Head temp sensor question

Bruce Allert · 12-20-2002, 10:52 AM

If the HTS is bad will it cause lack of power? I changed the TPS last night after discovering it was the cause of my bucking but still don't have the power I used to before it started bucking. I installed the pertronics ignitor too. Runs good but not the power I expected.
Also, when checking the HTS do you hold the neg. to the neg of the battery and the positive to the sensor? Doesn't this give you 2500-3500 ohms? I can't find the dat-berned article.
bruce

bob174 · 12-20-2002, 10:58 AM

Make sure that you check your timing, and also that the centrifugal weights in your distributor are working to advance the timing as the engine RPMs are increasing--you should see the timing mark advance as you rev the engine up to 3500. I recently had a power loss problem and diagnosed it down to some stuck fly weights in the distributor that were not advancing the spark as the revs increased. The result was a REAL loss of power.

Bruce Allert · 12-20-2002, 11:16 AM

Did all that when I replaced the points. Had I checked the TPS I would've been further ahead... but, oh well, such is life.
bruce

pbanders · pbanders's Garage

On a 1.7, with the engine COLD (not running overnight, measure in the morning), disconnect the CHT from the wiring harness, and measure the resistance between the CHT and ground (battery ground is fine). Should measure about 3K ohms with a room temp of 61 deg., lower if warmer, higher if colder.

When the engine is fully warmed up (30 minutes+ of running), the same measurement should give a value of under 100 ohms.

As others said, make certain the timing and dwell are correct, valves properly adjusted, and that you have good compression.

mike mueller · 12-20-2002, 02:33 PM

A couple of weeks ago I helped a local '75 1.8 owner trouble shoot and repair his car. He had spent hundreds of dollars at a few local shops just to have the problem reappear a few days later....it turned out to be a loose CHT sensor.

I measured the CHT while in the car and the values had been within spec for that temperature. As soon as you rev'd motor up to 3k the motor would run way too rough. I checked everything and finally hooked up a new CHT to the battery and the other lead to the ECU...car ran perfect, so we go to replace the old CHT and it almost falls out. I guess when I was testing it with my DVM the ground was just enough for me to get a good reading, but once the car was running the CHT had a bad ground.

Mueller