86 Grand AM 3.0L hard starting

[jamx13]

I've got an 86 with 3.0L V-6 & have had this "hard starting" problem for a while now. I believe the problem is with the fuel injection system not holding line pressure. The problem is at it's worst in the morning after the car sits overnite. Basically, it takes anywhere from 5-10 tries to get the car started...it fires & stalls, fires & stalls, then finally fires & runs. (if I give it a shot of ether, it fires up immediately...sometimes it will continue to run, sometimes it won't). I can hear the fuel pump kick on (it was replaced about a year ago) & I usually wait til I hear a "click" from the relay on the firewall before trying to start it again. I hooked up a fuel pressure gauge on the injector rail & there was zero pressure...turning the key to the "on" position brings the pressure up to about 35-38 psi but when the key is turned off, the pressure slowly drops off to zero again...the pressure drop takes less than a minute. I believe the line should always remain under pressure, even when the car is off & has been sitting for a while, correct? Anyhow, once the car starts, it runs fine (slightly rough idle) & I'm getting over 25 mpg. There's no sign of any leaks & I've tried replacing the fuel pressure regulator. I've also tried adding injector cleaner to the tank several times, but that appears to have no effect. I've listened to all the injectors with a long screwdriver, & all 6 of them are clicking, so it seems they're all working. I'm wondering if a partially clogged injector isn't fully closing & it's causing the pressure to bleed off. It does idle slightly rough, but smooths out as soon as the rpms go up a bit...so that kinda confirms it could be a leaky/dripping injector.

Any suggestions on how to narrow it down to which injector is the culprit?

Thanks in advance....

[Slade901]

The fuel injectors must be bench tested using a device that can test its flow volume. You can try to use a two fuel injector cleaner bottle and some ISO-HEET water remover. Also, you can remove the the spark plugs to see which one smells heavy fuel smell.

If the fuel pressure regulator is leaking due to ruptured diaphragm inside the fuel pressure regulator then the fuel is being sucked in through the vacuum hose which is connected on the fuel pressure regulator and to the intake manifold. A good working fuel pressure regulator diaphragm just adjust the fuel pressure to correspond with the intake manifold vacuum. If the fuel pressure regulator diaphragm is ruptured then fuel is now getting sucked into the intake manifold (not good). Check the vacuum hose attached to the fuel pressure regulator and see if the vacuum hose has fuel in it after starting the engine for a while.

Most fuel pump is controlled by its own fuel pump relay and a secondary backup that depends on oil pressure. If the fuel pump relay is not working properly then the engine can be started by starting the ignition switch at least 3 times (build up oil pressure) and then the fuel pump would work after that and hence the vehicle starts after 3 restarts. Check or replace the fuel pump relay.

You can actually bypass the fuel pump relay and there is usually a red wire dangling next to where the fuel pump relay is located and just connect a wire from the battery positive terminal and see if the pump works.

[jamx13]

The fuel pressure regulator is good...I've tried 3 different ones & there was no change with any of them...& there's no sign of fuel being sucked up thru the vaccuum hose.

"Most fuel pump is controlled by its own fuel pump relay and a secondary backup that depends on oil pressure. If the fuel pump relay is not working properly then the engine can be started by starting the ignition switch at least 3 times (build up oil pressure) and then the fuel pump would work after that and hence the vehicle starts after 3 restarts. Check or replace the fuel pump relay."

While this explanation does seem to fit my problem, it doesn't explain why there's no fuel line pressure after the engine's shutdown for a few minutes. If I was to walk out to my car right now (just got to work a little while ago) & push in on the Schrader valve on the fuel rail, nothing would squirt out.

I'll look into the relays though & post back later...

Thanks.