90 XJS V-12 High Idle

I can't get the idle below 1100 rpm, 1400 when cold. I have looked at all the vacuum lines, sealed any that were loose, retorqued the intake manifolds, checked the butterfly settings. I changed the carbon canister.

Is the pcv valve to be open at idle?

The idle adjustment is screwed in all the way.

This car has a manual transmission kit installed and the vacuum port for the auto trans modulator is capped.

What else is there?

Any suggestions?

I suspect that your Aux Air Valve is stuck. I'll try to dig up the link that shows how to repair it....

Cheers
Doug

Well, I pulled the Aux air valve and cleaned with brake cleaner to get what little gunk might be causing it to stick out. Idle adjustment seems to work by the threaded bolt reducing the size of an opening as it is screwed in and enlarging the opening as it is screwed out.

I reinstalled. I also attempted to adjust the throttle potentiometer to see what could be done with the high idle. I tried a couple of settings (32 ohms between yellow and red) and (36 ohms between yellow and red). On each start I encountered the hunting (surging) open the throttle some and it stops but is rough.

I tried adjusting the idle adjustment, but was not able to stop the hunting.

Suggestions anyone?

This is a 90 XJS V-12 Marelli ignition car.

Not drivable.

Michael, Get a new throttle potentiometer and install it using the procedure that is well decribed by Kirby Palm in "What Every XJS Owner Should Know". As he says, you will need a digital Voltmeter. The procedure is under Fuel Injection, Engine Management. This should solve your idle hunting problelm. If it doesnt, you have a problem that has been brought about by the transmission conversion and that is no mans land. You might have to experiment with the calibration voltage of the throttle potentiommeter. Sorry for the long delay, I have been on some extended travel.
Jack Farrington

P. S. Regarding your idle speed, check very carefully the linkeage bushings (small rubber parts) at the joints between the tower control rods and the butterflies. They can also be troublesome in that the butterflys will not be precisely controlled in oopening at low RPM settings.

I pulled the AAV and performed the boiling water imersion test. The valve is stuck open. I have a spare and tested it and it closes.

Idle is now adjustable, but I am running so rich I am belching black smoke.

I think that I am following Kirby's instructions on page 281 - 282 wrong. I have been reading ohms. The procedure is measuring volts. I am going to check it again.

I found that replacement of AAV got idle in range.

Does anyone know about the idle mixture adjustment on the ECU? Which way is lean and which is rich? Kirby Palm's book does not say. I am still rich and need to lean out I tried several clicks each way. I am going to study the ajustment procedure, but I don't have the diodes needed yet. I want to try setting one click at a time, if I can find out which is rich and which is lean.

Michael, The idle richness adjustment on the ECU does not have that much range to make a significant difference in its adjustment, you are not going after the right cause. If you are belching black smoke you better check your fuel rail pressure range (35 to 40 PSI) or your injector open dwell times. Most of the fuel injection sensors effect the opening times but do not get focused on the oxygen sensor since that does not have that strong of an effect on the fuel richness. Also there is a possibility that the ECU calculation of opening time could be faulty and cause rich running. You need to work with somebody who has some experience with the type fuel injecton your V12 is using. Contnued running of a V12 with gross rich fuel mixture can do damage to the engine internals.

Therein "lies the rub". Experts in the greater Lafayette, LA area are hard to find. I expect that I will have to find someone to work this out with me via email. Can you recommend someone?

Michael, I deal with problems like you are having very frequently at my Toy Store. Part of the problem in dealing with a 90 vintage Jag fuel injection is that you do not have built in diagnstics such as OBD2. Thus you are limited to componenet substitution in order to verify correct condition and/or performance. Some of the componenets are pricey and substitution without solution is frustrating. For a start you must verify performance on these componenets that have a strong effect on fuel/air ratio.
1. The coolant temperature sensor. 2. The ECU for the fuel injection. 3. The fuel rail pressure which is controlled by the fuel pump pressure being regulated by fuel pressure regulators. Your situation indicates that you are running rich so the pressure might be too high (over 45 psi). Too much pressure also might be caused by a stopped up return line back to the tank. Have you obtained a throttle potentiometer and calibrated in volts according to the kirby Palm procedure? Do you have a schematic diagram of the fuel injection eletctronics and are you fluent in reading electronic diagrams? I will try to stay in touch but there is nothing like hands on diagnostics. Best Regards and Merry Christmas.

Thanks John;

I have obtained and installed a potentiometer that I adjusted in acccordance with Kirby Palm's procedure. I also went back and followed the complete throttle linkage adjustment procedure. I found some adjustments were off and made the corrections. After swapping out the stuck AAV, the idle problem solved.

Black smoke is now replaced by light grey to white. I had encountered this earlier and retorqued the heads twice. Each time, retorquing lessened the smoke. During build-up, I installed new head gaskets dry. I am using 100% propylene glycol as the coolant. So one problem that I have is that there is no steam in the smoke. I decided to use this after seeing the poor condition of head gaskets in two other V-12 engines that I torn down. I did not want to use a water based coolant. The fuel mixture is still not right, but I cannot tell if this is because of whatever is being burned to produce the smoke. This could be coolant or perhaps the rings are not seating. I had honed the liners to break the glaze, used the 60 degree cross hatch and used new rings. Whether coolant or oil, the smoke was masked by the black fuel rich smoke.

At this point, before going any further, I will pull the intake again and run a compression check. I think that I need to rule out coolant leaks.

Michael, White/grey smoking can be caused by unignited fuel being discharched into the exhaust system and catalytic converter. The fuel injectors are fired in groups of three and banks of the left and right cylinder heads. The pulsing of the injectors comes from the ECU as a result of the ignition amplifier signal that pulses the coil and also goes to the ECU as a trigger. There are small strobe light instruments that are available and will give a you a signal that confirms that the ECU is pulsing the fuel injectors. The injector pulse may also be observed by an oscilloscope trace signal and that will measure the injector signal duration. Get either of these test instruments and determine if all 12 injectors are receiving proper pulsing. I have also encountered the situation where a fuel injector is stuck in the on mode all the time and overriding the pulse from the ECU. Also determine that all spark plugs are being triggered by the coil secondary circuit through the distrubutor cap and spark plug leads and that the spark plugs wires follow the proper firing order. All of these situations may cause unburned fuel to be discharged from the exhaust. One diagnostic problem with the V12 is that power and smoothness of the performance masks the engine not operating on all 12 cylinders. The results of a compression check may also prove interesting. Look for reduced compression on two adjacent cylinders. That is a signal for a head gasket failure. (Incidently, head gasket failure is usually caused by head warpage due to oveheating and the head must be made level again before gasket replacement. Retorquing will not eliminate the problem.) Coolant in the exhaust will also look like white smoke. One last tip: If your V12 has been running very rich, the catalytic converters will burn the residual fuel deposited in the converter for a few miles until this fuel is used up. While this is going on the exhaust can be white/gray smoke. Best regards for the New Year. Jack.

I checked the injectors with the engine running with a mechanics stethescope and could hear each clicking like they should.

I am going to study up on what Kirby says about checking the duration of the pulse though.

Having some knee surgery next week, so I will be underground for a while.

Will post an update on what I find.

Michael, Good luck on your knee surgery. I have had both knees replaced with excellent results. The original cause was from a soccer injury while playing for West Point as a naive cadet. I hope your knee turns out as well as mine did, they are doing miracles these days. Regarding your 12 cylinder problem, I will hang in there with you, I think we can solve this one. The fuel injectors can click but they can still be not opening up in a specification way. Lets look at the problem from the grass roots when you get back from surgery. Jack

Micheal J.
Good luck with the surgery. Just a couple of suggestions. (I happen to work in the research labs for one of the companies that makes knees and other stuff.) This may be coming a little late, but make sure your doc does lots of knees, like 50 or more a year. They should be able to do it in their sleep, so to speak. Studies show that one of the biggest influences in successful joint replacement is THE DOCTOR. Also, follow the rehab instructions. Don't be afraid to ask a lot of questions, it's your hardware they are working on, you deserve answers. And good luck with the Jag.

John F.
Just by chance, did you grow up in NE Indiana?

John;

Thanks, I'll keep that in mind. My ortho has done quite a number of my friends, so I'm hoping for similar success.

I was able to run a compression test with the engine cold. Results were:

6A 218
5A 215
4A 180 the first time and 218 for the second and third.
3A 230
2A 225
1A 195

6B 218
5B 235
4B 225
3B 225
2B 230
1B 215

Since the smoke is about the same from both exhaust, It appears that your thgoughts on the smoke being possible gas in the CATs, it looks like I need to look at duration and possible spray pattern for the injectors. I listened to the injectors with a mechanics stethyscope and all solenoids were clicking, but that does not mean all are closing or spray clean.

All twelve plugs had a heavy carbon build up.

Any thoughts on measuring duration of pulse?

The coolant temp sensor was new about a year ago. Thoughts on testing it and the two air temp sensors?

Both fuel regulators were replaced a year ago when I was fighting richness.

I'm going to read up an thes in Kirby's book while recuperating.

More to come.

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Michael J.:

All twelve plugs had a heavy carbon build up.
<hr></blockquote>

I don't know much (just ask my wife), but I do know that's usually a sign of too rich a mixture. Hopefully John (or someone) can help youfigure out why its burninf too rich. This has been an interesting thread to follow.

Basil

Michael, The coolant temperature sensor has much influence on fuel air mixture. The air temperature sensors do not. Your can check the coolant temperature sensor with ohms resistance check. I think the standard is about 3K ohms at room temperature. (that is off top, Palms book should tell you or I can look it up) The temperature sensors are cheap ($20) and commonly used in most Jag fuel injection set ups. I also think the air sensor might have the same resistance spec. Also measure your fuel rail pressure even though you recently replaced the pressure regulators. You should read about 40 psi on the rail and it varies with intake manifold vacuum about 5 psi. If you are seeing over 50 psi, it will run rich. You can have a blockage in the return line, etc., What you need to begin to isolate the problem is access to a properly running V12 of the same vintage as yours. (Marelli ignition) Substitution of components such as the fuel injection ECU is also important to confirm that componenet. The only way to measure the injector dwell time is with an oscilloscope (measuring the length of the time axis trace). If your injectors are spraying with a good pattern, then the ECU could be in error in its output signal. I would observe the spray patterns and then substitute an known good ECU to see if that makes a difference. In answer to my roots question, I grew up in Belleville, Illinois. My West Point roomate was from Indiana. Good luck with your knee and remember that the rehab is as important as the operation. Take it seriously.

P.S. Michael, The results of your compression check look OK. Particularly with the temperature not at operating level The variations are OK considering cold pitons and rings and the level of compression exceeding 200psi, if anything, is a little high indicating carbon buildup. I think your headgaskets are OK.