[xj] Intermittent Hesitation Hot or Cold Update

XJ
1

I thought I would post an update to this thread as my cat is
finally back to a pre-hesitation performance level. The original
post was:

''A couple of weeks ago I began to experience an intermittent
hesitation when I depressed the accelerator. It did not happen
every time nor with any pattern although it did get progressively
worse over the days. It was almost like someone cut off the fuel
until I let up on the accelerator and then it recovered. By the
time I put it in the garage, I had to occasionally feather the
accelerator to get up to highway speed. It really felt like a
clogged fuel filter but that was new and pressure is okay. Since I
needed a few things refreshed under the bonnet I did the following:

New air cleaner
New plugs,
New plug wires
New rotor
New cap
New coil
Removed and cleaned the breather screen’’

Okay, lots has happened since then including removing the AAV and
checking it out. I also found the hose from the manifold to the
back of the AAV was loose. I pulled the injectors and sent them
out for cleaning and all six came back with a good report. I had
the fuel rail modified to add a gauge and replaced the O2 sensor
which was completely plugged. I cleaned the over-run valve and
replaced the throttle body hoses. Cleaned the Mass Air sensor, all
of the electrical connections, replaced all of the fuel line hoses,
replaced the fuel pressure regulator and thermostat while I was at
it. After all of that the pressure on the rail was 28 pounds. So I
replaced both fuel filters, still 28 pounds. Swapped out the fuel
pump, still 28 pounds. Put the old regulator back on and it jumped
to 35 pounds where it remains. It now looks a bit better too.

http://www.jag-lovers.org/v.htm?1277376604

So now she is running pretty decent again but the engine temp now
ramps up to about 110C instead of the 90C it used to. The water
level is okay and the pump was replaced last month (when it was
staying at a solid 90C) so I took out the termostat and boiled it
on the stove, gradually raising the temperature. It began to open
at 85C and was fully open at 95C so no idea what’s going on there
except it is frigging hot outside. I guess I’ll wait till it gets
cooler and see if it goes back to normal.

Thanks all for your help in this.

Cheers.–
Scott - 1985 XJ6 SIII
Pennington NJ, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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2

sawmkw wrote:

New air cleaner
New plugs,
New plug wires
New rotor
New cap
New coil
Removed and cleaned the breather screen’’

Okay, lots has happened since then including removing the AAV and
checking it out. I also found the hose from the manifold to the
back of the AAV was loose. I pulled the injectors and sent them
out for cleaning and all six came back with a good report. I had
the fuel rail modified to add a gauge and replaced the O2 sensor
which was completely plugged. I cleaned the over-run valve and
replaced the throttle body hoses. Cleaned the Mass Air sensor, all
of the electrical connections, replaced all of the fuel line hoses,
replaced the fuel pressure regulator and thermostat while I was at
it. After all of that the pressure on the rail was 28 pounds. So I
replaced both fuel filters, still 28 pounds. Swapped out the fuel
pump, still 28 pounds. Put the old regulator back on and it jumped
to 35 pounds where it remains. It now looks a bit better too.

http://www.jag-lovers.org/v.htm?1277376604

So now she is running pretty decent again but the engine temp now
ramps up to about 110C instead of the 90C it used to. The water
level is okay and the pump was replaced last month (when it was
staying at a solid 90C) so I took out the termostat and boiled it
on the stove, gradually raising the temperature. It began to open
at 85C and was fully open at 95C so no idea what’s going on there

It’s reacting according to general specs, Scott - given it is marked
‘88C’…:slight_smile:

While 110C isn’t ‘alarming’; you do have a cooling issue. The first step
is to check water rail temp with an infrared or ‘manual’ thermometer to
verify that it is not a gauge/transmitter problem. Point is that the
thermostat is there to keep the engine warm - it can do nothing to cool
it…:slight_smile:

No particular reason why your work should have altered temp readings -
though the wholesale changes do not clarify why you had the hesitation
problem. But ‘pretty decent’ running - is there an issue that may
explain the hot running? With all the work done there is always the
‘fiddle factor’ that may introduce anomlies. At least some of the items
changed can function as good spares - though not which ones…:slight_smile:

And to clarify; the pressure readings were taken with only the pump
running, right? 28 psi would be about normal for an idling engine - and
given a calibrated gauge at that…

Frank
xj6 85 Sov Europe (UK/NZ)>except it is frigging hot outside. I guess I’ll wait till it gets

cooler and see if it goes back to normal.

===================================================
The archives and FAQ will answer many queries on the XJ series…
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3

In reply to a message from Frank Andersen sent Fri 25 Jun 2010:

I did replace the temperature sensor and by problem still exists.
I’m wondering is there any way that a new water pump could cease
working while appears to be okay? Is is possible the the impeller
shaft could break and it appear to be functional? Or is it time to
backflush and start down the ‘‘plugged’’ path?–
Scott - 1985 XJ6 SIII
Pennington NJ, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

===================================================
The archives and FAQ will answer many queries on the XJ series…
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4

sawmkw wrote:

In reply to a message from Frank Andersen sent Fri 25 Jun 2010:

I did replace the temperature sensor and by problem still exists.

Its more a matter of verifying if the temp gauge is showing the true
engine temp, Scott…

Certainly a water pump may fail, but there is no viable way that the xk
can cool satisfatorily on thermosyphon - it would overheat very
excessively whatever the driving conditions. The water pump can weaken
for other reasons, a slack belt springs to mind - but there are no
spec’s or approved checks for water pump testing in the car.

I can suggest that you remove the thermostat, clamp the bypass hose,
disconnect the top hose from the radiator - and connect a hose to the
radiator hose. Running the engine in this configuration to can find the
pump pressure by watching how high you can lift the attached hose
without water spilling. Or connect a pressure gauge to the radiator hose

  • for the same reading. You can also connect a pressure gauge screwed
    into, say the water temp tap-off at the water rail - with or without
    blocking outlets…

But I won’t suggest it - I have no idea on what you are expected to
get…:slight_smile:

Simply backflushing and checking for ‘plugging’ is at worst harmless,
and may do some good in finding a problem - and, somewhat unlikely,
solve it.

The onset of the overheating after work done unrelated to the cooling
system is suspicious - but one would somehow expect an engine reaction
beyond mere overheating if there was a relationship. And the thermostat
must be positively taken out of the equation - but your testing of it
shows normal, and we are usually satisfied with that…hm…

Frank
xj6 85 Sov Europe (UK/NZ)>I’m wondering is there any way that a new water pump could cease

working while appears to be okay? Is is possible the the impeller
shaft could break and it appear to be functional? Or is it time to
backflush and start down the ‘‘plugged’’ path?

===================================================
The archives and FAQ will answer many queries on the XJ series…
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5

In reply to a message from sawmkw sent Mon 28 Jun 2010:

So my situation may be related to the gauge or just a factor of an
aged radiator and really hot weather! I guess I’ll see if I can
find some way to check the temperature of the rail.–
Scott - 1985 XJ6 SIII
Pennington NJ, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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6

sawmkw wrote:

In reply to a message from sawmkw sent Mon 28 Jun 2010:

So my situation may be related to the gauge or just a factor of an
aged radiator and really hot weather! I guess I’ll see if I can
find some way to check the temperature of the rail.

That’s just to make sure if you have an overheating issue, Scott - but
not the cause…

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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