[dhinten]

Guys,
My Cobra has a stock 5.0 and fuel system and has been running fine for a couple of years. A few weekends ago I stopped to visit a friend and afterwards it would not start - I could not hear the fuel pump running so I figured the pump had gone south. Later troubleshooting I found that if I tapped the fuel pump relay it would kick on and start as normal. I replaced the relay and it seemed to operate and start fine.

Now, however - a week later I have some more issues when I went to start it:
1. Initially the fuel pump relay would not kick on the pump.
2. The battery was a little low from the previous cranking so I put it on the charger. Then the fuel pump comes on, but does not turn off. This was very reproduceable with the battery on & off the charger.
3. The car will not start with the fuel pump running continuously.
4. After a few seconds of the fuel pump running I can hear a hissing sort of noise in/around the intake - can't tell if it is gas or air? No gas leaks are observable anywhere.
5. When I put the old relay back in it does the same thing (after a couple of taps).
6. When I bleed the Shrader valve I get a stream of fuel out, but it does not seem to be at as high a pressure as I would expect. I don't have a fuel pressure gauge (yet) to see what the pressure is building to.

Can anyone give me some direction as to where to go next? Could it be a bad fuel pump, or bad regulator, (bad computer? - hope not!)

Thanks for any advice!

 

[bill32]

There is a fuel pressure regulator somewhere in the system that maintains the fuel pressure to the injectors, I don't know where. It sounds like it is stuck open, thus the fuel is just recirculating back to the tank through the return line. Hopefull someone will be able to tell you where the regulator is.

 

[dhinten]

The regulator is on the top rear of the intake manifold. I guess I'll try changing that out - I haven't heard of a regulator failing before - but I suppose they must. Anyone else seen anything like this?

 

[Chris Evans]

The regulator is on the rear of the fuel rail assembly. And they do fail. Most commonly, the diaphram rips. But I've heard of the spring going weak and lowering fuel pressure too.

 

[Rex]

The hissing sound is normal. The regulator on the rail feeds the fuel back to the tank. Rather than guessing, round up a pressure gauge and see what is really happening. You should be able to cycle the key to run and hear and 1 sec. pump run. You will not hear a continuous run unless you jumper the relay. Check the pressure. Also see that it holds pressure and does not bleed down. One cycle of the key will bring the pressure up, then watch to see that it stays there. You can contact me directly if you would like a step by step... 530-243-1992 or 530-945-9000

 

[paul burchett]

With the engine not running, the fuel pump should not run continuously no matter what the fuel pressure might be. If the fuel pump doesn't shut off after a couple of seconds, either the fuel pump relay is stuck closed or the EEC is defective. Since you say that the engine won't start when pump continues to run, I'd guess that the EEC is the problem.

 

[dhinten]

I have replaced the regulator with no change in the symptoms. The fuel pump runs continuously with two different pump relays so I doubt the relay is sticking. Although I haven't been able to check the fuel pressure yet, the car did actually start one time and seemed to idle and rev up fine (didn't have the chance to drive it and it would not restart after I shut it off). I also tried to extract the error codes from the EEC but did not seem to get any response. It looks like the available data is pointing to a bad EEC computer - any concurrence?

Anyone know a sure-fire way of making sure that's the problem before I invest time and money in looking for a replacement?

 

[Rex]

One more time, you can shot-gun parts in all day but you are not going to fix it unless you get a little scientific about it. I left my ph. numbers on my last post...................if the pump runs continuously you could have ruled out the regulator. Need to go one step at a time or get yourself buried. Don't poke anything with a test light, the impedence will smoke EEC circuits. In EEC school years ago I was taught to never use a test light on any EEC related circuit. I broke the rule once and promptly smoked a circuit in the processor. Take me up on the offer.........I'll walk you through the steps of getting a handle on it...or just load up the shotgun.........and start blasting