XJS ( X27 ) 1975 - 1996 3.6 4.0 5.3 6.0

1991 V-12 Engine issues

 
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Old 04-22-2019, 07:21 AM
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Default 1991 V-12 Engine issues

Hello,

So I have a 91 XJS V-12 that is definitely not running correct. Here is the background, the other week I was driving the car and it was running like a top, purring along with nary an issue. As I was coming down a hill the car suddenly shut off (electrically died completely) I pulled over and it would not start or anything. I got a jump pack starter and the car started up, however there was an odd mechanical noise from the front of the engine and it was idling around 350-400 RPM. I had the car towed back to my house and put her in the garage.

I started looking at the car and here is what I have done thus far:

1. Checked both "A" and "B" bank coils. They are working properly such as they are receiving voltage and outputting voltage.
2. I pulled the Distro Cap and verified that the rotor (Marelli) did not short out
3. I verified all plugs (used a timing light) are sparking
4. I swapped the Ignition Amplifiers, no change

I have isolated that it is not the ignition system at all, so I believe I am at the CPS, but do not have an "O"-Scope to see if it is outputting correctly.

So my question is what should my next steps be? Any help and ideas will be very appreciative as it is almost summer time here in Northeast Alabama and the Black Cat needs to cruise down the roads!

Thank-You,
Jeremy Sharp
 
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Old 04-22-2019, 04:30 PM
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You said the car started with a jump. Check battery voltage with a meter it should be around 13.8V with the negative lead disconnected.

If it is low, 12V is flat and would not be enough to start the car. The car might crank but not start due to the low ignition voltage. Re-connect the battery lead, If you can jump start the car measure voltage on the battery, charging voltage should be about 14.4V, if this is low then the problem is the alternator.
 
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Old 04-22-2019, 04:50 PM
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The car starts and does run voltage is good and idles around 400 500 RPM and will not run up beyond 1200 RPM
 
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Old 04-22-2019, 06:24 PM
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Are all cylinders getting sufficient fuel?
 
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Old 04-23-2019, 04:18 AM
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As per above... Fuel filter/Fuel pump?
 
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Old 04-23-2019, 05:06 AM
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I don't see this as a fuel problem - surely everything points to an electrical issue. Could the 'mechanical sound at the front of the engine' be a bad alternator (shot bearings)? I'd be checking the battery leads are properly secured as a starting point, then testing voltage output of the alternator with a test meter.
 
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Old 04-23-2019, 04:02 PM
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Hi Gunner77

Can you hear the Fuel Pump running?

Let us know and then report back, as its starting to sound like a fuel pump issue to me, although of course it could be anything
 
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Old 04-23-2019, 04:11 PM
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Yes the fuel pump is turning on and have verified fuel pressure at the rail
 
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Old 04-23-2019, 07:02 PM
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Hi Gunner77

Just had a thought on what could be the cause of your engines problem

Where this could be the very often overlooked resistor pack which controls the Injectors, that is located right down by the front of the Headlight Nacelle

Its basically a Silver box (aka the resistor pack) with a Socket and a Plug and just a little PIA to get to, though it would pay to take it out and clean the Plug and Socket of this Resistor Pack

As dirty contacts on this Plug and Socket can play havoc with the Fuel Injection System

At one stage my own Car was starting to 'Bog Down' but when I clean the Plug and Socket of this Resistor Pack, the problem instantly went away and pleased to say that She has been running fine ever since

You can see how I did this and what the Plug and Socket of the Resistor Pack looks like on Page:11 of my 'Cherry Blossom' Restoration thread

Click the Link below to see the Plug and Socket Cleaning of the Resistor Pack which instantly Cured the Bogging Down Problem on my XJS V12
Cleaning the Plug and Socket of the Resistor Pack as my Car was starting to Bog Down and Cleaning that Plug and Socket instantly Fixed it
 

Last edited by orangeblossom; 04-24-2019 at 02:56 AM.
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Old 04-24-2019, 01:07 AM
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Originally Posted by bladerunner919 View Post
I don't see this as a fuel problem - surely everything points to an electrical issue. Could the 'mechanical sound at the front of the engine' be a bad alternator (shot bearings)? I'd be checking the battery leads are properly secured as a starting point, then testing voltage output of the alternator with a test meter.
It's not a carbed engine, so it needs all 12 injectors firing. If only half of them are running, then you won't get a properly running engine. The injectors are also all electrical.
 
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Old 04-26-2019, 12:45 PM
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Default Had a similar thing happen

Different car ('98 XJ8) but coming off an extended highway run, went down a hill on the exit ramp and suddenly the car just died. Right before it did, all the dash indicators put on a random light show for a few seconds. Did you get that as well?

Turned out to be the alternator. Replaced it and all was well again.
 
 
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