After-Market Temp Gauge Causing Misfire?

[Boltjd]

Hello, 

 

I'm new here, so forgive me if this post is redundant. I recently acquired an 88 Comanche 4.0 4WD and the previous owner had installed an aftermarket temp gauge, which seems to be hooked up to the thermostat housing coolant temp sensor. I've noticed a misfire during idle, which I've tried to remedy by way of a tune-up, replacing the entire distributor, MAP, crankshaft position, TPS, and checking my cylinder compression, which reads at about 150 psi for each cylinder. I stay up at night racking my brain for solutions, and then, I realized it might the after market temp gauge. The sensor attached to the thermostat housing seems to be modified with a wire that runs along the valve cover, through the fire wall, and directly to the temp gauge. I'm wondering if the modified temp sensor and possibly the temp gauge/bulb is not grounder well enough and if this could cause an intermittent misfire. I also looked at the wiring harness under the dash, where the fuse box is located and it is a complete rat's nest, with a few connectors unplugged. I was also wondering if anybody would be able to send a photo of a relative clean "area" to give me an idea of what connections are possibly missing. There isn't much online other than confusing wiring diagrams and I'd like to clean it up.

 

Help is much appreciated.

[yxmj]

Motor would run without the gauge......disconnect it so that it is out of the picture altogether....does your misfire go away?

[Boltjd]

I think the coolant temp sensor, which is on the thermostat housing, is responsible for changing fuel/air mixture and thusly engine timing based on temp, while the sender on the back of the cylinder head connects to the temp gauge. So I don't think that would be good. I really just need to know the correct color of the wires that hook up to the connector so I can solder it back.

[87MJTIM]

You wrote you have an 88 4.0.  The factory temp gauge sensor is located at the back of the cylinder head, close to the fire wall.  It only controls the dash gauge.  The sensor for the computer is on the block, below the manifolds.

 

If your sensor is on the t-stat housing, then a PO changed the housing to a later style.  If the PO ran a wire from the original location to the t-stat housing, that does not change the computer functioning (unless a PO did a HO swap).

 

If yours is still RENIX, the temp gauge wiring does not run through the computer.  I "should not" effect engine firing.