EGT probe tech

Curtis

Curtis

Well-known member
I have 2 duel Westach EGT gauges hooked to 4 EGT probes in my current racer. I was running this stuff on another car 15 years ago and on something or another ever since. It is old but has been very reliable.

Can I replace just the one probe I broke tonight and still have readings comparable to the other three probes? Or do I need to replace them all?

Not cheap for one let alone a full set of four so thought I would ask. Anyone have relevant experience to share? Or a random 700-1700 probe gathering dust?

Thanks
 
ditch it and get a wideband AFR gauge........FAR more useful. The proble with EGT's is that the temp curve is like an upside down U with AFR on the x axis. You never know for SURE if you are on the lean or rich side of peak....so which way do you adjust?? With a wideband AFR.....there is no guessing.
 
Curtis, as mentioned , you should be fine just repalcing the one probe. At the Mitty for the first time, I had both on my vintage MGB, dual EGT to separate each carb (dual HS6s),and then the wide band O2, after I got everything dialed in, I was seeing a tick under 1300 degrees on both EGTs and 12.6 on the O2. I like having both on dual carb car.
 
Hmmmmmmmm. I guess the value of Hap's setup on a dual carb car is if overall AFR goes wacky, and you know peak EGT has not changed on 1 carb you can focus on the other though. If avg AFR goes richer you need to lean the wacky carb and vice versa. Not a bad system.

Or you could just use 2 AFR sensors with 1 gauge.
 
It's just that I've had SO much trouble with EGT sensors failing and giving goofy/erratic/inconsistent results.....I've just given up on them 100%. Others likely disagree.
 
Curtis, what you REALLY need to do is calibrate all 4 probes. Stick all 4 probes in a tight bundle in a 500F oven....wait 30 minutes, check for consistency. Assuming you are using type K thermocouple....they are normally pretty inconsistent.
 
I like having both on dual carb car.
Click to expand...

and after having trouble with bent throttle shafts
(yes, my linkage was a failure, it turned out,
but it also caught a leaky starter circuit
AND a mis- machined Spanish carb)

I run 4 EGT's and one wideband.

If the EGT's agree, I look at the wideband.
If they're all over the place, I fix that first.
Often, it means fixing the EGT's!

t
 
Swap the one in. If it reads out of range, move them around to verify the point of issue.
I used the EGt in my airplane and all of them read so high that I removed them and read the plugs and Cyl head temps.
You really just need to know a good range reading for your car. A spike might show a plugged jet or injector before it slows down. But you really have to watch as it happens quickly.
Reading the AFR is very nice and shows air density changes well. You need 4 to show the same symtoms as the EGT of course.
 
EGT is not a particularly useful tool for measuring AFR . Yes, like driving a nail with a baseball bat, you can do it, but it is not the most efficient of methods .

Use the right tool !

WBO2 meters ARE the correct tool for AFR . EGTs however are a VERY useful tool for ignition timing; once you know what they should be reading .

Aircraft use EGTs because they are adjusting the mixture in flight to match the pressure/altitude air density changes . Since the pilot is changing the mixture, the EGT just allows the pilot near instantaneous feedback on whether the change was in the correct direction . The CHT and plug readings are only useful in a gross sense . The CHT takes so long to change for a mixture change that you will probably have molten pistons well before the CHT has a chance to register . CHT indicates you are applying too much continuous power - not for mixture control . Plug readings are really difficult at 10,000 ft .

If your EGTs are higher than normal, then your ignition is retarded - end of story . If you run too lean, your temps will actually decrease . Too fat and you have the same story . What is normal then ?

Dyno time . . .

>>Tim
 
For me, I like both, because I have two carbs, so each carb get monitored via it's own EGT, then I've got AFR to tell me the total picture. I think these days with more modern cars, if I had one carb, or a throttle body injection system, I would just go with just AFR.

One major flaw with a EGT set up, is if you were grossly rich, you could dump raw fuel in the headers and it would ignite there and give you false reading on the EGT probes, I seen this exact thing before, the guy kept richening his LP/HP 1275 Spridget up and it kept running like crap, so we got him on a chassis dyno where we could hook up a AFR and see those numbers, sure as hell, he was big time rich. EGT are good as mentioned once the car is dial in, but can run you on a wild goose chase , if not.
 
A single probe replacement worked just fine. Thanks to those who reassured me

I have never used the EGT to jet from scratch. I set the engine up on the dyno with wide band AFR in the pipe and record the EGT when the AF is correct. From then on that temperature determined by the AF probe just seems to be the right temp target for that particular engine.
As a bonus the EGTs are not bothered by the leaded fuel. Running one for each cylinder can help ID and isolate the location of a problem.
 
This is worth mentioning, if you are using mutilpe EGT probes, it 's damn fine idea to flame check the probes, to make sure you are looking at the right one on the gauge/s. If we're honest with ourselves, this is very common mistake made by many of us, but using a simple propane torch to check you have correctly identified the probes to the gauge can help offset future confusion :)
 
Just a comment re wideband vs EGT -

At Race Technology, we sell both. But I recommend wideband to 95% of customers as I really think it is much more broadly useful. I was initially shy wrt the issue of leaded race gas ruining the O2 sensor - which it will. But it happens quite slowly in actuality. The best educated guess I've heard is about 50 hours run time - which is a near eternity for most of us hobby racers. And they fail "safe" ie give a false lean reading. I've had one in my Scirocco for about 5 years of my admittedly pathetic race schedule, and it's working fine.

Al Seim
Race Technology USA
www.race-technology.com
 
Al,

That's pretty amazing life for a wideband sensor. I have the innovate and I re-calibrate it every weekend (as recommended). The sensors usually last about a season (6 races) before the innovate throws a code. The good news is that the sensors are readily available and about $50.

Do you have a way to clean them? I've heard about using torches, etc.

-Kyle
 
The basic problem with EGT's is that the shape of the temp vs. mixture curve is an upside down U....with temp on the Y axis....peak EGT at the top.

You never really know which side of the peak you are on........should you richen it to increase EGT or lean it out to increase EGT?????? You end up guessing when you shouldn't be guessing

Lots of wasted effort and if you guess wrong possibly some melted pistons. With an AFR in each pipe you NEVER have to wonder.

More expensive?, yes. Worth it?, yes.
 
Kyle,

With unleaded fuel you should never have to clean the probe.....I never do on my SM.

I ran an AFR gauge on my 16:1 CR Bugeye with heavily leaded fuel and cleaned the probe between every race. Just unscrew it, heat the insulator area till it glows with a propane torch, reinstall. Very EZ. Be sure to use anti seize on the spark plug threads (yes they are the same, careful to ONLY coat the threads) or you may soon be cursing. ;^)
 
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