faithful test of shutting it off, and seeing if it will start up...and it did so 5 times! Another 1st for this car, although it did take a few seconds to fire on the 5th try...so I left her alone.


I guess my question is (and google hasn't helped me):


What does unplugging that sensor do? Why would it run so good? Also...could you, in theory, leave it unplugged? Just trying to understand what is going on...

GaryDoug

https://learn.sparkfun.com/tutorials...e-a-multimeter

Formula Steve

That's actually pretty useful for me. But...I meant that when looking at the instructions from shbox...I'm not sure what I'm supposed to be looking for. It's not very definitive. There's a table that shows temps and ohm readings.


So...I would ASSUME that since I have a -40 temp...then I should get a 100700 ohm read. Is that correct? And is that with the key on, key off...car running...I have no clue.

Injuneer

Hopefully you understand that the table of resistance vs. temperature is only the first page of a multi-page article. You have to scroll down to read the entire guide.

You measure the resistance of the sensor, with the harness connector off the sensor. Meter set to ohms, Kohms scale would be best. Read Gary's link. Leave the ignition key on "off". The red lead touches one pin on the sensor, the black lead touches the second pin. Does not matter which lead touches which pin. The reading on the meter should be very close to the resistance shown in the table, for the actual temperature of the sensor. Test it when the engine has sat over night, and is cold. If the ambient temp is about 50*F, the resistance of the sensor should be about 5,670 ohms. If it isn't close to that, the sensor may be defective. If it's 50*F, and the resistance reads 100,000 ohms, the sensor has an open circuit and is defective.

Now, harness still off the sensor, turn the ignition key to "run"..... Do not start the engine. Now you switch the meter to DC volts, touch the red lead to the harness pin for the yellow wire, and the black lead to the harness pin for the black wire. Should read about 5.0 volts. If it is significantly less than 5.0 volts, there is a wiring problem.

Nothing above that isn't in Shoebox's guide.

GaryDoug

The -40 temp resistance of 100700 Ohms is for a working sensor. Your resistance would be higher or no reading at all (over-range or "OL", same as no connection of the probes) for a defective sensor.

shoebox

I'm sorry. I thought I wrote the instructions carefully enough that anyone could understand them. They say when to turn the to RUN to test and don't say to do so when you are not supposed to. It mentions that you are looking for resistance (ohms). It tells you what to do with the meter leads. If you are testing a sensor, obviously you will have the connector off, so whether the key is on or not has no bearing on the outcome.

Other than maybe a few words that could be changed here or there, I don't know how to make it more clear and easy. Sometimes I may assume the reader has a certain level of expertise. This particular article doesn't assume a whole lot.

Injuneer

I guess my problem, like Gary's, is our training.... some of the processes and steps are intuitively obvious to someone with an engineering degree. I try to simply my answers based on my perception of the OP's skill level, but I don't always get it right.

Formula Steve

UPDATE!


I finally uncovered my Firebird after a very long northern Michigan winter.


I swapped out my Camaro rims for some old school t/a rims and bigger tires...looks pretty cool to me (posted photos for before after).


Finally replaced my coolant sensor (on water pump)...and would you believe it...started up everyday now and ran just fine!!!!


Unfortunately, my laptop died, so I can't run a scan for a while. Everything seems to be good though.


After doing some checks on everything, I found that my passenger headlight won't pop-up, radio just stopped working the other day (main fuse is fine and windows work), and the one I'm most worried about...my steering wheel is very loose...had nothing to do with the nut...it seems to be something loose in the column...hoping tomorrow to get the proper bolts to pull the steering wheel off. I have to see google and hope to find the correct size.


Just letting you guys know that I didn't ask for a bunch of help and leave...just been a long winter!! Most of you have probably forgotten about my whole story on this car...but feel free to skim through the earlier posts. Still can't believe a $7 sensor solved my headaches...

Formula Steve

And the rear view...

GaryDoug

Good for you. Can't help much with the steering column, never taken one apart before.

Jagdtiger65

My 94 z28 did the same thing,would die after running a while,would turn over had spark but no start.If you waited a while it would crank fine and run fine.
Ended up being computer and you have to have the flashed before using.
My Camaro is doing the surging and I have put in a MSD distributor.I talked to a mechanic that owned a Corvette with the LT1 and he told me the engine temperature sensor can cause this so I will start looking.
I know I am way past all of y'all since these post were 2015 and this is 2021...

Buzz2233

if you still have this charm.li is all data has everything on your car you will ever need.. that temp sensor is tap into your injectors. the other one for gauge he smallest thing can be a great big pain in the...