Flooding symptoms

[gmcman101]

I recently purchased a 90 Grand Prix for my girlfriend. It has the 3.1 MPFI and for some reason it runs like it's flooding out. It even has the black smoke coming out of the tail pipe at start up. What would cause this? How can a fuel injected vehicle be flooding out? Is there a fuel pressure regulator on this?

Thanks

[GTP Dad]

There are several reasons for a fuel injected car to run rich. First of all do you have a check engine light? I suspect that the O2 sensors may be bad causing the car to run rich. Secondly, it is possible for the injectors to be staying open too long because of incorrect signals from the ECM. The O2 sensor is probably causing this so change the O2 sensor first. If that doesn't help then check the injectors with a noid light to see if they are opening and closing appropriately. If you find they are operating properly then you may have a problem with leaking injectors which usually means they will need to be replaced.

[tblake]

Pull the vacuum line off the fuel pressure regulator and check for fuel contamination. (wait, is the fpr under the manifold on the 3.1mpfi?) Could also try a fuel pressure test with key on engine off, and key on engine idling.

[CrazyHorst]

Originally Posted by gmcman101

It even has the black smoke coming out of the tail pipe at start up. What would cause this? How can a fuel injected vehicle be flooding out?

Consider the ECM measures coolant temp at startup to set an initial open loop air-fuel ratio and an injector pulsewidth.

If it thinks it is -40F outdoors there's going to be a serious amount of fuel added...many engines have been validated thru this in test chambers to make sure they'll start reliably at those temps.

[gmcman101]

I was thinking the fuel pressure regulator but if this is faulty would it allow to much fuel to the injectors? Also, where is this located on the 3.1? One more question, where is the O2 sensor located on this? Thanks guys...

[gmcman101]

oh never mind on the O2 sensor, I'm pretty sure I can find that, but yea, where is the fpr located? Thanks again...

[doctorhrdware]

If I remember correctly it is on the front fuel rail. It has a vacuum line attached to the front side of the regulator.

[tblake]

Yep it is on the fuel rail, but the fuel rail is completly covered by the intake plenum. Its not hard to remove. You can sort of leave everything connected and just angle it upwards just enough to access the FPR. Be carefull with the plastic vacuum lines. Also make sure if you pull the upper plenum to replace the gaskets.

I would just rent a fuel pressure guage and see if it holds pressure before ripping into the plenum, however it seems like if the motor is over fueling that gas could be being comsumed through the FPR vacuum line.

[gmcman101]

So if it holds pressure the fpr is good? What should the pressure be on this vehicle?
Thanks again...