Hi, i have a 1985 XJS v12 engine that i am putting into a 1987 body which won't run, turns over a treat, fires and dies every time but only when with WOT from capstan which activiates injector pulse. I have spark, power to injectors, have swapped out ignition amplifier, fuel pump, ECU and relays. have jumped the CTS and have 6Vs to the trigger wire (is that correct wattage?). The biggest issue i seem to have is the fuel pressure........... it's way too high around 80-100psi, when i take fuel hose off the return line and let flow into a can, as expected pressure drops (car did not run as i read in another post) and fuel flows out so it is not blocked before fuel tank. Can fuel tank be blocked and causing high pressure (has been completely cleaned and renovated)? Also noticed that everytime we turn the key the psi keeps going up, it appears the FP not being told the pressure is sufficient and it keeps increasing it. Does this increase in PSI to > 45 mean i have blown the RH fuel pressure regulator. Any help at this stage would be much appreciated.

 

Usual 2 suspects.

1) Fuel return pipe under the car is crushed/blocked. Easily done by misplacing the floor jack.

2) the ign pulse TO the ECU is not happening via the well documented shielded wire that travels from the Ign Amp TO the ECU. With that out , the engine will fire on the prime fuel, and since no pulse to the ECU, it dies.

Careful, systematic, one item at a time, is the ONLY way here.

 

Sounds like a regulator failure but, just to clarify and understand, how/where are you taking the pressure reading?

I "tee" into the rubber section of item #11 in the illustration below......

https://www.jaguarclassicparts.com/u...ator-5-3-litre


........which means replacing the rubber section afterward. No big deal but a nuisance. Some elaborate pressure testing kits have adapter fittings to put in place so the rubber section need not be tampered with. In any case, that's where the pressure should be tested to get an actual reading of rail pressure....which should be about 36 psi.


The inlet regulator (RH side) can be eliminated and bypassed entirely, if you desire....and may be preferable as you work thru the problems. The LH (outlet) regulator controls pressure at the rail.

A blockage anywhere in the return system will increase fuel pressure, yes. I'd disconnect the return hose in the engine bay at the outlet regulator and blow some air thru it. Should be no restriction. If restricted, start working aft until you find the cause.

Cheers
DD

 

Power to the injectors is good but is not the same as the injectors actually operating.....which is where 'shielded wire' mentioned by Grant comes in.


Cheers
DD