[xj] Starts, but won't run

Looking for assitance, prior to towing to shop…My 1987 XJ6 Series
3 starts, runs for 2-3 seconds, then dies. Car will run when Air
Flow Meter ‘‘Flap’’ is held fully open. Where do I start trouble
shooting?–
My Onyx
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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The archives and FAQ will answer many queries on the XJ series…
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Looking for assitance, prior to towing to shop…My 1987 XJ6 Series
3 starts, runs for 2-3 seconds, then dies. Car will run when Air
Flow Meter ‘‘Flap’’ is held fully open. Where do I start trouble
shooting?

Opening the fla just adds fuel, sir - so there is a serious lack of fuel…

The ‘proper’ way is to first check fuel pressure, the most likely cause -
but also required to be positively eliminated as a factor before tearing
things apart…:slight_smile:

However, do a couple of easy preliminaries. Routinely run the engine on both
tanks - to see if it run normally on the ‘other’ tank. Then, with ign ‘on’,
push in the AFM flap to ensure that the fuel pump starts with the flap
pushed in half an inch or so. It is necessary to ensure that the pump is
running at all times - opening the flap as you did there is a slight
possibility that the engine draws enough fuel, by vacuum, to run. With
normal fuel pressure a wide open AFM flap will immediate stall the
engine…:slight_smile:

With the pump running, disconnect the vacuum hose at the fuel pressure
regulator - if fuel is leaking out from the hose spigot; the pressure
regulator is defective and must be changed. Leaking means a failed diaphragm
which will cause wrong fuel pressures irrespective of other possible
faults…

Carefully inspect for vacuum leaks, particularly, but not only, in the
ducting between the AFM and throttle body. A vacuum leak will cause lean
mixture, which like any other cause of lean fuelling, can be compensated by
opening the AFM flap. However, if there is a vacuum leak, but other
fuelling factors, like fuel pressure and injectors, are OK; opening the flap
will cause the engine to rev above normal idle…

If nothing ‘odd’ is found; run a fuel pressure test. First connect the
pressure gauge, EFI rated to stand some 150 psi, to the inlet hose at the
rail. Run the pump, using the AFM flap as a ‘trigger’ - as new, a pump will
show some 100+ psi. A ‘good enough’ pump will show some 70 psi - at 40 psi
or below; the pump will not reliably run the engine. While the gauge is
connected, do a routine leak-down test, waiting a couple of minutes to see
if the pressure drops - which is immaterial at this stage…:slight_smile:

Then connect the pressure gauge to the CSI tap-off at the rail, or use a ‘T’
connection at the rail hose connection at the rail - to read ‘regulated’
pressure. It should read 36 psi, give or take 3/4 psi. If not, and the ‘raw’
pump pressure is OK - change fuel pressure regulator…and if changed; the
fuel pressure should be rechecked…:slight_smile:

Again; opening the AFM flap compensate for all possible causes of fuel
starvation - including blocked lines to the pump or blocked fuel filter,
which may not be directly detectable by a fuel pressure test…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)-----Original Message-----
From: My Onyx
Sent: Tuesday, April 23, 2013 10:47 AM
To: xj@jag-lovers.org
Subject: [xj] Starts, but won’t run

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

To remove yourself from this list, go to http://www.jag-lovers.org/cgi-bin/majordomo.

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