EGT resets itself during run - why?

[J Banning]

I've just recently run into a problem with my EGT setup (Extech 421501 digital single input). During a run (say around the 1/2 shift) my EGT gauge will reset itself and not record the run. This just recently started. The unit and install is only about 2-3 months old. This only happens when I have the "MAX" mode selected (records highest temp).

Any ideas? Could the wire's proximity to the coil pack & plug wires be causing problems? I have the wire routed back behind the coil pack and into the factory hole in the firewall near the brake booster.

Thanks,
-Banning.

 

[J Banning]

I may have found the problem, and if it's what I think it is I'll feel pretty retarded. It's possible that I might of hit the Celcius botton on the unit by accident. When this is done, a small "C" appears in the right corner of the display but it's hard to see. Also, the max recording temp for Celcius is 1300*. I haven't done any conversions, but perhaps I passed 1300* C and it reset the unit??

I'll post my results after I do some more testing.

-Banning.

 

[Russ Merritt]

Yea, I hate when that happens!

 

[salvageV6]

I hope not your engine would be a puddle of metal.

What kind of wires and connector are on the thing?

Look for a shorted braid or problem at the clamp area and also the connection to the meter itself.

RF can definately mess up a thermocouple reading.

Mine is run in the same area no problem. Just don't tie it to spark wiring and you should be okay.

Could also be the battery holder vibrating inside the meter and you lose power momentarily.

What exactly happens at the reset?

No peak hold or display blanks.... or ???

 

[J Banning]

The wire and probe are from SMC. All connections appear to be tight.

I rerouted the wires in the engine compartment in hopes that my problem was related to RF interference. No luck there.

I also tried remounting the main unit thinking that something was loose and when I would launch hard it would cause the unit to reset. I remounted it and laid it flat on the passesger seat. No luck there either.

This is what happens...
When you first turn the unit on, a "OL" briefly flashes. I'm not exactly certain what that is, but maybe it's short for "Overload"?

On their web site (extech.com) they list "Overload" as:
Overload - A signal that is greater than that which a measuring device can accurately or safely accept. Many meters have overload protection in the form of a fuse, or similar device, to protect the meter from such a signal.

Obviously if I was running over 2000 degrees (high range of unit) I wouldn't have a running car. This problem has happened 6-8 times so far, and each run the car has run great and with no knock.

I've emailed their tech support for answers, and I'll try and do some further testing this week and see what happens.

-Banning.

 

[salvageV6]

Could be a bad thermocouple junction, ie. bad EGT probe.

 

[J Banning]

How could I test? Maybe pull it out and put a flame to it?

-B

 

[ijames]

Pull it out and put a match to it slowly. 1300 C is 2372 F so you weren't over range with an actual signal but you might have a bad connection or short to ground that happens when the motor torques over.

 

[J Banning]

Results of further testing:

1) Checked all wires & connections. Everything is ok.

2) Set sensor to record Max temp and slowly put a propae torch to it. I took the temp gradually all the way up to 2000* F, where the sensor "OL'd" out (out of range).

3) Tested the car with the sensor set to NOT record MAX temp. I made three full runs to WOT in 3rd gear (1590* F). Each run was recorded perfectly.

4) made two more runs with sensor set TO record MAX. Each time the sensor "OL'd" out at approximately 1200* F.

I'll email Extech again tomorrow with my results. They've been very helpfull by the way.

-Banning.

 

[salvageV6]

James, how does the meter "record" runs.

Data logging output to a computer?

Display plays back the runs on the meter?

Just wondering how it works.

I understand the max. thing and how that works, sounds like a software problem that won't let it record a peak over 1200F.

 

[J Banning]

Sorry if my post was confusing. The sensor doesn't "record" runs, it will just tell you the MAX temp. There's no data logging capabilities... it's just a basic single input handheld sensor.

-Banning.

 

[salvageV6]

Gotcha.

If the thermocouple will display over 1500 degrees and all not on max. it's gotta be in the meter part that resets the Max. reading.

No way should you get an overload condition unless the sensor really is out of range. Which according to your tests it isn't most likely.

 

[J Banning]

I've emailed Extech's support people a couple of times and they've been very helpfull in trying to diagnose the problem. I just received the following message from them...

"Hi Banning,

Thank you for your response and all your test results. Reviewing the supplied information indicates that there is a problem internally with the meter’s “Max” function. Unfortunately these types of problems do occur (occasionally, not often) in electronics even if the meter has never been dropped, bumped or damaged in anyway.

You state that the meter was purchased 30 days ago from Grainger. If you have had your meter for 30 days or less it is the distributors responsibility to replace it. If you have had it longer than 30 days then it is Extech’s responsibility to repair or replace it if necessary. I recommend that you contact Grainger and let them know that the meter is defective and that you need a new unit to replace your current one. They should be able to assist you.

I apologize for any inconvenience that this problem has caused you. Please contact me if you have any further questions or problems. Thank you.

Best Regards,
Extech Technical Support"

-Banning.

 

[salvageV6]

Cool, sounds like you will get a new one.

 

[J Banning]

Ok, I just put another Extech unit (421501) in the car and it does the EXACT SAME THING! Right from the get-go it would not record "MAX" temperature. The meter works fine (records up to and over 1600*) as long as I don't have it in the "MAX" recording mode.

I'm pretty sure it's something in the wire/connections/egt probe that is causing this. Is it uncommon for EGT probes to go bad? I'll start by replacing the wire this week and see what happens.

All thoughts/opinions appreciated.

-Banning.

 

[TurboDave]

EGT problems usually always manifest themselves in the probe or wiring.
I've only ever had to make one repair and it was the probe/wire.

 

[salvageV6]

Maybe the circuit opens or shorts for a split second and resets or messes up the recording reading in Max. mode?

I'd try opening a lead while "recording" car off in the drive way.

Get a max. reading of say 100 degrees or whatever ambient is.

Then open one leg and see what you get.

Then short the two wires and see what you get.

If you can duplicate the results you may know there is a problem with the probe or wiring.

 

[Fast231]

Originally posted by TurboDave
EGT problems usually always manifest themselves in the probe or wiring.
I've only ever had to make one repair and it was the probe/wire.

The same happened to me, my first probe lasted for one year, worked great in the summer, but didnt like sitting and doing nothing in the winter.

I also thought it to be my fluke thermometer, I got a ohm meter, got the spec off of the westack site...the thermocoupler was toast.