Hello Gents,
I have a mystery sensor or switch in my cylinder head. Drivers side hidden behind the fuel filter canister. it is not plugged in and I can't find the harness side for it.

It's not the Coolant Temp Sensor. It's in the back of the head and plugged in.
It's not the Air Temp Sensor. It's installed into the intake plate. Not plugged in because my EGR fell off and I can't find it.

I have been searching for hours and can not find the answer.

One possibility I read was an Engine Coolant Thermal Switch (auto trans) but I can't find the wire harness end to plug into it to confirm.

It's for a 97, w/auto trans, used to be an EGR truck.

Any ideas?
Anyone with a like truck tell if they have the same sensor and where the harness plug leads?

Any help is appreciated, Thank you.

 

Search MAP sensor and IAT sensor....in 24Valve engine and drivetrain...Manifold Absolute Pressure and Intake Air Temp...

 

97 should be 12V and no MAP sensor. IAT only for the grid heaters.

IMO it could be an additional water temp sensor to block high EGR rates at high coolant temps, but this is a really wild guess.. No experience with 12V EGR engines.

What's the cause for looking for the sensor/wiring? Anything not working correctly or just intellectual curiosity?

 

Mystery Solved! It was a temp sensor for the EGR valve.

AlpineRam, the reason is a search for what is causing excessive valve noise after a re-ring, bearings & regrind on cam and lifters.
Noise is most noticeable at #1 cylinder and increases with RPMs.
Was doing my basic checks for ticks, lift pump, overflow valve etc.
I am thinking the cam is to blame. Maybe a bum regrind, I don't really know.

 

I assume you checked your valve clearance?
Any re-grind problems I had showed very quickly by a change in valve clearance and a difference in valve lift between the cylinders.

Personally I do not like ground lifters, usually they do not get hardened and faced as well as new ones that cost about the same. (Experience from my side of the Atlantic, your mileage may vary)

Why did you get a cam re-grind?

 

I did check valve clearance. The motor was still out of the truck and in pieces so everything was adjusted from square one. And now rechecked at least a dozen times.

I had the cam reground with the companies "RV Grind". That grind was claimed to cut exhaust temps and get better fuel mileage.

They did resurface the lifter but I just assumed not enough to take away any hardness. May be just a lifter issue I don't really know.

May be a combination of reground cam, resurfaced lifters and 60LB springs I put in.

Or may be my first 12V rebuild gone wrong. Kind of at wits end and am temped to pull the motor and check everything.

 

I have a local gent that may be able to take a look and give some insight.

One thing I am having him check is pump timing. Don't know why #1 cylinder would be loader from this but I am at the "check everything" point.

 

Well, the cam may be seating the valves rather quickly, that leads to some noise. Some old school cams were made like that to operate better with an exhaust brake. (Harder hit breaking up carbon on the seat)
#1 being louder is normal, you just hear it better.
If it runs OK, I'd record valve clearances for all 12, valve lift ditto and drive some time and re-check. If no change it's just the nature of the beast.

 

AlpineRam, I appreciate all the good info, thank you.

I am just about 950 miles since rebuild.

Have been checking valves approx. every 150 to 200 miles because of the extra noise (more so on #1 cylinder).

Sent in an oil sample at 200 miles, all good nothing abnormal.

Sent in an oil sample at 500 miles, all good nothing abnormal.

Will be sending in another oil sample as soon as I hit 1,00 miles.

If this is the nature of this cam grind, I will be looking to get a stock replacement. May try to find a used one in good shape first and see if that does the trick.

 

You could ask @oliver foster for the parts.

About the noise- did you check your injectors, especially pop-pressure, spray pattern and sealing at close pressure?
Fuel dribbling in after the correct injection event can lead to very weird noise.

 

Have not tested the injectors. They are a new set from the rebuild.
I will check out the link you posted.
I appreciate all your assistance. Thank you.

 

Pleasure,

Oliver is a long time member on this site who sells second hand parts for our trucks. He also has a lot of knowledge on them.

Happy Easter!

 

Oh yeah! Whoops.....