vapor lock.... searched

98XJ
4.0L
Auto
3" lift, 31" tires
Rustys intake package(filter and TB spacer)
Cherry bomb exhaust.
Today i got off of the highway after a 30 mile trip in 90 degree wheather, needless to say the engine was hot. I got something to eat and i went back out to start my jeep. When i first started it up it ran rough and i gave it throttle and it died. i couldent get it started after that. I pulled the cap off of the shrader valve on the fuel rail to see if i had pressure. All that came out was pressurised air with a small mist of fuel. I kept cycling the key and doing it until finally fuel was coming out. It started fine after that. I have noticed a lack of power lately and it has just plain died on me at idle when it is hot. This has only started happening recently after i put a cherry bomb in but it has also been alot hotter here lately. I read a post about wrapping injectors 3 and 4 but the TSB is only for 99-01's. Any ideas on where i should start? Wrapping the injectors or fuel pump/ regulator? Thanks in advance for any advice.

sounds kinda like a clogged filter, but the pump/filter is one unit in the 98. It might be the problem, but alot of work if not.....

sorry, I was not alot of help

My wife's 2000 has done this to me twice now. The first time was on the trail and the jeep was working hard and starting to get hot. Last night we sat for about 20 minutes in a drive thru line, then pulled onto the street. Got to the first redlight and the engine just died. After about 10 minutes of bleeding hot boiling gas out of the fuel rail I started to get a good liquid mix and finally got the engine started.

It doesn't look like the fuel line runs too close to the exhaust, and it's got a pusher pump in the tank from the factory. I'll try wrapping the injectors, is there something else that I'm missing,

goodburbon said:

My wife's 2000 has done this to me twice now. The first time was on the trail and the jeep was working hard and starting to get hot. Last night we sat for about 20 minutes in a drive thru line, then pulled onto the street. Got to the first redlight and the engine just died. After about 10 minutes of bleeding hot boiling gas out of the fuel rail I started to get a good liquid mix and finally got the engine started.

It doesn't look like the fuel line runs too close to the exhaust, and it's got a pusher pump in the tank from the factory. I'll try wrapping the injectors, is there something else that I'm missing,

Click to expand...

Just a thought, but the fuel supplied to the rail is generally way more than the motor uses. The excess is recirculated back to the tank through a relief valve. It doesn't seem likely, do to the cooling action from the circulated fuel, the rail would get hot enough to vaporize the fuel (for long).
Just guessing, but a plugged relief valve could keep the fuel in the rail long enough to over heat. Or low pressure/flow from a plugged filter or a weak pump might cause the fuel to stay in the rail long enough to vaporize. The vehicle sitting (off) and hot might do it.

It seems more likely for the fuel to turn to vapor, with the motor off and sitting (no circulation). If it happened to me very often, I'd do a fuel pressure test, both at low RPM and high RPM. If the pressure seemed OK, maybe think about wiring in a purge switch to run the pump manually/electrically, to purge the fuel rail when necessary. Maybe do a fuel pressure test during cranking. I'm not real familiar with late model XJ's, but most XJ's pump max fuel during cranking
Maybe the heat shield the old Renix used to have on the intake manifold, actually did do something.

There is no return line from the rail on the 97 -01 models, don't remember about the previous models. There is only a feed line in and 6 injectors coming out of the fuel rail. A relief valve with a return line on the back end of the rail would be/ should be a basic part of the design but it isn't. I don't know where the Regulator is, maybe in the tank?

Which means that fuel is not being circulated through the rail keeping it cool, it sits there until it is used, and the further down the rail you go, the slower it is used. Therefore in high heat, low consumption situations (idling through drive through) enough heat can build up to boil the fuel in the rail. This in turn, actually will overcome the pressure produced by the pump, forcing liquid fuel back into the tank through the regulator.

Bottom line is that it is a shitty design, now I can't figure out why my jeep hasn't done it. i've gotten mine so hot that the plastic loom that holds the injector wires together melted, and it never missed a beat. Hers has only gotten hot once, the first time that it vapor locked.

Welll, if you are going to take the time to wrap the injector(s) you might as well wrap the rail while you are at it...speed shop nearby me only sells it in minimum length of 3 feet so might as well use it up... speedshop pro says lots of guys even wrap the exhaust header in their race motors...

Well I have had it. The jeep just abandoned my wife in a parking lot today. Saturday it wouldn't restart at the house. and 2 weeks ago it did this when we stopped on the interstate because the tranny puked. When it stopped 2 weeks ago I had all of my tools with us, so I pulled out the fuel pressure gauge and checked. Pressure was normal, but the fuel was hot as hell and boiling out. I cycled the key a few times and got cool fuel to the rail using the guage set as a bleeder, but the jeep still wouldn't start.

I dumped some cool water on the CPS and after a few minutes it started, but I had also dumped cool water on the fuel rail. Incidentally the jeep never dies when it is running at any speed, only when the engine drops back to idle.



I completely wrapped the fuel line in reflective insulation tape yesterday. I went to pick her up and the fuel was still boiling hot in the rail. I guess it could be the CPS... 85 bucks on a guess is a bit steep though.

Time for hood vents?

I have them on the other jeep, and the prospect of changing 2 TPS's every time it rains is a bit daunting.

there's a couple tsb's on this very issue, pertaining to xj's and tj's with the later style intake. something about the newer set up causes injector/rail heat soak/vapor lock issues-although my '96 had these same issues. i wrapped the fuel rail and all six injectors with some "thermo-tec" heat insulating sleeve from summit racing and i've never had a vapor lock problem since, not even stopping for short periods in the dez when it's 118* out.