[maccwall]

My Steward Warner pyrometer that I have had in my truck forever (at least 5 years) does not seem to functioning properly recently. I do not know if it's the gauge itself or the thermocouple which is a K type or maybe my EGT's have just cooled off. I have taken some Ohm load readings of the gauge and the contacts from the thermocouple but I do not know what these readings mean other than the fact that they are reading something. I have bought another gauge, a Hewitt Industries gauge, but have not hooked it up. The Ohm readings on that gauge differ though from the Steward Warner gauge. Can anybody help me out here. Leads at the end of my thermocoupler read 8.4 Ohms (that's at idle), SW gauge reads 66.2 Ohms Hewitt gauge reads 54.6 Ohms.
Thanks in advance

Peace,
Todd

 

[danjreed]

You're using the wrong measurement for the thermocouple. You should be using Volts.
Thermocouples use a bimetallic junction to create a small voltage between the two leads. This voltage is proportional to the temperature at the junction.
The EGT gauge is basically a voltmeter calibrated to read in degrees, so measuring resistance across it is meaningless. Hopefully the gauge has a high impedence amplifier, otherwise you might have damaged something.

Can you give us some EGT (gauge, not voltmeter) numbers before and after?

Daniel

 

[maccwall]

Thanks Daniel for the correction in reading that. I figured it was read in Ohms, but that goes to show you what I know.
Well, before it started going erratic this was what I was reading: Idle seems to be reading the same but is normal at about 300ºF and sometimes it will go lower recently. Normal hwy speed (70mph) unloaded has run about 600ºF and now it stays about 300ºF to 400ºF. Normal hwy loaded (loaded being pulling the horse trailer pictured in my sig) has always been between 800ºF or 900ºF now it's at about 600ºF and getting on it loaded up a hill it would never get above 1150ºF and now it get's to 900ºF. It's about 300ºF less than what it used to be. It's like I went from pre-turbo to post turbo. I have it mounted pre-turbo. Hope that helps. I'll measure the volts of it when I get home. FYI, the needle on the gauge has just nuts at times, like it was getting voltage spikes or something. Doesn't do it very often but has done it.

Peace,
Todd

 

[danjreed]

I do remember reading somewhere about a pyro gauge going nuts occassionally. I don't remember what was causing the interference, but moving the wires fixed it.
Have you checked the pre-turbo exhaust system for leaks? I.E. manifolds at the block, up pipes, collector doughnuts, etc... I seem to remember during one of my conversations with Dale Isley that he mentioned blowing a doughnut on the interstate (up hill, w/ trailer, playing with dodge/cummins), and he lost several pounds of boost along with EGTs going down about 300deg. Has your boost changed any?

 

[maccwall]

Thanks for being a help Dan.
Boost hasn't changed. Came back from a ride in N. central OK last weekend and went through the Arbuckles on I-35 (it's a decent climb for flat landers) and my boost gauge was reading upwards to 20 psi at one point which is about as much as I can get out of my truck (no intercooler) so I don't think I have any leaks. I'll check that out though. At that point though the Pyrometer was reading around the 900ºF mark which it used to be about 1150ºF (has only moved to the 1200ºF mark once that I remember) sooo... I'm going to get another probe and see. My set up has the clamp, not the bung and it's mounted right below the drivers side manifold in the up-pipe.
I was investigating some other posts and I'll go and check my wiring this evening.


Peace,
Todd

 

[maccwall]

Checked out wiring. Still reading the same. I've checked out the exhaust system up and down and can not find evidence of a leak anywhere. I'm guessing that I need to replace the sender/probe as the new gauge I bought seems to read, well, nothing at all. I will say that after messing with the wires it has not gone beserk, reading from one side to the other, like it was on occasion. It' s just reading lower than it has normally. It's almost like someone switched to the post turbo side.

 

[danjreed]

It's entirely possible that the gauge is out of calibration. I'd expect that to show gradually, not like what you're describing.
After 5 years, it might be time to replace the probe. Maybe it's not quite what it used to be?
If you can, check the temp w/ a laser gun. Or just add 300deg in your head and run with that.
I'm out of ideas.

 

[MidTennPSD]

I know its really random, but on the way to Indy last month, mine started goin absolutely nuts, like goin from 1600 to 100 and everywhere in between, it was caused by the CB. Most of the guys with us had DiPricol gauges and they all did it. You could key the mic and they start goin crazy. I dunno if this helps but it was wierd and it took us forever to figure out lol.

 

[maccwall]

Hey Dan,

Well, I figured it out. Kinda stupid really. I had an old electric oil pressure gauge before I switched to my mechanical one, and I had obviously forgot to take the wire out for the old gauge. Well I guess this wire was tied into the pyro somehow and I was hooking up my airhorns this week, I found that wire wrapped around the underneath of the steering column and shreaded so I guess it was grounding out the pyro. I have since removed the wire and all is well. Told ya it was stupid. Thanks for all your suggestions though. I don't know how I missed it the first time.

 

[danjreed]

Good.