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Username Post: 1994 C3500 - Mildly Rich Running - Coolant Sensor?        (Topic#373749)
Posts: 43

Age: 29
Loc: North Carolina
Reg: 08-13-16
09-10-23 10:07 AM - Post#2862446    

Hi all,

My manual 94 C3500 died last week. I had air and fuel and wound up narrowing it down to a corroded distributor.

Installed new distributor, rotor and cap and it fired up. Instead of using a timing light I just listened to how the engine was running and twisted the cap slowly back and forth until it was idling great where the RPMs were no longer bouncing, engine wasn't shaking, and it was running smooth.

Now if I run the RPMs up around 4200 I can hear an occasional backfire. No backfires at all below 4200.

During this process I noticed the electrical connector for the coolant temp sensor between cylinder 1 and 3 by the headers had broken.

I know that particular coolant sensor feeds the engine temp in the cluster (because my gauge quit working), but does it also feed the computer to manage fuel input? Can it cause a mild rich condition?

The sensor in question has a blade connector and pin. See here at rockauto:

Blue Collar Farmer and Computer Programmer

-Way back in a Holler in Southern Appalachia

Senior Member
Posts: 772

Reg: 10-31-01
09-10-23 10:40 AM - Post#2862452    
    In response to rachki

Is there another sensor on top of the motor where the coolant hose connects just above the thermostat?

Valued Contributor
Posts: 3104

Loc: Lake George, NY
Reg: 11-11-15
09-10-23 11:00 AM - Post#2862455    
    In response to JeremyB

Yes, should have 2 wires, that is what the pcm reads.

Posts: 43

Age: 29
Loc: North Carolina
Reg: 08-13-16
09-10-23 11:55 AM - Post#2862456    
    In response to Shepherd

Thanks, the broken one between 1 and 3 only has 1 wire. It must only feed the temp on the cluster then.

The one by the coolant line has two wires, that must be the one that feeds the PCM.

Blue Collar Farmer and Computer Programmer

-Way back in a Holler in Southern Appalachia

Edited by rachki on 09-10-23 11:55 AM. Reason for edit: No reason given.

Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
09-17-23 08:39 AM - Post#2862608    
    In response to rachki

The temp sensor on the cylinder head between 1 and 3 is strictly for your dash gauge; no input to the PCM, will not affect how the engine runs.

The temp sensor for your PCM is on the intake manifold near the thermostat.

Please set your timing correctly.. it's easy. Engine warmed up, disconnect the tan/black timing bypass wire, set timing to 0° if it's a small block, or.. 4° if big block. Snug distributor back down and re-check, then re-connect the bypass wire.


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06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually

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