[xj40] STUMBLING IDLE--CYL. #2 AND #3 NOT FIRING

XJ40
1

Dear People,

I fixed my ignition module (see other posts last week), and
now the car starts up very quickly (always did), but it
stumbles when idling (as if some cylinders were not firing).

Well, as the engine idles, you can pull each spark plug wire
at the distributor, and all make the engine stumble VERY
bad, EXCEPT cylinders two and three. When they are pulled,
there is no change.

My apark is VERY blue and strong to all wires (including the
bad #2 and #3).

I got a stethoscope and listened to the injectors while the
engine runs and they are all clicking strongly and click up
and down as you rev the engine.

We OHMed the wires themselves–and they ohm okay, at about 6
to 7K each. Just like the rest of the wires which are
firing okay.

I went and changed the plugs with new plugs. Same problem:
cyl. #2 and #3 are no go.

I’m puzzled. We are going to do a compression check either
tomorrow or this weekend. But I do not feel its the head or
its gasket (I hope, knock on wood).

Anyone have any palpable suggestions?

RLCII
91 Sov. ‘‘GreyGhost’’–
RLCII
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2

If you have good plugs at cylinders 2 & 3, as well as blue spark at the
plugs and fuel injector pulse at those cylinders, then you may have a
blown head gasket if removing the plugwires to cylinders 2 & 3 has no
effect on idle.

One mode of head gasket failure if for the sealing rings between
adjacent cylinders to fail, so that compression is lost from one
cylinder into the other (which has a valve open), thus affecting
compression and power on each of the adjacent cylinders. A compression
test should give a difinitive diagnosis.

Glad to know you found an ignition module substitute. Please let us
know what it is.

George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: NYCBullet rlcii007@hotmail.com

I fixed my ignition module (see other posts last week), and
now the car starts up very quickly (always did), but it
stumbles when idling (as if some cylinders were not firing).

Well, as the engine idles, you can pull each spark plug wire
at the distributor, and all make the engine stumble VERY
bad, EXCEPT cylinders two and three. When they are pulled,
there is no change.

My apark is VERY blue and strong to all wires (including the
bad #2 and #3).

I got a stethoscope and listened to the injectors while the
engine runs and they are all clicking strongly and click up
and down as you rev the engine.

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3

In reply to a message from NYCBullet sent Thu 24 May 2007:

I’m afraid you will find zero compression in those two cylinders
when you do the compression test (or about 30 psig, as I did in my
Green 88). If you have an assistant turn the key to crank the
engine while you stand at the right side of the engine compartment,
you may hear air leaking through the exhaust valves (I did).
But have no fear. A valve job is straightforward. Valves are like
$18 each and the complete gasket set is $170 or so. Follow the
procedure in Haynes, and don’t forget to drain the antifreeze from
the block before you loosen the head or you will end up with
antifreeze in the oil.
Don’t automatically take the head into a shop and have them grind
the valves. You won’t need it and the factory CD does not
recommend it. Instead, hand lap the valves and check the seal
patterns. They will lap in easily. Just let your local machine
shop tank clean your head and check it for flatness. Don’t let
them machine anything.
While you have the engine apart, pay close attention to the
fittings and hoses attached to the intake manifold as well as the
mounting bolts. I found a split hose on my Green 88 and loose
manifold bolts on my Gray 88 when I did the valve jobs. I believe
an intake manifold leak will let a cylinder ‘‘go lean’’ and that
causes the burned valve. A valve burns awefully fast – within a
mile at highway speeds and loads – from my experience.–
The original message included these comments:

cyl. #2 and #3 are no go.
I’m puzzled. We are going to do a compression check either
tomorrow or this weekend. But I do not feel its the head or
its gasket (I hope, knock on wood).
Anyone have any palpable suggestions?

–
Pete 70 XKE (193K) 88 XJ6 (239K) 88 XJ6 (226K) 60 Mini
Severna Park, Maryland, United States
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4

Sounds like you diagnosed your gasket failure between 2-3 cylinders
rather nicely. No need for OHM meters.
Jay 90 VDP Majestic
PS it could just be two burned exhaust valves and only a compression
test will tell but from the sound of your post its a blown head gasket.
Refer to archives for further details as its been covered many many times.

NYCBullet wrote:

Dear People,

I fixed my ignition module (see other posts last week), and
now the car starts up very quickly (always did), but it
stumbles when idling (as if some cylinders were not firing).

Well, as the engine idles, you can pull each spark plug wire
at the distributor, and all make the engine stumble VERY
bad, EXCEPT cylinders two and three. When they are pulled,
there is no change.

My apark is VERY blue and strong to all wires (including the
bad #2 and #3).

I got a stethoscope and listened to the injectors while the
engine runs and they are all clicking strongly and click up
and down as you rev the engine.

We OHMed the wires themselves–and they ohm okay, at about 6
to 7K each. Just like the rest of the wires which are
firing okay.

I went and changed the plugs with new plugs. Same problem:
cyl. #2 and #3 are no go.

I’m puzzled. We are going to do a compression check either
tomorrow or this weekend. But I do not feel its the head or
its gasket (I hope, knock on wood).

Anyone have any palpable suggestions?

RLCII
91 Sov. ‘‘GreyGhost’’

–
RLCII
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !