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

Stumbling when warming up RESOLVED

 
  #1  
Old 09-03-2014, 11:04 AM
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Default Stumbling when warming up RESOLVED

Wow. This is the first actual "issue" thread I have had to post since I got my SIII 18 months and 8k miles ago !! What a great old girl.

Anyway, I'm starting to get the following issue:

Cold start..... car starts fine and idles fine, just above 1000rpm in "P"
After I have driven off, after the first one or two stop signs I start to feel a loss of power. Not a missfire, just a lack of power. It feels like it's either not getting enough fuel, or it's getting too much fuel. There is no strong smell of fuel however.
After about 5 minutes and the temperature gauge starts rising, the issue goes away. Car is perfect apart from the 5 minutes immediately following a cold start.

I am guessing there is a coolant temperature sensor telling the ECU the engine is cold, so please overfuel, and maybe something in that area is going off the boil a bit.

Any advice welcomed
 
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Old 09-03-2014, 04:40 PM
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the CTS (coolant temperature SENSOR), not the gauge temperature SENDER, but the SENSOR. Check the wires going to it. Remove it, clean it, see if it fixes the issue.
 
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Old 09-03-2014, 09:00 PM
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Originally Posted by Sarc View Post
I am guessing there is a coolant temperature sensor telling the ECU the engine is cold, so please overfuel,

Yes! On the water rail



and maybe something in that area is going off the boil a bit.

Very possible. It might be skewed in the middle ranges....not fully cold, not warmed up either.

If cleaning the connection as Jose mentiones doesn't help (it often does, though) we can give the specs for checking the sensor readings with a ohm meter. Or, as guesses go, it's not very painful to just replace it at only $20 or so

Cheers
DD
 
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Old 09-03-2014, 10:16 PM
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@Jose

Cleaned and replaced some old and green looking connectors.

Will report back after tomorrow mornings cold start.

@Doug

Ordered the sensor anyway........
 

Last edited by Sarc; 09-03-2014 at 10:58 PM.
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Old 09-04-2014, 01:59 AM
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also check the plastic ducting/bellows from the air filter "trumpet" (at the very front) all the way back to the intake manifold/butterfly aluminum elbow, make sure all the parts are well-seated and tight, (but not over-tightened). Use a 6mm socket and a small ratchet to check all the clamps.
 
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Old 09-07-2014, 02:55 PM
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Update :

Checked all air intake parts for integrity, all ok, Thanks Jose.

After cleaning the contacts its improved quite a bit, now it only does it maybe 1 in 5 cold starts. The EFI temp sensor is on its way so I will fit that and report back
 
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Old 09-20-2014, 03:03 PM
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Fitted new EFI coolant temp sensor and replaced the wiring and connector.

Car is back to perfect again. It is generally a lot happier warming up than it was before. It must have been gradually getting worse over time.

Also swapped out my cruise control bellows as one of the solenoids had failed........ back to perfectly working cruise control.

It's been a good day in Series III land

Hope all are well
 
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Old 09-20-2014, 05:19 PM
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I'm very pleased to hear you are enjoying your Series 3 and that it's running well. These are the last of the old "analogue" Jaguars, with their beautiful 'boulevard' ride, but one must always bear in mind that the build quality was never very good. It took Ford, and a budget that must have equalled the US Defense Department budget to sort out the production facilities and component quality.
 
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Old 09-20-2014, 07:54 PM
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Thanks for reporting back of the fix, pleased for you.
 
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Old 10-30-2014, 03:35 PM
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I hope this isn't a faux pas but rather than start a new thread with a link to this one, just to see what's been done already, I'm going to follow up with this.

As you may or may not know, I've been the proud new guardian of SARC's fine Series III for about two weeks now. It's a great car and I couldn't be happier.

However, the cold start stumble is either still present or, more likely, has returned. If I don't give the car a full 6 minutes to warm up, it will stumble a few times, like it's going to die (but doesn't) when I put pressure on the throttle whilst in Reverse or Drive (but not in N or P).

If I let the car warm up a full 6 minutes, the stumble doesn't happen until I let it get cold again. The stumble never happens when the car is warm.

Taking into consideration the steps SARC took above, what should I check? It's a minor annoyance but I'd like to resolve it.

Thanks in advance,
Rhett
 

Last edited by Rhett; 10-30-2014 at 05:25 PM.
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Old 10-30-2014, 04:55 PM
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I would simply buy a new Coolant Temperature Sensor and substitute yours to see if it cures the stumbling. If it doesn't, you have not lost anything because sooner or later you will need to replace the CTS.

Another possiblity if it only happens when engine is cold, could be the Bosch Cold Start Injector, which has always been problematic. I think I have replaced mine 3 times since 1989.

what you describe is the system electronics trying to correct themselves.

A fix (now forgotten) but which used to be popular in the 1990's, is to add a Ground Strap to the 1-wire oxygen sensors. It stabilizes the idling and makes it more "positive" (no pun intended, no snake oil either). (2-wire O2 sensors in 1986 and 1987 XJ do not need this fix, they already have a separate ground).

By now, these cars have deteriorating Ground due to grease and rust at the manifolds, so adding a dedicated ground to the O2 Sensor has the desirable result of "energizing" the signal to the computer from the O2 sensor.

I added a Ground Strap to mine around 1995 and the result was inmediate, a more stable idling, even faster starts as a side effect.
 
Attached Thumbnails Stumbling when warming up RESOLVED-xj-o2-ground-strap.jpg   Stumbling when warming up RESOLVED-xj-ground-strap-3.jpg  
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  #12  
Old 10-30-2014, 05:22 PM
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Originally Posted by Jose View Post
I would simply buy a new Coolant Temperature Sensor and substitute yours to see if it cures the stumbling. If it doesn't, you have not lost anything because sooner or later you will need to replace the CTS.

Another possiblity if it only happens when engine is cold, could be the Bosch Cold Start Injector, which has always been problematic. I think I have replaced mine 3 times since 1989.

what you describe is the system electronics trying to correct themselves.

A fix (now forgotten) but which used to be popular in the 1990's, is to add a Ground Strap to the 1-wire oxygen sensors. It stabilizes the idling and makes it more "positive" (no pun intended, no snake oil either). (2-wire O2 sensors in 1986 and 1987 XJ do not need this fix, they already have a separate ground).

By now, these cars have deteriorating Ground due to grease and rust at the manifolds, so adding a dedicated ground to the O2 Sensor has the desirable result of "energizing" the signal to the computer from the O2 sensor.

I added a Ground Strap to mine around 1995 and the result was inmediate, a more stable idling, even faster starts as a side effect.
I believe the coolant temp sensor is brand new so I'll try the ground strap first and look into replacing the cold start injector next.

Thanks!
 
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Old 11-21-2014, 07:17 PM
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Per advice from a parallel thread on Jag-Lovers, I've had the "cap mod" installed and the cold-to-not-so-cold stumble seems to have vanished, hopefully for good.

I found the photo on the cap mod write up a little hard to see clearly (camera movement maybe)so here's a couple in progress shots, in case they're useful to anyone else:

wires stripped:
http://1.bp.blogspot.com/-r4bJtTdV4h...0/IMG_0817.JPG

The capacitor soldered into place and sealed with liquid rubber:
http://3.bp.blogspot.com/-cB5F3ESXVF...0/IMG_0810.JPG

Thanks for helping me through this.

Rhett
 
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Old 11-21-2014, 09:13 PM
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Where did you get the capacitor?
 
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Old 11-21-2014, 11:01 PM
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Old 11-22-2014, 09:23 AM
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Is it the 100-25A capacitor
 
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Old 11-22-2014, 11:02 AM
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Honestly, I just asked for a "100 Micro Farad, 25 Volt Electrolytic Capacitor" and the man disappeared for a moment, came back with two versions; one with both poles coming out of one end and the other, which I bought, with positive and negative coming out opposite ends.

It was less than $2.00 U.S. with tax. Drop them a line, I'm sure they can help.
 
 
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