Starts then just cuts out

1986 XJ6 Vanden Plas in US. I thought I had got some water in the petrol. I had just filled up and driven a bit then when I went to restart it tried and caught a couple of times but would not run. I changed tanks and it was fine. Since then it has happened a couple of times where it starts straight up, revs fluctuate and then it dies. I change tanks and it starts, and once started I can change back to the original tank. Drove it all over yesterday with no problems. Today it started and then stopped. I changed tanks and it started and then stopped. After that it wouldn’t start at all. Fuel pump(s) do you think?

I begin with something easy and free.

Remove the fuel filter and empty the contents into a clean jar. What you see or don’t see will dictate your next steps

Cheers
DD

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I second Dough, Michael - check/change the fuel filter…

As this happened just after filling the tanks, it does indicate contaminated petrol. While petrol stations are usually careful to eliminate petrol; if you filled both tanks they would be equally affected - with symptoms as described…

Water, being heavier than petrol, tends to separate and collect at the bottom of the tanks. By design, the tanks have a sort of sludge sump, below the in-tank filters, to generally suck clean petrol. But while driving, the water gets stirred up and enter the fuel system - not necessarily in great quantities, but it may eventually accumulate to cause a non-start…

The filter will detain water to some extent, but cannot keep water from entering the fuel rail - and the engine won’t run…

In which case, verified by filter stat; remedial actions are effective and straight forward…

Frank
xj6 85 Sov Europe (UK/NZ)
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Michael,

everything said so far seconded.

Another easy bit: open the filler lids. Clogged up charcoal filters might create vacuum in the tanks that the fuel pump won’t overcome. On SIII cars there’s only one fuel pump, isn’t it?

Good luck

Jochen
75 XJ6L 4.2 auto (UK spec)

Hello. Fuel in the filter looked good but I replaced it anyway. Tried the fuel pump by putting it in drive and switching to start, no pump. Followed the fault finding list kindly provided on this forum. Pump is good and and fault seemed to be relay. Changed it and still no pump. I have a new starter relay, Bosch, so I thought well I might just as well get a new diode pack. Everywhere I look says DAC1861 discontinued and not available. Surely there is an alternative item!

Michael,

your first steps are conclusive, then things get blurred: “Pump is good and fault seemed to be relay”. What did you do to get to this conclusion: Jumpered to the pump and jumpered to the relay’s trigger circuit? Even if you did the former, but not the latter, the problem might still be a broken fuse or some bad contact before the relay. I’m just a bit skeptical because relays don’t fail that often … So maybe the trouble of finding a replacement part is unnecessary.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)