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90 XJS V-12 High Idle

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PPS, Michael If your plugs have bemome carboned up, that is also a source of incomplete combustion. Clean them up or get new ones. I recommend Champions rather than Bosch or NKG. They seem to last longer.
 
PPPS, Michael, I keep getting second thoughts after I send messages. In checking the fuel injectors, not only check actuation and spray pattern, also check for stuck "on" operation and dribbling while not being pulsed. Dribbling (dripping under pressure while not being pulsed) is a very common cause of rich running. I cannot stress the importance of measuring correct fuel rail pressure. You need a pressure gage with a range of up 100psi. While testing the injectors, I vary the rail pressure with a controllable source to look for performance clues between 20 to 80 PSI. On the earlier model Jaguars without OBD 1 or 2, I keep a suppply of ECUs and control modules to use as substitutes; they prove to be efficient and accurate diagnostic tools for the type of drill you are going through. Make sure that a substitute ECU is correct for your application (V12 with Marelli). I realize that this is coming late in our discussions, but a properly running V12 should have the exhaust throb more like a six rather than a V8. Very constant with a minimum of "puffing" at the tail pipe at idle. A V8 throb suggests missing cylinder detonation on a 12. What does yours sound like? If you have an irregular exhaust throb you can locate the culprit cylinder by pulling off spark plug wires and listening for any differences including a slow down in RPM. If you have a bad cylinder (either ignition or fuel injection) you will not hear or see a difference with the culprit wire off of the plug or distributor cap. Forgive me if this sounds too basic but I am trying to cover all pssibilities.
 
Surgery went well last week, although I'm not to fond of the physical therapy.

Back to the problem:

When attempting to depressurize the fuel system to run the compression check, the boost pump would run with both fuel system relays removed. I encountered this once before and found that the O2 sensors were carboned up. I had saved the original sensors when I replaced them at 50K miles. I temporarily installed the original sensors and the problem stopped. I then cleaned the newer sensors with brake cleaner and reinstalled them during the prior incident. I'm going to look at replacing them as soon as I can crawl around on the garage floor.

The pump does shut off when the system is pressurized though.

I'm going to follow John's advice and replace the plugs at this point as well.

More to come.
 
I forgot to mention, I have two coolant temp sensors in addition to the temperature guage sender. On the right side is the green sensor and the temp guage sender both mounted on the coolant rail.

On the left is a white sensor identical in appearance to the green sensor other than the color.

I'm going to read up on testing both.
 
Michael, Your discussion of the boost pump is confusing. I gather you are calling the fuel pump the boost pump. The fuel pump on your model was a single pump that derived about 80psi unregulated pressure. Later models beyond 91 began to use two pumps that were a normal pump and a secondary to handle high throttle loads and triggered by a seperate relay (in the trunk) Does your XJS have two fuel pumps? That is not a standard configuration. In normal operation the single fuel pump runs when you hit the starting position on the ignition key and continues to run all of the time that the engine signals that is is running. If you have an alternate configuration, that might be the source of some of your problems depending how the two fuel pumps are hooked up. They should be in parallel, not in tandem. For now I would use only one pump as per the original configuration. Look underneath your battery mount in the trunk and find out how many fuel pumps you have. Two pumps in series could swamp the fuel pressure regulators and cause a rich mixture. Install fresh spark plugs and while your at it run a compression test on the engine. Are you using a fuel pressure gage to measure the 40 psi on the rail? That is very important for ;your fuel injection. (different subject) Happy to hear that your surgery went OK. The physical therapy is very important though painful for a satisfactory result for your ne knee. Give it all you have and you will be back on full power in a month. Best regards, Jack Farrington
 
PS, The coolant sensors should both have about 3K resistance at 20 deg. centigrade. This resistance is critical for proper fuel/air mixture. The documentation will give you a range of resistances vrs. temperature. Check them out through the range between 0 and 200 deg. The color of the sensors is usually white base. Also do not confuse an air temp sensor with a coolant sensor. The air temp sensor is on the intake maanifold inlet on the left side. The air temperature sensor also has a small hole in its brass base.
 
John;

I took your advice and replaced the plugs with Champions. Since I have a Marelli ignition, I set the gaps at .025" as is called for in the owner's manual and also in Kirby Palm's book.

I also shopped around for O2 sensors. Discount Auto Parts was merged/bought out by Advance Auto Parts here in central Louisiana. Lots of the part numbers mentioned including in Palm's book aren't valid any more. I ended up getting universal sensors from Beck Arnley, P/N 156-8300, Advance Stock Number 18033788 at $112.99 each, which is about $70 cheaper each than Bosch. You do have to spice on the connectors from the old set.

Reading your comments about my being confusing, I reread some of my earlier entries and agree that I was not too clear in my explaination above. Sorry about that. My discussion about the single fuel pump coming on with both relays removed (Black connector and the Red Connector relays), These are referred to as the Main relay and the Fuel Pump relay in the book. There is a third larger unit called the interface unit under the same access cover that allegedly feeds data to the trip computor. My car has just the two relays and the interface unit. Normally, just pulling the red connector relay deactivates the pump and you can turn the engine over a few times and the injectors spray, bleeding off the pressure so that the fuel lines are depressurized allowing the pressure line on the right side of the engine to be disconnected without spraying fuel all over the place.

Although cleaning the sensors had worked once before at stopping what ever is allowing power to bypass the relays and hot wiring the pump, it did not help this time, which is why I replaced the sensors. I was also not too sure how many times they can be cleaned without causing a problem.

Unfortunately, the pump still wants to run. I will check the coolant sensor resistance and report back. The '90 has two sensors. One is green and the other is white. One is refered to as the thermotime switch in the factory book, but it is not clear whether the white or green is being called such. You suggested that the white sensor is the coolant sensor, so I will start with that one. It is on the left side of the car, the green is on the right coolant rail at the front by the thermostat and temp guage sender. There is a seperate sender for the temp guage.

I have not started the car again, since there seemed little point if the pump is going to run until the system is pressured with the relays removed, I think it will be rich again.

I have the wiring diagrams for the car. I have not been able to find a schematic for the 16U ECU internals. While I can determine which pin of the connector goes to what, I,m not sure about how the ECU actually works. There are several memory chips inside on the main board.

More to come.
 
Here is where I am today;

I checked the resistance on the white water temp sender as John suggested. I got a resistance of 3.15k Ohms. I had a spare from Welsh Enterpiizes made by Intermotor Automotive Components Welsh P/N 73198. Both the car and the spare sender have been sitting in the garage for several days, so I presume the ambient temp is the same. The Welsh sender reads 2.03K Ohms.

The green sender in the car read 2.7K Ohms and a Bosch replacement marked 0 280 130 055 Welsh P/N DAC4737 read 2.35K Ohms.

I still had the problem of the fuel pump wanting to run and disconnected the ECU and reconnected the battery. The problem had stopped again. I reconnected the ECU and the pump still remained off until the two relays were reinstalled.

I started the car and the idle was back to about 1500 RPM cold after about ten seconds of hunting, but no white or black smoke. I drove the car and still had roughness at other than idle with some stumbling

I attempted to adjust the idle again when the engine came up to temp, but could not get below 1000 RPM whith the AAV adjustment screwed in all the way.

When things cool down, I will check the throttle pottentiometer setting and look for air leaks and will recheck the linkage since I had removed the intake manifolds and fuel injection rail as a complete assembly in order to do the compression check and replace the plugs.

Although this is "not brain surgery", it is "electronic brain surgery". I'm still working out how to install a fuel pressure guage in the line and will report back with readings. I also have not pulled the fuel rail and checked spray pattern yet.

No one has asked, but yes, I am a little frustrated at being back where I started again.

I know what rebuilt ECUs cost, but does anyone know the pricerange for a used 16U ECU?

More to come.

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Michael, This is a first order answer without a great deal of analysis from your reported observations. Do not attempt to go into an ECU for repairs or modifications. The best test device on a V12 of your vintage without OBD 1 is another that is running OK. Substitution and/or verification by exchange is by far the easiest and best way to go. In my business, I keep an array of surrogate ECUs and logic modules for this purpose. I would not recommend any internal exploration on ECUs. If you are lucky, you can come by used ECUs such as you need for $500 to $800 for XJSs that are known good. You really need a test vehicle for this comparative substitution. Your resistance measurements of the temerature sensor sound OK and indicate that your coolant sensor is in the ballpark. Your model XJS does not have a thermotime switch. That is a special device used for fuel enrichment for about 10 seconds after cold start. It is irrelevant to a Marelli ignition model which uses an ECU calculation for warm up. The way to measure fuel rail pressure is to obtain some fuel feed and return hoses from a salvage car to "Tee" a pressure gage that will have a scale of 100 psi. I usually select the "tee" point at the input to the fuel rail. (drivers side rear). You must determine if the fuel regulated pressure is about 40psi. I would give that first priority since that is very critical for proper operation of the Jaguar constant pressure fuel injection. A lot of parameters that you are concerned with do not effect the fuel air mixture that much (such as lambda (O2)sensors). Whatever is causing your problem is having a major effect on performance so you should address the major players. Dont be concerned with the small change. MEASURE THE FUEL RAIL PRESSURE.
 
Thanks John.

Fuel rail pressure will be next.

Idle at cold is about 1900 RPM. I checked the throttle potentiometer again and the voltage is .34 v. The car hunts when first started, RPM surging up to 2500 and down to 1000. Turn the throttle turntable about 0.040" open and the hunting stops and the car idles smooth as silk at 1100. Potentiometer voltage at that point is about .45 V.

I have a new Distributor cap installed, rotor looked ok. I installed a new set of wires. I have the new Champion plugs set at .025 gap for the Marelli ignition, I think ignition is ok.

The car has good accelleration, but the engine sounds rough. at 25 - 30 mph in third gear (about 1200 rpm) it stumbles with some bucking and an occasional backfire. Coolant temp runs about 3/4 scale, as if it were running lean.

The other thing I am not sure about is how you actually check the injector spray pattern. Are you pulling the rail loose and positioning one injector at a time in a jar with only that injector connected? The logistics has me scratching my head.

The exhaust at idle sounds smooth on both sides. Of course, I have a performance exhaust that amounts to a pair of glorified glass packs, so I'm not surethe sound at idle is representative of how you described it.

12 cylinder Jags are hard to find around here. None others other than E-types with Carbs in the New Orleans club. I will attempt to locate a used ECU.

More to come.
 
It sounds like you are making good progress now. If the throttle pot adjustment eliminates the surging, (which is being caused by ECU logic and being triggered by the throttle pot and rpm signal) leave it at .45 volts. The way I observe injector spray patterns is to take the fuel rail with injectors hooked up from the engine and set it up in a cardboard box so that the spray pattern will go on a wall. Plug up the fuel return and connect the fuel intake to a container of cleaner and or gasoline that may be pressurized by a variable control regulator and gage with an air source. It must also have a means of depressurizing with a purge valve for leaks, emergencies, etc. Regulate the intake pressure to 40psi or thereabouts and trigger each injector with a 12 volt power supply. This procedure lets you dynamically test each injector and clean it at the same time. Use caution since you are spraying gasoline into the atmosphere. The 12 volt power supply should not be near the injectors. I have devised this rig since I work on a lot of fuel injection systems. I cant make a judgement as to whether the effort makes sense for you. If you do this, play it on the safe side and avoid accidental fuel leaking since a leak will become a significant spray under pressure. You need the purge valve at your side for quick reaction. Another caveat: since you are putting the rig together you must assume full responsibility for its performance or accidental spill. (Forgive me for sounding like a lawyer, I am an engineer!) Let me know the the results of the fuel rail pressure test. Good luck.
 
John;

I stuck a penny between the turn table stop to just open the throttles and eliminate the hunting at idle until I deal with the throttle potentiometer setting. With a smooth idle at 1100 rpm with the car cold (some white smoke from both exhausts)and the fuel pressure guage installed between the outlet of the fuel rail and the second fuel pressure regulator, fuel pressure was 30.5 psi. At 2500 rpm the engine ran rough, but the pressure was 35 psi.

Soooo.... It looks like I will be pulling the injectors to look for dribbling and spray pattern. I have a few ideas about how to implement your description of a jig. What type of cleaner do you use? It seems as though you need a quart can or two rather than emptying an aerosol can into a jar to get enough liquid to fill the rail to do the test.

I have made a few inquiries about used 16U ECUs, but have not heard back yet. If the injectors are not the problem, is it safe to conclude that the ECU is the likely cause?

More to come.
 
Michael, The fuel rail pressure is too low. It should vary between 38 to 45 psi depending on intake manifold pressure. A fuel pressure of 30 at the rail would cause lean running. This is surprising since all of the indications thus far led me to look for rich mixture. Take a direct reading of fuel pressure directly into the gage from the fuel pump. This should read about 75 or 80 psi if the fuel pump is healthy. Another cause could be fuel injectors stuck on and lowering the pressure by their draw. Look at the injectors and see if they have severe dribbling or are open all the time.
 
John;

I will check the pressure at the connection of the fuel pump line where it enters the first pressure regulator.

The more I thought about how to test the injectors, the more confused I got. I had to "step back" in order to "see the forest for the trees". It eventually occured to me that injector cleaner comes in a bottle and not an aerosol can. DUH!

My problem was what to use for a pressure vessel to supply cleaner under pressure. I bought a Fram G3850 in line Fuel Filter. This part number had the largest can of any fuel filter on display and I figued out how to connect regulated air to one end and the other to the Tee for the fuel pressure gauge.

I found a 1/2 gallon clear glass screw top cracker jar with a metal screw on lid. A quart jar might also work, but I wanted something larger. I bought a Help! 02365 Wire Grommet Assortment at Auto Zone. At least one of the grommets has an inside diameter that the tip of the fuel injector just fits in. I'm going to drill a hole in the lid just large enough for the outside diameter of the grommet. I added a 1/8" hole on the lid to act as a vent. I should be able to see the spray pattern with all the solvent/cleaner/gasoline spray kept in the jar.

I also check at a NAPA Parts store. The 2-17427 "Wired Housing" connectors that fit the injector electrical connection and the coolant and air temp sensors can still be purchased. List is $11.58 ea and Napa sells them for $8.49 each. So anyone needing to replace broken connectors, here is a cost effective way to repair the harness. Each comes with 3" pigtail wires. The boots are not available. I'm going to try heat scrink tubing.

Keep your spring clips! They are available from NAPA under p/n 2-17417, but Napa charges $1.49 net and $2.02 EACH!!!

I had a cheap push button on switch from Radio Shack that I will hook up to my 12 VDC supply to power the injectors one at a time to test them.

It will take me a few days to pull the rail, check the spray pattern and check for leaks.

More to come.
 
Michael, I will pass on this thought on how to put together a fuel injector testing rig. You will need an air compressor that will give you a source of over 50psi. The plumbing is up to you and what is available. I have used a readily available spray paint container for a large source of a paint spray rig external to the paint gun. They come with a pressure regulator and a gage. Mine is a 2 gallon size. The quick disconnect for the rig is a quick snap on connector commonly used around pneumatic systems. That is your emergency purge valve. Instead of filling the paint container, I use a can of injector cleaner that sits in the 2 gallon enclosure with the feed tube in that container. (injecotr cleaner has about the same viscocity as gasoline and produces a similar spray pattern. That is important since it is not flamable. If your want an exact repetition of the spray pattern, you can change to gasoline or alcohol) With this rig and its outlet clamped to the injector rail inlet and the rail exit blocked with a clamped seal you may pressurize the reservoir to the required simulated fuel rail pressure. Your repair fuel injector harness and a 12 volt power supply with a pulse control switch completes the rig that will simulate performance of the rail in a cantainer (cardboard box). You might want to simplify this rig to your own requirement but I hope the layout of my rig used for my "toy store" testing will help generate ideas for your rig. Gool luck and take the emergency disconnect feature seriously since **** happens.
 
PS. Injector cleaner does not do favors on automobile paint. Seperate the test area from where your XJS is.
 
John;

I tested the pressure at the outlet of the initial fuel pressure regulator. With the fuel pump pressured up (having run until it stopped) and the car sitting static, the pressure was 34 PSI.

I next tested the fuel pressure at the inlet to the initial fuel pressure regulator and the pressure was 50 PSI.

With the car running pressure to the inlet of the initial regulator was fluxuating very rapidly, but seemed to be 40 to 45 PSI.

I tested the injectors at 60 PSI. Spray patterns were all uniform and the injectors opened and closed smoothly when the solenoid for each was activated. There is no dribbling of fuel.

 
John;

I tried to paste/insert a small photo of the injectors being tested. I was not successful. I have the photo as a JPEG file anf it is about 573 KB in size. If anyone is interested, I will attach it to an email.

I'm going to reinstall the injector rail and retest the pressure at both sides of the first regulator again.

Based on what data is hear, does this point to the ECU?
 
John;

You had also asked me to look at the plastic povot bushings for the throttle linkage shafts. Those look good with no play and were changed about two years ago. I am going to check the linkage one last ime in accordance with Kirby Palm's book just to rule that out.
 
Michael, The pressure from the pump to the regulator would be too low for static conditions. Put the gage directly on the fuel pump outlet with no other lines out of it. The static pressure should be at least 70 or 80 psi. If it isnt you need a new fuel pump. If the pump is only generating 50 psi or lower, the dynamic pressure in the rail with the car running at speed and under load will demand more fuel delivery and will cause the pressure to drop to unacceptable levels. Hook the gage to a "tee" on the fuel fail (first regulator exit) and take the car for a drive and watch the gage pressure. You should be seeing 38 to 45 psi even when the car is under acceleration and the fuel demand is high. If the pressure drops off under load, even if it after a period of high demand, the pump is not maintaining proper pressure and should be replaced or there is a clog in the filter or delivery line. Things are pointing more and more to the ECU but dont give up yet. Tell me the results of the test drive with the gage on the rail.
 
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