I’d reported in the past some ugly cold start problems,
which persisted after I had done tune-up (new sparks, wires,
everything in the ‘‘vee’’ cleaned or renewed, but the
This time, I decided to remove the rail with the injectors
and have them tested and cleaned by our own SD Faircloth.
While Dave was doing his magic, I designed a rig to test the
fuel pressure, since this was brought-up in the past, and I
never knew the answer. I will post the pictures once they
are vetted. The test-port is on the rail, just before the
All is back together and the results from the fuel pressure
testing are in. Again, this is the 1995 V12 with the 6.0L
engine with only one FPR on the A-bank, rated at 3 bar (44-
- Key in ignition, after 2 seconds pressure is near 38-40
- Normal start, pressure drops to about 34 psig
- Engine runs, warms up to N, pressure at idle steady at
around 32 psig
- Removing the vacuum (simulating load), pressure boost to
- Re-connecting the vacuum (simulating load), pressure
drops to 31 psig.
- Engine shut off from normal operating temperature,
pressure raises back to almost 40 psig
- 5 minutes after shut off - fuel pressure still above 35
I’ve suspected all along that my FPR is acting up and have
asked on this forum for replacement alternatives. The BOSCH
unit is NLA, only a few vendors have them and they cost
Before I splurge on one, could someone please confirm that
this is indeed the FPR (and not the fuel pump(s) or
something else I missed). Human error in the measurement is
always possible (:-)), but I don’t see how my numbers can be
that much off from 3 bar of the later 6.0L motor (31-32 psig
is even lower than the 2.5 bar rating of the 5.3L motors).
Also, for a full disclosure, I am using a calibrated gauge
from a vendor of scientific equipment, and would not suspect
the gauge itself. The engine started/ran OK, but the ‘‘blip’’
when turning the throttle to increase engine speed seems to
suggest I’ve got fueling issue(s) to solve.
Thanks much for your input.
'95 XJS V12 6.0L, saphire/tan
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