Hi everyone, getting close to the end Jag season here in Ontario. Completed lots of projects this summer but have not solved my warm start issue. I changed the ignition amplifier today, changed the coolent sensor, still no luck. Runs and drives perfectly, warm start is rough, misfire for a minute or so then clears……
This is on my 79 XJL 4.2 Fuel injected

 

There are a few easy tricks to see if you can narrow issue down:
1. After run and warm, before restart place transmission selector in Drive and turn ignition switch to start for 4-5 seconds, do 3-4 times and try normal restart. if this helps you have introduced cooler fuel into the fuel rail. Warm fuel should change the fuel regular pressure via. the vacuum valve on the fuel rail.
2. Second trick is after a good run and warm, disconnect wire leads from CTS and hook leads up to your spare "room temperature" CTS you just removed last week (Rap in rage and lay on manifold). Try a normal restart. If better, then your idle mixture is to lean. Either mixture screw on air flow meter, or inside an adjustment.
Lets us know if these make any difference.
PS: From my notes: I wired a resistor in series with one of the leads to the CTS. Added a (.5 k ohm resistor, about 40 degrees C change at full warm). This help with my warm restart problem.
Rgds
David

 

Thanks I will give these a try

 

Jordanmc
David's advice re using the fuel pump to purge the hot fuel out of the engine bay and introduce cool fuel is "spot on".
I have owned my 79 S3 Daimler for 30 years and in our hot climate doing that never fails to get a clean start.
I used to teach pilots to apply this same purging technique on fuel injected aircraft engines.

 

Exactly how did you wire the resistor and assume I'm an idiot.

 

I cut back the rapping on connector to expose both wires.
About an inch & a half from connector, I cut out 1/2" of one of the leads. Remove 5/16" insulation from cut wires.
I slipped a 1 & half inch piece of shrink rap tubing down the cut wire away from connector.
Filled in 1/2" cut with the resistor and twisted & soldered leads to cut wires.
Slid heat shrink tubing over the splice and heated with match.
Used black electric tape to seal cut covering of the wire leads.
Rgds
David

 

I like this idea -- but I was wondering if the problem is really just starting, why not stick the resistor at the TT sensor since that wont change anything other than restarts. altering the signal from CTS changes everything all the time. What do you think?

 

Not sure which sensor you referring to, the cold start injector circuit has a 35 C switch and timer for cold start, does not trigger on warm restart. see attached diagram.
Rgds
David

 

Thanks -- I get it now. I did the soldering this weekend and hot restarts are improved. I'm idling a little higher too, so I think I need to adjust that as well. The idle should go up a little, correct?

I just hope by lowering the idle, I'm not just undoing what I did?

 

Yes if the mixture is corrected, then a slight increase in RPM is the confirmation. Just reset to book Idle RPM value.
https://www.jaguarforums.com/forum/a...tments-1a.docx
Rgds
David

 

A final word on this after tinkering with my 1986 Jaguar XJ6 that had some hot or warm restart hesitation. I had confirmed it wasn't fuel pressure as shown above. I found the CTS was giving a lower resistance than spec (about 150 Ohms off when engine warm but not hot). I installed a 500 Ohm resistor as David indicated he did. My idle went up and I was unable to achieve a decent idle with that installed. So I removed that and installed a 150 Ohm resistor. I have a good idle for me (1200 or 1150 with AC off and in P). Hot restart issues seems to be solved. More importantly, I was getting some near stalling when I placed the car in reverse with AC on prior to the resistor placement. Now that seems to have stabilized. I haven't tried it in all circumstances, but I'm pleased so far.