Page 14 (Updated 24-Oct-08)
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Preventive Maintenance
On Car Computer Environment
- Computer environment ; General Overview
- Design flaws - pushed onto us
- How to Improve my System
- Checking The Connectors
- Harness Evaluation
- Voltage measurements to diagnose
- Engine Compartment Connectors
- Adding Di-electric Contact Grease
- Microsoft Terror - Coming?
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General Overview
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Year 1984:
Control Data Supercomputer wirings in a climate controlled room. ...Is the Problem Here?
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Computing
Standard computers were designed to work under climate controlled conditions. Humidity plus temperature had to be tightly controlled in complex computer centers. This was not only to guard the electronics from overheating, but also to minimize heat variation induced micro-level expansion on various parts like connectors.
It is also known that during years, electron level migration is possible in all electronics components. This together with oxidation, soft connector surface metal 'escape' under pin load and metal fatigue [connectors all use spring loaded pins] results envitably to loss of connection in any connector. The only question is the time scale: when? When will the resistance raise above the limit and connection is lost, or signal becomes so distorted that computer makes wrong decisions based on this biased, wrong input.
Ford Jeep -43 instrument panel: Advanced 'electronics' from 40's:
Automatic fusebox, Amp & Fuel gauges are electrical, not
too complicated...
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Nowadays this computer technology from eighties has been taken out from its protected environment and shrunk to work in our cars. The chip technology has been advanced most, and does not suffer too much of this change. However, the system is now more hampered by problems from wrong input: the main culprit in cars is the extended wiring, and signal distortion in its connectors (signal distorting resistance). Ten years is way too much in a computer environment, but still we demand that from the computer systems in cars, which are located on one of the harshest environment on earth.
Cars are susceptible to moist, salt, dust etc corrosion and vapors, not to mention ultimate sudden heat exchanges: in winter, under the hood temperatures could constantly fluctuate somewhere between 200F to -40F, depending on the driving rhythm. This environment stresses all components, wirings and connectors to their limit. Like the connectors which have been made as cheap as possible to beat the manufacturing cost cutting competition...
Every small cavity forms its own breathing micro-climate. When an object (cavity) warms, expanding air pushes out. When it cools, outside air rushes in - bringing moisture and dust. This same moisture -phenomena also 'kills' car body which is formed by hundreds cavities.
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Maxima from the 90's. In the very basic composition, three main computers,
multiple electronic printed circuit board's (PCB’s), tens of low voltage sensor
inputs and outputs, thousands of oxidized pins...
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Design flaws - pushed onto us
Biggest problem: Wirings, Connectors:
From the historical reasons, computer sensor technology still applies sensors with low voltage power input. The signal errormargin is critically low, and the long sensor wirings to computers are anemic from the very beginning. The errormargin decreases as oxidation growth starts day one, does not depend on driven miles but environment. Half Volt level -change in an input is critical to a computer. What happens when one connector in a long wiring harness-chain accumulates resistance that is near the threshold level? Flip-flopping input around this threshold will result to intermittent error messages given out by the computer.
Generally can be said that a used five year old car, has always one or more transfer resistance connector pin problems hampering its performance ...in one of its tens of thousands contact points. This undesired fact starts already on the factory floor...
Still no maintenance education exists where and how to take care of the asset of well maintained inputs to the computers. Taking care of harness, and leak proof connectors is the first and the only standing base on which all car function reliability rests.
The main point is to take action on the harnesses overall in the preventive maintenance, starting from cleaned connectors plus well maintained (and upgraded groundings in case of older than five yr. cars.)
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Pics from Nissan -93 Service Manual shows small part of the complexity (here shown probably half of the connectors in your Maxima)
Free Service Manual, Free Download.....see FAVORITE LINKS -page 26- FAVORITE LINKS
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How to Improve my System
One of the most important task for any electronic device user is to understand, that over 2/3 of all electronics problems are result from increased transfer resistance, mainly in connectors. This happens in wirings that are already from the beginning too thin for their task [resistance = voltage drops].
To get such a problematic system running, requires only someone who is able to open (or just move) and close connectors. Even a slight movement changes the connectors conductance. To get lasting results, the goal is to clean all connections.
Maxima ECU connectors under the dash:
After disconnecting battery, take the connector out, clean, let dry, put back.
Not to worry how its internals work... To open, the nut is rotated ccw. While
nut rotates, the connector self-propels out, (no need to pull). Even one turn
ccw (You may leave it there) makes real difference - if oxidation is the problem.
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Is there a steep learning curve?
Absolute no understanding of the internal logic functions are not needed (but of course is good to have). One has to be able to locate and take off battery cable, open a connector, use
electronics spray cleaner on both the wire and computer connector sides, let dry and close connectors. And with this capability, it is a 60-80% chance that any electronics problem will be corrected.
So next hop, is to a electronics S hop!
Buy electronics contact cleaner, locate all (=All) connectors, open, spray liberally (see that all debris and liquid drops on some paper) let dry and close. This job takes hours, as cars typically contain so many computers and thousands on connecting pins.
Biggest problem typically is to reach those connectors, and -How To- open paneling to reach them. There the manuals which (sometimes) give right answer...
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Arrows in the pics show where the connectors are located:
cleaner spray has to hit directly in to flush all clean, then let it drip dry or
blow with bottled electronic cleaning air (do not use std compressed oily air!)
If a device fault is suspected, one way to troubleshoot to use electronics freezer: on PCB’s the typical problem is bad soldering, or broken print. They make intermittent problems which are very hard to trace as they disappear as the serviceman gets near. Spraying freezer contracts all cold areas and thus makes mechanical changes, possibly duplicating the problem. This freezer can be used on live PCB’s and connections for troubleshooting.
Freezer usage Note: Many electronics chips will change behavior as they get cold, so a change in operation characteristics during freeze is not always a problem, but feature.
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Checking The Connectors
Connectors; structural overview:
Connectors come in various types, but all have some common denominators.
Male (3.) pin contact, (2.) wire socket [to be crimped], (1.) bare wire inserted.
These pins are locked into the connector blocks with connector specific tools.
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Next explanation will focus on what user can do as the oxidation buildup is a fact on day one, and how slow it down.
The factory made connection (1.) is hidden inside the connector block, and there is not much one can do except verifying possible transfer resistance. How well this area is shielded, determines the harness lifetime. Cleaning and shielding will prolong connectors lifetime.
The connector is mated to female connector that exerts spring load on the connector male pin. This load is good on new connectors, but due to metal fatigue, decreases continuously. Heat fluctuation cycles makes this expansion/contraction worse, and is the root cause for the sooth carrying airflow.
Spring loaded pin with minuscle contact area. In the beginning, spring (4.) load is perfect, contacts clean. 
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How "closed" connectors can oxidize?:
As time passes, micro climatic changes bring dust, soot, and myriad oxidizing particles into the connector. The more open the connector is, the faster is degrading. Age dependent spring load will decrease, along with male part metal fatigue: metal escapes from this spring pressure, forming a small pit. In worst case, the pit will come deep enough that contact will be lost as oxidation pushes in. This accelerates degrading as the soot =resistance buildup will warm up the connection...
Old oxidized connector which has lost contact long ago. 
If at this stage, the connector pin would be moved even one millimeter (5.) as arrow indicate, the connection would probably be corrected up to a point. Cleaning would be needed to reinstate original connection. Would this correct the connection totally, maybe: only on some connectors it is possible to later retain the spring load by bending. in most cases this needs original tools to get the pins properly out for corrective measure.
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The oxidation speed depends a lot of local conditions: air acidity/soot/salt/moist particle qualities. This is because just about any small 'box' continuously breathes in and out due to heat expansion/contraction = 'pumping local' air in/out with the air particles, to those device micro cavities, connectors etc...
Minimum "service":
If one is not familiar with electronics and is afraid to open connectors, just causing slight connector movement is not too dangerous issue [power supply off]. If the touched connector is oxidized, movement results at least into temporary fault change. Thus taking the car to electronics specialist, this knowledge might point to fast corrective measure, and save lots of money spent otherwise on troubleshooting.
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Harness Evaluation
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After cleaning, spraying contact grease on all connectors, the harness should be evaluated as whole: how well it shields the connector blocks?
Throttle Position Sensor TPS:
On the Throttle Position Sensor this shielding has been done remarkably well. Harness shielding fits to special connector jacket seamlessly. The connector itself has rubber seals that mates with the TPS block well. But next we face free fall: The TPS itself is an open box from all sides to dust and water. ---> never wash u car engine! ...at least if all electrical components have not been sealed as in this TPS.
TPS & Zero position sw connector: Harness shielding (6.), Connector rubber
jacket (7.) Connector with o-ring (8.) The TPS (9.)
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The connector backsides should be also protected from soot, and connected to the harness shield. Here TPS harness connector shielded with self vulcanizing rubber tape by me. Typically these connector wires are glued individually shut, and will not let water in. But soot accumulation along with plastic harness degrading/cracking will possibly cause shortages.
TPS Position Potentiometer -Connector with new backside shield.
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Alternator:
Another example is in the alternator. The voltage regulator wire has a high quality sealed connector to the alternator. But does it help if rear is open, no rubber jacket, harness 'is halfway done'? No, this should be sealed with self vulcanizing rubber tape. Similar problem is at +12VDC supply, it should be sealed as it is open to flying soot from the road. The add on ground connector has been shrink-wrapped as well as possible to contain the connector. The goal is not to expose wires for corrosion which will 'travel' down the wire degrading it also.
The regulator wire (10.), +12VDC supply (11.), Extra grounding to chassis (12.) ; at right alt supply connectors and oxidized white soot on the gnd wire, nut.
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Voltage measurements
to diagnose harness condition:
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If you want to know your car reliability, you do this measurement few times a year. Also before any further electrical analysis, this should be known. Just to have this basic knowledge, I have installed a separate voltage gauge which is always on, on my dash. That along critical engine info, keeps the driver informed, which is always good to have before you hit the road. I don’t wanna be towed...
Testing:
Test voltage with a multimeter at battery as car has been standing overnight. Start the engine and repeat the test.
This test gives info of your battery condition and alternator supply capacity. A healthy battery has 12.5Volts or over. Lower voltage in the morning indicates poor battery or excess standby power consumption, both require attention. Engine running & charging, voltage should be between 13.8 to 14.7, depending on alternator regulator type (cars up North have higher charging voltage).
This voltage level (-minus wire length & dia induced resistance drop) should be present at various point in the harness, inside cabin etc. The bigger the difference to this measured reference battery voltage, the worse off is harness and connector oxidation -situation. If significant (over one 0.5 volts) differences are detected, problems ahead. Start cleaning the connectors.
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Switches and connectors always have their nominal resistance, but the voltage drop is so small that one cannot see the difference in new applications.
While measuring, activate the device you suspect in the circuit you want to measure: Depending on the on turned appliance power consumption, voltage level drops on the circuit. If wiring /connectors feeding the device are really badly oxidized, the circuit loses contact, and voltage drops to zero. Cleaning, rewiring is needed, also the device condition itself has to be verified (might be shorted).
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Engine Compartment Connectors:
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I opened all connectors under the hood in my Maxima. The car had originally contact grease on some (oh, why not all!) ABS connectors, rear reg plate light and some random places. I did add this contact grease to all connectors. It is done under good light, (+magnifying glass?), with a toothpick: one minuscle drop on each contact point supposed contact (the pin contact point is somewhat scratched). If too much grease enters, it will NOT (now have been convinced) short circuit the pins, but be careful not to spread it as all grease attracts dust. In case too much grease was entered, it has to be thoroughly cleaned. And do not forget the grounding points! See page 10 for groundings.
Just recently I found an superior silicone di-electric spray product. It will flow in places where access is restricted.
Maidenly view into the pastures of oxidation, Amp connectors, RH my VW glow plug ctrl relay
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Fuses
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Fuses can also be tricky: eye inspection and connectivity can be there, but under load they drop dead and do not connect. This happens quite seldom, but swapping similar fuses will clear this possibility out, its also quick check -method in darkness.
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Glycol
One special tricky condition: If the car history contains splashed coolant in engine bay or whatever, the Glycol residues are left in place. These are microscopic grains that will mushroom in moist weather ripping water from the air. The water conducts electricity, forming problems only on humid day. Washing with water thoroughly is the only way to get Glycol off - and thus gettin' soot flow into those badly shielded connectors...
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Relay packs
Maxima has few relay packs under the hood, a nightmare! They have good covers on top, but underbelly is somewhat open to the rushing wind while driving. This allows sand and soot to be pushed in, causing all kind of problems. For maintenance, the relays should be uninstalled one by one, contacts cleaned and tightened. The amp females connector edges can be slightly bent inwards to tighten them. Add very small contact grease tip on the relay amp contacts.
What to do for the relaypack open bellies? On some cases one can make/fill silicon to shield the system. Some silicon’s do contain aggressive oxidants, so getting directly on contacts might be counter productive. Whatever plastic shielding is done to hinder air circulation IN THE STORM WIND -condition is beneficial. (storm = u drive 80mph, do you?).
The 'funniest' place in Maxima is the front relay assembly under the coolant bottle, in front of battery. It is positioned to take in all incoming wind/soot. This pack has relay for ECU, tranny etc. One hurry morning as engine revs and nothing happens [ECU braindead =no power], take a look here. Or today, in advance...
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Conditions under the hood while driving:
Why are our cars such bellyopen soot -air scoops? Consider the amount of waste energy at full throttle: 2/3 of used gas goes away as heat (about 80kWatts). On Maxima it means that with your releases waste-energy you could heat 'ten houses' - all under the hood... Prom this perspective, the cooling airflow ("at storm -level") is very essential! Otherwise waste heat 'would melt the plastics' under the hood.
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Adding Di-electric Contact Grease
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On two sides of the battery, there are relay & fuse box; see page 5. The harness route into these boxes are partially open for soot travel during the highway 'stormy' conditions. They should be closed, but some drip openings should be left in case of water condensing inside.
Engine fuse/relay box at battery right side, Relay box under water container.
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Adding contact grease to a relay's contacts. Notice arrow pointed oxidation traces.
The contact grease should be used on all connectors under the hood: connector pins, relay pins, fuse pins, grounding connectors... On smaller connectors, use 'toothpick' to insert only minuscle amount only right on target.
I have now used a silicone based contact grease spray in the computer connectors inside cabin, works fine. Note: I used this thick grease on ABS computer pins, great! Volvo even recommends this grease on its poor quality fuses.
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What Is Di-Electric Grease:
I have been trying to mine info about this "di-electric grease". The more I try, the more I become assured that basically ALL grease is di-electric... If so, this "di" -title is used as a marketing gimmick to milk us with gorgeous prices: di-electric grease is std vaselin in gallons -or- $mall nice bottles; hopefully those pricey concoction (?) properties surpass vaseline.
If you know better, please inform... I'll continue to believe and to pay.
- "A dielectric, or electrical insulator, is a substance that is highly resistant to the flow of electric current... Dielectric materials can be solids, liquids, or gases... a high vacuum." copypaste from 'Wikipedia, the free encyclopedia'
- "A dielectric material is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic fields... Materials with moderate dielectric constants include ceramics, distilled water, paper, mica, polyethylene, and glass. Metal oxides, in general, have high dielectric constants." http://whatis.techtarget.com/definition/0,,sid9_gci211945,00.html
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Note: Di-Electric Grease should not be mixed with lube-substances manufactured specifically to conduct electric current, like some 'copperdust' etc. containing lubricants. (A di-electric grease conducts only through minuscle thin layer; no resistance measurement is possible with std multimeters.)
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This shop info page doesn't contain the di-electric word, but as far as I understand, the susbstance is the same, also known as 'contact grease'. Their article on connectors is excellent! See also their product variety...
http://www.echeloninc.com/contactlubrication.htm
Contacts "...microscopic examination reveals peaks and troughs on the surface and when the contacts come together, only the peaks are actually touching. The true current carrying surface area is therefore far smaller than it would appear. As the current is carried by a fraction of the designed surface area, the heat generated is concentrated at the peaks. This, in turn, causes the formation of high resistance oxide layers. As the resistance increases, more power is converted into heat leading to further oxidation. This spiraling effect creates hot spots reducing the efficiency of the switch and can cause complete failure as the two surfaces weld together.
The application of an Electrolube contact lubricant solves this problem. The lubricant film dramatically increases the effective surface area as, in thin films, the lubricants allow the passage of electricity. The switch now has the surface area that the designers planned. Hot spots are eliminated and the contact resistance remains low and stable. ...
Contact lubricants are specially formulated greases and oils that reduce friction and enhance the electrical performance of current carrying metal interfaces in switches and connectors. Electrolube products are electrically insulative in thick films, preventing tracking. In ultra thin films, i.e. between closed metal contacts, they allow the current to flow, owing to the "Quantum Tunneling Effect". They also exhibit a neutral pH thereby avoiding surface corrosion." ...check mentioned link for more.
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CRC Di-Electric grease product info datasheet:
http://www.sino-crc.com/images/product/crc/TDS/TDS-02083.pdf
Nota that CRC and other manufacturers have now this contact grease also in spray cans.
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!Note1:
First thing before working on car electronics and/or welding: disconnect battery negative cable..
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Microsoft Terror Coming?
Where are we going?
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- Microsoft has just (2005) formed alliance with Fiat to create software for its automobiles. Hello!? Virus infections from Fiat's on the highway? Call microsoft help desk from your stranded - what a nightmare. Viruses jumping from passersby?
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Detroit News Apr 2005:
"When Mercedes-Benz rolled out the new E-Class sedan in March 2002, the luxury carmaker said it had drawn a line with the past: The redesigned car would showcase Mercedes' new and improved quality. Three years later, Consumer Reports magazine rated the 2004 model-year E-Class the most unreliable car sold in the United States.
Time after time, Mercedes and its parent, DaimlerChrysler AG, claim to have identified problems plaguing the carmaker and addressed them. Executives have said repeatedly that the Mercedes cars coming off assembly lines since the beginning of 2004 were trouble-free.
Not entirely. Mercedes announced its biggest ever recall of 1.3 million vehicles last week, including sedans built as recently as March...
To some extent, faulty parts from suppliers and a huge infusion of electronic systems and cutting-edge gadgetry has undermined the quality of luxury cars. Rivals such as BMW and Volkswagen AG's premium Audi nameplate have been tainted, too, but not as badly as Mercedes, once renowned for its wonderful engineering and outstanding reliability...."
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By Christine Tierney / The Detroit News
http://www.detnews.com/2005/insiders/0504/05/C01-139820.htm
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I have seen an end of all perfection: but thy commandment is exceeding broad; Psalmist.
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