The last couple days, I have noticed that my pyrometer was not responding to throttle nearly as quickly or highly as is normal for it.

When I expect it to read around 900*, it would barely make it to 600*

Before, just sitting still, a burst of throttle would result in jumping to 400* or so; now, it barely wiggles the needle.

The gauge is a mechanical ISSPRO double-needle combo PYRO/BOOST with 300 being the lowest reading.

The TYPE-K thermocouple/probe was replaced about five years ago.

I just got done pulling and visually inspecting the probe.

To my eye, I did not see any evidence of burn-through, cracks, or pin-holes.

The probe did have a heavy layer of soot on it.

I re-installed the probe but have not yet ran the engine since cleaning and inspecting it.



Does my situation point toward the probe or the gauge being at fault ??


Thanks.

 

sorry i cant help, but does isspro offer any type of warranty on their gauges? id try calling them or the place you bought the gauge from. good luck man

 

Sounds to me like dirty electrical connections.

 

x2. I'd say check your connections BK. High resistance = bad readings.

 

Whatever was going on is definitely at the thermocouple/probe end of things.

All I did last night was to remove the probe from the manifold, wipe a handful of soot from it, and inspect it for obvious signs of impending demise.

Today, it is all back to normal and responding immediately.


I will dis-assemble the two connections where the probe leads connect to the wires that proceed to the gauge and give them a good cleaning; just in case my little exploratory invasion may have possibly wiggled things into good contact.



One more question :

This IS a 100% mechanical pyrometer.

I have always left the original double-wire cable at the generous length that it is, thus I have a few loops of it neatly zip-tied into coils.

Is it important that the cable be that particular length, or does it matter not how long or short it is ??


Thanks.

 

I've read before to leave it the same length. So I have always done so, something about the resistance from the coupler to the gauge? IDK for sure though.

 

BearKiller, you're pretty sharp when it comes to electrical quandries, what do you think? My opinion is that the length of cable won't matter. There's so little internal resistance in 8' worth of cable that it shouldn't make any difference to the readings.
I wonder about the 'fully mechanical' part though, I don't know how that would work. Maybe if I understood that, I'd be better informed to say for sure whether shortening that cable is going to affect anything!

 

I don't see where you're calling the pyrometer a mechanical unit.

It has wires. It's electrical.

Mechanical gauges have either capillary tubes or fluid lines between the engine and gauge. Think old temperature gauges or oil pressure gauges.

 

Ok, I'm no genious here, but I have worked with thermocouples. This may or may not be the same way these work, but it's pretty simple. The part that gets stuck in the hot gas stream is made of two dissimilar metals, usually chromel and alumel, and when heated, the resistance at that point changes allowing more electricity to flow through with less resistance. Like I said no genious, and I may have this backwards, but that's what I know on the subject.

 

That's how I thought it would work, but as KAyers said, that isn't mechanical. Well, the metal part is mechanical, the signal is not. Beats me, I'm just a recent student to this stuff, unlike some of the folks around here who seem to have been born with an innate understanding of it all.

 

I had the same problem,I just removed my probe ( well broke off the threads in the manifold, and waiting on a new one) I cleaned the soot from the probe and had to "jam" the thermocouple in the manifold so I could make it home, it started to read higher, like it should, after just cleaning the soot off with a dry rag, when the new one come I will let you know how it reads

 

I didn't mean to confuse anyone when I said it was a "mechanical" pyrometer.

What I was meaning is that it has absolutely no connection to the electrical system of the truck, like a "mechanical" water-temperature or oil-pressure gauge, rather than being "electrical".


Many of the lesser-quality pyrometers require connections of the gauge wiring to battery + and -; I wanted to imply that this particular unit was NOT like those. ( of course, the little light of any gauge must have + and -, but it has no bearing on the function of the gauge. )



Back to the soot business :


When I had the Dodge-specific exhaust manifold, the probe was pointing straight down into the manifold from the top.


Since my recent change to a regular Cummins manifold, I had to relocate the probe such that it now lays laterally, instead of longitudinally.


Never before had I ever had any problem with soot gathering on the probe.


I am now curious if I will have to repeat this cleaning every few months.

 

So me removing and inspecting the probe most likely resulted in the connections getting wiggled back into better contact and the soot was merely a coincidence.

I will dis-connect, clean, and re-connect those connections at the nearest convenience and hopefully forestall any more such inaccuracies.


d'Arsonval --- I will try to remember that.


Thanks.