Knocking
#1
12-06-2009, 01:02 PM
Join Date: Nov 2009
Location: Hardy, VA
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Knocking
Yet another mystery. Parked her in the garage last night and everything was fine. Upon taking her out today I'm getting knocking under light acceleration and the occasional backfire through the intake.
It seems more prominent on the left bank of cylinders but that may just be my imagination.Any ideas?
UPDATE: I also have a fluctuating idle as well. It bounces back and forth between 500 and 1500 rpms. I pulled the hard plastic vacuum line from the back of the right manifold, plugged the port and the idle smoothed right out. I haven't had the car long enough to figure out where everything is but I'm guessing this line runs to the computer in the passenger foot-well?
Yet another update: I disconnected the battery and allowed the ECU to reset. Started her up, let her reach operating temp and the problem is gone.
Last edited by johnlittle01; 12-06-2009 at 02:49 PM. Reason: Update
#2
12-07-2009, 12:09 PM
Veteran Member
Hi John
Glad it's back up and running, somehow :-)
As I read the first few lines of your post I was thinking Marelli coil failure on 1 bank as thats how mine felt when I lost a coil (which effectively turns off 1 bank). It also idles very low with only 1 bank running.
As you are a new XJS owner and your car has Marelli ignition (I think from the 1990 year), please read up on the Marelli Ignition issues and the potential catalytic convertor overheat/fire issues that can occur. I had actually read up on these issues and thought I knew what was what, however when I did actually lose a coil, it was by no means obvious what had happened, and during the 1 mile I drove the car back to the house it just felt off power and there was what sounded like the occasional backfire. This was in fact fuel burning/exploding in the left hand catalytic convertor. Once I pulled into my garage and there was no more cooling air from the car movement the steering rack boot and the chassis leg caught fire from the heat coming from the cat. Luckily I always carry a fire extinguisher in the car and I managed to put everything out before more damage was done.
Not trying to frighten you or anything, but it's good to be aware of this particular quirk of these cars with Marelli ignition
Glad it's back up and running, somehow :-)
As I read the first few lines of your post I was thinking Marelli coil failure on 1 bank as thats how mine felt when I lost a coil (which effectively turns off 1 bank). It also idles very low with only 1 bank running.
As you are a new XJS owner and your car has Marelli ignition (I think from the 1990 year), please read up on the Marelli Ignition issues and the potential catalytic convertor overheat/fire issues that can occur. I had actually read up on these issues and thought I knew what was what, however when I did actually lose a coil, it was by no means obvious what had happened, and during the 1 mile I drove the car back to the house it just felt off power and there was what sounded like the occasional backfire. This was in fact fuel burning/exploding in the left hand catalytic convertor. Once I pulled into my garage and there was no more cooling air from the car movement the steering rack boot and the chassis leg caught fire from the heat coming from the cat. Luckily I always carry a fire extinguisher in the car and I managed to put everything out before more damage was done.
Not trying to frighten you or anything, but it's good to be aware of this particular quirk of these cars with Marelli ignition
Last edited by Sarc; 12-07-2009 at 12:12 PM.
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