DomsZ28

Hello there! My car is having starting problems and I suspect its the fuel pump. Can anyone tell me if the fuel pump from a 1999 Camaro will fit a 1995? Does the engine matter, or are all 3.4,3.8,5.7 fuel pumps the same.? Thanks

Injuneer

This is "LT1 Based Engine Tech". Let's move this to the "Fuel and Ignition" forum.

OBE1 95Z28

I would install a used pump; it's common for the check valve in the pump to fail. It's a lot of hassle to install only to find out the replacement pump is bad too.

Injuneer

"would" ....... or "wouldn't"?

DomsZ28

Sorry Injuneer, new here... Im assuming you mean "wouldn't"? Im not even 100% sure if it is the pump. But its been happening since I bought it last week and the guy that drove it when I had my tires changed said it was, because after you turn the key to on and off a few times it starts up first try. Normally it takes a few tries. Whats the easiest way to tell if its the pressure regulator, relay, or fuel pump? I can still hear the pump come on when i first turn my key so I know it does come on...Thanks

DomsZ28

Could a clogged fuel filter cause this problem also?

bobdec

Here are "my" odds of problem from reading quite a few posts on hard starting requiring key off-on sequence to be done a few times to build pressure in the rails. 1st Verify problem with a fuel pressure gauge, saves a lot of work if pressure is good..You may have a flooding problem, that's completely different to isolate... For low/no pressure after sitting a while. 1- Check for fuel leaking from regulator into intake vacuum line by pulling vac line to regulator and smelling , looking for fuel 1 to 5% fix rate. 2 - Defective regulator leaking pressure back to fuel return line 1 to 5% fix rate. 3- Leak in fuel line inside tank less than 5% fix rate. Leaking injectors causing pressure loss 1 to 5% fix rate. 4 - Defective check valve in fuel pump greater than 90% fix rate. To test regulator leaking to tank, you somehow have to plug the return line. Shobox has a procedure to look for pressure problems 4th Gen LT1 F-body Tech Articles . I doubt it's the fuel filter as pressure is has to be there there when you stop a good running engine, and then pressure gone when you restart after sitting. Fuel filter can not cause pressure to bleed off, unless it's leaking on the ground.. However it's a 'good practice' to keep fuel filter clean to prevent future problems.

DomsZ28

Wow thank you for the info Bob. I will be checking the regulator first.

Injuneer

Flooding is not a separate issue from rapidly dropping fuel pressure. Leaking injectors can be added as item 5) in the above post. The flooding could also be caused by the leaking diaphragm in the FPR, so its hard to separate flooding from the extenced start problem.

The way to check the injectors is to pull the rails up and turn the key to prime the pump. If the injectors are leaking you will see them dripping.

Checking for fuel leaking past the FPR into the return line requires that you block off the return line. While easy to say, hard to do. Some people suggest pinching the nylon return line with pliers, but I would strongly discourage that. You will damge the nylon line. The factory shop manual shows a valve that you insert in the connection between the hard line coming off the FPR and the nylon line. Not everyone has one of those. So you have to look for a way to block the return line. You could pull the quick-connect nylon line off the hardline, and try to block off the hardline with your thumb. I've never tried it, because I no longer have the stock fuel setup.

As noted above, the leaking diaphragm will put wet fuel in the vacuum line, so that one is easy. If you have ruled out the FPR and the injectors, and there are no visible leaks in the external fuel lines, you've narrowed it down to the check valve in the fuel pump and the line internal to the tank. Someone had a problem recently with a brand new Racetronix pump..... lost pressure rapidly, and it was a pinhole in the corrugated plastic internal fuel line, from being folded in the shipping package.

DomsZ28

Ok well I just did an Ohm test on all the injectors and all read at the same 12.3. I then connected a fuel pressure gauge to the schrader valve. After I connected it and started the car fuel pressure was about 35PSI, from my understanding it should be 41-47 PSI correct? As soon as I shut the car off it drops back down to a big fat 0. I also disconnected the vacuum line from the pressure regulator and smelled a very small hint of fuel. It looked as if it may have been wet but was really hard to tell. So I am leaning towards the regulator then...?

Injuneer

The important test at this point does not involve running the engine. Turn the key to "on", not to start, and watch the pressure gauge. Should peak at 40psi or higher, and hold that pressure, dropping very slowly. Sounds like yours will drop rapidly to 0 in this test.

Once the engine is running, pull the vacuum compensation line off the fuel pressure regulator (hold thumb over it to prevent a vacuum leak). Pressure should be 43.5psi, with GM accepting anything from 41-47psi as within spec. Reconnect the vacuum line, and fuel pressure should drop proportional to intake manifold vacuum - about an 8psi drop with a stock cam. So.... measuring 38psi does not indicate a problem with the pump, as long as that was measured with the vacuum line connected to the FPR.

Sounds like your pump is healthy, once the engine it running, but the check valve (or one of the other possibilities listed above) is the problem causing extended starts.

DomsZ28

OK I turned key to on and psi jumped to 40-45psi but then declined to 0 pretty quickly. I started the car and when I disconnected the regulator vacuum line psi jumped to around 43, when I reconnected it it dropped back down again into the mid 30s. So what's the problem? Should I be replacing the regulator then?

DomsZ28

How can I tell if its the check valve or regulator....confused..

DomsZ28

Well after looking around my car I noticed under the carpet there was a big square someone cut out. And boom there was the filter. But anyway I ordered the Fuel pressure regulator on RockAuto for $43 shipped. So hopefully that will solve my problems.

Injuneer

Are you saying someone cut a hole in the floor of the car so that the fuel filter, attached to the driver's side subframe rail, was visible from inside the car? Not very bright if someone did that, but what is the relation of that to the starting problem? Or do you mean you found a patch under the carpet where someone had cut a hatch to replace the fuel pump? Confusing.

As I explained already, unless you have a way to block off the fuel return line, there's no way to test the fuel pressure regulator to see if that's the cause. I would say that statistically, a leaking check valve in the pump is the more likely cause.