Vapor Lock? - My Issue is Vapor Lock? Causes? Test?

[dinanm3atl]

Story...

First start on hot/cold/rainy/snowy/whatever conditions it fires RIGHT up. No problems what so ever. Drive to work. Doesn't die or sputter or anything...

Part it at work. I am there from 10-7. Get in the car. Bam. Fires right up no matter the condition.

Now the problem.

IF the car sits for 30 minutes or 1 hour... If it DOES fire immediately it will stutter and die. I can keep it running with the gas pedal but it will smell like gas.

If it does NOT fire immediately it will take a while to crank and then will fire, smells like gas. I have to keep it running with the gas pedal.

Now... It runs and drives fine. Gets good mileage. No other real problems... I THINK this is vapor lock...

What do I replace? Leaking injectors and then that dries out if you let it sit long enough? Bad valve somewhere? What is going on?

[jlevie]

Vapor lock on a fuel injected engine, and especially on an M20, is pretty far down on the list of possibilities. That's because the fuel pump pushes fuel to the rail from the rear of the car away from engine bay heat.

A bad DME engine temp sensor, leaking injectors, or intake leaks are more likely possibilities.

[dinanm3atl]

So I should check my injectors, engine temp sensor first?

I don't think intake leak is going to cause what I have personally... Because if I let it sit for 10 hours I still would have the same intake leak...

How do I test and which one is the engine temp sensor... and testing injectors?

[a32guy]

Did you get that from the simpson's episode when joe namath's wife fixes the vapor locked car?

[E30_pilot]

Did you get that from the simpson's episode when joe namath's wife fixes the vapor locked car?

i was jus thinkin the same thing...lol!

[jlevie]

don't think intake leak is going to cause what I have personally... Because if I let it sit for 10 hours I still would have the same intake leak...

True, but the DME will run a richer mixture for a cold engine, which would help counter the affects of a moderate leak.

A simple test for the temp sensor is simply to unplug it and see if that makes any difference. Leaky injectors could cause this and the diagnostic for that is to pull the fuel pump relay, pull the plugs, and see if fuel is pumped out when the engine is cranked over. Or pull the injectors and have them tested and cleaned.

I'd also want to know what the fuel pressure at the rail is prior to and during one of these events.

[AndrewBird]

After an hour, the engine wouldn't be hot enough for vapor lock to occur. Vapor lock only happens when the engine is really hot. The fuel hits the hot engine and boils, resulting in vapor lock.

[Ruffian]

Vapor lock destroys valve trains. In my experience, you have a fuel pump that's about to go out. Here's why. When you drive it after it's been sitting for an extended period, the pump is nice and cool. Once it's spinning, it'll keep spinning. You drive it and it works till you shut it off, and by only sitting for a short while, it has a time to come to rest, but not cool off significantly. Then when you restart, it's only going to spin intermittently, so your car runs like poo if at all. You also know that the pump needs a quarter tank or more of gas to keep it running cool. any less, and there's more wear and tear on the pump.

I was able to diagnose mine by waiting till the car wouldn't start, then jumper the relay as outlined in the bentley, and no pump. I was able to limp home by tapping on the top of the pump through the hole under the rear seat.

jim's the man though, he helped me when mine was going bad.

[dinanm3atl]

Interesting..

Why does it smell like gas then? The pump suddenly comes to life and sprays a ton of fuel? This would not be possible if my understanding of the fuel system is correct... unless it builds so much pressure it pushes it out some of the lines :)

[delphini]

Maybe , just maybe you might be having an issue with your
dme (fuel) relay.

[DaveSmed]

Vapor lock destroys valve trains. In my experience, you have a fuel pump that's about to go out. Here's why. When you drive it after it's been sitting for an extended period, the pump is nice and cool. Once it's spinning, it'll keep spinning. You drive it and it works till you shut it off, and by only sitting for a short while, it has a time to come to rest, but not cool off significantly. Then when you restart, it's only going to spin intermittently, so your car runs like poo if at all. You also know that the pump needs a quarter tank or more of gas to keep it running cool. any less, and there's more wear and tear on the pump.

I was able to diagnose mine by waiting till the car wouldn't start, then jumper the relay as outlined in the bentley, and no pump. I was able to limp home by tapping on the top of the pump through the hole under the rear seat.

jim's the man though, he helped me when mine was going bad.

Huh? How?? How does vapor lock destroy valvetrains? A beat fuel pump would result in not enough fuel, not running rich.

To check the injectors, either hook up a fuel pressure gauge and watch it after you shut the car off for a decrease in pressure, or pull the rail, reconnect it to the fuel feed and return lines, and jumper the fuel pump relay. There should be no dripping from the tips of the injectors. To up the pressure briefly, pinch the return hose off for roughly a second to see if it starts leaking.

FWIW, that Caddy in my sig never even experienced vapor lock, and thats a hot running carbureted big block. (did experience plenty of the damn GM starter heat soak though) Your return style high pressure fuel system is most likely not vapor locking.

[Ruffian]

Huh? How?? How does vapor lock destroy valvetrains?

I mis-typed. I was referring to hydrolock. With that said, I'm still leaning toward bad pump.

[DaveSmed]

I mis-typed. I was referring to hydrolock. With that said, I'm still leaning toward bad pump.

Ah makes more sense, hydrolocking breaks lots of things, mostly in the bottom end.

As far as the fuel pump goes, a fuel pressure test will tell either way, though I disagree.

[92 mtechnic cabrio]

Usually when the fuel pump goes bad, the car won't start at all, even after several tries.

It's either a working or it's not kind of part. Not a "eh it kind of works but I think its going bad" part.

[Doughnut]

What about your cold start injector valve?
That could be your problem leading to over fueling at warm startup (smell of fuel).
Try leaving it unpluged next time you start your warm engine.
I get your exact problem too, and I'm trying this method tomorrow.