To: "80s COOL Aust" <80scool_aus@yahoogroups.com> From: "Stuart McMurtrie" Date: Wed, 18 Feb 2004 17:44:01 +1000 Subject: [80_aus] Fw: Toyota Landcruiser wagons Reply-To: 80scool_aus@yahoogroups.com Received the following email at work from our fleet manager. All 100 Series LandCruisers in this fleet are 1HZ engined DX type spec - ie barn doors. ______________________________________________________________________ To All Operators of Series 100 Toyota Landcruisers. There have been some recent electrical problems with Series 100 Toyota Landcruiser fuel systems. The problems are: - The gauge may show fuel in the tanks when they are actually empty; and - Not being able to switch to the sub tank after the vehicles main fuel tank has run out of fuel. Both tanks operate on the one fuel gauge which is controlled by a switch on the dash. It appears that the circuitry can be damaged by 'spikes' thereby causing faulty fuel gauge readings and an inability to engage the sub tank when switched. One indicator of this condition is that the sub tank 'on' light may not illuminate. Drivers are requested to ensure the main tank does not run dry under any circumstances. If you have any reason to suspect that the gauge is faulty and the tank is not switching, contact your Toyota dealer, Please note - the problem does not affect all vehicles. Toyota has not considered the matter serious enough to warrant a full recall, however any affected vehicles will have the entire dash instrument modules replaced. regards Stuart McMurtrie Brisbane To: 80scool_aus@yahoogroups.com From: "Jim Potts" Date: Thu, 19 Feb 2004 08:02:19 -0000 Subject: Re: [80_aus] Fw: Toyota Landcruiser wagons Reply-To: 80scool_aus@yahoogroups.com --- In 80scool_aus@yahoogroups.com, "Stuart McMurtrie" wrote: > Spike = high voltage impulse usually caused by back EMF off an > electromagnetic coil of some sort - starter motor, relay, solenoid, > etc. In this case I suspect the fuel changeover solenoid may be the > culprit. Spikes can be prevented by installation of a reverse biassed > diode across the coil. Of course the circuit parameters will dictate the device to be used (eg reverse biased zener). Main thing is that they should be placed as close to the offending back emf generator, preferably on its contacts. Cheers Jim To: <80scool_aus@yahoogroups.com> From: "Stuart McMurtrie" Date: Thu, 19 Feb 2004 18:13:22 +1000 Subject: Re: [80_aus] Fw: Toyota Landcruiser wagons - now diodes [chat] Reply-To: 80scool_aus@yahoogroups.com ----- Original Message ----- From: Jim Potts Sent: Thursday, February 19, 2004 6:02 PM Of course the circuit parameters will dictate the device to be used (eg reverse biased zener). Main thing is that they should be placed as close to the offending back emf generator, preferably on its contacts. Cheers Jim Jim Definitely NOT a Zener Diode. A small signal or rectifier diode with a Peak Inverse Voltage (PIV) much greater than the operating voltage is necessary. Typically PIVs are in the order of 1000V. A Zener is designed to regulate when it is in the reverse biassed mode. At manufacture the silicone junction has been doped to have a very low PIV. eg a 5.1V zener has a PIV of 5.1V and conducts at that voltage when reverse biassed but still conducts at approx 0.6V when forward biassed. regards Stuart To: 80scool_aus@yahoogroups.com From: "Ian" Date: Thu, 19 Feb 2004 09:10:15 -0000 Subject: Re: [80_aus] Fw: Toyota Landcruiser wagons - now diodes [chat] Reply-To: 80scool_aus@yahoogroups.com --- In 80scool_aus@yahoogroups.com, "Stuart McMurtrie" wrote: > Jim > > Definitely NOT a Zener Diode. A small signal or rectifier diode with > a Peak Inverse Voltage (PIV) much greater than the operating voltage > is necessary. Typically PIVs are in the order of 1000V. A Zener is > designed to regulate when it is in the reverse biassed mode. At > manufacture the silicone junction has been doped to have a very low > PIV. eg a 5.1V zener has a PIV of 5.1V and conducts at that voltage > when reverse biassed but still conducts at approx 0.6V when forward > biassed. Hmmm, on the contrary Stuart! A zener (say 18V, 5W) used in this application has the advantage of suppressing spikes of both polarities, and also, a signal diode probably wouldn't dissipate enough power to regularly take care of spikes from a decent size coil, whereas a nice chunky zener would have more than ample dissipation. I'll leave a more elaborate explanation to Jim! Cheers To: 80scool_aus@yahoogroups.com From: "Jim Potts" Date: Thu, 19 Feb 2004 09:46:09 -0000 Subject: Re: [80_aus] Fw: Toyota Landcruiser wagons - now diodes [chat] Reply-To: 80scool_aus@yahoogroups.com --- In 80scool_aus@yahoogroups.com, "Stuart McMurtrie" wrote: > Jim > > Definitely NOT a Zener Diode. A small signal or rectifier diode with > a Peak Inverse Voltage (PIV) much greater than the operating voltage > is necessary. Typically PIVs are in the order of 1000V. A Zener is > designed to regulate when it is in the reverse biassed mode. At > manufacture the silicone junction has been doped to have a very low > PIV. eg a 5.1V zener has a PIV of 5.1V and conducts at that voltage > when reverse biassed but still conducts at approx 0.6V when forward > biassed. I wondered why I suggested the zener, until I remembered that some fuel pumps eg the English SU ones actually incorporate a zener. "The Zener is a cheap, little device that acts as a shunt to bleed off excess voltage spikes generated by the coil when the points are opened. They are used on most relay/solenoid designs today, in order to protect any electronics which is turning on the coil." http://www.team.net/sol/tech/SU-diode.html Surprised me also. I would of thought a decent PIV silicon would of been the go. Cheers Jim To: <80scool_aus@yahoogroups.com> From: "Stuart McMurtrie" Date: Thu, 19 Feb 2004 21:49:51 +1000 Subject: Re: [80_aus] Fw: Toyota Landcruiser wagons - now diodes [chat] Reply-To: 80scool_aus@yahoogroups.com ----- Original Message ----- From: Jim Potts Sent: Thursday, February 19, 2004 7:46 PM I wondered why I suggested the zener, until I remembered that some fuel pumps eg the English SU ones actually incorporate a zener. "The Zener is a cheap, little device that acts as a shunt to bleed off excess voltage spikes generated by the coil when the points are opened. They are used on most relay/solenoid designs today, in order to protect any electronics which is turning on the coil." http://www.team.net/sol/tech/SU-diode.html Surprised me also. I would of thought a decent PIV silicon would of been the go. Cheers Jim Thanks Ian and Jim I stand corrected. Had not considered a zener in the 18V range. Cheers Stuart