3.0 engine starts but immediately dies

[Steve76Targa]

Newbie here. I've got a 76 Targa with a rebuilt 1980 3.0 that I've owned for a whole week. It ran great until yesterday. It started right up as usual but then died right away. It does the same thing over and over. It starts, runs for a second, then dies. There's plenty of gas coming from the fuel filter discharge and appears to get a decent spark. Any help will be greatly appreciated.

Thanks,
Steve.

[divezic]

Kind of a newbie myself, but I did notice this same thing when I had the oil cap off. Not yet sure how a loose oil cap fits into the fuel injection equasion but you might want to check it.

[FrayAdjacent911]

I believe the oil cap can mess with the vacuum pressure in the system. Not sure. I'm a n00b too.

[MotoSook]

No..the oil cap allows un-metered air into the intake. If the mixture is set too lean, it will die.

As for Steve, you may have control pressure issues resulting in mixture error. The cold start injector gets you started, but then the your mixture changes and it dies. Get a CIS test and test the cold and system pressures. That's a start. It could be other things like a faulty AAV since you were running fine before. Did you do anything to the CIS? You need to post more information about the sympthoms so we cna narrow down the cause of your problem.

[Steve Marshall]

I had a similar problem with my 74 Carrera fitted with a 3.0L motor. It turns out the problem was that I blew the pop off valve out of it's hole. On the initial start up the car back fired, ran briefly and died. Then it fire start to run and die.

To see if this is your problem, take the cover off your air box. THere are two rubber straps that hold it on. Remove the air filter, and see if the spring loaded pop off valve is laying in the box and there is a big hole in the bottom of the box. If this is the case, glue it back in the hole and it should fire right up.

[MotoSook]

Yep..that would do it too. On cranking the cold start injector richens to and compensates for the un-metered air through the dislodge PO valve..then it leans and nada!

The thing to take away from this, is that there can be good fuel pressure and flow, but if you have an external or internal (AAV) air leak it will not work right. Some folks compensate for a small air leak by richening the idle mixture, but then have other issues off idle.

[Kayser28]

Check the points. Mine did this and the problem was the points weren't opening to create the spark. I also replaced the spark plug wires and fuel injector o-rings looking for the problem.

I messed around with the CIS for a long time before I realized it wasn't the problem. Good luck.

Mike
77 S

[MotoSook]

Michael, a 3.0 does not have points.

[Porsche_monkey]

I agree with Souk. Too lean, starts only because of the cold start injector (which fires when the starter is running).

Check fuel pressures.

[Superman]

When this happens, the Cold Start Valve located in the back of the air box is working, and spraying fuel during startup like it's supposed to. For a second or two. Then, the regular injectors are supposed to take over and they're not doing that. One reason they might be failing to do that is if the air flow sensor plate is not moving. Normally, it moves because air flows past it to get into the engine.

[john walker's workshop]

check that pop off valve.

[john walker's workshop]

start and die is usually a big air leak into the intake. check that pop off valve, and see if the airbox is separated at the seam. a clue to a blown airbox is to see if any of the screws under the air filter or around the outside of the box are out, or half way out.

[Steve76Targa]

Thanks to all of you, the response was truly overwhelming. Pop off valve was sitting sideways in the air box. I put it back into position and it fired right up. Idle is funny now and things run a little rough when driving but I haven't actually sealed up the valve yet. Doing that next.

Thanks again.

[stlrj]

Your air boot may have popped off.