Accuracy of boost and egt gauges

[Wizard52]

Hi all

Had a quick search of threads but did not see this topic.

I have Autron boost and EGT combo gauge but question the accuracy. Misplaced (lost) instructions of course.
Boost seems ok but read out for EGTs seems to high so we wound fuel back to extent it now goes like a slug compared to previous set up and uses more fuel. Probe is post turbo about 60 to 70 mm from flange bolting to turbo. Standard GUIV pump.
3" exhaust and was dyno tuned when exhaust installed about 3 or 4 years ago but EGTs always spiked over 500 very quickly (and I've seen 600 on occasions before backing off quickly) when giving it heaps up hills etc. No noticeable smoke but vision is a bit restricted due to canopy. Using a lot less throttle keeps temps down and still had excellent performance but is a real pain having to watch temps closely. Does not appear to be a problem in lower gears but 4th & 5th have to be watched.
Any ideas on how to calibrate gauges or to get accurate comparison?

[Ben-e-boy]

To test the boost gauge you could hook it to an air compressor with a regulated air supply, and I guess you could put the egt probein the oven.

[threedogs]

For EGT you could use one of those thermal guns, would give a ball park reading.
No two 4x4 are the same so hard to have a set value .IMo

[@GUte]

I have two analogue boost gauges, an Autometer and a Calibre. They both read reasonably close to each other after some initial differences probably due to probs with the hose. I recently fitted the digital Auber gauge which has confirmed them both out enough to warrant them reasonably inaccurate. The Auber can be reset to zero whenever needed.

[Dales300exc]

I have two analogue boost gauges, an Autometer and a Calibre. They both read reasonably close to each other after some initial differences probably due to probs with the hose. I recently fitted the digital Auber gauge which has confirmed them both out enough to warrant them reasonably inaccurate. The Auber can be reset to zero whenever needed.

How much out?

[@GUte]

How much out?

At 2000 rpm about 2-3 psi.

[Dales300exc]

Guess its 10-15%.

Its one of those things though I guess. It doesnt have to be 100% accurate. Its more a reference point. And that reference point remains constant with your vehicle.

Same with all engine vitals.

[rottodiver]

Egt,s....... When putting my foot down I see 500 to 600,s then it settle back to 350 to 400 normal driving (sometimes less) with the camper trailer in tow when overtaking up hills I have seen 700 then settles back to 450 when over drive is off. If overdrive is on 600 to 700 while towing on the flat.

Boost... Mine reads pretty close to scan gauge, I seem to see the fluctuations on the needle garage more than digital but am fairly confident reasonably close, have had them hit just over 17psi then limp mode and over boost code which I believe to be close to ecu parameters..

Scotty

[Wizard52]

Follow up to original thread.
Wound fuel back a bit with very little change in EGTs but big decrease in power and noticeable increase in fuel consumption-about 1 lt per 100k. Noticed I was a gear lower in a lot of circumstances so had to work harder.
Wound fuel up again back to normal and bingo. Good to drive again and very little change to EGTs so will just have to watch temps under load.

[threedogs]

Guess its 10-15%.

Its one of those things though I guess. It doesnt have to be 100% accurate. Its more a reference point. And that reference point remains constant with your vehicle.

Same with all engine vitals.
Agree 100% its something to look at and as soon as you notice it varying you'll know something is up.
EG your battery volt gauge may start reading 16v then zip then 14.v time to check your Alternator.
some of the 4.2 boys may be able to share their egts only as a guideline not gospel

[Wizard52]

Agree 100% its something to look at and as soon as you notice it varying you'll know something is up.
EG your battery volt gauge may start reading 16v then zip then 14.v time to check your Alternator.
some of the 4.2 boys may be able to share their egts only as a guideline not gospel

I agree now. It is only a reference point but would have a bit more confidence if they were accurate, especially at higher temps.
The sticky thread on EGT logging is good for comparisons

[threedogs]

not sure with the 4.2s but I'd back off at 500c regardless

[Gecko17]

For EGT you could use one of those thermal guns, would give a ball park reading.
No two 4x4 are the same so hard to have a set value .IMo

Agree with 3D. Try and get a thermal gun. Best way to get (fairly) accurate temp.

I have the two Autron gauges as well.

Also with 3D, I back have set mine to go off around 500C. (Haven't had to yet but with the Autron gauges, you can program colour warning at a set temp.)

[Wizard52]

Agree with 3D. Try and get a thermal gun. Best way to get (fairly) accurate temp.

I have the two Autron gauges as well.

Also with 3D, I back have set mine to go off around 500C. (Haven't had to yet but with the Autron gauges, you can program colour warning at a set temp.)


My Autron gauge is one of the older ones with boost and EGT. I can only program alarm for the boost (which I have at 16psi) with a beep and change of colour. Boost controller is set at 15psi so never hear alarm.

The problem with a thermal gun would be ute only gets high EGT temps when under load and a boot full of throttle which means it would have to be on a dyno and not in the shed.
I manage to keep at or under 500c but it is a pain to have to monitor gauge so much especially when you need to watch road or beach.
Any thoughts on increasing boost to reduce fuel/air ratio thereby reducing egt's?

[threedogs]

As to how accurate boost gauges are I have now fitted and run full time Yendors old ECU-talk obd2 diagnostic set up;
Just driving along my boost gauge was reading 5 psi and the ECU-talk read 6.4, so to answer your question,
I would have to say no they are not very accurate. I'll now be backing my Dawes vale off a touch and set my boost via the ECU-talk
Highly recommend one to all Di owners, again thanks Rod

[mudski]

As to how accurate boost gauges are I have now fitted and run full time Yendors old ECU-talk obd2 diagnostic set up;
Just driving along my boost gauge was reading 5 psi and the ECU-talk read 6.4, so to answer your question,
I would have to say no they are not very accurate. I'll now be backing my Dawes vale off a touch and set my boost via the ECU-talk
Highly recommend one to all Di owners, again thanks Rod

Why do you want to back the Dawes off John? Your not getting limp mode so all your going to achieve is less power.

[the evil twin]

As to how accurate boost gauges are I have now fitted and run full time Yendors old ECU-talk obd2 diagnostic set up;
Just driving along my boost gauge was reading 5 psi and the ECU-talk read 6.4, so to answer your question,
I would have to say no they are not very accurate. I'll now be backing my Dawes vale off a touch and set my boost via the ECU-talk
Highly recommend one to all Di owners, again thanks Rod

How do you know the factory sensor for the ECU is any more or less accurate than your boost gauge.

I suggest it probably is (unless you have a high quality aftermarket gauge) but it wouldn't suprise me if the factory sensor was out by a reasonable margin as well.

[BillsGU]

How do you know the factory sensor for the ECU is any more or less accurate than your boost gauge.

I suggest it probably is (unless you have a high quality aftermarket gauge) but it wouldn't suprise me if the factory sensor was out by a reasonable margin as well.

The only way to really tell would be to compare it with an instrument that has been calibrated to some sort of standard - with traceability (usually NATA standards).

[threedogs]

true who's to say which is out and which is reading correctly
I'm not going into limp mode, so I'll be leaving it as suggested
sick of fiddling with, dawes/needle valves

[the evil twin]

true who's to say which is out and which is reading correctly
I'm not going into limp mode, so I'll be leaving it as suggested
sick of fiddling with, dawes/needle valves

Winner... :tongue:

[Hodge]

My local diesel places completely bypasses the in-car gauges and use their own calibrated ones.
I've been questioning my autron gauges or it's install/setup. It seems very "moody". For example sometimes on a hot day, hard driving the EGT's seem rather lower than usual. Then for instance this rather coolish morning, I was just crusing down to bunnings and EGT's jumped to 400, the car wasn't even warm enough. So whos to say whats accurate.
This sort of concerns me, as when it comes to my dawes/valve setup I haven't got a solid confirmed reading to calibrate up against.

[threedogs]

@ hodge higher revs will give you lower temps. travel at 60 kph
check your temps them hit the OD button EGTs wiil get lower as revs increase

[BillsGU]

My local diesel places completely bypasses the in-car gauges and use their own calibrated ones.
I've been questioning my autron gauges or it's install/setup. It seems very "moody". For example sometimes on a hot day, hard driving the EGT's seem rather lower than usual. Then for instance this rather coolish morning, I was just crusing down to bunnings and EGT's jumped to 400, the car wasn't even warm enough. So whos to say whats accurate.
This sort of concerns me, as when it comes to my dawes/valve setup I haven't got a solid confirmed reading to calibrate up against.

Any tuning place worth their salt will use consistant readings from their own instruments and not rely on the unknown. Next time you have a tune ask them to put a "T" piece in the vacuum line and compare your gauge. The EGT is a bit more difficult as he will have to replicate load and revs twice - with his gauge and then with yours.

I have Autron gauges and they always seem stable and consistant - but I have not had them calibrated or compared so I don't know how accurate they are. Also - I don't know how accurate they have to be. Within 1 degree C, 10, 50, 100? What would be considered to be too inaccurate?

[threedogs]

yeah good point billsgu why do they have to be accurate ,cant they be ballpark for example.
No two 4x4 are the same so who cares, PSI values aren't set in concrete again ball park or a guide

[Wizard52]

Any tuning place worth their salt will use consistant readings from their own instruments and not rely on the unknown. Next time you have a tune ask them to put a "T" piece in the vacuum line and compare your gauge. The EGT is a bit more difficult as he will have to replicate load and revs twice - with his gauge and then with yours.

I have Autron gauges and they always seem stable and consistant - but I have not had them calibrated or compared so I don't know how accurate they are. Also - I don't know how accurate they have to be. Within 1 degree C, 10, 50, 100? What would be considered to be too inaccurate?

Hopefully they could be within say 50 degrees because if it shows 500 or 550, and is really 600+, we could be approaching disaster.

[the evil twin]

EGT gauges are easy to check.
Pyrometers are a milli-voltmeter and quality ones like Autron, VDO etc are usually very accurate around +/- 10 degrees C.
The easiest way to check your calibration is with a millivoltmeter across the thermocouple at the back of the gauge.
Because of the laws of physics thermocouples put out quite specific voltages across their temperature range.
In our trucks it is 99% a K type thermocouple in use so if you google a K type chart you can see what temp should be indicated for a particular voltage reading.
To calibrate the gauge on it's own on the bench I use a millivolt source
Pyrometers usually either work OK or go off scale when faulty BUT they do need to be installed with the correct thermocouple wire.
Intermittent jumps etc is usually indicative of a wiring issue or loose connection.

Boost gauges are a tad more finicky to check
Easiest way on a mech gauge is to pop the line off and tee in another gauge
Elec gauges were the sensor goes under the factory sensor on the intercooler are a tad more problematic as it is usually harder to tee in.

[BillsGU]

EGT gauges are easy to check.
Pyrometers are a milli-voltmeter and quality ones like Autron, VDO etc are usually very accurate around +/- 10 degrees C.
The easiest way to check your calibration is with a millivoltmeter across the thermocouple at the back of the gauge.
Because of the laws of physics thermocouples put out quite specific voltages across their temperature range.
In our trucks it is 99% a K type thermocouple in use so if you google a K type chart you can see what temp should be indicated for a particular voltage reading.
To calibrate the gauge on it's own on the bench I use a millivolt source
Pyrometers usually either work OK or go off scale when faulty BUT they do need to be installed with the correct thermocouple wire.
Intermittent jumps etc is usually indicative of a wiring issue or loose connection.

Boost gauges are a tad more finicky to check
Easiest way on a mech gauge is to pop the line off and tee in another gauge
Elec gauges were the sensor goes under the factory sensor on the intercooler are a tad more problematic as it is usually harder to tee in.

Then I guess you would need an accurate / calibrated thermometer so you can work out the mV output at a certain temperature. How accurate it a normal thermometer?

[the evil twin]

Then I guess you would need an accurate / calibrated thermometer so you can work out the mV output at a certain temperature. How accurate it a normal thermometer?

Hiya Bill,

You don't need another thermometer, the thermocouple is your thermometer, you just can't read it.

A thermocouple generates a specific voltage at a specific temperature. The "accuracy" of the temperature indication is governed by the display.

You can therefore either...
a) monitor the voltage from the thermocouple with a millivoltmeter and use the K type tables for the temperature.
As an example if your millivoltmeter reads 12.5 millivolts (mV) the gauge should display 305 deg C, 12.6mV is 310 deg, 10.0mV is 245 deg etc etc
OR
b) disconnect your thermoucouple leads at the gauge and connect a millivolt source. Most of the field process test gear will do this next bit and any instrument/elec workshop will. Apply the voltage as per the table and check the displayed temp

EDit... you can even make a test setup at home out of a dry cell battery and a couple of resistors if you have a good multimeter

[BillsGU]

Hiya Bill,

You don't need another thermometer, the thermocouple is your thermometer, you just can't read it.

A thermocouple generates a specific voltage at a specific temperature. The "accuracy" of the temperature indication is governed by the display.

You can therefore either...
a) monitor the voltage from the thermocouple with a millivoltmeter and use the K type tables for the temperature.
As an example if your millivoltmeter reads 12.5 millivolts (mV) the gauge should display 305 deg C, 12.6mV is 310 deg, 10.0mV is 245 deg etc etc
OR
b) disconnect your thermoucouple leads at the gauge and connect a millivolt source. Most of the field process test gear will do this next bit and any instrument/elec workshop will. Apply the voltage as per the table and check the displayed temp

EDit... you can even make a test setup at home out of a dry cell battery and a couple of resistors if you have a good multimeter

Thanks ET. I see what you mean now.