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Pete's Buick

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Any owner of an old car will be quite conversant with being under the hood, or flat on his or her back for the afternoon. This is not the problem, as working on the beloved automobile is supposed to be part of the enjoyment of ownership. The problem really starts when you arrive at the corner parts store with the offending part, which you have just wrestled off the car, and say, " I need one of these". To which the reply might be, "What year did you say ", or, " Sorry that's a dealer part". On arrival at the dealers the answer to your question may be something like "Sorry my computer does not go back that far ", or, " This part is no longer manufactured". Of course the next stop is the wrecking yard where the answer might be " Oh! we just crushed one of those yesterday". Most likely you will find the part to be scarcer than hens teeth at a duck farm. If you should be so lucky to find a part, it will probably be in worse condition than your own. So where to now? If you have to have an original part , the only alternative might be to get the part rebuilt at a auto restoration shop. This is of course expensive, if it is an unusual part. Perhaps a more inventive solution is possible. Such as determining exactly what the parts function is, and trying to find a more modern equivalent for substitution. Another possibility is to cobble together an assortment of parts to perform the same function. This is what I am intending to show in the coming text. The subject of the article is a 1978 Buick Le Sabre Sports Coupe with a 3.8 Litre turbo engine.

THE TURBO CARS

I have no intention of giving a full history of the turbo cars, as there are many other sites that deal with this subject in detail. A brief overview will put into perspective what I am trying to achieve here. Buick introduced the V6 turbo cars in 1978. The purpose was to get better fuel mileage than the V8. Not only was this achieved but a better performance was also realised. Improvements and innovations increased the performance of these cars right up to the end of production in 1987.Some of those innovations included Electronic Spark Control, Direct Ignition System and Electronic Fuel Injection. Although the 1978 versions were fraught with problems, the culmination of the series, the GNX was considered the fastest production vehicle of its time.

The pre-1984 cars used 2 or 4 barrel carburetors, with a vacuum controlled device [ Power Enrichment Control Valve ] to control the power valve in the carburetor, and Electronic Spark Control. It is these two devices that I wish to address here.

PECV [Power Enrichment Control Valve]

This is one of those parts that are unobtainium.

This valve is used to control the Power Piston in the carburetor, to increase the fuel delivery during boost conditions, and prevent boost pressure from reaching the power valve. It is screwed into the top/front of the manifold where it senses the vac./boost pressure. There are three other vac. lines connected to it. The centre port is connected to the carburetor power piston and controls the richness of the mixture. The other two ports are connected to the carburetor vac. source and the vent of the carburetor.

Below the valve threshold, the carburetor power piston is connected to the carburetor vac. source and is controlled according to the engine load. As the pressure increases to a point above the valve threshold the carburetor power piston is connected to the carburetor vent. This allows the power piston spring to lift the power piston fully and the carburetor goes to full rich.

When the diaphragm in this valve fails, the carburetor power piston will most probably see positive pressure under boost, leading to a lean condition. There are then two choices, connect the carburetor for a full rich, or full lean condition. Neither of these choices is good. Under full rich conditions the fuel consumption will be atrocious, and excess fuel will wash the oil film from cylinder walls causing premature wear. The full lean condition will cause detonation on boost. Either of these conditions can result in severe engine damage.

PECV ALTERNATIVE

This is the simplest option I have found and will give better results than the full lean or full rich conditions. It only requires obtaining one part from your local parts store or wrecking yard, and a simple bit of wiring. The part required is a "three port vacuum switch". I obtained mine at the wrecking yard from some unidentified Japanese car. Any three port switch will work.

To get power to energise the switch, connect it to the yellow boost indicator light. I found on my car that the yellow light comes on at zero boost, and the red light comes on at about 5 P.S.I.. On the firewall there are two vacuum switches which operate the boost indicator lights,one for the red and one for the yellow light. Check the switch that operates the yellow light for the ungrounded side. This is where one side of the three port vacuum switch should be connected. The other side of three port vac. switch should be connected to a 12 volt switched source. With this wiring the switch will change the power valve from vacuum control, to full rich, at zero P.S.I..

The original PECV should be removed from the manifold and the hole plugged. Three vacuum connections are required. The common port of the vac. switch should be connected to the power valve port on the carburetor. The normally open port should be connected to the manifold vac./boost port, and the normally closed port to the carburetor vent port. It will be necessary to use some "T" connections to accomplish this, as you do not want to disconnect any other original vacuum connections.

INSTALLATION

The installation is simple and only requires finding a place to mount the three port vac.switch, and then piping it into the system as shown. The switch should be mounted as close to the boost switches as possible to avoid long vac. lines. Only two wires are required, one from the boost light to the vac. switch and one from the vac. switch to a 12 volt switched source, as shown in the wiring diagram. Under the dash there is convenient grommet where the wires can be passed through from the cockpit to the engine compartment. The grommet is located just above and to the right of the steering column.

If the vac. switch ports are not identified, mine were not, they can be identified in the following manner.
Blow through the ports. The two that you can blow through are the common and normally open. Now energise the switch and blow through again . The ports you are now blowing through will be the common and the normally closed. The common port will be that which you can blow through under both conditions.

TEST AND ADJUSTMENT

To test the function just drive the car and listen for a click as the yellow light comes on. This is the vac.switch switching, at which point the carb. goes to full rich. There are no adjustments to be made because the whole process is controlled by the boost light switch.

ESC { Electronic Spark Control }and PECV COMBINATION

The ESC was a device used by Buick to control the spark advance and retard. I have had no luck in obtaining a schematic for this device so I do not know it's exact function. However, from my own experience, the Buick manual and other references I believe it to work something like this. A Knock Sensor [ a piezo electric device which develops a voltage under pressure ] is screwed into the manifold and detects the vibrations of detonation. This signal is processed by the ESC [ turbo control centre ] and results in the ignition timing being retarded until the detonation stops. This retard can be as much as 20 degrees depending on the severity of the knock. As you can see from this brief description this is a post problem device. In other words the retard sequence is not initiated until the detonation has occurred. This is OK as a safety device to stop detonation under adverse conditions, but from my experience this device is controlling the ignition under all boost conditions.

When detonation has already occurred, it takes more ignition retard to quench it than it would have taken to prevent it in the first place. As an example, if the engine starts to detonate at say 5 P.S.I. it may take as much as 5 or 6 degrees of retard to quench the detonation. However if the ignition was retarded initially 2 or 3 degrees at this point, the detonation would not have initiated. Of course this is all a delicate balancing act, and I am not sure exactly how this was managed in the Buick device. If anyone can give me more details of this device it would be more than welcome.

I was experiencing lots of detonation problems at WOT [ wide open throttle ], and assumed, after lots of tests, that it was the ESC to blame. I was later to find that the ESC was indeed functioning. However, having already designed the device, I built it and installed it anyway. The performance of the car was vastly improved. The detonation stopped and the acceleration improved. All of this is by "the seat of the pants method" and I can not back this with numbers. Yet!

OPTIONS

There are three basic options available commercially to retard the ignition. The first is a unit which will give a fixed amount of retard over the full range of the distributor settings. The MSD unit used in this project is an example of these. Using this is like advancing or retarding the distributor, except of course it can be done from the drivers' seat.

Then there is the type that retards based on boost pressure. These will generally give a fixed amount of retard for each increase in boost of one P.S.I.. For example, dial in one degree of retard and you get one degree at one P.S.I. and ten degrees at ten P.S.I..

The final option is the fully programmable. This can be set up with a lap top computer and will of course be totally flexible.

The first two types are relatively cheap but have some obvious limitations. The programmable type overcomes these limitations but at considerable cost. The circuit I have built is a compromise between the first types and the fully programmable. It can be built for about $200 -$300 and has "programmable" functions as well as in-cockpit adjustments.

Before entering into this project the minimum gauging in the car should be WATER TEMPERATURE and BOOST GAUGE.

CIRCUIT DETAILS

I have no intention to give a detailed description of how these circuits work, because they are standard electronic building blocks. If you are interested they can be found in any I.C. [Integrated Circuit] manufactures data book, where you will find more than enough information. However a description of the interfaces to the car electrical system is in order.

Thecircuit starts with a MAP [Manifold Absolute Pressure Sensor] sensor. An ideal device can be obtained from GM as Part# 16009886, or from an after market source. This part is a 2 bar [2 Atmospheres] device, and will measure from 25 in/hg to 15 P.S.I..The MAP sensor tells the control circuit the vac./boost conditions present in the engine manifold. A return signal from the MAP is processed, by the Ignition Control Unit, to control the three port vac. switch and the MSD unit. The point at which the power valve changes to full rich, and the level of boost at which the timing is retarded, can be adjusted with the front panel potentiometers. The front panel controls enable the full rich condition to be adjusted from 25 in/hg to 0 P.S.I., and the retard point from 25 in/hg to 15 P.S.I.. There is also some internal "programmability" which I will deal with later. The power supply, which will accept all the voltages produced by a normally functioning car system, has output voltages available to power the circuit, and provide a stable voltage to power the MAP sensor.

CONSTRUCTION

The purpose of this article is not to give a tutorial in electronic circuit construction, so a brief outline of some considerations will be given. Although the circuit is relatively simple and cost effective, some electronic

The pictures shown here are of the finished enclosure, and an internal view which will give some idea of the construction techniques I used. The circuit has no critical stages and can therefore be built using any construction method that you may prefer. I used perfboard. Choose an enclosure of proportions to contain the board, and of whatever style pleases you. The enclosure I used is large enough to accommodate any future circuits that I may want to add. You may want to choose a smaller enclosure and layout the front panel in any arrangement that pleases you.

It is desirable to use I.C. sockets to prevent damage to the I.Cs while soldering. The relays are also socket mounted for the same reason. The transistors tend to be a little more robust and do not need this treatment. All of the other components are simply pushed through the holes and soldered on the other side. I used enamelled wire for all of the under side connections, and some thin single stranded wire for the plug wiring. The parts list shows all of the items required.

Heat sinks should be used on the power supply regulator and the power transistor that drives the three port vac. switch. Some heat will be noticed in these heat sinks, but they should not be unbearable to the touch. The picture shows that large heat sinks are not required and any small available heat sink will suffice. The ones I used are different only because they happened to be at hand.

The plug and socket, to connect to the car's wiring, can be of any type as the amperage on all of the wires is low. However, some consideration should be given to the physical strength of the external wiring, to the engine compartment, to enable it to withstand the rigors of the under hood environment. The size of the plug and socket has to be of sufficient proportion to accommodate these wires. I used a sub "D" plug and socket which proved to be large enough.

You can see that I have fitted a fuse inside the unit, but I believe that an external car type in-line fuse should be used in this application, and the wiring diagram shows this. Some of the resistors can be seen to have been paralleled, this was to increase the brightness of the LED's, as I found them not to be bright enough when installed in the car. The wiring diagram and parts list reflect these changes.

INSTALLATION

The installation diagrams show the entire "in car" connections. There are two possible ways to install the Ignition Control Unit. The first, and preferable way, is together with the ESC unit. This will give the advantages of both ESC and the Ignition Control Unit. In this case use the "with ESC diagram". However, if your ESC unit is beyond use, in other words the car will not run with it in place, then use the "without ESC diagram" , which shows the installation without the ESC connected.

A wire type that is robust enough to withstand the under hood environment should be chosen. Choosing a different coloured wire for each function will make life a little easier. IE; Black for ground, Red for 12 volts, etc.. Mounting the Ignition Control Unit unit, MSD unit and the map sensor using Velcro avoided drilling holes, and damaging possibly irreplaceable parts. The map sensor was mounted on top of the heater box as shown. Mounting the Ignition Control Unit unit under the dash, as shown, makes the ashtray inaccessible. You may find a better spot. The MSD unit is not waterproof and it is therefore not advisable to mount it in the engine compartment. I mounted it up under the dashboard. I found a grommet, under the dashboard just above and to the right of the steering column, that allowed all of the required wires to pass through to the engine compartment. The use of spiral wire covering, on the under hood wiring, for protection is advisable. If you can find a matching plug and socket to the distributor/ESC connection, it would be possible to install the unit without damaging the wiring. I could not, and I had to use Radio Shack connectors as shown in the photo . Not a pretty sight!

The vacuum connection to the MAP unit can also be seen in the MAP sensor photo. The three port vac. switch is mounted and piped as previously shown in the PECV section.

TESTING AND ADJUSTMENT

When the installation is complete, testing and adjustment should be carried out before driving the car. DOUBLE-CHECK all wiring in the car and in the unit BEFORE turning on the ignition. Before connecting the unit to the car wiring, adjust the potentiometers. The front panel potentiometer [ R7 ] that adjusts the PECV and the other seven retard potentiometers [ R9 ] should be adjusted fully clock wise. The internal potentiometer [ R21 ] should also be adjusted fully clockwise.

Plug the unit into the car wiring and turn on the ignition. If everything has gone according to plan the green power light should illuminate and no smoke appear. If this does not happen turn the ignition off and re-check all of your wiring.

With the ignition on, turn the inside potentiometer [ R21 ] counter clockwise until the red light just comes on. This is setting the upper limit of the change from vac. control to full rich condition. This should definitely not be set higher than atmospheric pressure as you do not want boost going to the carb. power valve. You can turn the potentiometer back and forth a couple of times to ensure it is set correctly. You should hear the three port vac. switch switching on and off as you do this. It should be left just in the "on" position. Next turn the retard potentiometers slowly counter clockwise until the yellow lights comes on. This is finding the atmospheric pressure [ zero boost ] position. Remove the knobs, without disturbing the potentiometer's position, and re-set them with their indicating markings in the vertical position. Now the potentiometers are adjusted to give 0 P.S.I. to 15 P.S.I. when turned clockwise from the vertical, and 0 to 25 in/hg when turned counter clockwise.

Now start the car. All of the lights should be off except the green power light, which will remain on whenever the ignition is on. Before driving the car turn all of the Front panel knobs to their fully clockwise positions.

Test-drive the car. With the knobs in this position it should drive normally. The red light should come on as the boost gauge registers 0 P.S.I.. You do have a boost gauge don't you? If any detonation occurs below zero P.S.I. there is another engine problem that should be fixed before continuing.

This next stage of adjustment could be hazardous to your health and condition of your car! The car will be travelling at high speed and it is essential to have a co-pilot to assist you. Do not do this on your own!

If you have built this project it was to eliminate the detonation problems that you have been having. We now get down to the nitty gritty. In order to get a good adjustment the car has to be driven at a steady pace, and with no gear changes inter-fearing. It should also be at full operating temperature. Drive the car at 0 P.S.I. as long as you can without endangering yourself, your co-pilot or incurring the wrath of the local constabulary. I would expect there to be no detonation involved in doing this. Slow the car and repeat this process at 1 P.S.I.. Continue to repeat this process increasing the boost 1 P.S.I. at a time. At some point audible detonation will occur. When this occurs repeat the run at 1 P.S.I. below the detonation point, and get your co-pilot to turn the first of the retard knobs counter clockwise until the corresponding yellow light comes on. You have now set 2 degrees of retard at that P.S.I.. [ Why 2 degrees? Each knob represents 2 degrees. Check the "programming and modification" section for details. ] Slow the car and repeat the run at the P.S.I. that the detonation first appeared. It should no longer detonate. Continue to repeat this process using each knob in turn until you reach the maximum boost pressure. You will by now appreciate having a co-pilot to help in this process. At this point it should be possible to do a full throttle acceleration, at maximum boost, without incurring any detonation. If detonation should occur during gear changes, a likely situation due to boost spikes, dial in a further 2 degrees at a level just above the last level that you set.

Retarding the ignition too much can be just as damaging to the engine as too much advance. Typical results of ignition timing that is too far retarded are; loss of power and engine over heating. You do have a temperature gauge don't you?

When should the PECV front panel knob be adjusted? Maybe never! As you rotate the knob anti-clockwise the point at which the carb goes to full rich will increase in hg/in [ lower pressure ]. In other words the carb will go to full rich sooner on the acceleration curve. More gas sooner. Why would you want to do this? Although this adjustment will only effect the carb. air/fuel ratio below the zero boost level, some advantage may be found at the drag strip. For instance it is customary to load the torque converter at the line to give maximum acceleration when releasing the brake. If the car is incapable of "getting into boost" at this point [which a standard car may not] it may be advantageous to increase the carb. richness, and get a quicker get away from the lights, sorry I mean "tree".

It is detrimental to the engines longevity to run it too rich. The excess gas will "wash" the protective oil film from the bores, and piston rings, causing metal to metal contact and increased wear will be the result. Some of the signs of too richer mixture are; loss of power; increased fuel consumption; black smoke from the tail pipe; a dry black deposit in the tailpipe. [ A black sticky deposit is a sign of oil burning.]

"PROGRAMMING" AND CIRCUIT MODIFICATIONS

Earlier I said that each retard knob represents 2 degrees of retard. You are probably thinking that 2 degree steps are too large for achieving optimum timing. With 2 degree steps it is possible to optimise the timing to within +/- 1 degree at all parts of the timing curve. Most engines will not object to being within 1 degree, and it will probably suffice for "seat of the pants tuning". If you have access to a dyno., or your rear end is more sensitive [ I am not talking rear axle ratios here ] to these adjustments, then there are some "programming" and circuit modifications that can improve the accuracy of the timing curve.

The MSD unit used in this project is capable of 15 degrees of retard/advance. The original control is a 10K potentiometer. From the circuit diagram it can be seen that this potentiometer has been replaced by resistor chain R14 thru' R20. Seven steps for 15 degrees is equal to approximately 2 [ 15/7 = 2.14 ] degrees. If you wish to change the size of the steps, it can be achieved with a few assorted resistors and a deft flick of the soldering iron. If you substitute 680 ohm, 330 ohm or 150 ohm resistors in the resistor chain, they will approximate 1, 1/2 or 1/4 degrees of retard respectively.

NOTE WELL : The resistor chain must add up to approximately 10K at all times. [ +/- 500 ohms ]

If you decided to have two 2 degree, two 1 degree and three 1/2 degree steps, the total resistance value would be 5350 ohms. Therefore it would be necessary to add 4650 ohms resistance to the chain to maintain the original 10K value. A standard value resistor of 4.7K [ 4700 ohms ] would fit the bill nicely in this example.

If you alter any of the resistors from their initial 1.5K value, you will change the total amount of retard available to you. In the case above there will be a total of 7 1/2 degrees of retard available. This may be enough for your purposes. However if you require finer degree adjustment and the full 15 degrees of retard, this can also be achieved. If for instance you add two more LM 399 ICs to the circuit and build eight more Ignition Timing Circuits, for a total of fifteen, you could now have 15 steps of 1 degree. Mixing and matching the number of circuits and the resistor values will give you any ignition "curve" you may desire. This is not lap top technology, but it works for the price.

The ignition timing front panel knobs, as shown, have a full range from 25 in/hg to 25 P.S.I.. You may not require any retard in the vacuum range. Changing the range to cover boost only, will make the adjustment less sensitive and easier to adjust. This can be accomplished by inserting a 10K resistor and a 20K multi-turn potentiometer, in series, between R9 and ground. This is similar to the PEVC circuit.

The LEDs on the front panel can be varied in brightness. You may find them too bright at night or not bright enough in daytime. The resistors R6 and R10 control the brightness. Reducing the resistor's value will increase the light output, while increasing the resistor value will decrease the light output.

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