My D-Jetronic fuel injected 1975 XJ12C will occasionally spill fuel on startup (quite copiously) from somewhere near the back of the engine. When I shut it off, and restart after sitting, oddly, no leak. I have been unable to find the source of the leak, mostly because I don’t want to allow it to run for very long while I look for the leak. I have checked the injector hoses and cold start injectors with no luck.
If anyone with experience with the early fuel injection systems has any ideas, I am listening.
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As Bob says, David - just run the pump for leak testing…
I cannot see that engine running or not should make any difference to a leak. The intermittent nature of the leak is puzzling - have you also inspected the return lines and fuel rail connections…?
Does it have a vacuum referenced pressure regulator, can the intakes somehow fill with fuel (I don’t think so), how old are the hoses, is there a cold start injector, can you pinpoint the location by running the pump? Maybe the engine shakes on startup and fouls something. Be careful, that’s a lot of fuel in the wrong place…
I had a 76 XJ12C that one day started to dump so much raw gas it’d end up in the air filter. I also had no money. The solution was to stick a bolt in the leaky cold start injector fuel line to block it off. It would start just fine off the cold start injector on the other side even in a Boston winter. As a diagnostic, you may wish to block the fuel line to a suspect cold start injector.
Thank you to all who have replied. Yes, turning on the ignition without start up was the smart thing to do. I found the problem was the driver’s side pressure regulator, leaking profusely. Haven’t had time to figure out if the regulator is bad or the hose feeding it. Will report when repair is complete.
OK, I am still baffled. After running the fuel pump without starting the engine I observed the left fuel pressure regulator, which appeared to be leaking at the seam on the round cylinder of the device. I removed the regulator and hooked it up to my compressor, covered the thing in soapy water and could detect no leak in either the hoses or the body of the regulator. I changed out the hoses for good measure, reinstalled the fuel pressure regulator and I have no leak (so far). We shall see, but I am carrying a 20 lb. ABC fire extinguisher in the car for good measure.
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Wise precaution. David - the intermittent character of the leak warrants it…
The regulator contains a spring, calibrated to open to the return line between 28,5 to 30,8 psi. A vacuum membrane counters the spring pressure to vary fuel pressure with manifold vacuum. A failed vacuum membrane will cause fuel being drawn into the engine.
However, with any verified leak from the regulator body; the regulator should be changed. That the leak is only unexplainedly intermittent makes no difference - better safe than sorry…?
If you applied air pressure in the opposite direction to the “normal” direction of the fuel running, I feel pretty sure that you tested only half of the regulator for a leak. If you applied air pressure in the same direction as the fuel normally runs, then you tested the complete regulator.
As Frank says- Change it anyway!
I applied pressure to the barb on the side of the cylinder, not the one at the end, which is the side that comes from the fuel rail, which I suppose is the pressure side of the device.
That is what I suspected. Much easier connection. As the FPR is also a one-way check-valve , the pressure you applied would only be felt on the downstream side, not all the way through. If you had applied pressure the same way the fuel pump does, as the pressure rose above 33 psi or so, the spring loaded disc inside the regulator would have moved off its seat, allowing pressure to be felt through the complete regulator, assuming the exit was blocked off!
As Frank says- etc etc!
OK, so taking the advice of Frank Andersen, I want to change BOTH of the FPR, however I am unable find the replacement part. Mine have the adjustment bolt with a lock nut on the top and hose barbs in both inlet and outlet locations. All the replacement I can find have a vacuum nipple on the top rather than the adjustment bolt.
Suggestions? I have already reinstalled the FPR, so I will have to go pull it off to get he Part Number. Tomorrow is Thanksgiving Day, so I don’t think this will get done before Friday.
I find the part 0280 160 200 all over the place for under $100. What’s the purpose of the vacuum nipple? Is this a replacement part for the original 0280 160 001?
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For some reason, David; early V12 versions had two pressure regulators, adjustable. Later cars had one, and I don’t know if the latter was adjustable - ie have the adjustment bolt. So you may be looking at the later versions…
In principle, both types work the same; inlet (from the pump side), outlet (return line, via the fuel cooler if fitted) and a vacuum connection (to manifold). However, adjusting the fuel pressure regulators on the early V12s was rather complicated - and involved separate adjustments of the regulators. So whether a ‘non-adjustable’ can replace an adjustable one is a question - when locating a source, verify ‘early’ or ‘late’…
In theory; mixing ‘fixed’ and ‘adjustable’ should be possible - the have the same pressure specs. I sort of suspect that in the ‘two-regulator’ V12 set up; each regulator controlled one bank…?
As shown in DL’s picture; the regulator is a simple device. A usual fault is a leaking diaphragm, easily diagnosed - though the failure on ‘non-regulated’ versions is detected by non-spec pressure when tested - with no further autopsy. They are nominally non-repairable - including a regulator body leak,
Incidentally; the barbs only denotes that hose clips are not required…
