99 XJ Stumble

[sinkrun]

My 99 4.0 XJ stumbles a bit when first started and you try to pull out for about 20-30 seconds no check engine light (I think that means no codes) Any thoughts?

[terrawombat]

When I had my '99XJ mine did something similar and it nearly caused me to get T-boned as I pulled out of my driveway immediately after starting it and tried to beat the oncoming traffic. The XJ stumbled and had no power and the traffic wasn't slowing down. Eventually just hit the brakes and backed it up.

 

I never got to fully diagnose the issue but it would only happen to me when the XJ sat for at least a couple of days so I attributed it the fuel pump not building up enough pressure in the rail until after about a minute or so. One of the things I noticed between that XJ and my '01XJ is that my '01 will NOT start if I have low fuel pressure at the rail. The '99XJ started up no matter what - even if there was low pressure at the fuel rail. My theory was that my fuel pump wasn't able to 'keep up' when the engine was first started but would gradually build pressure and it wasn't until the normal pressure was achieved that it ran flawlessly. I didn't really know what else it could be since every sensor on that truck was either new or checked out good. I always wanted to have a fuel pressure gauge inside so that I could see exactly what was going on at the rail when I first started it and it did it's stumble. I sold it to my girlfriend's mother so now it's her problem ;)

[Justin_k]

If the low fuel pressure is your problem couldn"t you turn your key back and forth a few times to prime the fuel lines and build up pressure?