All the wiring in/over the V is new within 3 years, including that running inside the distributor, so I'm not thinking that is the fault. The wiring to the ignition module has also been redone about 3 years ago.

I looked at the TPS voltages. At idle it's around .28 to .30 volts. After that it's predictable up to full throttle, which tops out at 4.88 volts.

Last weekend I tried bypassing the fuel sump and ran the line to the fuel pump directly into a can of gas, and ran the return line into the same can. It didn't solve the problem, but I could see there was a good strong flow of fuel returning back to the "tank".

No reducer or valve on the fuel line coming into the engine compartment. I'm in the US.

The spark I wonder about. It certainly is not a large blue cracking spark. It's yellow to yellowish-white. Just a few days ago (after this problem cropped up) I replaced the original dual coil arrangement with the DAC6093 single coil. Could a faulty ignition module be responsible for insufficient coil output?

The DAC6093 has a total of four terminals, two marked "+" and two marked "-". Since the second coil has gone away, one of the "-" terminals has no where to go. Since the coil came with zero documentation, I wonder if the unused "-" terminal is supposed to be connected to something. You can't see in clearly in the photo but it's lurking right behind the insulated silver connector.

Thanks,

John
1987 XJ-S V12
"Queen of the garage"

 

My single coil setup has the front tower with two prongs connected and the back tower with one. A faulty coil/shorting coil will take out the ignition module. I'm waiting for my new coil and my nos module to arrive before I do any further trouble shooting. I think we are both chasing the same problem.

 

OK.

That TPS voltage is too low, the ECU will have no idea what to do with that low signal. One here a long time ago was at that setting and teh engine constantly surged. Once set into range all was sweet.

The fuel seems OK.

The spark is a worry. I have had NO dealings with that coil, so others who have used it will have to assist there. The module is basically just a switching device that replaces teh old contact points. Granted, it also sorts a few other bits as well, but that switching of the coil is what supplies the ability of that coil to spark.

Also agreed, if any coil on any module controlled system shorts internally the module is toast 99% of the time.

One other thing to look at is the +ve supply from the ignition switch TO the +ve post of the coil. With ign ON, that post should be very, very close to battery volts. One of mine got fitted with an IGN relay (by me) as I simply could not find the voltage drop in the time available from the switch to the coil. That relay sorted many issues. Since that +ve post also supplies the +ve power TO the module, a low +ve reading would have the module also see low voltage, and may effect its operation somewhat.

 

Just finished adjusting the TPS. It's now a .336 volts idle, 4.9 something full-throttle. No improvement, in fact now it won't even start.

I don't blame that on the TPS adjustment, but of something (ignition module) going from bad to worse. After all, when I put in the new ignition module it started right up. But it quickly went down hill to the point of taking tons of effort to start. Now it cranks and cranks but is acting like it either not getting any spark or any fuel.

So...two NOS ignition modules are supposed to arrive April 1st (insert joke here). I do have the old coil(s) I can reinstall to see where that gets me.

Persistence is the key they say...

Thanks,

John
1987 XJ-S V12

 

Bugga.

While you are waiting, I luv that also, take the DVM and probe the +ve and -ve of the coil, NO wires attached, and write down that reading. You should be seeing "about 0.7ohms" or there abouts. Anything over 1.0ohms is too high for that module.

The 2 original coils were 1.2ohms each, and when paired as they are, gave a reading of "about 0.7+/-". Theoretical, HAHAHA, said 0.6, but were all know what theory means dont we.

Now do the same on those 2 old coils, and note them as well. If they give 1.2 each, pair them up, and do a total reading. If its close to the above spec they "should" be OK.

I run single coil down here, but not that Ducellier thing. Just a simple "Universal Electronic Ignition" coil. It has a primary of 0.78ohms, and none of the cars is lacking in spark. The amp stays "cool" as designed, so smiles all round.

 

J-C-R I'm pasting my post from my thread on my similar problem....

>>>Success! Changed out the coil (new coil) and module (NOS Delco Remy NOT aftermarket) Fired car up...................runs like a champ! (where's some wood to knock on!) Drove 5 miles, shut her down, let sit, re-fired......no problems.

"Disclaimer"...this is in NO WAY intended to deter, poo poo, or be critical of anyone's advice here...it is GREATLY appreciated AND there are some amazing and pure geniuses here......

.....that being said, be very careful of diving in feet first when there is a "running" problem, ie, fix one thing and try the car....if the car's "down" be careful of running through a mired of items because you want to know "what" fixed it and you want to make sure you don't further complicate matters by fiddling something loose or off kilter that will further frustrate you.

In my case the problem was intermittent, then worse, then OMG it won't even idle. I checked the advance, no joy, checked the sump, no joy, checked harness connections, no joy, replaced the module with a known good, older one...some initial success then rapid failure. I deduced it was the coil intermittently failing then complete failure which quickly toasted the older module.

I resisted the urge to fiddle with anything until the module and coil arrived. Once here yesterday I went out and put them on, VIOLA! fixed. never touched the coaxial, TPS etc until I knew what I suspected was off the list then I would move on one item at a time from there. Over doing trouble shooting w/o the ability to "check" functionality after each item begins a "chasing your tail" mentality where you start to wonder and question everything you've done..

If my problem reappears soon then I'll move over to an intermittent TPS failure and replace that and then re-check, fingers crossed I've resolved the issue.

Thanks to all who have provided help and insight, you're input has been invaluable in getting my car back on the road and is what makes this a great place to hang out. Cheers!<<<<

 

HaHA!!!! Spoke too soon! 3rd time wasn't a charm! Went out after she cooled for an hour our so and it's right back! It's doing what it did before, chugs in gear but pretty good in "P" and "N". So at least I know what it wasn't . My TPS is reading a solid 34 to maybe 36 at idle so I really don't think that's it. I'm pretty sure I've ruled out ignition, I'm thinking of moving towards fuel delivery, maybe pump dying? I'm going to go out for grins and pull the condensor wire in the amp and check my coaxil wire end then reattempt.

I'll quit mooching off your thread J-C-R!

 

Oh, mooch away my friend, mooch away...

Interesting discovery here. The two NOS modules arrived today. They look different than the original module that was in the car, and they look different than the after-market (BWD the box says) modules that the local auto parts store has been selling me. These are supposedly GM modules, but not sure what that really means in these days.

Anyway, so I throw one in, and try and start. Instead of the 5-minute starting order with the other module, this is only about a 1 minute ordeal. Eventually it lights off and I give it a minute or two to warm up. I then put my hand on the TPS, crank it, and...much to my surprise, it runs well up into the RPM's with not a hesitation. "Success...success" I cry! I do it again...success again!!!

Yet.........I spoke too soon :-(

After giving it a few more minutes to come up to temperature, I give it the throttle and it's back to the bad-old-days, power instantly drops out. Sigh.

So, it's turned into something temperature related???

I suppose I can put the old dual coil arrangement back in, but if these funky ignition modules took out my new coil I suppose they could have done the same to the one ones, so I'm not sure where that would get me.

I could order another new coil, install it with the yet-untried "new" module, and see what happens.

Better yet I think I'll stick my glass under a box of my favorite chill-able red wine, open the tap, and just reflect on what to do next.

It doesn't seem like it should be this hard...

Thanks,

John
1987 XJ-S V12

 

A bad module will not take out a coil but a bad coil WILL take out a module. If that makes sense. If one doesn't use the white silicone grease on the bottom of the module they'll last about 3 miles or 3 minuets, which ever comes first.

 

A thought after I prematurely toasted both of you, no harm, I needed a JD anyhow.

Unplug the CTS (Coolant Temp Semsor), and bridge the 2 contacts in the actual plug. A paper clip will do, just dont let it short on any metal nearby.

This will "trick" the ECU to think it has an engine at "normal" operaing temp.

It could be a mongrel to start cold, but the issue of a CTS going flaky and reeking havoc are eliminated for now.

2nd thought. When the thing fails to do what it should, place your hand on the coil. If its about the same temp as the surroundings, no issue. If its hotter, then you do have an issue with the ignition system.

Also "feel" the amp, it should be "warm" to the touch, although damn hot after a 20 minute run with the bonnet shut. With the bonnet UP, as I reckon you are doing at this stage, it should only be warm to touch. I relocate that amp out the front of the radiator, and simply extend the wires, and that has been a Godsend for me down here.

The "shielded wire" is also on my thoughts. It is a damn fickle thing these days. Again, I dont run one inside the engine bay at all, and pick it up again at the RH bulkhead connector.

 

Interesting discovery today...

Went down and measured voltage across the coil, it's right at 0.7 volts.

I realized that these past few times of changing modules I've been cheating a bit...I didn't put on the heat sink compound and firmly tighten it down (I did tighten the one bolt that grounds the module, but not the other). This time I did. It was still a struggle to start, but once it fired off I let it warm up just a bit and was able to get the RPM's well above 1000. So I waited and let it come up to full temperature, and was able to get it somewhere over 2500 RPM! Waited a few more minutes and tried again...success and more success!

More interesting may be this. In an act of desperation a few days ago I took off the air intake hoses so that the butterflies are breathing unfiltered air, as well as to inspect for crud and contamination. After my success this afternoon I decided to put them back on. I had screwed the four bolts into each butterfly housing completely in when I took them off a few days ago, and this afternoon I started screwing one of the bolts out. I remembered that would give more air that the engine would want, but something told me to just pull one bolt out to see what happens. The engine acts the exact same way as the problem I've been fighting! Well, almost. With my problem, it will idle ok but any attempt to open the throttle results in it revving and dropping out, revving and dropping out. When I pulled the one bolt from the butterfly housing, it does that exact same thing at idle...revs and drops out over and over again. Sticking the bolt back in results in good behavior.

What does it all mean??? Somehow in all my mucking about under the bonnet I've possibly created a vacuum leak that is presenting me with two problems, one I may already have solved with my first replacement of the ignition module, and the hidden vacuum problem I didn't even know I had.

I'm going to let it cool and then start looking for a vacuum leak or something loose.

Thanks,

John
1987 XJ-S V12

 

John, I learned the hard way on the silicone grease. I had an 86 C10 pickup with the Chevy HEI distributor, it uses the exact same four prong module, wouldn't start, dropped in a new ungreased module and it went about three miles before stopping, my neighbor informed me of the grease that evening, got a new one, greased it, ran it for years. That heat sink grease is that important.

 

Remember, 50% of your maintenance is caused by 50% of your maintenance.😊

 

The struggle continues...

Pulled out my last unused amp today. Greased it up with the included goo, fastened it down properly (as well as the case, bolted it firmly to the intake manifold). Fired it up...the usual 60 second struggle and it comes to life. Let it warm up a minute or two and, once again, good throttle response up to about 2.5K or so (I'm scared to take it past that with no load on it, should i be)?

I let it run 15 or 20 minutes in this condition, and each time I try it response is good. So, I shut it down, wait about 5 minutes, fire it back up (fires up immediately), and I'm instantly back to power dropping out above 1200 or so RPM.

My guess is that the shutting down/starting isn't the problem, but eventually something (ignition module?) got hot enough to become erratic. If I let it run long enough without stopping it I'd probably get the same result.

Ignition amp cover is much more than warm, it's hot enough that I can only leave my fingers on it for several seconds. Ambient temp is about 70 degrees F, bonnet is open.

Another, off-the-cuff theory...something is getting hot enough to expand something else and let air in, leading to the situation I described previously where having a bolt out of the throttle butterfly assembly can cause similar behavior. I know it's supposed to work the other way, but this is what desperation leads to :-)

This weekend's experiment will involve finding a way to keep the ignition module cool using some extreme method I've not come up with yet, and seeing if that makes the problem go away.

Always willing to hear other ideas though...

Thanks,

John
1987 XJ-S V12

 

Dont worry about the revs, the V12 is just fine, its us mere mortals that have no faith.

That amp that hot after that short time is not correct.

That amp is being overloaded by the coil/s, plain and simple.

The amp has to "dump" a lot of unused "energy" (my wording is crap, but I know what I mean), at idle and unloaded revs, and that is the task of the paste, to allow a good heat path for that "energy".

If the coil cannot get the energy out via the spark plugs, it "backs up" and the amp has to deal with it, hence the heat build up.

This can also be caused by wrong spark plugs, spark plug gap, bad engine earth path (cables I mention every time), spark plug leads.

I dont use "resistor" spark plugs on the V12's (my choice of course), and a lot of issues I once had are gone. The plug lead resistance is also a contributor to this energy loading. I always use Magnecor HT leads. All my V12's have leads that are 10 years old or more, and are still as good as when first fitted.

The fact this engine takes about 60 seconds of cranking to start cold, is also NOT right. They should fire clean and strong within 3 rotations of the engine at any time. All mine do. This can be spark related, fuel related, injector pulse related, so lots of searching is needed.

When the amp is as hot as you state, IS the coil also HOT, I reckon it might be.

 

I don't think that amp is overly hot for having run the car for 20mins, everything in there is going to be HOT. Mine is the same (heat wise after 20 min run) and so far it's running just fine. If you've got a new coil and new amp it's time to move on to something else. The V-12 gets HOT and anything bolted to it does too. Your amp worked fine before this problem right where it is as well as 100's of others. Moving it or making it cooler isn't going to miraculously fix your problem. You have a new amp and coil, should work well and last a long time. When the running goes to pot have you tried jump wiring the CTS to see if it improves? I'm considering my problem was a flaky CTS since the day it seemed to want to work right I had pulled the CTS plug and checked the OHM's three times and I think I may have "adjusted" the plug fit unknowingly fixing the problem. I just got my new lucas OEM CTS for a steal and a new pigtail with rubber boot for around $7 off ebay. I'm going to swap those out for good measure. Even though it still seems to be running right.

 

A very experienced Jag mechanic friend of mine told me when I was having rough running problem that the first thing he would do is check and even just change out the CTS as its cheap and causes all sorts of problems and will just give up without any warning
Heres a video of my car with bad CTS and then one after changing it out

 

Gotta love that manual trans in the V-12 Crankmaster....very nice.

 

Thanks

Here she is accelerating, its a getrag 265 conversion

 

Very nice...trying not to high Jack here BUT what are you running for exhaust?