Consulta sobre el amplificador de injection

Hello, buy a jaguar xj12, I do not dryI can know if the injection amplifier works well, disconnect all the injectors and try them one by one, clean them and check all the connectors, I tried with an LED lamp, each of the connectors and they all flash when I tried to start the engine, and I noticed that the cold start injectors is stronger the light than in that of the cylinder injectors. it’s normal, I haven’t been able to start the engine again. Thank you for your attention

@Paul_M_Novak may be of help.

Have you checked the fuel pressure at the rail? Do you hear the fuel pump run for 2 seconds when key first turned on? If all injectors are flashing, it should indicate a functioning ignition system and injection computer…
If your injection computer is labeled “6CU” fuel pump circuit failure is common. You can jump the fuel pump relay to bypass this type of failure.

Hello, Paul :
Lots of grace
I don’t know how to properly test the injection amplifier,
already ripped off once but stopped
So buy spark plugs coil and oil, clean absolutely everything from fuel tanks, injectors
But it doesn’t start the engine.
I’ve already tried to have a spark and also place an LED lamp on each of the injectors to prove they have a pulse, I don’t know if it’s too low

As you can prove this, in fact I hardly saw them say the forum they make clik, that I have not reviewed.
Sorry about the translation, I speak Spanish, I’m from Mexico city… And I really appreciate your help.
Jorge Meza.

What year is your XJ12?
Do your fuel injectors make a noticeable click when you crank the engine with the starter? Get a mechanics stethoscope and have someone crank the starter while you listen to the injectors.


thanks, Robert I check this right now.

thanks Paul, is 1979, I check with a stethoscope, I already did it with an LED lamp and if I turn on I feel that there is very little voltage. now I’m going to check as you tell me, thank you very much I reported after.

Jorge Meza

If they click you have enough voltage.
They never get full 12V.

thanks for your answer, before the gasoline empty, star excellent, so I full the thank, spark plugs news, clean everything, injectors, gasoline lines, pump gasoline, change pipes, and now doesn’t want to turn on…

Hello, thank you all,
If he didn’t have enough voltage, is it possible to do something to him amplifier? I don’t know possibly has a bad land or a reley with false contact et cetera.


  • Is the fuel pump working, can you hear it?
    You can by-pass the ECU/relay to test and be sure, info in the archives
  • Fuel pressure
  • Can you hear the injectors clicking wen you try to start?
    Also, with ignition on, if you turn the throttle turntable fast by hand you should hear the injectors click once.
  • Do you have spark?

If by injection amplifier you mean the black box on top of the intake manifold it’s called Ignition Amplifier. It controls ignition but also tells the ECU that the engine is turning and how fast via a coax wire that often couses trouble. Nothing to do with injector voltage though, that’s the ECU (Unidad de control electrónico). Lots of info in the archives as well.

Revisit all the areas you worked on, you may have disturbed/disconnected something.

I suggest you download this and have a read:

And added bonus, by the time you finish you will also have learned how to speak English !!
All the best.

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Aristidos, thank you very much for all that information and start reading everything.
I’m sorry I’d already done everything on your list, I just lacked the clik of the injectors that I don’t hear because the starter engine makes a lot of noise.
I’ve got a spark.
I hear the gas pump
and when it accelerated it sounds like clockwise some cliks.
all you have to do is listen to the cliks when I try to turn it on.
Thank you very much for your help
Jorge Gabriel Meza

What was the initial problem, before you did work on it ?

Check the Throttle Position Sensor. (details on the book)
Check the continuity on the co-ax wire (blue I think) between the Ignition amplifier all the way back to the ECU.
Also check that you have correct values at the Air temp sensor and Water temp sensor and that you have the same values at the plug of the ECU.
The ballast resistor could also create problems.

If everything else checks ok, next thing could be the ECU.


AIR Temperature Sensor - XJ – XJS V12
Temp 'C Resistance

-10 ---- 9100 - 9300
.0 ----- 5700-5900
10 ---- 3764
20 ---- 2400-2600
30 ---- 1698
40 ---- 1100-1300
50 ---- 833
60 ---- 500-700

Coolant Temperature Sensor - CTS

Temperature vs. Resistance

0 C 32F 5.9 kohms
10C 50F 3.7 kohms
20C 68F 2.5 kohms
30C 86F 1.7 kohms
40C 105F 1.18 kohms
50C 122F 840 ohms
60C 140F 600 ohms
70C 158F 435 ohms
80C 176F 325 ohms
90C 194F 250 ohms

Just a note…

Jorge has a 1979 V12…which would be “Pre-HE” and have the older D-jetronic fuel injection, Opus Ignition, a 3CU ECU, etc. These systems are quite a bit different than what we have on an HE V12

I’m a little worried that the conversation might get a little confusing.

Apologies for not having anything of substance to offer that might help Jorge. I have zero experience on the Pre-HE cars


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Aristides, has been invaluable
I tell you that the problem initially is that I bought the car here in Canada, it’s been stopped since 1991 indoors, I live in Mexico City and I came on vacation I saw it on the Internet and I couldn’t believe it, I’ve always wanted that jaguar, so without thinking about it I bought it and I’ve been fixing it for several months. I want to take him to Mexico and finish repairing the bodywork, but I want to take him by road. I’m very adventurous and that jaguar has to arrive even though sometimes I think I’m not going to make it, that’s why I really appreciate all the information I’ve received!!! Thanks again.

As Bart Simpson would say ¡Ay, caramba! - that’s going to be quite a journey. Just driving a hired VW beetle around the ring road in Mexico City was enough for me.

jajajajajaja, saludos.

Well, if you pass through Denver, contact me and I’ll compre almuerzo!

Mi Espanol esta MUY pobre, pero, trato!

Thanks for clarifying that Doug.

It’s best to put your year and model on your signature so we know what we are talking aout and avoid confusion.

Me too have zero experience on Pre-HE cars.
So the engine hasn’t started since 1991? That’s a long long time…
Was it kept in a garage or outside?
Where in Canada? I lived there for 8 Years.

You didn’t mention anything about changing your Fuel Pressure Regulators. I think they must be very much kaput and may be why your engine doesn’t start.
Also, I doubt that if your injectors haven’t been professionally cleaned and tested will ever work properly.

As a test, put some starting fluid in the intakes and see if your engine ignites.
If it does you will know that the problem is fuel related.

muchas gracias, creo que no paso por Denver, estoy en Toronto Canadá, mi camino sería hasta Texas y de ahí Mexico city, pero gracias por la oferta!! saludos

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