shaner517

Will a MAP sensor cause the xj to vapor lock. Because after I have run mine for a while it skips a but misfires if at idle to long. And when I have ran it hot I have to purge the air out of the fuel line before I can start it.

jakbob

someone else can chime in but i think this is what's called heatsoak.

cruiser54

Sounds like the fuel pump may be failing due to heat?

Perhaps the fuel line inside the tank from the fuel pump to the fuel pump module is bad?

Bustedback

No such thing as vapor lock on a fuel injected engine. If you're running rich after idling too long you need look at the O2 sensor, coolant temp sensor, MAP sensor, and check for exhaust leaks (cracked header before the O2 sensor).

cruiser54

But he says he has to purge air out of the fuel line to get it to start again.....

shaner517

There no exhaust leaks just fixed the header. Would I need to test the fuel pressure to find out if the pumps bad. I also have taken heat wrap and put it around the fuel rail.

420blackxj

This is not so. It may not be called vapor lock, but the result is the same. Very hard hot starts, and severe misfiring after hot start. Heatsoak is what it is commonly called in XJ country. Gas boils in the fuel line, causing improper atomization. If you let the engine cool, (lift hood,) after 15 minutes, it starts fine I'm guessing. My XJ suffers from this alot, and the solution (for me) is to open the hood for 15 minutes before starting hot. There are plenty of other means for preventing heatsoak. Do a search, and you will be enlightened.

shaner517

Ok thank you thats what I have come to do it just suck when you have to be some where

cruiser54

Do the fuel pressure test.

djb383

'96 XJs have a heat soak problem?....I thought that was mostly limited to '00-'01 XJs with the (really hot) dual cats just under the intake manifold, no?

cruiser54

That's what I thought, too. And it sure ain't summer yet either.

Thekid320

I'm pretty sure mopar sells a kit to fix it it's heat soak and iirc it's not the fuel rail it affects certain injectors when it happens

XJ-92

Very very false. i have seen it happen before. for a vapor lock to occur, you need a heat source by a fuel line. that heat source heats up the fuel line causing the fuel to boil. once the fuel starts to boil you get air in the lines. once air has formed in the lines it makes it harder for the fuel to get to the fuel rail. so the engine will be trying to run off the fuel vapors instead of the liquid fuel. this makes the engine stall out and skip a beat. i mostly see it happen to airplanes both carb and fuel injected. i work on planes all day and im in college for them and we just went over it 2 weeks ago. not as common in cars but common in poorly maintained airplanes or not seeing a birds nest in the cowling, letting the engine bay heat up

djb383

......but it's 5 o'clock somewhere. LOL