Sorry for the multi posts! Having picture problems...the new unit needs to have a top lug like the one in the picture...not like two of the bottom lugs, you will not get good grouding contact in our "module" box, plus one of the "new" modules I bought came with dilectric grease BIG NO-NO use white silicone heat sink grease availible at radio shack. I think when the new units fit on the plate in a GM HEI distributor they work fine but from experiance the new units didn't work at all in my module box with the "suspect" top hole/lug. The NOS one in the picture I got off e-bay for $22, worked like a charm. Compare your new module with your old one and see if there is a differance.

 

Here's a WELL's one...big differance.
GMC Suburban Ignition Control Module - AM Autoparts

Here's a Delphi...close but no cigar (one I got was just like this, no workie)
1979-1986 GMC C2500 Ignition Control Unit - Engine Electrical - Delphi 79-86 C2500 Ignition Control Unit - 3818-05235071 - PartsGeek

 

Thinking some more.

Is there spark out of the coil lead going to the cap?. Even if the "V" coil has died, that LT connection to the "front" coil will still supply spark and start the engine, it just may lack power and the ability to rev properly.

If there is, and no spark at the plugs, lift the distributor cap, and ensure the carbon contact up inside is intact. That is another item I have go AWOL over the years.

 

Thanks, JTsmks, I clearly see the difference in the solid lug top hole. Now, I guess I need to shop around and find an older style.

 

IMHO if your getting power into the module but not anything out of it then it's the module, don't start chasing your tail as they say by checking/moving/replaceing multiple parts....50% of car maintenace is caused by 50% of car maintenance if you know what I mean. When the modules fail they usually just "give it up" all at once or sometimes pull the old "won't start hot but will start cold" routine. I'm not saying your new module isn't going to work but I went through 3 new ones with no luck till I got an old style one. Contact David Boger at everydayxj.com, he will pull a known good one off one of his many XJ6's (same module) and get it to you in the post for you at a fair price so you can rule that part out.

 

Grant, you mentioned "Coming out of that "magic box" on the inlet manifold is a coaxial cable that travels to pin #18 of the ECU". I found a crack in that cable, and I decided to change that cable. Is there a technical name for that cable or will a Jag dealer know exactly what I need when I describe it. Also, could you direct me to a better place to buy one.. Thanks.

 

Aha, good find.

Jag dealers will have NO idea what you are talking about, due to that wire being part of the engine bay loom, and was/is just a loom part number.

I used TV antenna coaxial cable, from the local electronics/television/computer suppliers. Radio Shack comes to mind in your area I think.

Trace that wire behind the engine, you may have to partially unwrap the loom for access, to where it exits the engine bay somewhere near the RH bonnet lock (RHD talk here), but I think the LHD looms are the same. Most I have replaced have had damage mainly near the amp, near 6B spark plug, and near the oil switches dead centre at the rear.

Carefully seperate the coax wrapping, and locate the inner thin wire, join the new thin wire, and insulate very carefully, then join the coax, and insulate even better, then wrap it back up. SOLDER only here please.

This is time consuming, but unless the ECU sees a steady signal down that this wire, the engine will not run.

 

If it was running normally and just shut off, you may have lost the fuel pump?

With these v12's you have to check sensors and switches before you start replacing parts. There is a sequence: Check Fuel Pressure, Air Temp Sensor, Water Sensor, Fuel Rail, There is a sensor near the right door in case you have an accident or impact-press the reset button if it tripped.
Also need to know that the fans are working as well as look at all ground points.

The engine will not start with out some of the sensors. Look at your battery connections and grounds. The ECU will not let it run with bad connections or weak battery.

Good Luck

 

Ok, I've replaced the module, coil, coolant temp sensor, and repaired a seemingly damaged coaxial cable. Still not starting. Am I just missing something? One minute, running beautifully, next...dead.

 

Bugga.

I will read all this post later tonight, and reply. It will be a loooong systematic reply, so please be patient.

Time for a date with the wife, see ya.

 

OK, dinner is over.

My findings over many, many years are as follows, and in some sort of order.

Running for one minute, and dead the next is going to take some sorting.

I will stick to the sudden shut down claim for now.

I will assume the following:

1) The fuel pump is running when the ign is switched to ON.
2) There is spark at a spare spark plug inserted in any spark plug lead.
3) There is fuel at the rail.
4) The injectors actually "click" with the ign ON, and the throttle capstan is turned briskly towards WOT.

I am taking into account the following.
You have replaced the coil, fine.
You have addressed the CTS, fine.
You have replaced the ign amp, fine.

Next on my list, still assuming many things.

Your competence with a DCM (digital volt meter) will be very handy in some of these points.

1) On the main battery +ve cable, about 6" from the battery terminal are 2 heavy Brown wires under a plastic cover, and are a spade type terminal. They fall off/gunge up/loosen with age, and they power up the ECU, and the "main relay", and the "fuel pump relay". Check these VERY CAREFULLY, as they can fool you very easily.

2) The electrical section of the ignition switch is loosing its 12v supply in the "start" position. This I have had on 4 of my Jags, PITA to find. You got 12v at ignition, and 0v at crank.

3) There is actually a continuity in that thin wire of that coax cable all the way to pin #18 of the ECU. A loooong lead is the only way to test this, with the DCM set on ohm's, and whilst having it connected at each end of that wire, fiddle with that wire, just to ensure there is not a break further down that thin wire.

4) The inertia switch has not tripped, they do that. If in doubt, join the 2 wires together, just to eliminate it. My '85 went hissy at this switch, and joining the wires had the car running in no time. Mind you a clue was the fuel pump not operating at ign ON.

5) The 2 wires exiting the distributor casing via the rubber plug, and going TO the amp, have a habit of breaking INSIDE that rubber plug. Some serious detective work required to find that one.

6) Same goes the 2 pin plug located at about 3B spark plug area. This is where the amp wires and the distributor wires mate.


I also suggest unplugging the ECU, and checking for "gunge" on/in the plug. You will need it unplugged to carry out #3 above.

Some outside of normal thinking.

The distributor is actually rotating. The driven gears are known to shear off.

The pickup coil inside the distributor can die, rare, but it can happen, but erratic running is more the result here.

While you are checking things, do a continuity test of the actual coil HT lead. They can get some serious resistance over time, and that can/will "block" the voltage path.

I will leave it there for now and await some feedback.

 

Just remembered something else, its an age thing.

Inside that ign amp (magic box) is a condensor, held to the case by a small screw, and connected to the module + terminal. I have had 2 of mine with this condensor leaking to earth, NO GO is the result.

Simply remove it, as I did mine 14 years ago, and I simply do the same with any HE that has running issues, and there have been many. It has not fixed all of them, but at least it is out of the equation.

No ill effects will occur, the car will not do anything strange etc.

 

While checking the fuel pump, I turned to the on position and listened. I heard the pump for roughly 3-5 seconds, and then stop. I repeated this several times with the same result. Should the pump remain " humming" until I turn off the ignition or is that 3 to 5 second interval normal? While doing this, I also had my brother turn on the ignition while I just walked around the vehicle just to listen to anything else that might give me a clue. What I heard was an "electrical click" coming from either the main coil "inside the V" or the module in the box. Is that normal, or what can you tell me about that?

 

From what I have seen in this thread you guys have figured it out, my first thought was vapor lock.. Has happened to me about 3 times in my XJS (before I fixed the AC)

 

Yes the fuel pump only runs long enough to prime the fuel rail. Supposed to do that.

On the car that will not start: Is he sure that the car is in Park or neutral? Switch is bad or not making?

 

The organloft, yes, it was driving fine and as I was driving along, it just cut out on me and I haven't clue why.

 

Anzio, bit late, work gets in the way sometimes.

As said, the pump timed run is NORMAL. The pump "should" hum when cranked IF that coax wire is in fact sending its signal TO the ECU. That wire basically informs the ECU that ignition pulse is happening, so its OK to fire the injectors. That is all the communication between the 2 systems that these earlier cars has. the fuel system and the ignition system are seperate systems other than that. However the ignition systems does NOT rely on the ECU for anything. The ECU is a fueling device only. All this changed significantly with the Marelli system in 1989.

The clicking you are hearing is more than likely the many relays in the engine bay that come alive when the ignition is ON.

I seriously doubt you are hearing the amp, as it is a silent item.

If the coil is clicking, again I doubt you are hearing that actual item, it is shorting, then the "click" you hear is the arcing to earth of the HT spark. Not good.

I suggest trying this at night with the lights OFF, so nice and dark. Crank that engine and observe if you have any strange "nightlights" going on. Shorting HT leads give a wonderful display.

Having gone thru all that, you sound like fuel is getting TO the rail/injectors. Now establishing if the NO GO is spark or fuel related. Grab some ether (starting fluid), give the snout of each air cleaner a short spray, crank the engine, if it fires, then spark is present, and the injectors have lost their signal to fire, and that is either the coax wire, or the CTS (coolant temp sensor), and/or its wiring. As said before, if a HE is running and that CTS is unplugged the engine stops, NOW. That one sensor is a prime fueling sensor, and just as critical as the "thin wire" to pin 18 of the ECU I mentioned before.

The fact you have fuel pump "hum" indicates to me that the 2 relays in the boot (main and fuel) are fine. I say this coz the main relay powers the ECU, and the fuel pump relay. The 2 wires on the +ve battery cable must also be OK. One item eliminated.

 

I agree with this assessment of the situation. You lost ignition or you lost Fuel delivery. I bought a spark inductance tester that lights up when put near a spark plug wire. It gives you a general idea that you are getting a spark. An oscilloscope can give you an accurate measure of the spark but most folks don't collect those types of devices. I also have a set of Noid lights to test the pulse to the injectors. I got the Noid lights from Northern Tools.
Since you were driving along and she just shut down, and the engine will turn over tells me that you probably lost an ECU signal somewhere. I suspect something at the battery connection. I would take off all connections to clean and re-seat them. I think that something came loose.

 

Take a hard look at your chassis ground cables and the ECU ground points. If the Chassis ground cables look old and corroded, go buy new ones. They are cheap. A ground cable can fool you because it looks like something that would not go bad but a intermittent connection can be illusive. There are about four or more ground points on that car.
Then take a hard look at your wiring harnesses at each of the relay panels. If you see any corrosion, clean it up and replace stuff. Use dielectric grease to protect them when you reassemble.

 

Today will be the day that I put all of this advise and knowledge to use. I've been trying 1 or 2 of these toubleshooting "tests" everyday when I got home from work as to not overthink this. I'm in a good position to get it running today. I think.