XJ6 & XJ12 Series I, II & III 1968-1992

86 XJ6 - Engine hesitates badly under acceleration

 
  #1  
Old 11-18-2014, 05:35 PM
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Default 86 XJ6 - Engine hesitates badly under acceleration

OK....so "suddenly" my 86 XJ6 is shuddering and hesitating badly when I am trying to accelerate from a stop (usually when people are behind me). It starts "fine" and idles "ok" and then as soon as I shift into Drive and gently step on the gas it starts shuddering (idling unevenly) and hesitates (accelerates and then tries to die) and this happens 75% of the time. If I back off the accelerator it will either stop shuddering and go back to normal idle or die. If I can make it up to 20 MPH I can usually make it just fine to the next light where this all seems to start all over again.

About the engine:
- Fuel pump and filter replaced in past 5K miles
- Spark plugs, wires, rotor, and cap replaced within past 10K miles
- Fuel tanks replaced in past 10K miles

What was changed right before this all started:
- Heater control valve

Suspects:
- Ignition Coil ???
- Gypsy curse????

Any help / advice is appreciated
 
  #2  
Old 11-18-2014, 06:27 PM
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Thw Gypsy lives there, so leave it alone.

The coil is well worth replacing, simply due to age.

The fuel filter MAY be clogged, it does happen all to frequently, for no explainable reason.

The airflow meter "flap" may be binding, and not opening smoothly as designed. This is common to some degree.

The circuit board inside the black cap of that airflow meter may be worn out, that again, is age related, and can happen suddenly.

Doug will see this soon, and as I have said before, he IS the S3 guru.
 
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  #3  
Old 11-18-2014, 09:27 PM
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Just for the heck of it.....


Take a good hard look at the ducting beween the air flow meter and the throttle body. Properly in place, and snug? No torn rubber ducting?


The 'could be' list is long but ^the above^ is a really easy thing to check for.


Cheers
DD
 

Last edited by Doug; 11-19-2014 at 05:43 AM. Reason: sp
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  #4  
Old 11-19-2014, 09:45 AM
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Default AFM ducting

Doug,
I replaced the AFM ducting a year ago and my mechanic rebuilt the AFM shortly afterwards. I'll open the duct to the throttle body and clean the intake area just for good measure. It just got "cold" here in AZ (which means daytime temps in the 70s) and so perhaps that is also playing a role.

I will replace the coil however my coil has the ballast resistor type coil along with a revised amplifier and harness that is inline to the coil. (see description here-http://www.jag-lovers.org/xjlovers/xjfaq/coil.htm) and so I need to know if I can just replace the coil or if I need to replace both the coil and the ballast resistor.

I love my Jag... its a car that I wanted since the 1980s when other "kids" were hanging pictures of Lamborginis on their wall I had framed Jaguar VDP ads on mine. I just can't afford to take it to my mechanic right now and am trying to be more self-sufficient.

Originally Posted by Doug View Post
Just for the heck of it.....


Take a good hard look at the ducting beween the air flow meter and the throttle body. Properly in place, and snug? No torn rubber ducting?


The 'could be' list is long but ^the above^ is a really easy thing to check for.


Cheers
DD
 
  #5  
Old 11-20-2014, 05:51 PM
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While it's ticking over, can you hear the fuel pump in the trunk buzzing away nicely ? Your fault sounds like fuel starvation, but there are quite a few things that can cause this because it's an EFI car. So the supply from the tank to the fuel rail, and the EFI equipment that controls the injectors need checking and its analogue so no diagnostics I'm afraid.

I had similar symptoms to yours in the late 80s, but never found out the problem as I took it to a fuel injection specialist who just told me "Oh, we just adjusted it a bit " ! Right !!!
 
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  #6  
Old 11-20-2014, 06:45 PM
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Don't forget to go over the things that you've changed as well. E.g. the rotor arm as these can fail or chew up the contacts in the distributor cap, damp inside the distributor cap, etc.
 
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Old 11-21-2014, 08:56 AM
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Default Thanks for Fuel starvation tip

Fraser,
Thanks for the tip and I do hear the fuel pump buzzing away "nicely" but I did notice that the fuel hoses from the fuel rail to the full injectors are a little pinched because they were cut a little long when replaced recently. So... I am going to trim and re-fit those fuel hoses to remove the kinks, and find a way to check the EFI while I'm at it.


Originally Posted by Fraser Mitchell View Post
While it's ticking over, can you hear the fuel pump in the trunk buzzing away nicely ? Your fault sounds like fuel starvation, but there are quite a few things that can cause this because it's an EFI car. So the supply from the tank to the fuel rail, and the EFI equipment that controls the injectors need checking and its analogue so no diagnostics I'm afraid.

I had similar symptoms to yours in the late 80s, but never found out the problem as I took it to a fuel injection specialist who just told me "Oh, we just adjusted it a bit " ! Right !!!
 
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Old 11-21-2014, 09:16 AM
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Default Coil replacement help - Please take pity and provide a picture

Grant,
I am in the process of replacing the Ignition Coil and have ran into two snags:

- One is that I cannot get the existing coil free from its harness. I have loosened the cinch screw at the bottom of the harness and that didn't help. The large #4 screws attaching the coil harness to the top of the rail won't budge at all and I am afraid that I will further strip the #4 screws if I keep at it (they looked to have been partially stripped before I attempted this). So... any tips for that are appreciated.

- AND -

- Second is that I committed a Rookie mistake when I started trying to remove the Coil.... I didn't label the two main wires as to which side of the Coil (which terminal) they belong to. I know which side the the ballast resistor hooks up to but not the two leads - one has a large connector and one has a smaller connector. So.... if anyone who has an 86' JX6 with the ballast resistor type coil could snap a quick picture or two showing which wire goes to which coil terminal will be my Personal Hero of the Month! (tm) for November. I am normally very good about marking wires but was distracted by wife at that critical moment.

Thanks

Originally Posted by Grant Francis View Post
Thw Gypsy lives there, so leave it alone.

The coil is well worth replacing, simply due to age.

The fuel filter MAY be clogged, it does happen all to frequently, for no explainable reason.

The airflow meter "flap" may be binding, and not opening smoothly as designed. This is common to some degree.

The circuit board inside the black cap of that airflow meter may be worn out, that again, is age related, and can happen suddenly.

Doug will see this soon, and as I have said before, he IS the S3 guru.
 
  #9  
Old 11-21-2014, 09:17 AM
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Feel the coil as the car is running. If it gets hot, replace it. Ballast does not always need replacing when coil is changed.
 
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Old 11-21-2014, 09:27 AM
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A couple of ideas, ignition related.


A. Timing is advanced. Weights in the distributor frozen in "out" position. Or static timing too fast. a bit of both.


B. Dump the ballast resistor. But, making sure your new coil is a 12v and not a 6v. The resistor came into favor for point and condenser cars to save point wear. Not needed for electronic ignition cars. Caveat. Not all agree on that.


Carl
 
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Old 11-21-2014, 10:05 AM
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Originally Posted by mkprator View Post
- Second is that I committed a Rookie mistake when I started trying to remove the Coil.... I didn't label the two main wires as to which side of the Coil (which terminal) they belong to. I know which side the the ballast resistor hooks up to but not the two leads - one has a large connector and one has a smaller connector. So.... if anyone who has an 86' JX6 with the ballast resistor type coil could snap a quick picture or two showing which wire goes to which coil terminal will be my Personal Hero of the Month! (tm) for November. I am normally very good about marking wires but was distracted by wife at that critical moment.

Thanks

As originally installed the ballast resistor itself attaches to the "+" post of the coil. Then any/all solid white wires attach to the ballast resistor.

All other wires go to the "-" post of the coil.

That's it !

IF you elect to discard the ballast then simply attach all solid white wires to the "+" post of the coil.

Cheers
DD
 
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Old 11-21-2014, 10:10 AM
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Originally Posted by mkprator View Post
Grant,
I am in the process of replacing the Ignition Coil and have ran into two snags:

- One is that I cannot get the existing coil free from its harness. I have loosened the cinch screw at the bottom of the harness and that didn't help. The large #4 screws attaching the coil harness to the top of the rail won't budge at all and I am afraid that I will further strip the #4 screws if I keep at it (they looked to have been partially stripped before I attempted this). So... any tips for that are appreciated.

I'm having a hard time remembering/visualizing what's going on. Can you post a pic?

The harness is usually attached to the coil by little nuts on the posts.

Cheers
DD
 
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  #13  
Old 11-22-2014, 04:39 PM
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Default Success - thanks to all of you

Doug & all,
With your sage advice I was quickly able to get the Kitty up and running again - I replaced the Ignition Coil and trimmed the fuel injector hoses to reduce the kinks and she started up much easier and is running as perfect as she can foreign 28 years old. Thank you all for your advice and help. As requested I am inserting the image of the coil with the ballast resistor (new coil, original resistor).

- Michael



Originally Posted by Doug View Post
I'm having a hard time remembering/visualizing what's going on. Can you post a pic?

The harness is usually attached to the coil by little nuts on the posts.

Cheers
DD
 

Last edited by mkprator; 11-22-2014 at 04:42 PM.
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Old 11-23-2014, 08:36 PM
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I too was having difficulty with gas and sputtering, etc. Problem fixed when I discovered the spring was weak. Fixed.
 
 
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