Sensors and an unfortunate incident of unplanned ingestion

I’d planned for a while to change the intake air temperature sensor on the Renault because it had been reading a little “odd”- erratic and not really reflective of the world in general.
I ordered a replacement part- the closest I could get in terms of fitment is for a 1991 Jeep. The thermistor curve is the same as mine, as is the physical fitting. The only difference is the wiring connection.

undo

I don’t have a 19mm crow’s foot so slight tool abuse saw the old sensor undone.

old sensor

The offending article. Rather grubby (not that it really affects it) from being in the flow of fuel and air.

closeup

Closer inspection shows that the thermistor bead is cracked. That’ll be why the readings have been a bit strange.

comparison

Comparing old versus new. Same, barring the socket.

tools

Head inside into the warm to get set up with the tools required- I don’t have the proper Jeep socket so I decided that the heat of the engine in the location shouldn’t be so high to melt solder, so I would reuse the original connector.

chop chop

A quick spin of the Dremel later and the connectors are exposed.

trimmed and soldered

Trimmed the lugs down and soldered the old wires on.

heatshrink

I’d added a couple pieces of heat-shrink tubing to the wires before soldering them on. Fired up the propane torch outside to warm them up to shrink them down to the wires.

heatshrunk

A little bit toasted but shrunk down nicely.

reinserted

Inserted the new sensor and connected it all up. Noticeable difference now on cold start, before the oxygen sensor warms up and begins to give trim readings.

computer monitoring

I took the car for a drive and it was a lot better. When I got back I popped the hood to check on things and in doing so, leaned on the airbox, which was stone cold- that’s wrong for this kind of weather as the preheat damper valve should open up and draw warm air in from around the intake manifold. Took a bit of a looksee at what was going on. The vacuum operated valve was working when vacuum was applied to it. I took the throttle body hat off and found this:

thermo-valve

That’s about one-third of a thermostatic vacuum valve that controls the intake preheat damper flap. The rest of it is… gone. That will likely be the bad misfire the other day and the reason for the plugs being covered in dirt and having closed up, with bits of the valve being drawn into the cylinders and bashing about at the insides.

boroscope

I borrowed the 1979 Edmund Scientific fiber boroscope from work to have a look inside to see if there was anything left in the manifold that needed to be removed or any damage to the inside of the engine.

intake poke

Pushed it down the intake and had a look inside the manifold.

air sensor

It’s a bit difficult to get pictures from but that’s the new intake air sensor down the intake towards no.1 cylinder.

Took the plugs out and had a look in the bores.

crown

Top of one of the piston crowns. They all looked good. Put the mirror back on and took a look at the valves.

exhaust valve

Exhaust valve- looking good. A few signs of chips in the deposits in pots 1 and 2 but nothing substantial, thankfully. Looks like it broke up and was ejected in pieces out of the exhaust.

5 volts

Took a few readings from the throttle position sensor as it was acting a bit weird. Measured OK, and came up better after having been reconnected, so probable cause is a bad connection at the device. Back up and running, but I need to go to Dodge to see if they have the thermostatic valve.

Leave a Reply