91 Sovereign starts and idles fine for about 5 seconds. The engine
speed lowers from 1000 rpm to about 800 rpm and idles rough until
it reaches normal operating temperature. If you accelerate to
quickly while it is cold it will backfire through the intake
manifold. On occasion when the engine is warm and under hard
acceleration, it will backfire through the intake manifold and then
run fine. The following items have been replaced to correct the
problem without success: throttle potentiometer, mass airflow
sensor, Lambda (oxygen sensor), water temperature sensor, EGR
valve, and the fuel infection ECU. Do you have any
recommendations?–
M Rawlins
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You are experiencing a lean mixture most likely caused by a vacuum leak.
Check all usual external sources (hoses, vacuum lines and such) closely and
correct any you find. This is most likely a significant leak or imbalance
of metered air entering the intake plenum. Make sure you check the ISCV for
proper operation. Prove it’s non-involvement in this issue by disconnecting
it’s source hose from the downstream side of your intake hose just past the
MAF sensor and securely blocking both the small hose and the hole in the
large intake hose. With this blocked run the engine and observe the
backfire issue again.
You didn’t mention if you have done a preliminary compression test. May
be you are chasing a bigger problem? In any event this is a good point to
start.
Good Luck
Best Regards,
Greg
“Scotlander”
90 VDP Majestic
91 Sovereign
63 MKII 3.8----- Original Message -----
From: “M Rawlins” < Subject: [xj40] 1991 Sovereign Cold Run Problem
91 Sovereign starts and idles fine for about 5 seconds. The engine
speed lowers from 1000 rpm to about 800 rpm and idles rough until
it reaches normal operating temperature. If you accelerate to
quickly while it is cold it will backfire through the intake
manifold. On occasion when the engine is warm and under hard
acceleration, it will backfire through the intake manifold and then
run fine. The following items have been replaced to correct the
problem without success: throttle potentiometer, mass airflow
sensor, Lambda (oxygen sensor), water temperature sensor, EGR
valve, and the fuel infection ECU. Do you have any
recommendations?
M Rawlins
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 !
In reply to a message from M Rawlins sent Mon 22 Mar 2004:
I would also look at the fuel pressure regulator, this is a good
example of symptoms caused by variable fuel pressure. Of course, it
goes without saying that when facing an intermittent problem in a
Jag, it’s probably a loose connection somewhere. Backfiring in the
intake is a signal of a lean mixture, if this helps your search
any. Look at things that can cause leaness as you run through the
steps. It sounds like you have replaced some of the parts that
could cause this.–
The original message included these comments:
run fine. The following items have been replaced to correct the
problem without success: throttle potentiometer, mass airflow
sensor, Lambda (oxygen sensor), water temperature sensor, EGR
valve, and the fuel infection ECU. Do you have any
recommendations?
–
Brian Caro
Newport News, VA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In reply to a message from M Rawlins sent Mon 22 Mar 2004:
I have a 1990 Xj40. When I first got it it was running rough so I
replaced the plugs and checked the compression as well. After about
75miles I was experiencing the same problems. After removing the
plugs I noticed them to show signs of a lean mixture upon checking
the Egr valve I found it to be leaking and I also discovered that
the EGR selinoid nipple was broken as well. Replaced both and now
all seems to be fine. Note that the nipples on that selinoid are
CHEAP and easily broken by an inexperience Jaguar person. Good luck!
90XJ40
89XJ40
86XJ6
69XJ6
87XJ6–
Ron Jordi
Friendship, Wis., United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In reply to a message from M Rawlins sent Mon 22 Mar 2004:
I have a 1990 Xj40. When I first got it it was running rough so I
replaced the plugs and checked the compression as well. After about
75miles I was experiencing the same problems. After removing the
plugs I noticed them to show signs of a lean mixture upon checking
the Egr valve I found it to be leaking and I also discovered that
the EGR selinoid nipple was broken as well. Replaced both and now
all seems to be fine. Note that the nipples on that selinoid are
CHEAP and easily broken by an inexperience Jaguar person. Good luck!
90XJ40
89XJ40
86XJ6
69XJ6
87XJ6–
Ron Jordi
Friendship, Wis., United States
–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 !