I have been having trouble starting my car recently. Sometimes it fires right up and runs fine but sometimes it will just crank for a while without starting and sometimes it will start and stumble and die a couple times before starting and running normally. Once it is running normally it will run fine for hours until I stop it and try to restart it.

I put a Fuel Pressure Guage on the fitting on the rear of the fuel rail and got not reading on the guage. No reading with key on(could hear pump run) an not running and no reading after I got it to start up.

I assume the guage may not be accurate as the car obviously will not run with 0 PSI of Fuel Pressure. I don't think it is far off though, as I also pushed in the pin on the valve and let some fuel out while the car was running. Some fuel came out but it only seemed like a couple PSI. Certainly did not seem like anywhere near 40 PSI.

What is the minimum PSI for the car to run?

Assuming the pressure is very low, is there anything other than the fuel pump that might be causing this? What about the Fuel Pressure regulator? How do I test it? What about the relay/wiring? Could they be causing the problem? If so, how do I test/rule out?

If I do need a Fuel Pump, which is the best one to buy and where from? Price? Primarily a stock car, w/catback don't plan an major mods but you never know. May need rebuilt one day and may decide to do some mods if I rebuild.

Tips for easiest install/removal of fuel pump on convertible? Not adverse to the idea of cutting a hole in trunk if this will work but the posts I have seen on this technique have not been for convetibles. Will this work on convertible? If so, can you please give me a link with how to insturctions?

I do have lift so factory method may not be too bad, if that is what I need to do. Any tips if using factor Svc. Manual proceedures?

Thanks, Joel

PS. Car has a new fuel filter.

 

Get a fuel pressure gauge that works.

Better to do before you go through the hassle of changing out the pump.

 

if a gm pump is dead, it just plain wont start. to make sure, pour some gas into the throttle body and try and start it. it should fire. also, check all of your fuel lines....u might not be getting addicate pressure to bring it from the tank

 

My pump was shot in my car, but it still ran. The only reason I knew it was bad was b/c of the the wideband O2 they had when I dynoed it. I had starting issues with it every once in a while, but had no idea it was the pump. When i put a pressure gauge on it at WOT the pressure dropped to ~20psi, but was ok at idle

 

As I said in the first post. The car does start and run. It just does not start easily. Obviously there is some fuel pump function/pressure.

The fuel pressure guage that I used is only a few months old and worked fine (on this car) when I tried it last. Do not want to waste $40-50 buying another one and then find this guage is fine, just that the pressure is so low it will not register on the guage.

How about answering some of my other questions, there were several. In particular I would really like to know how to confirm it is fuel pump problem, vs relay, regulator etc. IF I do confirm that the pressure is very low and, What is the least amount of pressure that would allow the car to start and run?

 

If you can hear the pump running, then the wiring/relays are in proper working order. Your fuel pump should generate around 36 psi at start up. The fuel pump has an integral check valve that holds the fuel pressure for starting purposes. It's common for this check valve to fail and it will cause the hard starting problem you described, but once started the engine will run (because the fuel pump is then on full time). Have a buddy watch your fuel pressure while you cycle the key; what you'll probable see is that the fuel pressure comes up while the pump runs, but quickly falls off once the pump stops (2 second cycle when starting).

 

I replaced the pump several months ago. Not a fun project. The new pump improved the starting but it was still not great. Lately it has become very reluctant to start. Usually have to crank it for at least 5 seconds before it will start. If I turn off and try to re-start within a couple seconds it will fire rigth back up. Since the pump and filter (sock and canister) are new, I doubt that they are the problem.

What might be causing the problem now? Pressure regulator? Check valve?

How would I want to try to diagnose?

 

Checking the pressure is the vital first step. If the gauge is failry new and seems to have failed, try returning it for a replacement. Without good fuel pressure readings, you're just wasting your time, and possibly your money.

With the fuel pressure at 20psi (for example), you would still be getting 70% of the flow. Not a good way to run the engine, but it might still start and run.

The fuel pressure regulator will generally fail as a result of a ruptured diaphragm, and that will put fuel into the vacuum compensation line. Pull the line off and look for signs of fuel in the line.

You may have a problem with leaking injectors. Pull the fuel rails up with the injectors intact, turn the key to prime the system, and look for drips. Knowing the fuel pressure would still help.

The fact that you just replaced the pump may also point to a possible loose connection at the fuel pump. I've seen several threads with that solution. What pump did you install?

 

I installed the 255L pump.

If it is leaking injectors, what is the cure?

Is there an effective way I can clean them?

I had considered the possibility that the injectors were leaking but I have not noticed any fuel odor. I have also tried KOEO for a few seconds before cranking and this did not seem to have any effect. I had assumed (perhaps incorrectly) that KOEO for a few seconds would refill the fuel rail, even if the injectors had leaked off and therefore unless there was a "flooding condition" from the leaking injectors this would let it start normally. Is my assumption wrong?

 

When was the last time it had a good tune up?

 

What I have noticed is that with the Key on but engine off my fuel system pressurizes and holds. I have a special situation because of my nitrous where I can bleed the fuel pressure off and the fuel pump will not establish the original pressure until I either start the car or turn the key off and then back on. I tell you this so you will understand how the fuel pressurization works.

If you have leaking injectors or a faulty regulator then turning the key to start as soon as you hear the pump go off should avoid extended cranking. Waiting a while after the pump goes off will give you hard starting if your injectors are leaking down or the regulator is allowing the pressurized gas to return to the tank.

Are you not even considering that your opti-spark is failing?

 

Curious, have you changed the fuel filter? I don't see you mentioning it. It's about a 10 minutes and $20 or so and well worth doing, and I'm not talking the sock on the end of the pump...

 

Test your fuel pressure gauge by attaching it to a different car. Don't all cars have schroeder valves? That's not hard to do.