I had my car in the garage for some suspension work. After completion it sat for a couple of months while the Wife and I went on some Summer excursions, After a couple of months I decided to start it up. I had kept the battery up to full power with a tender. Since it had sat for so long I decided that it would be a good idea to prime it by turning on the ignition, counting to five, then turning it off. I did that five times. I cranked the car and it started up, running really rough and smoking. usually I can nurse it through this rough patch and it will smooth out after it warms a bit. I held the rpms up but stalled it backing out of the garage. Instead of idling it stalled and died. Wouldn't fire after cranking several times with throttle open wide. My opinion was that I had fouled the plugs terribly and would need to change them.

I've had the car for years and after replacing the transmission I drive it to work and around town occasionally. I've driven it in over 90 degree weather and it's never gotten hot or refused to start. My biggest problem is the the front suspension needs rebuilding. Because of that I only drive it around town but I've had it on the freeway lot's of times. My point is that the car was a runner and had never left me anywhere before, So what could it be?

I changed all the plugs, They were black and sooty. I restarted the car, this time without priming, and it started immediately but again rough running, smoky exhaust, etc. I tried to hold it at 3,000 rpms which it did for a short time then i dropped the rpms and it died. What it felt like to me was when I had mixed up some of the plug wires in the past or had reinstalled the distributor out of phase. But I hadn't removed the distributor.

I downloaded and printed out Grant's V12 trouble shooting guide and read through it completely. Thank you Grant for providing so much helpful advice.

All I did was to change the plugs. I was careful to label all the wires and hoses and especially the spark plug leads. I checked the routing of the plug leads on the distributor cap and the firing order,checked the vacuum line to the dizzy, and looked for anything that I might have broken accidentally. I had to splice in a section of wire from the ignition amplifier to the coil. I checked the coax wire and though it looked bad, when I peeled back some of the outer insulation the inner wire looked okay. I checked with a multimeter and the inner wire was not grounded out.

Now I start the systematic trouble shooting. ( Take a breath and post this!)

 

3rd straight cofee, so here goes.

Stale fuel.

We have NO Ethanol easily available down here, and I avoid it coz I can, but usually 6 months in the "Queens", and the fuel is OFF. Even the old MK7 and MKX, which will basically run on anything that explodes, NOPE, fresh fuel, good to go.

Your sooted plugs is what has led to that answer, and it is the simplest and cheapest to start with. I suggest a drain, via the sump tank spigot, and then some freshy, and let it get through to the front by running it, OR, you could detach the Inlet hose at the RH side of the rail, and let the fuel purge into a container, then all you will have is whats in the rail, and the V12 will consume that in seconds.

AND

While you are all warm and fuzzy in the boot, and the tank is drained, change the fuel filter. The paper medium stuff inside does break down and reeks havoc, more with Queens than Daily drivers.

 

My experience with E10 (it's been standard issue in my region since the 1990s) is that it'll smell like turpentine when is goes bad....so open the filler cap and have a sniff!
Besides the turpentine smell of the gasoline itself, the exhaust will stink to high heaven.

But even lacking any of that the fuel system is as good a place to start as any.

Beyond that.....

Sooty plugs and rough running could also be an old fashioned over-fueling problem. Excessive fuel pressure, coolant temp sensor skewed, vacuum line to the ECU unplugged. Or....this comes up from time-to-time....a crispy fuel injection harness shorting to ground causing some of the injectors to stay open all of the time. Changing spark plugs is a bit invasive on these cars so it's quite plausible that the over-backed wires might've been jostled a bit, breaking the insulation.

No matter where you step-off, proceed slowly, thoroughly, and methodically. You'll find the fault.

Cheers
DD

 

One of the things that jumped out at me in Grant's list was the problem of a condenser failure. There was a condenser attached to the coil mount so I disconnected it. I've had condenser trouble before on other cars so this seemed like a quick fix. The car started right up right away but ran rough and smokey, tried to hold enough rpm to "clear it" stalled out any way. Okay, time for a step by step approach,

I pulled the A2 plug and it was sooty. I grounded the plug cranked the engine and observed a spark. Since the engine starts and runs ( at least for awhile) I'm assuming it has enough fuel, but I haven't checked for pressure or volume.

Since It feels like the plug wires are out of order I checked that again. They are okay.

I decided to check the throttle position sensor voltage. It had .5 volts going in and 4.5 volts going out. That seems to be okay. I checked the injector resistor pack, the one bolted behind the right headlamp area and the plug and connectors looked pretty clean to me so I just re connected it. I've been searching the forum for any related threads. It seems like the engine is too rich, but what could cause this? I considered the idle air control valve, but in my experience when that isn't working, the engine dies after cranking and catching.

One thing that I've checked and found a problem with, is when I open the throttle completely, with the ignition on, and I'm supposed to hear all the injectors "click." I haven't heard that. Is it the TPS that is supposed to initiate that as it travels to full throttle. Or is it that little micro switch that is supposed to trigger it?

My micro switch was broken on top and only had one wire connected to it. I removed it to clean it and check it see if it was working. I imagine that it makes a ground connection when it is activated. Is this how the full throttle fueling system is activated? My switch didn't do anything when it was activated, There was no connection to ground at the terminal.

I found an older thread where the poster was overjoyed to realize that a broken microswitch was causing the full throttle enrichment system to be activated all the time, Always grounded always activated, means over rich running. I thought that I had found the problem.

I checked the installed switch and again found no ground connection, activated or not. I figured that the motor should run at low speeds without any problems if I was to just leave the wire unplugged. I thought that the wire should read "open" not grounded, if the wire was unconnected. When I checked continuity with my multimeter I found a strange thing. While it didn't make the sound for a closed circuit, the meter started displaying some numbers. Never seen that before! It's always been beep or no beep! Weird.

I pushed the car out of the garage before trying to start it, The smell of the smoke is terrible and some always makes its way into the house. The car started immediately and was sounding pretty smooth. I nursed the throttle and was intent on letting it warm up, hopefully burning the excess fuel accumulated in the system. After five or six minutes it was idling pretty good. It didn't seem to want to rev though, it would feel like it was going to die if I opened the throttle. In fact when I closed the throttle at the capstan by hand the idle smoothed even more. Of course instead of letting it idle longer, I thought that I could rev it up a bit. Both pipes were emitting some smoke and I still hoped to clear it out. That caused the engine to die. The engine wouldn't restart. Push it back into the garage - again. This happened this afternoon, now I'm caught up in real time.

I've commented on some recent threads on the forum and remarked that I was covering my spark plug replacement on my blog. In episodes. According to my blog I'm only half way through the process of replacing my plugs. Actually I was finished last week. I haven't posted anything there about my recent starting problems.

I've been producing my blog for five years and maintain a weekly posting schedule My Jags make up a lot of my content. My postings don't usually represent "real time" events. Usually they cover events that have occurred recently. Events have been edited to aid narrative flow.

Sorry for all the verbiage, now I'm ready to start. I just needed to bring my story up to speed.

I have a couple of concerns, Primarily about the throttle microswitch. I found the secondary vacuum switch located on the right side of the intake manifold.These switches are supposed to be wired up in parallel, The vacuum switch isn't connected at all! Since the microswitch is broken there shouldn't be any extra fueling occurring. But that single wire to the microswitch had that funny reaction when I checked it with the multimeter. The funny thing is that the car ran fine before, It passed smog twice already, and the smog guy said it was showing up super clean.

I'm also wondering if it's only running on the cold start valve settings. As it heats up it stops. It will sometimes restart if I wait fifteen minutes or so.

I think that I'll have to check the wiring at the ECU like it's described in Grant's list. I wonder if that co ax wire is really okay. If you've read this far, thanks for your time. I'm tired from all this typing, that's all for tonight.

 

I did add a couple of gallons of fresh fuel to a very low tank. Thanks for your suggestions. They will help point me in the right direction.

 

Some possibilities:

Excessive fuel pressure, coolant temp sensor skewed, vacuum line to the ECU unplugged. Or....this comes up from time-to-time....a crispy fuel injection harness shorting to ground causing some of the injectors to stay open all of the time


And it can't cause an over-rich mixture anyway




We can come back to this but the full load enrichment is only about 8%-10%. I have doubts that this is enough to soot the plugs or cause poor running. In fact, the engine might actually like the little extra richness.



The cold start fueling can be very rich, If the system is skewed full cold (due to a faulty coolant temp sensor) and stays there, the engine will object. It's definitely enough to soot the plugs

If the engine runs at all I'd say the coax is probably OK. Failures here are typically a go/no go scenario as far as I know...but let's hear from Grant on that

Cheers
DD

 

That's been my experience too, failure here is typically binary - it works or it doesn't, there is no grey.

 

Is a 1989 a Lucas or Marelli ignition? These symptoms seem similar to what I experinced with a failing Lucas ( GM) ignition module. A new module cleared everything up for me. Make sure it is a genuine GM (or AC Delco) module, as I tried some aftermarket ones that were no better than a failed GM module. I actually grabbed a GM module from the junkyard out of a Chevy truck and that worked better than a brand new aftermarket module.

 

Bugga.

I would unplug the CTS, shape a paper clip, and bridge the 2 terminals in the plug. This will fool the ECU to a Normal Temp engine, and eliminate that thing for now.

That TPS reading is TO high at idle. 0.32 - 0.36 is the spec, and I set them at 0.34.

The micro and vac enrichment switched are as Doug has said, and should not cause smoke or soot.

Cold start Injectors, if fitted, for sure. Unplug them.

The Coax, NOPE, as said, its either ON or OFF, niofemale moments with that in my years.

Pull the small vac hoses from the FPR units. Are they DRY, or WET with raw fuel???. Should be DRY.

Might pay to ADD Lucas, or Marelli to your XJS details, as you are at a change point. Makes a HUGE difference as we dig deeper.

You stated "checked for spark", GOOD, was it a FAT Blue CRACKER or a weakish excuse. No got FAT Blue cracker, the V12 will fight you.

 

Thanks everybody for your prompt responses. It is a Lucas ignition car. 106,000 miles on clock. Appears to have been regularly serviced. No records though. Bought from an estate sale, according to the deceased gentleman's daughter it was his favorite car before he became ill, and he used it often. It sat for a almost a year but after I bought it I was driving it occasionally. Anyway-

1) I can forget about the coax, good.
2) The spark was kind of weak, Maybe the ignition amp is bad per Jagboi. That would be easy enough to replace. It seemed to be warm to the touch. Did the unit from the truck look like the Jag unit?
3) I will jump the CTS plug per Grant.
4) Concerning the TPS readings, I checked my written notes this A.M.and they were reading between .341-.361 volts. Kind of hard to get accurate reading with my instrument.
5) I will check those fuel pressure regulator hoses.

I'll report back after I try these things. Enjoy your evening.

 

If you open up the aluminium Lucas box you will see a standard GM 4 pin HEI module. Used on millions of GM cars from the 70's to 90's. Part number is AC Delco D1906. A cheap and reliable place to get them is Rock Auto: https://www.rockauto.com/en/moreinfo...032275&jsn=627

The module dissipates about 6 amps under high revs, that's why the heat sink paste is important to put ion a new module, and also why the aluminium box is mounted where it is - the cool air coming into the engine acts like a heat sink, and the intake manifold is the coolest place in the engine bay ( I've measured my engine bay with an IR thermometer)

The higher spark demands of the 12 cylinder engine vs 8 cylinder pushes the module right to the limits of it's design, so that is partly why they do seem to fail in V12 service, yet last longer in a GM 6 or 8 cylinder engine.

 

YEP,

AND. while you are inside that AB14 amp, remove the condensor looking thing located in one corner, and held in place by a single Phillips screw. Throw it away, they leak to earth, OLD age related, and were supposed to be a noise suppressor waaaaay back in the day.

Spark related:

You are lucky your market gets the 11.5:1 comp engines, we get the 12.5:1 engines, and spark for that critter is 100% or nothing.

Lift the distribuot cap, CAREFULLY, and invert it, and ensure the centre carbon brush is still OK.. They can wear away, fall out, just plain go AWOL, and the car will run, althoough spark AT the plugs is weak.

When you have had it running, and it shuts down, say after a few minutes, there will be heat in the engine bay, OK, now place your hand on the ignition coil, is it ABOUT the sme temp as other items, or is it hotter??. Hotter indicates one, or both of the coils is going bad.

Plug leads. Age related, and the heat they are subject to, may need replacing. Average life of HT leads on a V12, is about 5 -6 years.

You will need a Digital Meter for the TPS, an Anologue will not be good enough.

ALSO

Earths, get a battery jumper cable, clip to anything metalic on the engine and the other end to a chassis ground, just MAYBE, there is an earth path misbehaving. This is a bit of a "poke in the eye" suggestion, but engine earths are important, as are all the others, mainly the 2 alongside the battery.

 

Do you mean putting your hand on the module or coil? The later cars should only have a single coil.

 

I’m just going to say that the full throttle enrichment is enough to seriously degrade MY idle. I’d correct those to switches, or bypass them ( and don’t floor it ) before going forward knowing that they are faulty.

 

On the coil itself.

Matters not 1 or 2, if the coil is hotter by heaps than the surrounding other bits, the coil has an issue.

A hotter than normal coil is usually the result of:

The ability, or lack of, the coil to dipsoe of its energy.

Caused by:

OLD HT leads, too high resistance.
OLD spark plugs, wrongly gapped new plugs.
Missing carbon contact inside the dissy cap.
Bad engine earth path, via the twin straps.

Once the basic temp of the coil is noted, then further work can continue.

Systematic, and not spending $$ without good reason. These are SIMPLE cars, only compliucated by a none systematic approach to issues.

 

Today I dismantled the ignition amplifier and ordered the AC Delco Ignition amp, When I receive the module I'll reassemble it and try it out.Thanks for all the help.

 

Here is a snap, coustesy of Greg the Cool, AKA Greg in France.

The condensor thingy I mentioned above is arrowed, and is reduntant.

 

Acknowledged by the Wizard! What an honour.
It is arrow labelled C, by the way.

 

WHOOPEE, at least ONE person read it.

Thanks Greg, did NOT see the "C", should have gone to Specsavers, HA.

NAH, a new left eye would be better, the current one is down to 10% at best.

 

I rebuilt the ignition amplifier and checked that the carbon plug was present in the distributor cap. I was busy with other matters and let the car sit for a while. To be honest I was a little afraid of trying to start the engine and suffering the disappointment of having it reduced to a wheezy stinking lump. Yesterday was my day for garage and car cleaning and rearranging. So I figured that I'd just get it over with, Fire it up , choke on the smoke and disappointment, push it back into the garage and forget about it until another day.

Didn't turn out that way. The engine started right up sounding pretty fine and settled into a high idle. My plan was to let it heat up completely, hopefully burning all the excess fuel that that built up in the motor. I let it run for about five minutes then tried to increase the rpm. As I opened the throttle it just died and wouldn't restart. It had started started easy enough but quit when it was warmed a bit. I wondered if if it was something in the cold start to warm running transition. I didn't want to do the whole ECU terminal pin check procedure . I was thinking through Grant's List and remembered the coolant temperature sensor. A malfunction could the prevent the motor from starting and running, but my motor had started up fine. Maybe the sensor was working when cold but failed when it warmed. Grant suggested jumping the terminals with a paper clip, that sounded easy enough. I used a bit of wire. That did it. The motor fired right up sounding great. This time I let it warm completely before giving it some throttle. It revved easily to 3 and 4 thousand rpm. without any noticeable smoke. I noticed that the engine would falter a bit if I wiggled the jumper wire. I figured that the terminals might be dirty so I cleaned them after I shut it down. I also noticed a small vacuum line to the fuel pressure regulator that I had knocked loose so I hooked that back up.

I had let it run for a half an hour, driving it forward and back up the driveway, revving it up in neutral. I'm going to replace the CTS just to be safe though this might have been caused by the dirty connections. Grant's List is a terrific resource. You have to troubleshoot the motor in a systematic manner. Just because a problem presents itself after something was done to the car doesn't mean that it was the cause. I had finished some suspension work before my engine problems started. Obviously that couldn't have been the cause. Sometimes sensors fail randomly it just seems it was caused by something you did.

I sure felt good the rest of the day!