So I managed to get my xj6 running again, YAY! now my friend is really wanting his 1986 series 3 sovereign with the 4,2 back on the road to. One problem is the engine has no power, about 4 months back we were in the car driving someone cut him off and he had to hit the brakes hard, we heard a light pop and suddenly he had virtually no power, the car could barely make 20mph to get it off the road. it's been slow going on working on it for him as he had to relocate for work for the last 6 months but now needs his car back. We checked the plugs, wires, coil etc ignition is solid. Fuel flow looks good. I have not had one fail before so don't know the symptom but was wondering if it could be the mass air flow meter, if it could cause a massive loss of power like this resulting in the car barely being able to move under its own power like that, and the engine sounds really rough more like a diesel at times, has great oil pressure. I just want to explore everything as I hate to be the one to say its a lost cause and plain on a rebuild on the motor. At idle the rpm is weak, takes a long while to rev at all and peaks around 1500rpm before maxing out.

1986 Jaguar Sovereign xj6 4.2 liter is the vehicle any info is appreciated and we checked the head is not leaking either, though maybe external leak but nothing.

 

I would check the fuel inertia cutoff switch. It is tucked up under the dash in one of the footwells, near the soor hinges. One of the other's will pop unsoon with better details.

 

Sorry about the spelling, I'm on my phone while riding on a train

 

always fun to text on a train, been there done that one, but thanks for the info will look into it as well

 

the Inertia Fuel Cutoff Switch is on the passenger side, (LHD cars), exactly above the kick panel, below the right corner of the dash. It's a black box with a grey connector at the bottom and a spring-loaded button on top.

I doubt it is the IFCS because you wouldn't be able to start the engine if the IFCS was tripped. However, just push the button on top, if it springs back, the switch is fine. It it clicks when you press the button, it was tripped. Think of it as a service panel breaker in a home. Just like a breaker cuts off any electricity when it tripps, the IFCS cuts off the fuel supply to engine when it tripps.

hard braking should not cause the engine to malfunction, something was about to go and it was precipitated by the hard braking. What could have caused the "pop" noise? no clue.

 

Was the battery loose?


Can only think the fast stopped caused something loose to hit something else and damage some wiring etc

 

Fuel cut off is good, the fuel pump kicks on, sounds funny , replaced the MAF, now it doesn't start even so this is going to be fun to track down, battery is very secure. So I think i'll pull my working fuel pump and give it a try, also replace the fuel filter to just in case, i do know that engine makes one hell of a racket when he started it up earlier damn scary sound indeed

 

WAG!!!!


1. The engine jumped on it's mounts. in itself not good and indicates need for service.


2. The intake includes a large flex hose. If displaced, it is a huyge air leak with either a no run or a poor run at best.


3. Fragile wires weakened further by engine movement.


4. the inertia switch is an on/off thing, No in between . Been there in another critter. As a sorta musician, Jose might recall 'don't mess with Mr. In between".


Carl

 

MAF ?? these cars don't have a MAF (Mass Airflow Sensor).

which sensor did you replace? Are you thinking of the AFM box (Air Flow Meter) ??

Carl is correct, the IFCS is either off or on, no mid-point.

but I do not recall the song "Don't Mess with Mr. In Between" ? I remember a song that has a chorus that says "Don't Mess with Jim".

 

air flow meter is what i meant, sorry to much time working on my land rover I think. The fuel is good, pump works fine i checked the wires today all snug, got it running (badly) and it didn't sound good there is a definite mechanical problem in the head, first i thought it was valve guides like mine did a visual they are all in place with a kit so i'm starting to wonder if the problem isn't down lower in the valves themselves. Mine made a loud racket when my valve guide slide up, this is a few times worse on the sound. So will keep digging.

 

Have you looked at the fuel pressure regulator on the fuel rail, i cannot imagine hard braking would cause an issue but it's worth another look and should be pretty easy to see if you are getting good fuel flow...

 

Jose:


Perry Como and Johnny Mercer sang it, "Accentuate the positive". Don't mess with Mr. inbetween is ion the lyrics.


Trivia, to be sure...



Good way to live as well.


Carl