Vapour Lock???

Not in the VX but in my Firebird. Lucky for me I have been trying to sell it for the last few months. Finally when someone is about to come out to the house to see it, the thing will not not start.

It cranks and cranks. So i remembered that my other half just got gas in it. So I opened and re-tightened the gas cap and it started right up. But since then it has been less predictable. Sometimes the gas cap trick works and sometimes it does not. I have not taken it to a mechanic yet. But friends and family say its Vapour locked?

Prior to this it worked GREAT, then all of a sudden after a long sit after putting a couple dollars of gas in it, it would not start.

Got any suggestions.
The battery is fine the starter has to be fine since it is cranking. It just wont fire. But when it does turn over there is no signs of a misfire and no check engine codes either.

Im confused. Ready sell, but want to sell it legit.

Vapor lock has gone the way of carburetors and mechanical fuel pumps but in any case the car has to be already warmed up for vapor lock to happen.

Can you hear the electric fuel pump power up when you turn the key on? If not then your problem may lie there.

What kind of sound should I be listening for? Never had to listen for a pump yet?

My daughter's Mitsubishi was doing something similar. By applying the KISS principle, I checked the spark plugs. The gap was twice what it should have been. But, while I was doing that, I disconnected the battery so the computer would reset as well. After that combination approach - all was well. Best of all, it didn't cost anything (well, I did replace the plugs the next weekend).

Good luck.

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Originally Posted by JHarris1385

What kind of sound should I be listening for? Never had to listen for a pump yet?

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Fuel pump is inside the tank as part of the fuel pickup assembly. Have someone turn the key to "on" but not far enough to crank the starter. Standing by the back of the car you should be able to hear the pump come on (humming noise) for 1-2 seconds, then stop. If you don't hear it, you may have a bad pump or bad fuel pump relay. I would try replacing the relay first-much cheaper and easier than replacing the pump, which may involve having to drop the gas tank to get to it.

Thanks for the info. Do pumps just all of a sudden go bad/fail. One minute it drives fine the next it just cranks. When it does start up it runs great. By relay do you mean the cube in the fuse panel?

If you run out of fuel and try to keep going or crank the motor hoping it will start you could burn up a fuel pump. The pump uses the fuel as a lube and/or coolant so if it is dry and operating... buh-bye. If the fuel pickup is clogged, same thing. The fuel filter should be an easy check though. I would pull a hose off at the engine block and turn the key to see if fuel is at least getting to the motor. If it is, then the problem is more than likely up front.


What year is this Firebird? An older 'bird could have a mechanical pump on the block or an electric on the frame rail. You would generally hear an electric if it were on the frame rail though, in my experiences. Some cars do have an access to a tank mounted fuel pump from above so you don't have to drop the tank to inspect things. It sounds like you may want to thumb through a manual or find another forum to ask more informed 'bird people though. It could be a number of things. Good luck.

Fwiw, in my experience when an electric fuel pump goes it's usually w/o warning, it just dies. You also mentioned the Firebird had been parked for a while, and I have also noticed on other cars that I have had which have been parked and not run for a while (a month or more) the electric fuel pump is dead when I try to start them again. I don't know why, maybe it's the gel that old gasoline turns into after a while somehow messes up the pump.

The relay is a cube, with four pins I think. Not sure about the Firebird but most late model GM's have that fuse/relay box under the hood, which hopefully has a label on it identifying what they are so you can figure out which one is the fuel pump relay. The relay itself is probably < $20 at AutoZone or similar.

First off, lets just say the Bird forum is no where near this forum. It takes hours or sometimes days if your lucky to get a response. Thats just another reason to love this community here.

Edit: There are multiple bird forums but not just one great one. (one for each generation, ones for just formulas, one for just trans ams, one for the RARE Black Bird (side note: google that its a pretty sick Bird) (extra side note Ill search and post: http://www.firebirdgallery.com/carlblacklot1.htm , http://www.cardomain.com/ride/429194 , and BAM http://www.classyauto.com/47161 = 605 HP and 604 torque)


It is a 98 fourth gen.

Yeah I pulled the relay. Ill go buy another as cheap insurance. It was only sitting for about 4 hours before being driven for 30 minutes or so. I hope its just a realy. Becuase I really dont feel like putting money into a car that I am trying to sell.

Relay = Check - works fine
Fuel Pump = Check - you can hear it turn on with the key turned.


Fuel filter? = next
Distributor cap????

I have not gotten it start recently but it was only starting after messing with the gas cap. It just throws a curve ball in it to me.

Maybe the gas cap vent or the gastank vent isn't functioning. It can't suck fuel out if air can't come in.

Does it start every time with the gas cap removed??? If yes then replace the cap.

Not everytime. But it seems to only luckily start after sometimes messing with the gas cap.

I didn't pay much attention to this thread earlier because I don't own a GM vehicle. But, last might I got to thinking that your symptoms sounded a lot like my '82 Mustang. For over a year it would occassionally fail to start, or it would start, run for a minute, then shut down. I suspected fuel problems, too. But, it got worse, until finally it flat refused to start. Further troubleshooting showed no spark. Turned out to be the Ignition Control Module, a notoriously common failure item. A $30 part from NAPA. Replaced it and haven't had a problem since. Check your spark. Your Ignition Control Module (or whatever Pontiac calls it) is probably built into, or attached to, the distributor. Good luck.