Tune up procedure XJ6 4.2 Liter Fuel Injected Models
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A customer recently asked me a question about a running condition problem on his 1986 XJ6. I had been meaning to write a procedure for a complete tune up routine as we do it in our shop for a long time. I decided to answer his question by describing what to do in the event of any running condition situation. Below is a helpful guide for all to follow but is specific to the Fuel Injected 4.2 Liter XJ6. Enjoy!
The first thing to do is cover the basics. Fuel filter, tune up, check fuel pressure and so forth. The tune up is an easy thing to say but there are allot of things to do that most "Mechanics" don't think about. Basically, it means to check, adjust and correct any issues relating to running condition. The basic tune up takes about 2 1/2 hours but if the basics lead you to other issues, that can add more. We are also assuming through most of this that your exhaust system is free flowing and the catalysts haven't started coming apart or melting interfering with the exhaust flow. One also needs to know that the valve condition, valve timing and so forth are good in order to expect the car to run properly.
When you suspect that the car is starving for fuel you might want to do the following before a tune up.
If fuel pressure is suspected, install the fuel pressure gauge and leave it on for the whole process.
The fuel filter itself isn't included in our basic tune up but if suspected, we change it before starting the tune up.
Run the car and check fuel pressure, test drive it to see if it still cuts out at the given RPM and watch the fuel pressure if it does cut out on you. If it doesn't, you might still have an intermittent problem anyway so your test drive might have to be extended. Another thing to check, if you have a car that's hard to start sometimes, is the fuel rest pressure. Note the fuel pressure while running. The fuel pressure will normally be about 32 psi at idle. It will fluctuate as a function of engine vacuum. It will increase under acceleration and decrease under deceleration. When you shut off the engine, the fuel pressure should hold around 30 psi. It's pretty normal for it to drop off very slowly but should maintain a pretty good pressure at least until the engine cools off. If it falls off immediately, your fuel pressure regulator or the non return (check) valve in the trunk could be a problem. If your fuel pressure does drop off, you can remove the air cleaner and turn on the key then when you reach inside the Air Flow Meter and push the flap open, a set of contacts will close in the Air Flow Meter causing the fuel pump to run. This will pressure up the system. As you release the Air Flow Meter flap, clamp off the feed line to your fuel pressure gauge. If the pressure still falls off, you need a fuel pressure regulator. If it doesn't, you need a non return valve.
f you find some problem with the fuel pressure through these tests you'll have to find it and fix it. There are also filters in each fuel tank and you may have debris in the system causing you to have to pull the tanks to have them cleaned out and sealed with a tank sealer.
The fuel changeover system can also play with you in those cars. So you might check to make sure the problem exists no matter which tank you are running on. If it happens when running on one tank or the other, you might have to investigate that system.
We only investigate the above if we suspect a problem there and it isn't part of a normal tune up
After you are confident that your fuel supply system is ok, you may want to do a compression test. This is something else that we do if we suspect a problem there and it isn't included in a normal tune up
Sometimes if we have a car that runs rough like it's missing on a cylinder or two, we'll do a compression test. That gives you an idea of how good will you be able to get the car to run. The Jaguar spec is no more than 5 lbs difference between the highest and lowest compression cylinders. In reality we normally see much more than that. Up to 15 lbs the car will be pretty smooth after doing all our tricks. But, the more the compression differences, the more the car will tend to idle rough. Compression is a function of the basic mechanical condition of the piston and bore condition, the rings, the amount of carbon buildup in the combustion chamber and on top of the piston, but most importantly it is a measure of valve condition. The amount of carbon buildup on the backs of the intake valves effects the amount of fuel/air mixture that will flow into the combustion chamber plus affects the smoothness of the mixture flow. Both the amount and flow greatly effect the running condition. While the carbon buildup will effect running condition, it will have little effect on the compression pressures.
Tune up:
If you haven't done so already, pull off the air filter canister. Visually inspect for vacuum leaks, you may want to run the car and pinch off all the vacuum supplies to various places to see if it makes any difference in running condition. If it does, chase down your vacuum leak and fix it. Use Carburetor cleaner to spray around the intake manifold gasket if you suspect a vacuum leak there. As this is sucked in to a leaky gasket or a bad injector seal the RPM's should increase and the running condition smooth out. Look at the condition of the air intake hoses that connect the Air Flow Meter to the Throttle body. Check the hoses to the Auxiliary Air Valve both on top and under the manifold. Sometimes one of those will pop off. While you are inspecting your vacuum hoses, replace any ones that are hardened or mushy. Under the manifold is a Dump Valve that is the source of a vacuum leak and we always get rid of it. There is one hose to it that goes to manifold vacuum and another that goes to ported vacuum. We take it out and connect the manifold vacuum directly to the supply for the ventilation system, removing the "T" in the line. We then connect the ported vacuum hose directly to the distributor vacuum advance module.
First, note which terminal on the distributor cap is connected to the number 1 spark plug. The brits numbered the engine from back to front but in reality it doesn't matter because it's a symmetrical engine. The point is to have your starting point when you go to re install the plug wires.
As part of your visual inspection, look at all the plug wires real good and see if any of them look like they're been leaking, looking for places close to the head where it looks like arcing has occurred, look for any deterioration or stiff cracking wires. Also look at the coil for evidence that it has been leaking oil out, look for loose terminals, cracks in the coil lead tower and so forth. If it has one of those ballast resistors hanging off the positive side of it, remove it and put a couple of spade terminals on the coil to reconnect the white wires to. This coil is a DAC3001 made by Ducellier in France that says on it "Use only with ballast resistor". But Jaguar officially came out and said you don't need the ballast resistor with this coil.
Then pull the wires out of the distributor cap and pull the distributor cap off and inspect it real good. Tune up kits with wires, plugs, cap and rotor are cheep enough so you might just want to change all of it as a matter of maintenance. But if you elect to not replace the whole tune up kit, you can clean the distributor cap by scraping the carbon from the terminals inside it. Check in the plug wire terminals for corrosion or cracks in any of the plug wire towers. Look at the center carbon brush and make sure it isn't stuck way up in there or there isn't any abnormal wear on the surrounding plastic. Sometimes the motion shaft of the distributor will come loose and as the car runs it will push upwards against the plastic and wear this area. Also look for cracks and tracking. Before you pull the rotor off, work it counterclockwise and let go to make sure it moves, about 10 degrees more or less depending on the year model, and snaps back. This will tell you if the mechanical advance mechanism is working properly. If it's stuck or sticky, you may be able to spray some penetrating oil down the shaft and get it freed up but chances are you're going to pull the distributor and take it all apart to clean, lube and repair as necessary. If you're ok there, check the vacuum advance by connecting a vacuum hose to it and either using a hand vacuum pump or by sucking on the hose, make sure the vacuum advance module holds vacuum and that it operates the motion plate in the distributor. Also take hold of the distributor shaft and push it one way then the other to check to see if there is an inordinate amount of slop in the shaft. Usually when the bushing wears out on the shaft it's due to lack of oiling which is accomplished by oil pressure from the engine oil pump. The passageways occasionally will become blocked up. I've had cars with allot of slop in the distributor that would get to a certain RPM and the shaft would start vibrating back and forth like the shaft in a worn out electric motor. They usually make a buzzing noise and the engine will cut out because of the signal interruption occurring by the reluctor moving in and out of range of the pick up module. Speaking of that, check that the reluctor is held static with the motion shaft. There is a little plastic ring that locates the reluctor to the shaft. Then bump the engine around until one of the points on the reluctor aligns with the metal point protruding from the pick up module. Then, while holding the shaft towards the pickup module to take out the slack in the distributor shaft, using a non magnetic feeler gauge, we have brass ones, make sure the gap is .010". The two screws holding the pickup module onto the motion plate can be loosened and the gap can be adjusted. Whether you're replacing the rotor or just cleaning the old one, we always polish the tip of the rotor on our jewelers wheel. It helps to lower the spark resistance. Now you're pretty much done with the distributor except for setting the timing which comes later.
If you haven't pulled the plugs already, clean around the plugs real good so crap doesn't fall down in there. I usually loosen the plugs a bit and blow around them with compressed air. Replace the plugs, in the 4.2 Liter XJ6 with Champion #38 plugs. These are non resistor plugs. Jaguar recommended resistor plugs but this is only for radio noise suppression. You have resistor wires and that's all you need for noise suppression. The resistance of the resistor plugs is very inconsistent. This results in a less consistent spark and a weaker spark too. Gap the plugs at .035", this is for all 4.2 Liter XJ6's with catalytic converters. The spec is 0.25" for non catalyst cars. Then apply some anti seize compound to the threads and put them in. You're ready to re wire it now so install your cap and rotor and route your wires and hook them up. Starting from #1 that you noted before you started, wire them counterclockwise in the order 1 5 3 6 2 4.
Get the crankshaft where you can see the timing marks. You'll probably have to clean off the timing marks and we usually use correction fluid to mark 0 degrees or the TDC Mark. Depending on what kind of timing light you have, you may want to mark the 17 degree mark. Actually the pulley is graduated in even increments so you'll see 16 and 18. Anywhere in there is ok. Note that this is different for earlier cars. This spec is for fuel injected models only. Early models can be 8 degrees BTDC or 10. I think some of them were 12 too. Now you're ready to start the car. Hopefully you wired it right and it will start. You can use either #1 or #6 to hook your timing light to and check the timing. If it's off, shut off the engine and loosen the 7/16" bolt that holds the distributor in place. Counterclockwise rotation retards the timing and clockwise advances it. Oh, The instructions recommend that you disconnect the vacuum supply to the vacuum advance before timing it. Actually with a closed throttle, there should be no vacuum to the vacuum advance anyway so if your plumbing is correct, and the throttle body is properly adjusted, you don't need to disconnect it. If in doubt, disconnect it. Once you have the timing set correctly, the ignition portion of the tune up is finished.
Now reach inside the Air Flow Meter and operate the flap all the way open several times. Each time try to put a slightly different bias on the flap. You're trying to see if the flap, at any point fowls on the case. if it does, the flap is bent or the fulcrum is worn out and this can interfere with it's movement at any RPM and cause the car to stumble or cut out. If it's bent, The Air Flow Meter needs to be replaced. Then you're going to want to pull off the air intake bellows, the air intake elbow and the air intake hose all connecting the Air Flow Meter to the Throttle body. Get some carburetor cleaner on a rag and hold open the throttle body and clean it real good and clean around the edge of the throttle butterfly. When you have it clean, close the throttle and slip a .002" feeler gauge in between the throttle body and the butterfly. There is a throttle stop with a lock nut on it, it looks like a 5/16" but it's actually a 0BA size. A sloppy 5/16 wrench will work. Loosen the throttle stop locknut and adjust as necessary to have a nice tight fit with your feeler gauge and then lock down the throttle stop locknut. Then you can put the air intake plumbing back together. You will need to run the car up to operating temperature now and adjust your idle. We usually set them at about 800 RPM. The idle adjustment screw is an Allen screw that is located in an aluminum housing on top of the plenum part of the intake manifold just to the engine side and under the Air Flow Meter. It takes a 7/32nd Allen wrench to adjust.
You're almost finished...yippee!!!
At this point you might want to stop where you are. But if you're as obsessive as we are, you will want to tweak your Air Flow Meter for optimum running. There's a little trick that I call the capacitor trick that we do to the wiper circuit, the circuit that actually sends the signal to the computer on the Fuel Injected Series 3 XJ6. Jaguar came out with this as a modification for 86 and 87 models but we've found that it helps all of them. This isn't a part of a regular tune up but if you love your car, do it. The specific symptom that brought this up originally was the car running rich when cold. Sometimes they would blow black smoke and sputter like you can't imagine. Anyway it is due to a dirty signal being generated by the Air Flow Meter. Although this modification was brought about from the rich running situation, we find it helps the cars run more smoothly by filtering out some of the voltage spikes that can occur by the mechanical nature of the Air flow Meter. If you are going to do this, you want to do it before trying to adjust the Air Flow Meter.
Capacitor Trick:
Using a 24 or 25 volt 150 to 200 micro farad electrolytic PC mount capacitor, these are available at any Radio Shack, pull back the rubber boot to the Air Flow Meter connector. You will have to strip a small, about 1/8" section of the Pink and Yellow Wire and the Pink and Green Wire going into the connector. Solder the negative side of the capacitor to the Pink and Yellow and the positive side to the Pink and Green. Pink and Yellow is pin 6 and Pink and Green is pin 8. Then pop the boot back over the connector with the capacitor inside.
Air Flow Meter Adjustment:
You might find out you need an Oxygen Sensor in this step. We use a Snap On Vantage graphing multimeter to monitor the Oxygen Sensor voltage. An oscilloscope will work too. You basically need a multimeter rated for work on computer circuits. A regular multimeter will blow the ECU (Electronic Control Unit) for the fuel injection. It also helps to have the graphical representation of the voltage that's available with an oscilloscope or graphing multimeter but you can do without it. Another device we use to set up Air Flow Meters is our 5 gas exhaust analyzer but you probably don't have one of those in your pocket. The Oxygen Sensor gets a 5 volt reference signal from the ECU. When the mixture is correct, the voltage while operating measured at the Oxygen Sensor lead with the sensor up to full operating temperature, should oscillate between .2 and .8 volts. The more regular the oscillations, the better the car is running. The Series 3 XJ6, as with all earlier cars, typically have a pretty sloppy signal coming out of them so don't expect a sign wave. You should monitor this voltage before screwing with the Air Flow Meter because you may not have to mess with it or you may only have to adjust the external adjustment. Towards the engine side at the rear of the top of the Air Flow Meter was originally a aluminum plug. If that's still there, you'll have to drill a hole in it and thread a screw into it to grab onto and pull it out with a pair of pliers. I have seen 2 versions of the adjusting screw in there. One takes a 7/32" Allen wrench and the other takes a blade screwdriver. All you are adjusting here is an air bypass passageway and by allowing more or less air to bypass the flap, it effects the position of the wiper connected to the flap in relation to the carbon strips that the wiper runs on. If you can achieve good Oxygen Sensor signals at both idle speed and cruise speed by just adjusting this screw, don't go any farther. By cruise, I mean to increase the RPM to around 2000 to 2500 and hold it there for 30 seconds or more and re check your Oxygen Sensor Voltage. If you still think you need to tweak the Air Flow Meter more, there are 2 more adjustments you can make to it. You will have to pry the black plastic top off of it to access these adjustments. After you pry it off, take a razor knife and clean all the sealant that glued it on off around the edges and out of the groove in the lid. Be careful when you pry the thing off there because they usually are very securely attached and you probably won't find a replacement if you screw it up. When putting it back on, we seal it by applying a bead of black silicone sealer RTV in the groove on the lid and pushing it back into place. After you have the top off you will see a wiper that is connected to the flap. You can push the flap open and watch it move. Inspect the carbon strip to make sure it isn't worn through. Typically this happens right in the idle area of it. First of all, screw the external air bypass screw all the way in then back it out 4 full turns. Inside the Air Flow Meter, you'll see a little silver rod that goes over and works on a set of contacts. When the engine is not running, the contacts should be open. These contacts operate the fuel pump relay. what you want is for the basic position of the wiper to barely open these contacts. We usually find that they are open too far. There is a Phillips screw that you can loosen and move the wiper assembly in relation to the air flap. You want to turn the key on but not start the engine, and move this so that it just opens the contacts and lock it down. Sometimes we find that by doing this, if the little silver arm is not correctly formed or is bent, that the base position of the wiper on the carbon strip is too far off to get correct adjustment out of it. If this is the case, it will be obvious when you are running the car to adjust the spring tension and do any final tweaking on the wiper to air flap adjustment. If necessary, you can bend that little silver arm a little. I guess I should mention that sometimes I'll find corrosion inside the Air Flow Meter and it may be necessary to use some tuner cleaner to clean up the electronics. Of course if it's too bad, you'll wind up replacing it anyway. When you have the wiper assembly where you think it needs to be, carefully open the flap all the way to it's limit. The wiper contacts should not go past the end of the carbon strip. If it does, you'll have to reset the wiper to flap adjustment and bend the little silver arm to get the contacts to open the way they should. When this is all set up you can start the car and run it to operating temperature so the Oxygen Sensor is working correctly and check the voltage. At first, before the Oxy sensor is up to temperature, you will see higher voltages and be able to watch them come down steadily as it heats up until it reaches it's normal operating range and starts oscillating. If it never does, you either have the mixture all screwed up or the oxy sensor is bad. You can play with the Air Flow Meter and purposely lean it way out to test for either situation. At this point, assuming you have it close, try adjusting the external air bypass screw to see if you can get the idle mixture correct as far as the oxy sensor voltage is concerned. If you get it where it needs to be, increase the engine speed to about 2000 or 2500 RPM and hold it there for 30 seconds and check your oxy sensor voltage. If it's correct, glue the lid back on and go down the road. If not, you will see a toothed wheel with a spring inside it, you can rotate the wheel to increase or decrease spring tension. It may be necessary to change your wiper arm to flap adjustment and the external adjustment a bit to wind up with something that puts all 3 adjustments in synch and to have your oxy sensor voltage correct at both idle and cruise speeds. Ideally, you want to see the spring very uniformly wound, not so tight that it is biased with all the windings toward the wheel's center and not so loose that the windings are toward the outside of the wheel. You also want to see that the wiper arm's travel doesn't run it off the carbon strip and that the external adjustment allows you to adjust the Air Flow Meter some in both directions. When it's right, you can turn the external adjustment and watch the flap, or wiper, move up or down.
If your problem continues, it's not a bad idea to change the coolant temperature sensor for the fuel injection. After that, if you still have a problem, you'll have to start continuity testing the wiring harness between the injection hardware in the engine compartment and the ECU or suspecting the ECU itself. The best way to test the ECU is by substitution.
One other note. The ECU on these cars do not sense battery condition. A very important thing to check or to go through is grounds and power supplies. The positive power to feed the main relay and in turn the entire fuel injection system comes from the left hand bulkhead connector just to the inside and below the battery on the firewall. The nut is a 5/16 British Standard brass nut. It's just bigger than a half inch. A 13 mm wrench or socket should do the job. You'll have to take the battery out to take this apart and sand all the ring connectors. It's a good idea to use a di electric grease to prevent corrosion on these and the battery terminals. We use a product called Super Lube. Then there is a gang of black wires connected to the rear of the water rail, it's that black aluminum housing that the coil sits on top of that runs the length of the manifold. This gang of ground wires is the ground point for the fuel injection system and is very important and the source of many problems because the bolt that goes through there likes to get corroded by its exposure to coolant, heating and cooling, and the fact that electrolysis likes to occur when you have 2 different kinds of metal in contact with each other. Take out this bolt, and clean all the ring connectors there and coat with the di electric grease. The engine ground is also important to make sure it's clean and tight. It's located on the right side of the bell housing and connected to the frame of the car. Take it apart and clean it up good while you're at it. If that connection isn't good, none of the other connections matter.
That's about as complete as I can think to make this. I hope it helps.
John McKeel
Jaguar Services of Tulsa/Lister Components & Cars
3112 E. Admiral Pl.
Tulsa OK 74110
Phone 918-664-4206, 918-836-5344
Fax 918-398-9472
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