Back firing

[fmster]

Hi to all!! Here is my situation,I was driving around and the car started to back fire bad to the point that it would not move and shut off.I push down on the fuel rail valve and saw some air bubles coming out with very little fuel pressure.I tried to use the fuel pump test wires but it had no power,but the pump would not come on. So I waited till the car cooled down about an hour started up ran till I got to drive way and again it back fired. My questions are 1 where or why are there air bubles in fuel? 2Why is'nt there power in the fuel pump test wire?

[chrisgarrett]

Are you sure you have fuel in the tank? And the pump test wire has no power; it needs to be supplied with power to make the pump run.

[Keller]

First, as far as getting the fuel pump to run via the "test" connector: There is no connector supplying voltage under the hood. There are two connectors that can mate, but should not be mated together.

Near the #1 cylinder and A/C compressor, there is a black female electrical connector and a green male electrical connector.

The black connector is the fuel pump test lead. When ~12V+ is applied, the pump should run. A good place to pick up V+ is from the rear of the alternator. The ignition does not need to be on. I've made my own cable to fit the black connector and clip onto the alternator spade lug. I've even debated making a permanenent, fused and switched wire under the hood set up for this since I use it periodically for pumping race fuel out or testing the pump. (Not yet a convert to alcohol...)

The green connector is a squarewave tach output. That should not be plugged into the pump test connector. Doing so may send voltage into the tach circuit if the ignition is turned on or the car is started.

[fmster]

Thanks fellas the problen is not fuel.I did test the fuel system.It's electrical,
loses it's timing when hot.Any guess!!

[Keller]

Sounds like it could be one of a few possible things:

- Ignition
- Wiped cam lobe / lifter losing prime / broken rocker shaft

As far as iginition, it could be a lot of things: Bad ignition module, cam sensor misadjusted or not clamped well, cam sensor disc coming off inside, cracked plug, or crossed / arcing / shorting plug wires.

For the cam, as these cars age, if you haven't been giving the car its share of zinc in the oil, the lobes can get rounded. Also, if junk gets in the oil it can mess the lifters up. Unusual, but not impossible. And rocker shaft breakage is not unusal with these motors.

Can you diagnose / isolate what is really happening? Perhaps down to what cylinders are involved, if it is that type of incident?

[fmster]

The motor is rebuilt has 500miles.Problem is not mechanical,it just started.Car runs fine the first 15 minutes then after its hot, the misfiring starts.The problem is in the ignition system but not the coil I changed that, and still the same.It's one of the 3 Ignition module,cam sensor or cranck sensor.Can any body explain the symptoms of each of the 3 Items when they are going bad.
Thanks!!!

[Keller]

Before you dismiss the mechanicals...

The first 30 minutes or so of a solid or hydraulic lifter cam's life is extremely critical to its future. How it is broken it, what oil is used for the process, etc., all determine how well it will work going forward. Or if it will. Hopefully you broke it in properly.

A bad ignition module can definitely be sensitive to time and temperature. And usually only section fails at a time. So you get one pair of coils that will not fire.

The crank sensor will cause all cylinders to either cease firing if it breaks or begins to fail, or if the crank ring moves or balancer is loose, fire completely off time.

If the cam sensor gets damaged or its gear is munged, the #1 cylinder signal is lost. I believe if this signal gets lost while the motor is running, it will continue to run but the Service Engine Soon light will go on, and the injectors will go into "batch fire" instead of individual cylinder mode. If the signal is not present upon startup, the car won't start.