My 1986 XJ6 4.2 Series 3 has been playing up for the past couple of months. It began with a complete loss of power and transportation to the mechanic. After several weeks and much scratching of heads, the fuel regulator was reconditioned, spark plugs and injector plugs replaced and electrics checked. All seemed Ok and for a week or so seems to be OK. But the same symptoms returned and the mechanics have no answer, not helped at the time by the apparent intermittent nature of the problem. If there is no issue when starting off, all is good. But otherwise, the engine runs rough, and if raised to 2000rpm starts to cough and splutter with black smoke, obviously rich mixture and the exhaust throws out a carbon mix that settles on the ground. If the vehicle is driven in this mode it seems to lose power, running rough, and when under strain - e.g.. taking off up a slight incline, reaching 2000rpm etc. I found that by restarting the car (maybe three, five times) the symptoms disappeared enough for that specific trip. However this option deteriorated over the past two weeks and the last attempt was failing after a few hundred metres each time.
I note from another forum that the oxygen sensor seems to have caused similar issues - would this also apply to this model though?

 

You are NEW, so welcome.

Please do a formal intro in the "new members area, intro a must" when time permits.

A few concerns from my point of view:

Recon FPR (Fuel Pressure Regulator)????, no idea on that one, as they are a throw away unit that I am aware of.
Injector plugs???, I know what they are, but why replace them?. The wires etc I can understand.

The Black smoke on a S3 was related to a fueling issue with the AFM (Air Flow Meter), and there was a rework that fitted a resistor across 2 terminals inside the large rubber cover of the AFM plug, but I forget the details now as the last one I did was 25+ years ago. Maybe there is something on here about it, or Doug or someone else with better S3 knowledge slides by when the time zones align.

I would be changing the fuel filter, first and foremost.

The Ignition module (front of the inlet manifold) looks like a Black Box, has a GM module inside that goes flaky.

The ECU temp sensor (the one with 2 wires attached), up on the water rail, just near the ignition coil, also dies with age, and it is now OLD. This can/will cause overfueliing.

HEAPS of threads on here about the ignition coil itself, again, it is OLD. I have replaced many over the years.

The general wiring that runs along the top of that water rail is ALWAYS a suspect. Again, it is OLD, and BRITTLE, and I bet there are bare wires in there that will reek havoc.

The list goes ON, but that is a starting point.

 

Like Grant I'm a bit confused on the rebuilt pressure regulator

Here is some light reading and conversation starters on rich running/over-fueling, some of which Grant already touched on

XJ6 Series - EFI Rich Mixture

And info on the capacitor mod to cure double-fuling on cold engines

XJ 6 Series III 4.2 - Cold Start EFI Overfuelling


What you describe sound fairly severe. I'd wanna make sure the fuel pressure isn't going too high, as that will cause over-fueling as sure as nightime following the day (and further calls into question the pressure regulator).

A fuel pressure test is in order, IMHO

If the temp sensor is suspect unplug it and jump the wires with a paper clip,,,and see what happens.

Cheers
DD

 

From the blue, as my knowledge of this system is abysymal:


Sensors are for the most part variable grounds, or merely on/off ground.


So, insert a switch to ground in the cabin. At start up, switch on. Mixture is richened. as the engine gets warm, switch off.


An electric version of ancient hand chokes or primers.


Just wondering.


Carl

 

My overfueling issue was caused by me having wires crossed so cold start injector stayed running. Although thatis unlikely your issue it may be faulty. Try squeezing hose to it with needle nose pliers and see it idle smoothes out.

 

Many thanks for all those suggestions. My bad re the reference to the FPR - it actually was the Air Flow Meter (did a check with the mechanic this morning).

Best wishes for a Happy Xmas.