I'm puzzled. Working on a 1995 Taurus 3.8L wagon that has symptoms similar to what I'd consider vapor lock. When it gets hot (over 80* ambient) and after driving for some time, it will start to cut out and die or fail to start. If it does start while hot, it will sputter like it's not getting enough fuel and refuse to rev. After sitting for 30-45 minutes to cool down, it will start fine and run normally for a period of time before repeating the cycle. Last summer it did this once when it had about 1/8 tank of fuel and adding fuel to it caused the symptoms to go away. Kept the tank full (over half) after that and the problem didn't re-occur until yesterday when it did it with over 3/4 tank of fuel. I didn't think that a fuel injected car like that could vapor lock but that's what it seems like. Can someone tell me whether vapor lock is possible? If not, I'm working on the assumption of a weak fuel pump triggered by heat. Other suggestions? Thanks in advance.

 

X2 on the pump thought! Put a new filter on it, and get a guage hooked up. Need to see what the pressure is when it starts acting up. I'll bet it'll be scary low!

 

First step is run it till it won't start then check for spark and fuel pressure. If low or no pressure it probably will be the pump(don't forget about the filter) If it has no spark my guess would be the ignition module(I think its mounted on the distributor)

 

My money's on the fuel pump too. Hook a pressure gauge on the rail that allows you to squirt out a sample of fuel (if you can get one). When the pressure starts to drop, shoot some fuel into a container; it'll likely be foamy and intermittent, instead of a clear stream of pressurized fuel, but you'll be able to tell by its temperature (with your hand) if it's hot enough to be boiling, or just not being pumped well.

 

They can't vapor lock like an old carbureted car because the pump is pushing from the tank. I'm with the rest of the guys, throw a fuel pump at it.

 

That old, you might find the tank is rusting out and the pump is sucking the rust up to the pick up and choking itself out. After it sits, some of the rust settles and it starts all over. Sometimes it's best to install a new tank, pump and sender in one unit to save a lot of labor and broken parts. Especially as touchy as some of the senders are. When it's dying out, put fuel down the intake and see if it wants to run. If so, fuel related. Also make sure the air intake hose is in good shape and sealed tight. That seemed to make a huge difference on a few ford and mazda engines I've helped work on. Morso than some of the gm stuff.

 

I had always been under the impression that the fuel injected ones couldn't/wouldn't vapor lock but the counter person at the parts house said that they could so I figured I'd double check.

Actually, the car has less than 60K original miles on it and spent it's whole life down here in OK so there was no rust. I pulled the tank and it was clean except for a fine film of silt that would show up if you ran a rag over the bottom of the tank. I threw a new fuel pump in so we'll see what it does now.

Thanks for all the input and diagnostic suggestions.

 

While it is rare on fuel injected engines, it is possible, especially on some of the newer returnless systems, where the fuel can sit in the rail and absorb enough heat during a heat soak to cause a problem. I remember actually seeing a bulletin on a Chrysler 300M regarding this condition.

 

Sounds like a fuel pump to me too. In tank fuel pumps are cooled by fuel. The problems with them are usually more imminent the less gas in the tank or the longer the pump is ran, especially in warmer weather. Let it sit and cool, it will usually work a little more.