Ignition Amplifier module

I thought I would try a new module in my ignition amplifier to help troubleshoot a severe misfire when the engine bay reaches operating temperature. Per some posts I found on this forum I ordered an AC Delco part number D1906. Visually it was very close to the GM branded module I found inside the amplifier however the car would not start with the new module (seems to fire for a few engine revolutions but won’t run). I put the old module back in and the car started right up and ran.

The only difference I could see was that the original module had what looked like some sort of internal ground bus connected to one of the two mounting holes on the module. Thinking that there might be a ground problem I temporarily installed a ground wire with a ring lug under one of the two mounting nuts. No luck, same no start condition.

Thinking I might have received a bad part I ordered a second one (from online distributor Rock Auto) but this had the same symptoms. Bad batch? Wrong GM part (Delco D1906)? Has anyone successfully used a Delco D1906 as a replacement?

Thanks,
Dave Culgan
1986 XJ6 Series 3

David,

I used the GM module and had no problems.

Aristides

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The two are supposedly interchangeable, David - but the general consensus is that the GM is 'better" quality…

Generally; both connects coil neg to ground - and interrupt ground when triggered from the ign amp. Triggering coil discharge and ignition. Good module ground is essential. As is using heat dissipating paste when mounting the modules - prevent module overheating…

You could also have a capacitor problem causing the misfiring - but such fault would affect both module types equally.

Frank
xj6 85 Sov Europe (UK/NZ)
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I know I’ve used the D1906 in the past with no problems…but I can’t remember if it had the extra ground strap thingy.

This part is marketed with both the AC Delco number and the GM “long number”. If you went to a GM dealer and ordered it, you’d get the same part.

The GM ‘long number’ on this module has changed several times since the 1974 when it was introduced. Often, a part number change reflects a design change or a supplier change. The AC Delco has remained the same. I suspect that the ground strap was considered superfluous and eliminated…and causes no problems in most of the applications this part was used in. But, the Jaguar CEI wants that ground for some reason.

Cheers
DD

Delco is GM???

I wonder if there is not a means to bench test the module. Understand the function and duplicate on the bench.

And, in the car, Check for spark at the coil output when cranking.

Just maybe something else is disturbed on the install.

Carl

Actually, there is a way to bench-test the module. The OP needs to go to the old site and pull up the XJS photo albums.
Look for XJS ignition amplifier repair- by Wayne- Jan 23 2016 It’s in one of albums 37-48.

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Thanks for all the replies. Busy with errands today when I’d rather be back in the garage. I am planning on doing a bench test and will report back with my findings.

Well I performed the bench test that “DavetheLimey” mentioned above ( 12V + to B terminal, 12V - to ground. Jumper G terminal to 12V+: read 12V across B and C) and both the old and new modules passed. Its probably not as good a test as doing it in the car would be but it was simple to perform. i have checked that I am getting a good ground with the new module, as Doug Dwyer mentioned there is a slight revision to the GM / Delco part, possibly a cost savings measure.

I have swapped the old and new modules several times and the old always works, the new one never does, so its not anything to do with the installation. Along the way I did replace some of the wiring around the coil due to brittle insulation, its heart braking how poorly the PVC held up to engine compartment heat.

At this point I have the old module installed, the capacitor (for radio noise suppression) and zener diode ( for protection against disconnected spark lead - I think) disconnected as in my experience with electronics these components can also be heat sensitive when failing.

I’ve driven the car a mile or so but need to do a good long test drive to get the temperature up. Before I do that I need to put together a little breakdown kit with some freeze spray (or canned air dispensed upside down), a reliable way of testing for spark (don’t want to blow the now unprotected working module from a reflected voltage spike), and a way to crank the engine remotely. Regards, Dave

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I don’t think the purpose of the capacitor is radio noise suppression, David - it is more related to the capacitor in the mechanical points system…

I was told that the Zener diode was routinely disconnected in racing circles - it is a sort of extra protection not necessarily vital. And if the Zener leaks to ground; it will seriously impair ignition…

Frank
xj6 85 Sov Europe (UK/NZ)
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Two points"

  1. Did you use the heat transfer “goop” when installing the unit? Apologies, can’t recall the proper name. Important as the units are very heat sensitive.

  2. My car has such a remote start capability. too simple. A wire at the solenoid extending up into the engine bay, Bare end taped over. If needed. Touch to battery +. it is nearbyl Caveat… it weill cranik in any gear!!!

  3. There are in line lamps that can be inserted in to a HT lead to denote the presence of spark. Or merely use a simple inductive timing light. or even an inline unit.

  4. I’ve messed with the idea of a limp home coil. Constant HT feed. A Ford T vibrator coil seem possible. Plug it in to the center post f the distributor cap. Feed constant spark, the engine should run, although might be a bit weird. Never tried.

I think there is a pro version…
Carl

I took a test drive with the original working but suspect module installed. Sure enough I made it about two miles and then the severe misfiring began. Pulling over I used a can of “canned air” upside down to flood the amplifier case with refrigerant, icing it down. The car started right up but I was only able to make it about a 1/2 mile toward home before misfiring stranded me again. Again I cooled it down and again made it another 1/2 mile to the end of the street I live on. This time I wasn’t successful in getting it going and by the time the canned air went empty, it still wouldn’t start. I called AAA (breakdown service in USA) for a tow.

An estimated forty five minute wait kept getting delayed and had turned into a couple of hours. In the meantime a man working on the roads came over and we talked old cars and old motorcycles. He suggested a Chevy V8, LOL.

By this time I decided to give it another try, evidently the module had cooled down sufficiently and it started right up. I made it uphill to about 100 yards from my house but eventually it began misfiring badly and I could go no further. The tow truck request was cancelled. I’m going to walk back down this evening and hopefully get it back into the garage without any more drama.

I think I have established that the ignition amplifier is bad, probably getting worse, but I still have no clue as to why the new Delco D1906 / GM 19180771 module will not run in my car. Besides shopping for another complete ignition amplifier (there is a used one on ebay with 30 day warranty for less than $100 or maybe I should quit being so cheap and spend the money for a new one), I will do some more bench testing on the new module and try and find out why it isn’t firing the car (even though it passed the simple bench test I mentioned in an earlier reply). Oh and yes Carl, I have been using the thermal compound / heat sink grease liberally between the module and the case. Slightly frustrated, Dave

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Two simple tests, David…

  1. Connect a test lamp between coil neg and ground. With ign ‘on’ the lamp should be fully lit (ign amp blocking coil current, coil windings OK). During cranking test lamp should dim and flicker (ign amp interrupting coil current to fire coil)

  2. Connect a spare spark, triple gapped, plug to any plug lead - to check spark quality while cranking. This will not prevent starting when the fault is absent…

Run both tests both cold and hot to compare what’s what with problem absent and present.

While the amp module is a clear suspect - it’s the actual sparking that gets the engine running…:slight_smile:

While the coil neg is grounded, the coil is charged. When the dist pick up triggers the amp; ground is broken - firing the coil. The quicker and cleaner the current cut-off, the higher the ign voltage. A faulty module will ‘stretch’ the cut-off (much like arcing in points dists) - and voltage drops.

Being electronic, the module is heat sensitive - and the fault may not be total. Making testing the module inconclusive…

I think acquiring a used complete amplifier, also called an igniter type AB14, seems a good back-up plan, while you are musing. Having a complete spare does not come amiss; it’s easily replaced ‘on road’ - and may confirm or reject and ign amp fault…

Frank
xj6 85 Sov Europe (UK/NZ)
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At times, my persistence is a fault. AKA stubborn.

I am convinced that heat is disabling the module. Thermal grease and all. So, heat transfer from the module to the case. assured by the thermal goop. Enough? perhaps not.
How about from the case to the water rail ? As I recall, vaguely, that is where the unit is mounted. Isolate or assure a better transfer ?
I don’t have a suggestion for that one…

Carl. .

Thermal goop is sparingly applied for best results. It bridges the gap to the heatsink - does not cool magically. The heatsink has the same capacity, so the module must be shot or overwhelmed. If connection to the intake manifold were a concern, we should know. So either the module and it’s replacements are broken in different ways, or some are broken and the module overheats because something ele is wrong. It’s just a breaker and the car runs well, so either too much voltage to the module or too much gap (we’d know that as well)? No idea, but worth a try maybe?
But first, find a substitute as a complete unit. I have one but can’t share. The Atlantic is in the way.
David

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The AB14 is grounded to the engine/intake manifold by the two mounting bolts, David - forming the ground for the whole operation; good ground required through the bolts…

The intake manifold is about the coolest thing on the engine…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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Thanks for all the thoughtful replies to my original post. To bring this thread to a close, I received a used ignition amp through eBay (supposedly with a 30 day warranty), installed it and my car fired right up. Took it for a ten mile test drive without issue but I’ll need to get some gas before I really give it a good workout.

Along the way I learned a lot about the ignition system and that is always a good thing. Next up, a very high idle (1400 rpm when hot ) that I suspect is due to a pretty big vacuum leak. Clamping off the easy to access hose from the AAV made no change. I’ll review the many forum posts on the subject and start looking. Regards, Dave

If you push in the AFM flap and the rpm do not go up significantly, it is not a vacuum leak but rather the throttle not fully closing, the overrun valve stuck open, or your timing changed by a fair amount.

Thanks. I took off the air distribution block to check the over-run valve and noticed that the bypass screw was open a lot more than I had thought it was. Previously I had put in a short piece cut off from an Allen key to help adjust it but it was stiff and still very hard to access so I must have thought I had closed it off more than I had, when trying to reduce the idle. This time I lubricated the screw with some anti-seize grease and inserted a much longer piece of hex stock, about as long as possible without fouling the AFM. This was much easier to access and I was able to properly adjust the idle.

Now onto a persistent bad oil leak at the oil filter head, probably at the ports for the oil cooler lines. I recently re-installed them with new O-rings, but I’m wondering about the quality of the parts. They were sourced from eBay but I don’t recall the packaging. Ironically, when I had first put all of this together with o-rings from a popular Jaguar parts distributor oil was practically pouring out. On disassembly I noticed a significant flat spot on one of the o-rings. Whether it came this way, or I somehow damaged it placing it on the hose end, or pushing It into the port I’ll never know. Not giving up.

Yep… been so, for a very long time.

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Right.

AC Delco is a parts merchandising/marketing division of General Motors. “Goodwrench” (later “GM Goodwrench”) was another GM brand…although I think it is now defunct after decades of operation. All under the umbrella of GMSPO- General Motors Service Parts Operations…which itself is the result of a reorganization and consolidation of various GM parts operations over the decades

Cheers
DD

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