Engine Coolant Temp Sensor for TBI 7.4L

[CapnDean]

Previous owner chased a high idle & rich burning condition for a couple of years. Said he could never cure it. TPS, MAP, EGR, EGR solenoid, Vacuum lines - after clearing all the codes and hitting all the common sense items (tune-up, hunting for vacuum leaks, etc) he gave up and just lived with it.

I erroneously figured that a bad ECT sensor....would show in a bad read on the temp gage. NOT SO -
The temp sending unit down low on driver's side talks to the temp gage inside. The ECT sensor mounted next to the water outlet up top is the one that talks to the computer.

For 2 years he dealt with high idle rich running. a $10 sensor and it sows down right nicely when warm.

Makes sense when you realize that the computer was fueling a cold engine all the time until the defective sensor was replaced.

 

[PlayingWithTBI]

Glad you/he found it, a 5 minute data log would have easily found it, sorry to say.

 

[someotherguy]

An ohmmeter and temp gun woulda showed it pretty quickly, too. Some simple troubleshooting goes a long way.

Richard

 

[Schurkey]

Previous owner chased a high idle & rich burning condition for a couple of years. Said he could never cure it...

...For 2 years he dealt with high idle rich running. a $10 sensor and it sows down right nicely when warm.

Makes sense when you realize that the computer was fueling a cold engine all the time until the defective sensor was replaced.

And folks piss and moan when my standard advice is to connect a REAL scan tool, and look at the data stream.

 

[CapnDean]

Glad you/he found it, a 5 minute data log would have easily found it, sorry to say.

I don't have a Scan tool for OBD1, nor a data logger. That said, I wouldn't have thought to ohm out the temp sensor up top because I too was assuming that the signal came from the same sending unit as the temp gage. I do know how to jumper the OBD1 port and get my codes, but thats it as far as diagnostic devices. The reason I posted this was to share my joy in finding a problem that the PO couldn't seem to find. The real joy is knowing that it was such a cheap fix whereas oftentimes it can be a computer swap or a TBI problem.

 

[Mark Gilbert]

I don't have a Scan tool for OBD1, nor a data logger. That said, I wouldn't have thought to ohm out the temp sensor up top because I too was assuming that the signal came from the same sending unit as the temp gage. I do know how to jumper the OBD1 port and get my codes, but thats it as far as diagnostic devices. The reason I posted this was to share my joy in finding a problem that the PO couldn't seem to find. The real joy is knowing that it was such a cheap fix whereas oftentimes it can be a computer swap or a TBI problem.

If you are ever interested, you can buy an adapter and a program that just about any reasonably recent laptop will use to run as a scanner. Overall will cost around $100 other than the laptop.

Moates and tunerpro. A basic google search will give you lots of reading material.

A good scanner will make your diagnostics much easier. Congratulations on finding the issue though, it is always a bit of fun when you succeed where others have failed.

 

[PlayingWithTBI]

The reason I posted this was to share my joy in finding a problem that the PO couldn't seem to find. The real joy is knowing that it was such a cheap fix

I didn't mean to berate you or your process in troubleshooting, just saying a scanner or laptop with TunerPro RT v5+ and an ALDL cable can data log, as @Mark Gilbert mentioned, will help point you in the right direction. HTH

http://www.tunerpro.net/

http://aldlcable.com/aldl.asp

 

[1997]

Previous owner chased a high idle & rich burning condition for a couple of years. Said he could never cure it. TPS, MAP, EGR, EGR solenoid, Vacuum lines - after clearing all the codes and hitting all the common sense items (tune-up, hunting for vacuum leaks, etc) he gave up and just lived with it.

I erroneously figured that a bad ECT sensor....would show in a bad read on the temp gage. NOT SO -
The temp sending unit down low on driver's side talks to the temp gage inside. The ECT sensor mounted next to the water outlet up top is the one that talks to the computer.

For 2 years he dealt with high idle rich running. a $10 sensor and it sows down right nicely when warm.

Makes sense when you realize that the computer was fueling a cold engine all the time until the defective sensor was replaced.

good job, always appreciate posts like yours and TBI's. Gunna have to get me software and cable.

 

[someotherguy]

I don't have a Scan tool for OBD1, nor a data logger. That said, I wouldn't have thought to ohm out the temp sensor up top because I too was assuming that the signal came from the same sending unit as the temp gage. I do know how to jumper the OBD1 port and get my codes, but thats it as far as diagnostic devices. The reason I posted this was to share my joy in finding a problem that the PO couldn't seem to find. The real joy is knowing that it was such a cheap fix whereas oftentimes it can be a computer swap or a TBI problem.

Common misconception on the temp senders, no worries. They're also a usual suspect in the event of a rich condition so it's surprising the previous owner didn't try it. I view them as a maintenance item since they go bad over time and often so gradually degrade that you may not notice until they've gotten really bad. An ohmmeter will easily show a very bad one but a marginal sensor may require comparing ohm readings against the chart relative to actual coolant temp using the IR thermometer.

I certainly wasn't trying to rain on your parade and don't let that other dude do it either - educated (or even lucky) guesses get the job done too, as long as they didn't cost you extra for unneeded parts as the P.O. already went through. We've all been there!

Richard

 

[bobby v]

I didn't mean to berate you or your process in troubleshooting, just saying a scanner or laptop with TunerPro RT v5+ and an ALDL cable can data log, as @Mark Gilbert mentioned, will help point you in the right direction. HTH

http://www.tunerpro.net/

http://aldlcable.com/aldl.asp

Seems like Ive heard this advice somewhere before, hmmm.
Side note, I replaced all the OP talked about and idle is still high at times, I give up until I get the suggested equipment then Ill really see what gives I hope