It has been some time but we finally heard this Jag. run, many many issues were resolved and as we resolved one issue the engine responded very well but not perfect. We repaired another issue, the engine responded well. Finally we repaired one of the 2 cad. converters, it started, not smooth but it started. The longer it ran the smoother the engine became. Prob. because it hadn't ran for nearly 2 years. Injectors started clearing, fuel became more stable, Distributor was still loose so we adjusted the timing some what, not knowing where the timing was. We let the car run for about an hour, adjusting the idle, looking out for any issues. We then shut the engine down. Immedeatly we started it back up, it started then smoothed out. We shut it down again then let it sit for a while, we had lunch. We then tried starting it again, it hesitated, while cranking the engine, the faster it became, finally starting. Adjusting the timing once more We shut the engine down, let it sit about 20 min. then tried starting again. This time while pressing down on the gas, the engine would start but seemingly run on 1-2-3 or-4 cyls. no matter where the throttle is, to the floor or at the top it barely ran, then suddenly it kicked in, running fine, until we shut it down and tried to start it again, same thing, hard starting, stumbling at low idle, no response when we pushed or let off the throttle. suddenlythe engine kicked in and ran fine.. this is where we are at, once running it runs great, but getting it there, why is it having a difficult time starting, then once started it stumbles until its ready to kick in, then boom, it runs fine, whats goin on?

 

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Ok, let me explain a little more, This morning I tried starting the Jag, while cranking the engine got faster and faster, tried to start, as I pushed the gas petal to the floor it tries harder to start, while I held the petal to the floor and released the key the engine stumbled, stumbled and stumbled like it was running on 3 cyls. then eventually stopped. It did the same thing when I have the throttle pushed only slightly down, stumble, stumble, stumble after releasing the key... Throttle positioning sensor?, Air switch? ...... its like its not getting enough fuel....... yesterday it did the same thing except after stumbling for a while, a long while, 2 min. then suddenly it kicked in and ran beautifully. after I shut it down, to start it, I had to go through the same procedure.....Any ideas?

 

Pretty weird. The fact that it eventually straightens itself out is odd.

Unplug the coolant temp sensor (the one for the fuel injection system) and use a paper clip to jump the contacts inside the connector.

Any change in running?

Also consider the "capacitor mod" which cures a double fueling condition...although that is something that normally happens only with a cold engine

XJ 6 Series III 4.2 - Cold Start EFI Overfuelling

Have you checked fuel pressure?

Cheers
DD

 

Weird is an understatement. I will test the coolant temp sensor and let you know what happens. I have checked the fuel pressure 36 psi steady.

Thank you for giving me some direction, I've been lost, I'll let you know

 

check your fuel pump, mine would run perfect and then miss, start and idle and then drop cylinders under the slightest throttle increase, replaced dizzy, pplugs,leads, sensors[robbed from spare engine] all to no avail, then it was idleing like **** and stopped, it was the fuel pump[86xj6], $60 later starts easy and runs smooth...

 

Ok, here we go, temp sensor is good. cold start switch does not work, I removed it, had my son crank the engine, as I observed no fuel ejecting from the sensor upon first crank, But the engine started, rumble is a better word, rumble, rumble, rumble. rumble then kinda like a stumble hicup, then ran great, smooth, I drove it 20 miles no prob..... Shut it down, went to start it, rumble, rumble, rumble, rumble, varoom, runs great. .... Do ya think if I replaced the cold start sensor it would clear everything up?

 

Good. How did you check it, if you don't mind me asking?




To be clear, fuel will not come out of the cold start switch (Thermotime switch). It would come out of the cold start injector. Is that what you removed, and what you meant to say? Presumably so.



No.

Cold starting and cold running are two different things. The cold start system, working or not, does has no effect on cold *running*. It merely helps the engine *start*. Once the key is released from the 'start' position the cold start system is out of the picture entirely.

Getting the cold start system functional again is a good idea but it won't change the running problem you've described

Cheers
DD

 

My series 3 xj6 did the same only when hot. Ran perfect once going. I replaced the fuel pressure regulator and problem solved. Have a read of my post " hot start issues"