Hello everyone, it’s my first post here I’ve got 1985 xjs 5.3 HE with lucas ignition system. Recently I finally managed to start the car and drive a bit(I bought car on copart as not running, turned out it was caused by bad fuel pump, fuel filter, ecu, injector cables and transmission filter clogged with dirt). Yesterday I was wondering why my tachometer is not working and I read on this forum that it may be ignition amplifier cable to tachometer(I checked all grounds on instrument cluster, all good, tach also looks fine). And here comes two of my questions:
I opened amp to check is it good inside, well could be worse i think, photo below. I’d like to ask do you know maybe what is the marked part/where to buy it? It’s corroded much and I’d replace it if it isn’t big money lol
2.I discovered that amp-ecu cable splits into two cables and I have no idea where the second one goes(one is yellowy white and the second is black) Also this piece of harness looked like it was tampered with some duck tape and some great tech skills.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
That’s an ignition condenser. You can buy one for a lawn mower in the garden center at Walmart, or just take that rusty one into any auto parts store and ask for one that looks like it. Specific capacitance rating not important, any such ignition condenser will be close enough.
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
3
The yellowy-white thing is actually a coax cable. It’s one of the common failure items on these cars. It gets cooked, brittle, cracks, and then the core shorts to the shield and the engine stops. The black wire is just the ground connection for the shield.
Thank you very much! Now I’m trying to fix my tachometer… I checked all wires, all good, maybe you know what can be wrong? Tach needle also looks good I checked that little tach electromagnet mechanism and it seems good too… I read about some resistors in ignition amp, do you know in which part of amp those are? Problem is that tach does not work, one time when i hit probably max RPM tach needle moved a little bit.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
6
The white blob inside the amp contains two resistors. One powers the tach, the other triggers the EFI. I think one of them is about 10K ohms and the other is about 6K ohms. Anything in that range is acceptable; they’re only there to limit current in the event of a short. But yeah, there have been occasional failures, so they are worth a check. If either one is open circuit, just install some regular 1/4-watt resistors.
Even if it wasn’t working you could have sold it for $100 USD if it was complete.
I have two plus an extra HAL sensor and ballast resistor.
When my 1972 original ign. amp died three years ago I had it professionally rebuilt and bought a few spares from Stoneleigh and had them rebuilt as well. Also the BUTEC alternator solid state voltage controller.
Correct me if I’m wrong here but I understood the little canister looking resistor was something to do with suppressing noise on the radio, which why I deleted it based on advice from this forum. If my memory serves me correctly. Anyway the car works fine without it.
Aha, sorry, I though you meant the entire Ingition Apmlifier, not a single resistor. And you may be right, I only have the one from 1972 in the v12 E-type.
Zener would probably be a 15 volt, 5 watt or higher. Resistors could be 1/2watt- any electronics distributor (Digikey, Mouser) will have them. Probably $5 including shipping.
The Zener diode is to protect the output transistor in the GM module from the ~300 V inductive kickback of the coil primary when current is switched off (this is the voltage that is multiplied by the turns ratio of the coil to become ~30KV at the secondary). I tested one once…the Zener voltage was ~500V very approximately (memory not so good). The idea is to allow the back voltage (EMF) in operation as required but to provide extra protection from larger voltages if for example the secondary isn’t connected to sparking plugs. The GM module has adequate protection without the Zener, which is omitted from non-Jaguar applications AFAIK. All IMHO.
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
14
You can simply disconnect the wire from the tach and connect it directly to the - post on the coil. If the tach works connected that way, you know it works, it must be the resistor in the white blob that’s failed.
I bought a new amp two years ago, full box, and it did not have a zenar diode. Or if it did, it was very tiny. May have just been needed for 80s-tech Gm modules?
You may be correct; I was thinking that it was in the circuit to protect the tach and ECM from the fly back voltage. Although it would do that before or after the resistors, it might affect coil operation and need to be higher wattage where it is.
The 4-pin module we know and love was part of GM’s “HEI” ignition system introduced in '74 and pretty much standardized by '75. I worked at an Olds dealer back in the day and we used to sell 'em all day long. The part number was 1875990 but has been changed 2-3 times in the last 25 years or so, almost certainly to reflect a design change or supplier change. One change, I think, was to replace the beryllium with…something else. If you have a module stamped ‘990’ it’s probably pretty old.
Circa 1980-81 GM ditched the 4-pin design and went to a 5-pin module for most applications. I can’t remember what the extra pin was for or why it was needed…but they seemed to be more reliable, as I recall.
“Jaguar” and “Lucas” are constantly criticized for poor quality and unreliability yet one of the more common failure points is a part sourced from GM. That’s always been a bit of a chuckle for me
I’ll wager a scientific analysis would ultimately show that the Lucas CEI is as reliable as any other ignition system…which can be interpreted a couple different ways.
Yeah, the modern ones must be superior as i rarely hear about this part failing on the forum (as long as its true GM.)
Where was this mounted on most GM cars? Although the intake manifold is a decent place on our V12s, I’ve recorded temps of 180F on the amp box with temp gun. Ive ordered some temp strip stickers, will put one on my amp box for more accurate measure.
Inside the distributor, hence the arc shape. Was part of the unitized ignition on Pontiac Ram Air engines in ‘71-72, then corporate wide called HEI for ‘75. Coil was on top of the distributor cap.
I’ve got 1985 xjs 5.3 HE with lucas ignition system. Recently I finally managed to start the car and drive a bit(I bought car on copart as not running, turned out it was caused by bad fuel pump, fuel filter, ecu, injector cables and transmission filter clogged with dirt). Yesterday I was wondering why my tachometer is not working and I read on this forum that it may be ignition amplifier cable to tachometer(I checked all grounds on instrument cluster, all good, tach also looks fine). And here comes two of my questions:
Now I’m trying to fix my tachometer… I checked all wires, all good, maybe you know what can be wrong? Tach needle also looks good I checked that little tach electromagnet mechanism and it seems good too… I read about some resistors in ignition amp, do you know in which part of amp those are? Problem is that tach does not work, one time when i hit probably max RPM tach needle moved a little bit.
