Champagnecamper

Rocketmouse i think the thermo housing was $20 or so. That helps explain how easily the last one broke!

OK I reinstalled new thermo sensor and checked the wiring. It all looks good and wiggling at flex areas everything feels sound. I got 1.5V between one pin and ground. No idea what this should be though. I reinstalled the original PCM then started it. Reluctant to start then idling rough. Hooked up the scanner and no codes. Took it for a drive and it did the buck-snort, pulled over and scanned again. Still no codes. Restarted, drove for a bit then repeated the process with same results.

it’s actually worse now that before I started. Before it would screw up and require restarting but no rough idle or starting reluctance.

BruceB

Opps...you may have stumbled upon your problem...I believe the sensor circuit should have reported 5 volts. At 1.5 volts you have some type of electrical issue, unfortunately that exceeds my diagnose and repair knowledge. There are people here who are active and have much more knowledge and experience and hopefully will jump in on this.

Champagnecamper

Interesting! I’ll double-check the readings later.

Thanks,
andre

Champagnecamper

Ok I was using a different meter earlier and obviously doing something incorrectly, I’ve got 5.14V to the sensor

BruceB

Well, at this point there is no more sense in throwing parts at it. Time to diagnose and clean.

Throttle body and IAC cleaning https://www.cherokeeforum.com/f51/th...eaning-179079/
Pull the spark plugs and check for condition and gap...they all should look the same...spark plug wires and distributor cap
I would also look at the electrical connections to all the sensors by removing, inspecting and the using contact cleaner. Careful with the connections, they are old..
Test your fuel pressure on the rail before start up and after....
Test you Throttle Position Sensor :THROTTLE POSITION SENSOR (TPS) TEST
The throttle position sensor (TPS) can be tested with a digital voltmeter. The center terminal of the TPS is the output terminal.
With the ignition key in the ON position, back-probe the TPS connector. Check the TPS output voltage at the center terminal wire of the connector.
Check this at idle (throttle plate closed) and at wide open throttle (WOT). At idle, TPS output voltage should must be greater than 200 millivolts. At wide open throttle, TPS output voltage must be less than 4.8 volts. The output voltage should increase gradually as the throttle plate is slowly opened from idle to WOT. (adapted from post https://www.cherokeeforum.com/f2/tps...eadings-99557/ )

one more item....and I don't have the reference material, but if both sensors and both PCM's didn't result in much of a change, the pin that connects the temp sensor to the PCM in the PCM connector may be corroded, broken or shoved back into the connector. Just a thought. Maybe somebody else can tell you what pin you are looking for.

There is much more to dive into, but these seem relevant to your issue.

Hope this helps

Champagnecamper

Thanks Bruce, much appreciated!

BruceB

As I was reading through Cruisers54 tips...I got reminded of an important fact...grounds....Jeeps don't like nasty grounds...

especially the dipstick ground point

from Cruisers54 tips:
"The components grounding at the dipstick tube stud areistributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff."

Don't look at it and assume it is clean, take it apart clean it and make sure.....

awg

known problems that could cause issue

bad fuel pump/regulator
bad cam sensor or wiring

I would measure fuel pressure, and examine the cam sensor harness

( of course there are many other things that cause it, but most will throw a code)

did you observe any live data on the scanner, such as O2 switching and fuel trims ?

BruceB

That stuff right there....I don't have a clue about....

Champagnecamper

Me neither. There was all kinds of data but it didn’t mean anything to me. I can get the scanner again and screenshot what i see. I should be able to get back to this over the weekend.

Champagnecamper

Ok time for an update and we seem to have a resolution!

i spent the afternoon a couple of weeks ago cleaning the throttle body, cleaning grounds, replaced negative battery clamp etc. That day when i started the jeep I got a code for the temperature sensor. Given the start-reluctance I experienced only with the new sensor and the new code I was now getting I put the old sensor back in and it remains in place. Either I was sold a bad sensor or the particular state of my system works better with whatever values the old sensor is putting out. At the end of the afternoon the original problem was unchanged. I gave up and made an appointment with a local shop, TWO WEEKS in the future was the earliest date.

Turns out it was the upstream oxygen sensor. Got that changed and it’s running like a top.

Thanks everyone for your help!

Champagnecamper

BTW Bruce your live data question about the O2 switching was dead on…

BruceB

Actually that was by member AWG....but I am thrilled that you got your Jeep running good again. Like usual, many brains are better than one..