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Engine Specific Info and Questions => IDI Engine => Topic started by: Cheesetoast on March 29, 2005, 11:12:06 pm
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my egt gauge now will mostly bounce around randomly, if I turn the car off and just have the gauge powered up, it will be normal and steady, turn the car on, and it goes nuts. Any idea what it could be? I'm thinking ground, looked aorund, everything looked ok, any hidden grounds that might have been disconnected?
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thats how my oil temp sensor was. i looked and found that it was just a screw that came loose for the ground. i'd try to take everything off then put it all back together to make sure everything has a good connection. also is it tied anyway into any other circuits? not really significant but i was hanging around the vw dealer here and the power mirror switch was changed sometime and on the same model car if you put the older one in, exact same from apperance, then putting it to left iirc would turn on the dash lights. this would happen because of a common ground back powering the dash lights through the switch somehow.
anyway good luck
Mark
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Dont forget the ground on the drivers side, under the battery tray. The negative cable should mount to the drivers inner fender, then a ground strap mounts from there to the end cap on the transmission. Since you had the tranny out for the clutch, I'd check that one. :)
Somehow I managed to drive my Rocco 430 miles with that strap disconnected. May have had something to do with the charging problems......
:shock:
Brendan
84 Scirocco 8v
00 Camaro L36 M49
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The EGT gauge should operate on an isolated, non-powered circuit. (A small voltage source from the thermocouple itself is what makes the gauge move.) However if there is an intermittent connection, it could go in and out randomly or with vibrations, or if there is a short somewhere you could get other haywire results... I would inspect your EGT gauge wiring from gauge to thermocouple, paying very close attention to where the wiring goes through the firewall (for chafing) and where it connects to the thermocouple (for good corrosion-free connection.) Also make sure the wiring is securely plugged in to the gauge.
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this is probably the case, i'll check that one tonight and report back.
Dont forget the ground on the drivers side, under the battery tray. The negative cable should mount to the drivers inner fender, then a ground strap mounts from there to the end cap on the transmission. Since you had the tranny out for the clutch, I'd check that one. :)
Somehow I managed to drive my Rocco 430 miles with that strap disconnected. May have had something to do with the charging problems......
:shock:
Brendan
84 Scirocco 8v
00 Camaro L36 M49
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The EGT gauge should operate on an isolated, non-powered circuit. (A small voltage source from the thermocouple itself is what makes the gauge move.) However if there is an intermittent connection, it could go in and out randomly or with vibrations, or if there is a short somewhere you could get other haywire results... I would inspect your EGT gauge wiring from gauge to thermocouple, paying very close attention to where the wiring goes through the firewall (for chafing) and where it connects to the thermocouple (for good corrosion-free connection.) Also make sure the wiring is securely plugged in to the gauge.
checked the wiring in the engine bay, looks fine, can't see it being back behind the gauge, tapping the guage doens't make a difference, and the guage works fine with the engine off. thx guys.
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I just did a thorough check under the car and above, couldn't see any grounding strap under the battery tray. Do I actually have to take the battery out to see this?
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The EGT gauge should operate on an isolated, non-powered circuit. (A small voltage source from the thermocouple itself is what makes the gauge move.) However if there is an intermittent connection, it could go in and out randomly or with vibrations, or if there is a short somewhere you could get other haywire results... I would inspect your EGT gauge wiring from gauge to thermocouple, paying very close attention to where the wiring goes through the firewall (for chafing) and where it connects to the thermocouple (for good corrosion-free connection.) Also make sure the wiring is securely plugged in to the gauge.
checked the wiring in the engine bay, looks fine, can't see it being back behind the gauge, tapping the guage doens't make a difference, and the guage works fine with the engine off. thx guys.
Could the problem be with a 'circuit' being made through the gauge casing?
Is it metal? Is it earthed?[casing] Can it be pulled for a closer inspection? Is there a connector on the thermocouple circuit that you can put meter probes on and check for correct voltage with ignition on or better still test for isolation wrt earth.
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I just did a thorough check under the car and above, couldn't see any grounding strap under the battery tray. Do I actually have to take the battery out to see this?
Shouldnt have to, although on my Rocco (which is an A1 and yours being an A3, might be different) the strap is directly under the right side (looking from the front of the car) of the battery. If you follow the negative cable down, it should mount to the body. The ground strap to the tranny is mounted in the same place. I did a quick look in ETKA and while it doesnt show a picture of this ground strap, it does list a ground strap "for battery side panel" which is about as clear as mud, but it lists it as separate from the negative cable. (which is also sometimes called a ground strap in ETKA. :P )
Good luck, I think when VW engineers encountered a problem, they just added another ground and another vacuum line and called it "fixed".
Brendan
84 Scirocco 8v
00 Camaro L36 M49
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hmm, the gauge is working fine again now, maybe had something to do with the battery being unplugged? who knows.
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spoke too soon, it's messed up again tonight, only thing I did was put it on ramps, spray the underengine in degreaser and rinse off a couple minutes later. I'll try reseating all my grounds, maybe they're corroded.
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spoke too soon, it's messed up again tonight, only thing I did was put it on ramps, spray the underengine in degreaser and rinse off a couple minutes later. I'll try reseating all my grounds, maybe they're corroded.
AFAIK all the original styled EGT systems were stand alone. BUT with lots of 'made for car' modern tack this may not be the case.
If you disconnect your car battery +ve; does the meter still read exhaust temp? If it does then its an independant circuit.
(If it doesn't then earthing on the car is likely.)
Get engine hot enough for a reading then 'pop the bonnet' ahh pull the hood ;o)
Play around with the thermocouple leads for looseness.
Find the chocolate block connector if there is one :wink:
Disconnect and fit a mV meter... site it so that you can see it when you are doing whatever it is that you do to get it jiggling all over the place and see if its repeated on the test meter. No? then create a false signal to the EGT meter itself using a 1.5 V battery and a suitable inline resistor and a variable resistor to sweep the scale from 0 to FSD
:mrgreen: Still no good? Sell your Rabbit and use the money as deposit for a Quantum :mrgreen:
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it's a 93 golf td, not a rabbit :)
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it's a 93 golf td, not a rabbit :)
Oops sorry Mr Cheesey Toes; does that mean that your car has 'fart flaps' rather than a heater valve? :wink:
:mrgreen: I'm a big cheese eater actually and recently bought some Monteray Jack... 'Uckin 'ell; I've eaten tastier power balls. (Does make good elastic on a homemade pizza though. :mrgreen:
I do hope you trace this EGT problem... The thing is how hard are you going to kick yourself when you discover what you've done?
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that's the problem, I didn't do the clutch, i'll just reseat the grounds, see how that goes.
it's a 93 golf td, not a rabbit :)
I do hope you trace this EGT problem... The thing is how hard are you going to kick yourself when you discover what you've done?
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You are wasting your time looking for the problem anywhere in your main electrical system, including it's grounding points.
The only circuit that matters is the self-contained circuit between gauge and thermocouple. This circuit is very low voltage, and so it is very sensititve to imperfect connections. It takes only a small bit of surface corrosion or contaminants between the connection lugs to break the function of the gauge.
I'll bet it's either merely coincidence your pyrometer started going haywire when the clutch was installed, or it is because the wiring was bumped or strained during the clutch work (IE: they removed the transaxle to access the clutch and tilted the engine down which strained the wiring, or they bumped the wiring during the work). This could have upset a weak electrical connection or moved it a little bit so it is no longer a perfect (or only an intermittently perfect as a result of heat, vibration, and/or engine movement) electrical connection. The pyrometer/thermocouple wiring also has a solid non-stranded wire in it, which is much easier to break from fatigue than standard stranded automotive wiring is.
You might want to also try the tips I posted in this thread: http://www.vwdiesel.net/phpBB/viewtopic.php?t=687
Hope this helps... Good luck.